W Klingenberg
email: w.klingenberg@rug.nl

J D Boksma

A conceptual framework for outsourcing of materials handling activities in automotive: differentiation and implementation

Keywords: OUTSOURCING, MATERIALS HANDLING, MANUFACTURING STRATEGY, MANUFACTURING Outsourcing, logistics, materials handling, transaction cost economics, resource-based, network-based, framework Outsourcing, logistics, materials handling, transaction cost economics, resource-based, network-based, framework

This article discusses the outsourcing of materials handling activities and investigates different options for its implementation. The article uses descriptive case studies found in literature from the Western European automotive industry to map out differences in current practice and to evaluate frameworks found in the literature. These frameworks appear to be limited to decision making at a strategic level. In addition, they only allow decisions relating to the outsourcing of the logistics function in general, not of materials handling in particular. Based on this study and other descriptions of materials handling practice in the literature, a new conceptual framework for outsourcing of materials handling is proposed, which facilitates decision making at a tactical/ operational level. The functionality of the framework is tested in a series of cases at a major production and logistics facility of Scania.

Introduction

Outsourcing, in particular the make-or-buy decision, has received much attention in practice and in the academic literature over recent years. Such descriptions usually focus on the outsourcing of parts manufacturing [START_REF] Venkatesan | Strategic sourcing -to make or not to make[END_REF], Gilley, 1994, Quinn & Hilmer, 2000[START_REF] Wu | An outsourcing decision model for sustaining long-term performance[END_REF][START_REF] Holcomb | Toward a model of strategic outsourcing[END_REF], Reichart & Holweg, 2008). Examples of such frameworks include [START_REF] Cáñez | Developing a framework for make-or-buy decisions[END_REF] and [START_REF] Platts | Make vs. buy decisions: a process incorporating multi-attribute decision-making[END_REF]. Outsourcing of materials handling activities is less well covered, although a number of researchers have reported on the outsourcing of logistics in general [START_REF] Rabinovich | Outsourcing of integrated logistics functions; An examination of industry practices[END_REF][START_REF] Aertsen | Contracting out the physical distribution function: a trade-off between asset specificity and performance measurement[END_REF], Bolumole, 2000[START_REF] Mathisson-Ölmertz | Influences of process locations on materials handling; cases from the automotive industry[END_REF]. Logistics is defined as "that part of supply chain management that plans, implements and controls the efficient, effective forward and reverse flow and storage of goods, services and related information between the point of origin and the point of consumption in order to meet customers' requirements" (Bolumole 2007, p. 35). Materials handling is an element of the logistics function, and is defined as the operational procedure that takes place when the materials are handled along a materials flow [START_REF] Mathisson-Ölmertz | Influences of process locations on materials handling; cases from the automotive industry[END_REF]. Materials handling excludes supply chain planning and supply chain management.

The focus of this article is on the outsourcing of materials handling of parts in automotive production. Industrial practice, as witnessed by the authors and also described by [START_REF] Mathisson-Ölmertz | Influences of process locations on materials handling; cases from the automotive industry[END_REF], shows that materials handling covers a confined set of relatively labour-intensive activities, which may not necessarily be core elements of the primary function of a production company. Materials handling may therefore be a good area for intensive study for companies seeking to minimise waste [START_REF] Liker | The Toyota Way: 14 management principles from the world's greatest manufacturer[END_REF]. Outsourcing may be an option worth considering, but the existing literature offers little guidance. Most of the authors mentioned generally describe the decision whether to outsource the (broader) logistics function or not. Possible options for outsourcing of materials handling specifically (including the choice of supplier/service provider, location of the activities, integration with other activities) have not been given much attention.

Aim

The aim of this article is to help managers and engineers in structuring and deciding upon options for outsourcing of materials handling. For this purpose a conceptual framework (consisting of two dimensions) is proposed for use in the automotive industry. The aim of the framework is to structure the available options. The use of the framework is tested in six cases at Scania Production Zwolle (SPZ) in The Netherlands. SPZ is a typical full-service automotive plant (logistics, parts assembly, truck assembly) operating a production system, the Scania Production System, which is similar to other lean production systems applied by major automotive production plants [START_REF] Liker | The Toyota Way: 14 management principles from the world's greatest manufacturer[END_REF]. Since all of the cases are with SPZ, the influence of the operational environment is equal in each case. [START_REF] Aken | Management research based on the paradigm of the Design Sciences; the quest for fieldtested and grounded technological rules[END_REF] calls this type of research 'design science'. [START_REF] Holmström | Bridging Practice and Theory: a Design Science Approach[END_REF] state that two phases can be distinguished in design 2 science, i.e. exploration and explanation. Within these two phases, further steps can be distinguished. The current article essentially covers the refinement of existing solutions (frameworks) and explanation and evaluation of the solution. The result is a novel framework, which is explained and tested to some extent. The next and final step [START_REF] Holmström | Bridging Practice and Theory: a Design Science Approach[END_REF], development of formal theory/ statistical generalisation, is outside of the scope of this article.

In Section 2, a brief overview of the literature on existing outsourcing frameworks will be provided and descriptive case studies from the literature are mapped out. In section 3, a new framework is proposed. In section 4, the new framework is evaluated using the case studies. Section 5 reflects the discussion and conclusions.

Available theory and literature examples

This section reviews existing theory on outsourcing and the frameworks found in the literature. During this review, we have searched for frameworks on outsourcing of materials handling specifically, but have only found frameworks of outsourcing of logistics in general. However, we did find descriptive case studies of outsourcing of materials handling. In order to appreciate the current frameworks and the case studies, it is necessary to first summarise the currently known approaches to outsourcing, since the frameworks use elements of these approaches.

Outsourcing approaches

There appear to be three commonly used approaches to outsourcing decisions (as also noted by [START_REF] Bolumole | Developing a theoretical framework for logistics outsourcing[END_REF]: transaction cost economics, resource based theory, and network theory. Other researchers have explained differences between these approaches (e.g. [START_REF] Mayer | Capabilities, contractual hazards, and governance: integrating resourcebased and transaction cost perspectives[END_REF], which can be summarised as follows.

The transaction cost economics theory (TCE) insists that operations should take place wherever the sum of production and transaction costs is minimised [START_REF] Williamson | Markets and hierarchies: Analysis and antitrust implications[END_REF], 2008[START_REF] Riordan | Asset specificity and economic organization[END_REF]. Transaction costs represent the costs of physical and human resources incurred in order to complete an exchange of goods and services between parties. The TCE theory was described in detail by other researchers [START_REF] Walker | A transaction cost approach to make-or-buy decisions[END_REF][START_REF] Ghoshal | Bad for practice: a critique of the transaction cost theory[END_REF][START_REF] Hobbs | A transaction cost approach to supply chain management[END_REF][START_REF] Grover | Transaction cost framework in operations and supply chain management research: theory and measurement[END_REF][START_REF] Mccarthy | The impact of outsourcing on the transaction costs and boundaries of manufacturing[END_REF].

The resource based theory (RBT) principally describes a firm as a set of resources, with resources defined as "those (tangible and intangible) assets which are tied semi-permanently to the firm" (Wernerfelt, 1984, p.172). According to its principles, an organisation must secure an efficient set and organisation of the right type of resources in order to survive and improve its operational performance. Competitive advantage results from the ownership of -or unrestricted access to -inimitable assets, innovations, and resource barriers, which enable the firm to shift market positions [START_REF] Grant | The resource-based theory of competitive advantage: implications for strategy formulation[END_REF][START_REF] Connor | A historical comparison of resource-based theory and five schools of thought within industrial organization economics: do we have a new theory of the firm[END_REF][START_REF] Bolumole | Developing a theoretical framework for logistics outsourcing[END_REF]. The concept of having a number of core competences, skills or capabilities which are prominent in helping a firm to achieve its purpose [START_REF] Prahalad | The core competence of the corporation[END_REF] is very much in line with RBT. The desire to focus on core competences may be a potent reason for firms to turn to outsourcing of 'non-core' competences (Espino-Rodriguez & Padron-Robaina, 2006). In addition, the ability to achieve economies of scope and economies of scale is relevant in this respect [START_REF] Kulkarni | Risk pooling advantages of manufacturing network configuration[END_REF].

The network theory (NT) of the firm focuses on the formation of external relationships, organisational structures and alliances required to support the integration of the firm in its network. The cooperative act of outsourcing should result in benefits for the entire network, of which the firm is an integral part [START_REF] Bolumole | Developing a theoretical framework for logistics outsourcing[END_REF][START_REF] Kulkarni | Risk pooling advantages of manufacturing network configuration[END_REF][START_REF] Ellram | The supplier selection decision in strategic partnership[END_REF][START_REF] Ford | Understanding business markets: interaction, relationships and networks[END_REF][START_REF] Mody | Learning through alliances[END_REF][START_REF] Varadarajan | Strategic alliances: a synthesis of conceptual foundations[END_REF]. Table 1 summarises these three approaches.

Insert Table 1 here

Logistics outsourcing

General frameworks for logistics outsourcing decisions have been proposed by other authors (e.g. [START_REF] Spear | Logistics: key to corporate strategy[END_REF][START_REF] Bolumole | The supply chain role of third-party logistics providers[END_REF]). Spear's framework uses 'critical success factors' and 'core competences' for evaluating logistics outsourcing decisions. This appears to be based on the resource based theory, which sees strategies as emanating from company resources and capabilities. Figure 1 shows [START_REF] Bolumole | The supply chain role of third-party logistics providers[END_REF] competitive strategy', which Bolumole described in terms of logistics being a critical success factor or not, and 'resource availability & operational performance of in-house logistics'. [START_REF] Bolumole | The supply chain role of third-party logistics providers[END_REF] appears to use high-level descriptions constituting several aspects for these two dimensions (for example, the term 'business value' could include various aspects). One could argue that the use of the framework hinges upon the exact definitions and the weighing of the aspects. In Bolumole's framework (Figure 1), the option 'smart source' refers to a 'smart' choice, to be made on the basis of resource, cost and control justifications, which separately or jointly influence an organisation's outsourcing decision [START_REF] Bolumole | The supply chain role of third-party logistics providers[END_REF]. Other variants of such logistics outsourcing frameworks were proposed by [START_REF] Sink | A managerial framework for the acquisition of third-party logistics services[END_REF], [START_REF] Dekkers | Decision models for outsourcing and core competencies in manufacturing[END_REF] and [START_REF] Bolumole | Developing a theoretical framework for logistics outsourcing[END_REF].

Insert Figure 1 here Validity in practice A relevant question for assessing typical decision frameworks currently available in the literature is whether the terminology used is sufficiently strictly defined and whether the frameworks are sufficiently detailed for making operational decisions related to materials handling. In section 2.3, we will try to answer this question with a specific focus on outsourcing of materials handling using relevant cases described in the literature. In our view, it is sensible to focus on a certain confined set of activities and debate these in detail, since this is the level at which engineers and managers will need to operate ('the devil is in the detail').

Literature cases of outsourcing of materials handling

In this section, the literature describing examples of outsourcing of materials handling in the Western European automotive industry is reviewed.

Materials handling activities defined

In the literature, several different materials handling activities were described. These are summarised in Table 2. From the descriptions, it becomes apparent that an important denominator for materials handling activities is the position of the customer order decoupling point (CODP). This separates decisions made under certainty from decisions made under uncertainty concerning customer demand [START_REF] Wikner | Integrating production and engineering perspectives on the customer order decoupling point[END_REF]. It is important to make a distinction between pre-CODP and post-CODP operations, since these have fundamentally different characteristics [START_REF] Olhager | Strategic positioning of the order penetration point[END_REF][START_REF] Olhager | An integrated push-pull manufacturing strategy[END_REF]. A materials handling activity could be the point in the supply chain where the CODP is located. Materials handling activities could also be upstream or downstream of the CODP. To allow for this difference, the dimension 'pre-, at or post-CODP' is added.

Insert Table 2 here

Warehousing and repacking could concern all types of parts. However, order picking is by definition positioned at the CODP. For simplicity, we have assumed kitting to be the same thing as order picking (both concern parts being picked for a specific order) (De [START_REF] Koster | Design and control of warehouse order picking: a literature review[END_REF][START_REF] Mathisson-Ölmertz | Influences of process locations on materials handling; cases from the automotive industry[END_REF][START_REF] Bozer | Kitting versus line stocking: a conceptual framework and a descriptive model[END_REF]. Sequencing requires order-information, so it can only take place at or downstream of the CODP. It is interesting to review the options for buffering. Buffers upstream of the CODP consist of parts, which are not related to a customer order [START_REF] Olhager | Strategic positioning of the order penetration point[END_REF][START_REF] Olhager | An integrated push-pull manufacturing strategy[END_REF]. This buffer or inventory is therefore generic. A buffer downstream of the CODP consists of parts, which are related to a customer order, and is therefore specific to that customer order. This is illustrated in Figure 2.

Insert Figure 2 here

A generic buffer can be used to cope with the delivery of parts with an incorrect specification in a batch, late delivery or the delivery of parts of insufficient quality. Absent, late or faulty parts can be replaced by parts from the generic buffer. A specific buffer can be used only to cope with the late delivery of exactly the items in the buffer. Other problems, such as incorrect or faulty parts are much less likely to allow the use of a specific buffer, since each part in the buffer is required for a certain customer order (taking into account the impossibilities or disadvantages of 'cannibalising' between orders). This means that a specific buffer is of less value in coping with irregular or unreliable delivery than a generic buffer. Absence of generic buffers is one of the reasons why Lean systems require perfect quality and accurate delivery. This difference, determined by the position of the CODP, is relevant for the organisation of materials handling activities. Options for outsourcing materials handling The literature describing automotive industry cases reveals several options for outsourcing materials handling activities for parts supply to, or inside an OEM plant. The two dimensions in which the descriptions in the literature were found to differ are: (1) the location of the materials handling activities; and (2) the type of service provider to which materials handling is outsourced. One should add that there may be other differences and choices to be made, e.g. the way the material is controlled.

(1) For the location of the activities, there appear to be three options: at a supplier, at an additional node in the supply network or at the facility of the OEM [START_REF] Mathisson-Ölmertz | Influences of process locations on materials handling; cases from the automotive industry[END_REF]. In general, an additional node in the network is known as a 'cross docking facility' or an 'intermediate facility', and the difference appears to be somewhat arbitrary. Cross docking facilities are characterised by the process of moving a product through distribution centres without storing it. Cross docking facilitates economies of scale by enabling the transportation of goods through the distribution channel in full truck loads [START_REF] Apte | Effective cross-docking for improving distribution efficiencies[END_REF]. An intermediate facility is defined as a facility in which additional materials handling activities, such as order picking and sequencing take place [START_REF] Mathisson-Ölmertz | Influences of process locations on materials handling; cases from the automotive industry[END_REF]. The decision for a certain location lies with (the supply chain staff and management) of the OEM, who may be advised and assisted by suppliers and service providers. One should add that there will always have to be some materials handling at the OEM plant.

(2) Either a supplier or a third party (i.e. a party other than the OEM and the supplier) can be used as service provider. A firm offering logistics services is called a logistics service provider (LSP). If the LSP is a third party, it is commonly called a third party logistics (3PL) provider [START_REF] Rabinovich | Outsourcing of integrated logistics functions; An examination of industry practices[END_REF]. In a case study at General Motors [START_REF] Howard | Automotive supplier parks: An imperative for build-to-order[END_REF]) some suppliers were reported to perform materials handling activities for parts delivered from other suppliers. These were denoted in Table 3 as 'supplier+'. In the cases described here, the OEM appeared to take the initiative to contract the service provider.

Descriptions of the car manufacturers Seat, Volvo, General Motors, Saab, the former MG Rover group (which ceased trading in 2005) and some anonymous cases obtained from the literature are summarised in Table 3. In the summary of the cases, order picking and kitting were regarded as similar, as parts are collected for a production order (De [START_REF] Koster | Design and control of warehouse order picking: a literature review[END_REF][START_REF] Mathisson-Ölmertz | Influences of process locations on materials handling; cases from the automotive industry[END_REF][START_REF] Bozer | Kitting versus line stocking: a conceptual framework and a descriptive model[END_REF].

Insert Table 3

Several car manufacturers in Western Europe were reported to make use of an intermediate facility for components, where both manufacturing and materials handling activities are carried out [START_REF] Howard | Automotive supplier parks: An imperative for build-to-order[END_REF]. The description of intermediate facilities appears to have similarities with typical materials handling facilities at supplier parks [START_REF] Mathisson-Ölmertz | Influences of process locations on materials handling; cases from the automotive industry[END_REF][START_REF] Howard | Automotive supplier parks: An imperative for build-to-order[END_REF], which appear to be increasingly common in automotive and other industries [START_REF] Howard | Automotive supplier parks: An imperative for build-to-order[END_REF]. Supplier parks are usually in close proximity to the OEM (in a Japanese context supplier parks may be linked to Keiretsu relationships, [START_REF] Ahmadjian | Keiretsu, governance and learning, case studies in change from the Japanese automotive industry[END_REF]. The reasons for locating facilities at a supplier park are: to enable sequential just-in-time deliveries [START_REF] Larsson | The development and regional significance of the automotive industry; supplier parks in Western Europe[END_REF]; to increase delivery reliability due to shorter transport distances [START_REF] Reichhart | Co-located supplier clusters: forms, functions and theoretical perspectives[END_REF]; to decrease transport cost [START_REF] Millington | Local assembly units in the motor components industry -a case study of exhaust manufacture[END_REF]; to increase face-to-face contact and to enable quicker problem resolution and better mutual understanding [START_REF] Frigant | Geographical proximity and supplying relationships in modular production[END_REF].

The differences in the outsourcing/organisation of materials handling activities for the cases in the literature (summarised in Table 3) were not described in the logistics outsourcing frameworks referred to in section 1 (which relate to decision making at a more strategic level). Given that the aim of this article is to differentiate between the available options when considering outsourcing of materials handling, a new framework is necessary.

A framework of outsourcing of materials handling

This section introduces a new conceptual framework that will facilitate decisions on the outsourcing of materials handling. In the previous section, it was shown that the outsourcing decision frameworks found in the literature were aimed towards strategic decision making relating to logistics in general, but they do not specifically assist with operational/tactical materials handling decisions.

Dimensions

In the previous section, a number of alternatives for outsourcing of materials handling were reported. It was noted that it is relevant to differentiate between activities upstream, at or downstream of the CODP, since these have fundamentally different characteristics [START_REF] Olhager | Strategic positioning of the order penetration point[END_REF][START_REF] Olhager | An integrated push-pull manufacturing strategy[END_REF]. In our framework, we have therefore included this dimension. Secondly, the location of the materials handling activity was reported as a relevant aspect, with three options: at the supplier, at an additional node, or at the OEM.

In the materials handling cases found in the literature, different options were described for the choice of a partner: supplier, 'supplier+' (as described before) or 3PL. We have ignored this aspect in our framework for three reasons: (1) differences between the potential partners would not fundamentally impact the outsourcing decision, merely the choice of partner;

(2) the choice of provider (i.e. supplier or 3PL) may not be independent of the choice of location and;

(3) abilities/ performance of the service provider is not used for further analysis, since it is specific to each individual case. One could simply say that only parties with sufficient capabilities should be considered.

The six options in the new framework are depicted in Figure 3. As will be shown later, each of the materials handling activities included in Table 2 can be organised within more than one section of the framework. The framework does not prescribe the way in which the activities should be organised. It merely facilitates discussion and structures the options. A company manager or supply chain specialist could use this framework (or a customised version) to differentiate between options and analyse the business case for each option considered.

Insert Figure 3 here

Assessing options for outsourcing materials handling

One may take a principled approach and select a certain method based on a deeply rooted concept (e.g. TCE, RBT or NT, see Table 1). In this article, we simply base our selection on maximising operational performance (arguably, this overlaps with elements of TCE, RBT and NT). [START_REF] Stock | Enterprise logistics and supply chain structure: the role of fit[END_REF] proposed four operational performance criteria: cost, delivery speed and reliability, flexibility, and quality. [START_REF] Stock | Enterprise logistics and supply chain structure: the role of fit[END_REF] did not appear to differentiate between types of flexibility, but in this article some differentiation will be necessary. [START_REF] Slack | Flexibility as a manufacturing objective[END_REF] identified five different types of manufacturing system flexibility; new product flexibility, product mix flexibility, quality flexibility, volume flexibility and delivery flexibility.

Cost

The first criterion, cost, is used in the TCE approach, and is extensively considered by other researchers.

A number of different cost elements may be relevant when appraising outsourcing decisions. Normally in logistics, personnel cost, transport cost, stock holding cost and overhead/facility costs are important cost elements which may be influenced by the approach adopted. The cost of capital and depreciation needs to be taken into consideration. Outsourcing reduces the need for capital equipment, reducing depreciation, while the type of risk changes. Overhead cost depends on the specifics of each individual case (in which the OEM is to be compared with the potential service provider). It will therefore not be reviewed in general terms in the current article. A few general comments on personnel cost and transport cost will be made. As well as cost, one should assess the value added by each activity. Value-adding materials handling activities "change the configuration of the materials and their packaging so that it attains the state required when the materials leave the defined materials flow system, i.e. the final state. This final state can be expressed in terms of position, mix, orientation and number of components, and it often includes several packaging levels. Practical examples of value-adding materials handling activities are kitting or sequencing of materials according to customer demand, in packaging required by the customer." (Matthisson-Ölmertz & Johansson, 2000, p 27). Naturally, one should always thrive to eliminate non-value adding activities (for example by managing the supplier to avoid unnecessary re-packing).

Delivery speed and Reliability

This is influenced by the performance of the service provider, the transportation distance to the OEM (an increase in distance is likely to cause decreased reliability, [START_REF] Howard | Automotive supplier parks: An imperative for build-to-order[END_REF], the buffer size at the OEM, and the buffer type at the OEM based upon the position of the CODP [START_REF] Olhager | Strategic positioning of the order penetration point[END_REF][START_REF] Olhager | An integrated push-pull manufacturing strategy[END_REF]. This is visualised in Figure 4.

Insert Figure 4 here

The delivery reliability to the assembly line of the OEM is often ascertained by introducing a (small) buffer.

It is noted that buffering is not preferable, not 'lean', but it may be necessary to allow a continuous flow [START_REF] Liker | The Toyota Way: 14 management principles from the world's greatest manufacturer[END_REF]. A buffer is defined here as a small inventory of parts, used to cope with irregular or unreliable delivery. In the strictest sense, a small buffer is almost inevitable as it would be uneconomic for the supplier to deliver parts individually. Requirements with regards to the buffer will determine choices 6 related to materials handling. The buffer size determines how long a process can be continued in case of irregular delivery. The type of buffer determines which aspects of unreliable delivery can be counteracted. The type of buffer can be characterised by the position of the customer order decoupling point (CODP), as explained previously.

Order Picking and Sequencing will by definition (Table 3) happen at or downstream of the CODP. In theory (and practice), the activities Warehousing, Repacking and Buffering may be carried out either upstream or downstream of the CODP. However, if these activities are carried out downstream of the CODP, the question arises if the activities cannot be avoided at all, given the limited use of having orderspecific buffers.

Flexibility

Of the different types of flexibility [START_REF] Slack | Flexibility as a manufacturing objective[END_REF], delivery flexibility appears to be most influenced by the way materials handling is organised (e.g. the location of the activities and position of the CODP). The reason is that the delivery flexibility refers to the ability of the system to shorten or lengthen its delivery lead time [START_REF] Slack | Flexibility as a manufacturing objective[END_REF]. If the supplier base is located across a wide area (e.g. Europe), transportation time is likely to be (much) longer than the materials handling process lead times (i.e. the lead times of the materials handling activities). The ability to optimise the delivery lead time is largely determined by the transportation distance (and the mode of transport used), since this determines the transportation lead time. Transportation distance should therefore be used as one of the determinants of delivery flexibility.

Naturally, delivery flexibility is also determined by the abilities of the service provider. As mentioned, abilities/ performance of the service provider is not used for further analysis, since it is specific to each individual case.

The influence of materials handling on volume flexibility appears to be limited to the use of smaller or larger buffers, which may not affect the outsourcing decision. The requirements for product mix flexibility may affect e.g. required warehouse space. The influence on new product flexibility and quality flexibility appears to be limited.

Quality

Quality as an operational performance criterion is mainly related to the manufacturing processes. Although materials handling activities can affect the quality of parts handled, this criterion will not introduce differentiation amongst different materials handling outsourcing options upfront. Therefore this criterion is neglected in the further analysis.

Assessment on operational performance criteria

The next step is to map out the possible influence of the six outsourcing options. A company manager or engineer could do this by analysing and considering each of the options. To a large extent, such an exercise will be company specific. Some aspects will have a generic nature, which we will comment on in this section. It should be noted that the framework can be customised to a specific situation if the assumptions we propose here do not represent a particular situation in practice. This will be discussed in the final section of this paper. Table 4 presents an overview.

Insert Table 4 here

Case studies at Scania

This article presents a new conceptual framework for outsourcing of materials handling activities in automotive. The article starts with a discussion/ evaluation of existing theory, and proceeds with the examination of the cases found in literature of outsourcing of materials handling practice in automotive.

Subsequently the new framework is presented, which is then explained and evaluated using six practical cases. [START_REF] Aken | Management research based on the paradigm of the Design Sciences; the quest for fieldtested and grounded technological rules[END_REF] calls this type of research 'design science'. [START_REF] Holmström | Bridging Practice and Theory: a Design Science Approach[END_REF] state that two phases can be distinguished in design science, i.e. exploration and explanation. Within these two phases, further steps can be distinguished. The current article essentially covers the refinement of existing solutions (frameworks) through a.o. inductive and deductive reasoning (the second step in exploration, [START_REF] Holmström | Bridging Practice and Theory: a Design Science Approach[END_REF], and explanation and evaluation of the solution (the first step of explanation, [START_REF] Holmström | Bridging Practice and Theory: a Design Science Approach[END_REF]. The result is a novel framework, which is explained and tested to some extent. The next and final step, development of formal theory/ statistical generalisation [START_REF] Holmström | Bridging Practice and Theory: a Design Science Approach[END_REF], is outside of the scope of this article. Appropriate for evaluating a novel theory is case study research [START_REF] Yin | Case Study Research: Design and Methods[END_REF][START_REF] Meredith | Building operations management theory through case and field research[END_REF][START_REF] Eisenhardt | Building theories from case study research[END_REF]. To evaluate the applicability of the framework proposed here (Figure 3, Table 4), materials handling was investigated at Scania Production Zwolle (SPZ) in The Netherlands, one of Scania's three truck assembly factories in Europe. 7 SPZ consists of an assembly centre with two production lines and a logistics centre. The operational strategy is based on the Scania Production System, which is based on the principles of the Toyota Production System [START_REF] Liker | The Toyota Way: 14 management principles from the world's greatest manufacturer[END_REF]. Therefore, there is a continuous effort to eliminate or minimise non-value added activities.

The supplier base of SPZ is mainly continental European. Currently, intermediate facilities (cross-docks) are used for transport optimisation (i.e. transport of full truckloads from the cross dock to the factory). Material handling activities are required for many of the parts presented to the assembly lines. These are traditionally performed in-house at SPZ. The management of SPZ is considering outsourcing of materials handling. Since all of the six cases discussed are with SPZ, the influence of the operational environment is equal in each case.

Strategic assessment (Figure 1)

During a number of structured interviews, the management of SPZ was asked to discuss outsourcing at a strategic level, and to apply the strategy to logistics activities by (1) discussing the business value of logistics (as described in the framework of [START_REF] Bolumole | The supply chain role of third-party logistics providers[END_REF]; and (2) assessing resource availability and operational performance of in-house logistics activities. The interviewees generally rated the business value [START_REF] Bolumole | The supply chain role of third-party logistics providers[END_REF]) of logistics at SPZ as high, since it enables the production of a wide variety of trucks to customer order at short delivery lead times. The findings from the second question indicated some problems with regards to availability of resources. In despite of the current economic slow-down, the availability of resources and facilities (incl. floor space at SPZ) may continue to be a challenge locally. These findings would place SPZ in the quadrant 'Smart sourcing' of the general framework of Figure 1.

Outsourcing could perhaps solve current resource limitation problems. A prerequisite would be that the reliability of line supply would have to be kept at the current level.

Tactical and operational assessment (using Figure 3 and Table 4)

Secondly, an additional set of structured interviews was held to discuss details according to the framework proposed here. Operational team leaders, management and engineers were asked to discuss the options for outsourcing of materials handling for various parts. We will present some of the highlights of these interviews first, and will then discuss six cases of materials handling outsourcing projects at SPZ. In some cases, the level of detail in the descriptions of the activities/ decisions is somewhat restricted for reasons of confidentiality. The results are summarised in Table 5.

First, the matrix in Figure 3 was customised and redrawn for SPZ. This led to the following conclusions:

• Materials handling activities required categorisation before the framework could be applied. Categorisation was done according to pre/post CODP and supplier transport distance; • For a number of part categories, options 2 and 4 were regarded are unsuitable, since currently generic buffers would become order-specific, which would mean that the buffer would be of less value in coping with unreliable deliveries (which appear to be related with long transport distances); • Options 5 and 6 could introduce savings on personnel cost, while the delivery reliability is not expected to decrease. The processes are of such type that the performance of SPZ can be matched without much risk; • For some part categories, options 1 and 3 were deemed suitable. The best options in this group largely depend on decisions relating to transport routes, location of a cross dock or intermediate facilities and the way in which buffering at SPZ is carried out. Figure 5 shows these options. Elements of the discussion on each of the options are reported below. This illustrates the use of the framework, which is to facilitate discussion at a level of detail suitable for decision making at a tactical/operational level.

Insert Figure 5 here

Case 1: Outsourcing of pre-CODP activities, carried out at supplier location (option 1) Lack of space at SZP's logistics centre was the primary motivation for investigating the outsourcing of materials handling activities. A Pareto-analysis on space consumption by parts (measured in m 3

) showed that a small number of parts consumed a relatively large share of the available space. Outsourcing the warehousing of such parts, in particular cross members, noise shields and air tanks, was investigated in detail. Warehousing (a pre-CODP activity) of these parts could be (partially) outsourced to a supplier facility. This means that inventory levels at SPZ would decrease whilst inventory levels at suppliers would increase. The supplier should have the parts available for transport pickup (like in the current situation), but should hold extra inventory as a buffer. The SPZ suppliers of the parts mentioned are located across continental Europe, most of them at a distance of several hundreds of kilometres from SPZ. Having the buffer stock at a large distance from SPZ was tested and resulted in a significant reduction in delivery reliability (due to the distance). Personnel cost at SPZ would decrease, however this would cause higher personnel costs at the supplier facility. Transportation costs were not affected, because the frequency of the deliveries was not changed. The large transport distance made it impossible to significantly shorten the delivery lead time, which resulted in limited delivery flexibility. Because of the reduced delivery reliability, there was an expectation of limited cost savings and limited delivery flexibility. SPZ eventually decided not to outsource warehousing to the suppliers.

Case 2: Outsourcing of activities at the CODP, carried out at supplier location (option 2) Scania is currently preparing for an increase in radiator and intercooler variants. An increase in variants of these parts means that more storage space is needed at the pre-assembly areas. Radiators and intercoolers are currently supplied in batches that consist of several identical parts on a pallet. The variants are sub-assembled near the assembly lines according to the production sequence.

In order to save space and reduce material handling at SPZ, radiators and intercoolers could also be delivered in the production sequence from the supplier facility to SPZ. This requires the parts to be picked according to the SPZ sequence of production orders, which causes the picking activity to become the CODP. Instead of having several pallets each containing a part variant, a single pallet with multiple part variants could then be stored at the pre-assembly area. This saves both space and walking distance at the pre-assembly area.

A major drawback of this solution is a decrease in delivery reliability and an increase in transport cost. Delivery reliability decreases significantly as the suppliers are located at considerable distances and SPZ has only specific buffers of radiators and intercoolers on site. If parts were to experience damage during unloading at SPZ, it would take a significant time before replacement parts would arrive from the supplier. In the meantime, the buffer at SPZ is of limited value as it only consists of part variants needed for specific customer orders (trucks) to be produced in the near future. Furthermore, transport costs would increase because several part variants in a pallet would be packed less efficiently than a batch of identical parts. Personnel costs are expected to decrease under the assumption that picking parts in the correct sequence can be carried out more efficiently at the supplier than at SPZ.

Case 3: Outsourcing of pre-CODP activities, carried out at intermediate location (option 3)

Space consuming parts, such as cross members, noise shields and air tanks (described in the first case) could also be stored at an intermediate facility. This involves warehousing (a pre-CODP activity) at a facility between the supplier and SPZ. The intermediate facility could be located near suppliers, for example using an existing cross-dock facility, or near SPZ. The latter alternative, an intermediate facility at a maximum distance of 20 km from SPZ, was investigated in detail.

An intermediate facility close to SPZ, which was also called 'external warehouse' by the interviewees could ensure that the delivery reliability is acceptable. The buffer of parts near the assembly line at SPZ can be delivered reliably and frequently due to the short transport distance. The buffer would be generic, which further adds to the delivery reliability. Delivery flexibility would be strongly determined by the transport time, which is short. However, preliminary cost calculations showed that using an intermediate facility would increase logistics operating costs for SPZ for two reasons: (1) the use of the facility would introduce non-value added activities as parts would need to be unloaded and loaded at the facility. This would increase total personnel costs for delivering parts to the assembly line; (2) the introduction of a frequent transport loop between the intermediate facility and SPZ would introduce additional transport cost. Due to the calculated increase in costs, management concluded the investigation by deciding against this option for the time being. However, in the future, if additional capacity demands were to increase, this option would not be ruled out.

Case 4: Outsourcing of activities at the CODP, carried out at intermediate location (option 4)

The process of order picking the springs consumes many floor square meters at SZP's logistics centre. Several spring variants are stored at pallets on the floor and placed on a mobile fixture with a manipulator. The fixture can hold eight springs and is transported to the assembly line. At the assembly line the various part variants are buffered. The spring variants in the buffer are coupled to a certain customer order (truck), making the buffer specific. Outsourcing this activity was considered because there is a lack of space in the logistic centre, as well as at areas more closely to the assembly lines. Order picking the springs at an intermediate facility was investigated. During order picking, the parts are sequenced. The production sequence is aligned with the sequence of customer orders, which means that order picking /sequencing of the springs happens at the CODP. A logistics service provider was asked to make a quotation for order picking the springs at their facility, located several hours away from SPZ. An evaluation of the quotation showed that the personnel/ handling cost would increase, which is not surprising due to the fact that extra unloading and loading is needed. Transport costs would also increase. This increase is explained by the fact that the springs need to be transported on fixtures instead of being stacked on a pallet. This results in less efficient transportation and therefore significantly higher transport cost per spring. Delivery reliability and flexibility decreased also due to the distance between the intermediate facility and SPZ. In fact the minimum transportation time from the generic inventory to production at SPZ would increase from a few minutes to more than three hours. Due to the lower delivery reliability and the higher costs, it was decided not to outsource the order picking of springs in this way.

Case 5: Outsourcing of pre-CODP activities, carried out at SPZ (option 5) Outsourcing the warehousing of parts to a service provider operating a warehouse located on the premises of SPZ could be an alternative for the option described in case 3. Warehousing at an intermediate facility seems infeasible due to the increase in costs. However, if space restrictions could be addressed (for example by re-arranging or extending current SPZ facilities) materials handling could still be outsourced to a logistics service provider (operating at the premises of SPZ). The impact of this option is limited. A plan was drawn up, involving the use of a facility at SPZ which is further removed from the assembly lines than the current warehouse. Internal transport cost would therefore increase somewhat, but the increase is much smaller than in case 3. The decision whether to outsource operations from this warehouse to a service provider would be based largely on personnel costs. Delivery reliability and flexibility would remain unchanged, as all activities and inventories are still carried out on the premises of SPZ. An additional argument at a strategic level for outsourcing these operations could be the decision to focus on core activities only.

Case 6: Outsourcing of activities at the CODP, carried out at SPZ (option 6) This is similar to case 5: SPZ could decide to outsource materials handling of parts downstream of the CODP at the facility of SPZ. Given the limited use of having order-specific (post-CODP) buffers, such activities would mostly involve value-adding activities in the supply of the assembly lines. The operation of the Scania Production System involves a continuous and stringent effort to eliminate any non-valueadding activities. Scania has decided not to outsource the remaining value-adding activities, since they are considered part of the core business at SPZ.

Implementation

The assessment of each of the methods on operational performance suggests that the framework can be useful for identifying and weighing up possibilities for outsourcing. The eventual decision can be taken based on further detailed performance evaluations (as well as management activities to optimise these).

Insert Table 5 here

Summary and conclusions

The aim of this article is to help company managers and engineers in structuring and deciding upon options for outsourcing of materials handling. The main contribution of the new framework is its tactical/ operational focus and specific applicability to outsourcing of materials handling activities. The article started off by reviewing the currently available outsourcing frameworks, which allow decision making a strategic level (e.g. [START_REF] Spear | Logistics: key to corporate strategy[END_REF][START_REF] Bolumole | The supply chain role of third-party logistics providers[END_REF][START_REF] Bolumole | Developing a theoretical framework for logistics outsourcing[END_REF][START_REF] Sink | A managerial framework for the acquisition of third-party logistics services[END_REF][START_REF] Dekkers | Decision models for outsourcing and core competencies in manufacturing[END_REF]. Based on a literature survey of cases in the automotive industry, the possibilities and nuances on a tactical and operational level are discussed. The investigation revealed that the decision criteria used in these cases differed from the ones in the strategic outsourcing frameworks. The new framework is aimed at filling that gap. Different types of materials handling activities were distinguished as repacking, order picking, sequencing and buffering. Since the framework was newly developed, its usefulness first needed to be evaluated. This was achieved through a series of case studies at Scania Production Zwolle (SPZ) in The Netherlands. The result is a novel framework, which is explained and tested to some extent. The next possible step, development of formal theory/ statistical generalisation [START_REF] Holmström | Bridging Practice and Theory: a Design Science Approach[END_REF], is outside of the scope of this article.

The new framework distinguishes between two dimensions, which determine options for outsourcing materials handling activities; (1) the location where the materials handling takes place and (2) the type of Options distinguished by the framework were assessed and the results were found to differ in terms of the performance criteria cost, delivery speed and reliability and delivery flexibility. An important denominator is the location of the CODP. One important finding is explained through the explanation of the difference between generic (pre-CODP) or specific (post-CODP) buffers. A generic buffer can be used generally to cope with a variety of supply problems. A specific buffer can be used only to cope with the late delivery of exactly the items in the buffer. Other problems, such as incorrect or faulty are much less likely to allow the use of a specific buffer, since each part in the buffer is required for a certain customer order. A specific buffer is therefore of less value in coping with irregular or unreliable delivery than a generic buffer. This difference is very relevant for the organisation of materials handling activities. If the activities are carried out off-site, delivery reliability can only be assured by outsourcing activities upstream of the customer order decoupling point (CODP), as is the case with warehousing and picking. If the activities are located at the OEM site, both pre-CODP and post-CODP activities could be considered for outsourcing. More detailed choices can be made by including transport routes, location of cross docks and/ or other intermediate facilities, and the way in which buffering at the OEM is organised.

Conclusions from the study of the six cases were that: (1) For Scania, a decision framework at strategic level was insufficient to structure and decide upon outsourcing of materials handling. Structured evaluation and decision making at a tactical and operational level appeared to be necessary; (2) the current framework offered structure to the discussion, based on which alternatives could be either eliminated or progressed to a further level of detail; (3) finally, one of the options was progressed on an operational level.

  which are to be outsourced. The service provider could be a supplier or a 3PL, which performs activities at either the site of a supplier, at an intermediate facility, or at the site of the OEM.

  Figure1. Framework for outsourcing the logistics function[START_REF] Bolumole | The supply chain role of third-party logistics providers[END_REF]

Figure

  Figure 4. Factors related to delivery reliability

  framework, which is another example of the type of outsourcing framework proposed in the literature. Bolumole uses the guiding factors '(perceived) business value of logistics to supply chain &

	F o r
	P
	e
	e r
	R
	e
	v i e
	w
	O n l
	y

Table 4 .

 4 Materials handling outsourcing framework

	Buffering	Assembly / MH
	Figure 5. Parts supply options
	F o r
	P
	e
	e r
	R
	e
	v i e
	w
	O n l
	y
		22

Table 5 .

 5 Summary of performance indicators and results of the six cases at Scania Production Zwolle

	Page 23 of 23

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Acknowledgements

The authors wish to sincerely thank Ton Vollebregt, Logistics manager, André Rook, Logistics engineering manager, Harry Gruben, Materials handling manager, Marcel Beij, Material planning manager, Hillebrand Diever, Transport manager and the other interviewees at Scania Production Zwolle, The Netherlands, for giving freely of their time. In addition, the authors owe gratitude to the two reviewers and the editor for their valuable time and outstanding suggestions.


Stefanie ; Dehnen

Susanne Burtzlaff

Malgorzata Holynska

Małgorzata Hołyńska

Synthesis and crystal structures of K2SnAs2 and a new modification of NaAs

Keywords: Zintl phases, Crystal structure, Binary Anions, Pnicogenido Stannates Zintl phases / Crystal structure / Binary Anions / Pnicogenido Stannates

published or not. The documents may come   L'archive ouverte pluridisciplinaire

Introduction

Although having been systematically investigated for nearly 80 years, Zintl phases still represent a hot topic in recent inorganic research. In the meantime, the pioneer work by Zintl himself 1 was enriched by first structural investigations in the 1970ies 2 and further extended by the synthesis and characterization of phases containing binary anions of different combinations of main group (semi-)metals. 3 Very recently, another dimension of Zintl anions was added by the investigation of intermetalloid Zintl anionsboth binary and ternary variations. 4 Depending on the combination of main group element atoms in binary Zintl anions, the resulting phases show very different chemical and physical properties. Having intensely studied the syntheses, structures and reactivity of binary Group 14/16 anions, 5 one of our current aims is the investigation of Group 14/15 anions with regard to their synthesis and structures and with regards to their reactivity toward transition metal complexes. We have recently shown that the latter provides an approach toward ternary intermetalloid Zintl anions. 6 Herein we report synthesis and structures of one new compound and one new modification of a known one, that yielded from reactions of alkali metals with Sn and As at high temperatures, the ternary Zintl phase K 2 SnAs 2 (1) and a new example of the binary Zintl phase NaAs (2), which was observed in low yield beside the known ternary phase Na 10 Sn 2 As 6 . 7a These investigations serve to add new results to comprehensive work by further working groups. 7

Results and Discussion

Compounds 1 and 2 were obtained under similar reaction conditions with the difference of the alkali metal used. Surprisingly, the crystalline product of the reaction with Na did not only comprise a ternary salt but also a binary Zintl phase. Scheme 1 summarizes the synthesis of 1 and 2.

x A + y Sn + z As

T = 920° A = K A = Na x, y, z = 2, 1, 2
x, y, z = 5, 1, 3

K2SnAs2

(1) Na10Sn2As6 7 + NaAs (2)

Scheme 1. Schematic synthesis pathways for compounds 1 and 2 at high temperatures. For details of the reaction conditions see the Experimental Section.

Compound 1 was refined in the orthorhombic space group Cccm (no. 66) with a = 14.653 (5), b = 25.415(6), c = 6.953(4) Å, V = 2589(2) Å 3 and Z = 8. 8 Compound 2 crystallizes in the monoclinic space group P2 1 /c (no. 14) with a = 6.242 (9), b = 5.849(7), c = 11.55(2), Å, β = 117.1(2)°, V = 375(1) Å 3 and Z = 4). The crystal structures of 1 and 2 are depicted in figures 1 and 2, respectively.

In 1, the Sn and As atoms form one-dimensional chains along the crystallographic c axis by trans-edge sharing [SnAs 4 ] tetrahedra. This motif is known from several binary atomic arrangements, among them the neutral prototype SiS 2 structure, 9 the [InTe 2 ] -anion in AInTe 2 (A = Na, K, Rb, Tl) 10 or the [FeS 2 ] - anion in KFeS 2 , 11 all of which are isoelectronic to the [SnAs 2 ] 2- substructure in 1. For binary Group 14/15 anions, several analogues of 1 have been reported, among them the isostructural heavier homologue, Cs 2 SnAs 2 12a and the lighter homologue Rb 2 SiAs 2 (space group Ibam). 12b We checked if it would be possible to refine 1 assuming the smaller cell as for Cs 2 SnAs 2 12a and the reported atomic coordinates. Both the attempt to solve the structure and to refinement the structure in Ibam were not successful, which suggests that 1 is not isomorphous with several reported salts besides Cs 2 SnAs 2 , such as Cs 2 MnSe 2 , 12c K 2 MnTe 2 , 12c Rb 2 MnTe 2 , 12c Cs 2 SiAs 2 12a and K 2 ZnTe 2 . 12d In the orthorhombic space group Cccm there are three symmetry-independent {[SnAs 2 ] 2-} n chains, in one of which (Sn1, As1a-1d) the As atoms 9) ppm; As-Sn-As 96.9(1)-97.5(2)°) are very similar to those reported for Cs 2 SnAs 2 (Sn-As 263.1(1) pm, Sn…Sn 347.7(2) pm; As-Sn-As 97.28(1)°). 12a . The anionic chains are stabilized and held together by interactions with the K + ions in between. The new modification of NaAs adopts the LiAs structure type. 13 As shown in figure 2, 2 contains infinite, idealized 4 1 chains of two-coordinate, formal As -atoms, as observed for the known modification of NaAs, 14 that crystallizes in the NaP structure type, 15 thus in the space group P2 1 2 1 2 1 . In this type, the idealized 4 1 helices, that possess crystallographic 2 1 symmetry, all show the same rotational sense within the crystal. In contrast, the { For the synthesis of 1, we did not detect binary by-products -at least no crystalline ones. However, in this case the product corresponded to the stoichiometry of the reactants. The stoichiometry used for the synthesis of 2 also accorded exactly to the atomic ratio within the desired -known -product K 10 Sn 2 As 6 . Therefore, reactions of Na with the SiO 2 walls of the quartz tube have probably led to a change in the available amount of elements and enabled the generation of the by-product 2 in low yields.

Conclusions

The attempt to synthesize ternary Zintl phases containing binary [Sn x As y ] q-anions led to the formation of the new compound K 2 SnAs 2 and a new modification of the binary Zintl phase NaAs in low yields beside a known ternary salt. Both structures comprise chains of 1-dimensionally extended Zintl anions; different to the known NaAs modification, the one reported herein adopts the LiAs structure type with the idealized 4 1 helices of the {[As] -} n strands according to two different rotational senses.

Experimental Section

Synthesis of 1: Potassium metal (1.978g, 46.1 mmol) and tin (2.744 g, 23.1 mmol) were combined in a Quartz ampoule under argon and melted by heating up using a Bunsen burner. Upon cooling down to room temperature, 2 molar equivalents of arsenic -with respect to Sn -(3.458 g, 46.1 mmol) were added and the mixture was heated to melt again. In order to gain a homogenous phase, 0.500 g (1.4 mmol) of the crude product was pulverized within a glove-box, transferred into a second Quartz ampoule that was subsequently sealed under high vacuum, and tempered in a hightemperature oven (50°C•h -1 to 920°C, 2 h at 920°C, 30°C•h -1 to room temperature. Dark needles with metallic glance of 1 were obtained in near quantitative yield (99%). Synthesis of 2: Sodium metal (2.206 g, 95.9 mmol) and tin (2.070 g, 17.4 mmol) were combined in a Quartz ampoule under argon and melted by heating up using a Bunsen burner. Upon cooling down to room temperature, 3 molar equivalents of arsenic -with respect to Sn -(3.920 g, 52.3 mmol) were added and the mixture was heated to melt again. A dark product with metallic glance results. Beside known Na10Sn2As6 LIT as the main product, crystals of 2 were obtained in low yield (8%). X-ray Crystallography: Data collection was performed on a STOE IPDS-I (1) or STOE-IPDS-II (2) diffractometer with graphite-monochromated MoKα radiation (λ = 0.71073 Å) at 203 K (1) or 173 K (2). ( 1) was solved by Patterson method and refined on F 2 by full-matrix least-squares methods using the SHELXTL program package. 16 In case of (2) the atomic coordinates were taken directly from literature 13 for the sake of simplified comparison. Crystal data for K2SnAs2 (1, M = 346.73 g•mol -1 ): 1 is described in the orthorhombic space group Cccm (no. 66), a = 14.653( 5), b = 25.415( 6), c = 6.953(4) Å, V = 2589(2) Å 3 at 203 K, Z = 8, Dc = 3.558 g•cm -1 , µ = 15.23 mm -1 , 6147 reflections measured (R(int) = 0.1686), 850 unique, 578 with I > 2σ(I) and final R values R1 = 0.0780 (I > 2σ(I)); wR2 = 0.1810 (all data)). The data are affected by twinning and/or intergrowth of the needle-type crystals; therefore several models have been tested: 1 was solved in the triclinic space group P-1 (a = 6.953, b = 14.631, c = 14.653 Å; α = 60.28, β = 89.96, γ = 89.86°). Subsequently the structure was transformed to the monoclinic space group C2/c (a = 14.653, b = 25.413, c = 6.953 Å; β = 90.04°; transformation matrix by rows: 0 0 -1, 0 2 -1, 1 0 0). Next the space group was switched to the Cccm reported in the text (transformation matrix by rows: -1 0 0, 0 1 0, 0 0 -1). At this stage another transformation is possible to P6/mcc (origin shift to 0.5 0 0, transformation matrix by rows: -1 1 0, 0 2 0, 0 0 -1). In all solutions the structure general features (described in text) persist. Crystal data for NaAs (2, M = 97.91 g•mol -1 ): monoclinic, space group P21/c (no. 14), a = 6.242( 9), b = 5.849(7), c = 11.55(2), Å, β = 117.1(2)°, V = 375(1) Å 3 , Z = 4, Dc = 3.465 g•cm -1 , µ = 17.76 mm -1 , 1562 reflections measured (R(int) = 0.0812), 473 unique, 392 with I > 2σ(I) and final R values R1 = 0.0677 (I > 2σ(I)); wR2 = 0.1541 (all data). Further details of the crystal structure investigation for compounds 1 and 2 can be obtained from the Fachinformationszentrum Karlsruhe, 76344 Eggenstein-Leopoldshafen, Germany, (fax: (+49) 7247-808-666; e-mail: crysdata@fiz-karlsruhe.de) on quoting the depository numbers CSD 421419 and 421420.

Wiley-

Entry for the Table of Contents

Figure 1 .

 1 Figure 1. General features of the crystal structure of 1. Fragment of the crystal structure (top, omitting disorder for clarity) and of one of the three crystallographically independent {[SnAs2] 2-}n chains running along the crystallographic c axis (bottom). Selected distances /pm and angles /°: Sn-As 2.620(3)-2.628(4) ppm, Sn...Sn 347.6(2)-349.8(9) ppm, As-Sn-As 96.9(1)-97.5(2)°

  [As] -} n chains in 2, that equally show crystallographic 2 1 symmetry, are alternately right handed (around [0,b,0]) or left handed (around [½,b,½]). The As-As distances in 2 (245.5(5) -248.4(4) pm) correspond well to the reported ones (246.5 pm on average). Whereas the As-As-As angles (109.2(2) and 111.6(2)°) in 2 are slightly smaller than those in the known NaAs structure (111.9° and 114.8°), the As-As-As-As torsion angles are identical in both modifications (2: 54.5(2) -68.3(2)°; reported: 54.2 -68.3°). The latter clearly demonstrates the derivation of the helical structures from a 4 1 symmetry in both structures.The Na ions in 2 are located between the As helices. In the NaPtype NaAs, they form one-dimensional helices that run through the crystal along [1,0,0], perpendicular to the {[As] -} n chains along [0,1,0]. Different to that, they form planar four-ring arrangements (Na1 -Na2(x, 1.5-y, 0.5+z) -Na1(1-x,1-y,1-z) -Na2(1-x, y-0.5, 0.5-z); Na…Na 331(2) -345(2) pm) that are topologically connected via trans-corners (Na2...Na2(-x,1-y,-z) 330(2) pm), and run through the crystal in a declined manner between the {[As] -} n helices. The Na…As interactions lead to c.n. = 8 for the As atoms (AsAs 2 …Na 6 ; As…Na 299(1) -314(1) pm). Vice versa, Na atoms possess c.n. = 6.

Figure 2 .

 2 Figure 2. Figure 2. Fragment of the crystal structure of 2 approximately along crystallographic b axis (left hand side) and arrangment of the Na + ions (right hand side). Selected distances /pm and angles /°: As-As 245.5(5) -248.4(4), As…As (along b) 584.9(7), As…Na 299(1) -314(1), Na…Na 331(2) -345(2); As-As-As 109.2(2) -111.6(2).

  Binary and ternary Zintl anionsSolid state reactions of K or Na with Sn and As have resulted in the formation of a new ternary Zintl phase, K 2 SnAs 2 (1) and a new modification of the binary Zintl phase NaAs (2, see figure), the syntheses and structures of which are report herein.

Acknowledgments

This work was supported by the Deutsche Forschungsgemeinschaft (DFG). ____________


Hans-Juergen Meyer

Markus Ströbele

H.-Jürgen Meyer

Professor Bernd Harbrecht

Dr H.-Jürgen Meyer

The crystal structure of Bi 2 W 6 Br 18 and a new synthesis of W 6 Br 12

Keywords: tungsten cluster, bromide, synthesis Tungsten cluster, Bromide, Synthesis, Structure

The new tungsten bromide cluster compound Bi 2 W 6 Br 18 was synthesized by reacting tungsten hexabromide with bismuth metal in a silica tube at 350 °C. The structure of Bi 2 W 6 Br 18 was refined by single crystal X-ray diffraction in the space group P2 1 /c with unit cell dimensions of a = 981.8(2) pm, b = 1305.9(2) pm, c = 1256.8(2) pm and β = 101.81(2)°. The crystal structure is constructed from [(W 6 Br 8 i )Br 6 a ] 2-anions being interconnected by outer bromine ligands with (BiBr 2 ) units, which behave as cations in (BiBr 2 ) 2 [(W 6 Br 8 )Br 6 ]. Short Bi-Br bonding distances at 261.3(1) pm and 265.9(2) pm in (BiBr 2 ) units suggest the presence of covalent interactions. Thermal decomposition of the compound leads to W 6 Br 12 .

Introduction

Tungsten halide cluster chemistry is represented by a remarkable widespread domain of different compounds and structures. Currently known tungsten clusters are represented by the octahedral [W 6 X 12 ] type cluster of W 6 Cl 18 [1,2], the octahedral [W 6 X 8 ] type cluster of W 6 X 12 with X = Cl, Br [3], and the centered trigonal prismatic cluster core in W 6 CCl 18 [4].

Mixtures of such clusters were obtained in the structure of W 30 C 2 X 68 (X = Cl, Br) containing carbon centered trigonal prismatic and octahedral cluster moieties in one structure [5]. More cluster types have been discovered in the field of tungsten iodides [6], just recently extended by the identification of the binary compound W 15 I 47 containing a square pyramidal cluster core [7].

Based on these tungsten halide clusters, several salt-like compounds have been synthesized

in which clusters act as bulky anions [8]. Compounds with [W 6 X 8 ] type clusters have been reported with monovalent A ions in AW 6 Cl 13 , A 2 W 6 Cl 14 [9,10,11], and with trivalent M ions in MW 6 Cl 15 M = Bi [12,13], Gd, Tb, Dy [14]. Corresponding cluster bromides were reported as NaW 6 Br 13 [15], AW 6 Br 14 with A = Na, Ag [16], and A 2 W 6 Br 14 with A = Ag [16], K [17], Rb [17],

Cs [18], Tl [17], Cd [19], and Cu [20].

The synthesis of W

Experimental Section

Synthesis of Bi 2 W 6 Br 18

Manipulations of the starting materials WBr 6 and Bi (Riedel-de Haen, 99 %) were performed in a dry box under argon atmosphere. A mixture of WBr 6 (0.5 g, 0.75 mmol) and elementary Bi (0.21 g, 1 mmol) were charged into a two chamber silica tube and sealed under vacuum.

This mixture was heated in a tube furnace at 350 °C for 48 h. Afterwards, the coproduced BiBr 3 was sublimed off from the bulk part (later identified as Bi 2 W 6 Br 18 ) into the receiver chamber of the silica vessel, being exposed with a lower temperature (near room temperature) over the period of two days. Finally, the ampoule was cooled down to room temperature, the receiver chamber was disconnected from the product chamber, and the content of the product chamber was collected inside the dry box. Dark amber colored rhombic crystals of the new Bi 2 W 6 Br 18 were selected for X-ray single crystal structure analysis.

When the mixture was treated at slightly higher temperatures (at 370 °C for one week)

Bi 2 W 6 Br 18 was decomposed into W 6 Br 12 and coproduced BiBr 3 , which was subsequently sublimed off.

Synthesis of (H 3 0) 2 [W 6 Br 14 ]•4H 2 O

Bi 2 W 6 Br 18 was dissolved in boiling concentrated HBr solution. Brownish crystals of (H 3 O) 2 [W 6 Br 14 ]•4H 2 O were crystallized upon cooling the solution to room temperature.

Synthesis of WBr 6

A Schlenk tube with two gas cocks was charged with 3 g (8.5 mmol) W(CO) 6 (ABCR, 99 %) in a dry box under argon atmosphere. Afterwards, the tube inlet was connected to an argon line in order to provide an inert gas atmosphere, and the outlet was equipped with three empty washing bottles. After the vessel was cooled with liquid nitrogen, 12.8 ml of liquid Br 2 (0.5 mol) were added to the solid W(CO) 6 . The reaction was initiated by allowing the vessel to warm up slowly to room temperature by removing the liquid nitrogen coolant. After resting for 30 min. at room temperature the three washing bottles were filled with alkaline sodium sulfite solution and the Schlenk tube was heated in a water bath to remove the excess of bromine from the reaction. The residual dark gray WBr 6 powder was collected inside the dry box.

X-ray Diffraction

The XRD patterns of reaction products were collected with a Stadi-P (Stoe, Darmstadt) powder diffractometer using Cu-K α1 radiation (germanium monochromator), with Bi 2 W 6 Br 18

and (H 3 O) 2 [W 6 Br 14 ]•4H 2 O being obtained X-ray pure, although WBr 6 contained some small amounts of WOBr 4 (about 5%) which may be a result of an oxygen contamination of W(CO) 6 .

A single crystal of Bi 2 W 6 Br 18 was coated with lithelen grease and attached to the tip of a glass fibre. Single crystal diffraction data were collected with an IPDS diffractometer (STOE, Darmstadt) using monochromated Mo-K α radiation. The unit cell refinement and data reduction were carried out using the STOE IPDS software. An absorption correction was applied by using the programs X-Shape/X-Red [23]. The structure was refined in the space group P2 1 /c by full-matrix least-squares procedures using SHELX-97 [24].

Results and Discussion

The ] compounds.

The two short Bi-Br distances with Br(8) at 265.9(2) pm and Br(9) at 261.3(1) pm are contained in a strongly distorted edge-sharing bi-octahedral Bi 2 Br 10 moiety, displayed in Figure 1. All the remaining bromide atoms of this moiety, with Bi-Br distances presented in Table 3 can be referred as outer ligands of the tungsten cluster (Figure 2).

The [(W 6 Br 12 i )Br 6 a ] 2-cluster (Figure 3) in the structure exhibits W-W distances ranging from 261.94 (7) to 264.13 (7)

Figure 1 .

 1 Figure 1. Projection of the environment of pairs of bismuth atoms in the structure containing two short Bi-Br distances each.

Figure 2 .

 2 Figure 2. Connectivity of (BiBr 2 ) 2 units with outer bromide cluster ligands. (W 6 Br 8 i ) clusters are shown as octahedra.

Figure 3 .

 3 Figure 3. Projection of an isolated [(W 6 Br 8 i )Br 6 a ] 2-cluster.

Figure 4 .

 4 Figure 4. Unit cell of (BiBr 2 ) 2 [(W 6 Br 8 i )Br 6

  All atoms were refined anisotropically. Crystallographic data and structure refinement results are summarized in Table 1, atom positions are listed in Table 2, and selected bond lengths are given in Table 3.

	A brown single crystal of (H 3 O) 2 [W 6 Br 14 ]•4H 2 O was measured under analogous conditions as
	Bi 2 W 6 Br 18 . The structure solution and refinement for (H 3 O) 2 [W 6 Br 14 ]•4H 2 O was performed with
	the space group C2/c with a = 1598.2(2) pm, b = 1066.4(2) pm, c = 1802.0(3) pm, and β =
	108.27(2) °, yielding R values of R1 = 0.049, wR2 = 0.076 based on all measured data.
	Further details on the crystal structure investigations may be obtained from the
	Fachinformationszentrum Karlsruhe, 76344 Eggenstein-Leopoldshafen, Germany, on quoting
	the depository number CSD-421436 for Bi 2 W 6 Br 18 and CSD-421437 for (H 3 O) 2 [W 6 Br 14 ]•4H 2 O.

  compound Bi 2 W 6 Br 18 was prepared by metallothermic reduction of WBr 6 with bismuth metal at 350 °C. However, Bi 2 W 6 Br 18 is thermally labile and decomposes slowly at temperatures above 370 °C to yield W 6 Br 12 and BiBr 3 , of which the latter can be sublimed off into the colder section (room temperature) of the reaction vessel. This procedure, as emphasized in the following reaction equations permits a comfortable access to obtain pure W 6 Br 12 .

	6 WBr 6 + 8 Bi → Bi 2 W 6 Br 18 + 6 BiBr 3	(1)
	Bi 2 W 6 Br 18 → W 6 Br 12 + 2 BiBr 3	(2)
	The composition Bi 2 W 6 Br 18 may suggest a relationship with A 2 [W 6 Cl 18 ] compounds containing
	[(W 6 Cl 12 i )Cl 6 a ] 2-ions [8]. However, the crystal structure of Bi 2 W 6 Cl 18 was refined to yield a
	structure which can be described as (BiBr 2 ) 2 [(W 6 Br 8 i )Br 6 a ], reflecting a structural relation to
	the already known bismuth chloro-tungstenate (BiCl)[(W 6 Cl 8 i )Cl 6 a ]. The structure of
	(BiBr 2 ) 2 [(W 6 Br 8 i )Br 6 a ] contains two bromine atoms being involved in covalent bonding with
	bismuth, thus allowing a (BiBr 2 ) moiety to act as a monovalent cation like A (+) in
	A 2 [(W 6 Br 8 i )Br 6 a

Table 1 .

 1 CsCl type like structural arrangement of bi-octahedral (Bi 2 Br 10 ) units and (W 6 Br 8 ) cluster units. Six out of ten bromides of the bi-octahedral (Bi 2 Br 10 ) unit are in fact outer bromide ligands of the cluster (Figure2). The given, straight forward synthesis of W 6 Br 12 would be challenging for the preparation of the corresponding tungsten dichloride, W 6 Cl 12 , too. The related bismuth chloro-tungstenate precursor having the formula BiW 6 Cl 15 has shown to behave thermally stable up to 340 °C.Thermal treatments at higher temperatures appeared inadequate for BiW 6 Cl 15 because W 6 Cl 12 has shown to react with quartz tubing above 350 °C. Therefore, a purification process via solution has been used subsequently for the synthesis of W 6 Cl 12[21]. Following this procedure, both, the chloride and bromide compounds can be dissolved into their aqueous HCl and HBr solutions to yield (H 3 O) 2 [W 6 Cl 14 ]•7H 2 O and (H 3 O) 2 [W 6 Br 14 ]•4H 2 O, respectively. A structure refinement based on a single crystal measurement of (H 3 O) 2 [W 6 Br 14 ]•4H 2 O (with crystal data being deposited in the ICSD) has shown that the structures of both compoundsare closely related to each other (space group C2/c). In addition, both compounds can be pyrolyzed to yield binary W 6 X 12 (X = Cl, Br)[3]. Crystal data and structure refinement data of (BiBr 2 ) 2 [(W 6 Br 8 i )Br 6

	The crystal structure of (BiBr 2 ) 2 [(W 6 Br 8 i )Br 6

pm, W-Br i distances ranging from 260.1(2) to 262.8(1) pm, and W-Br a distances ranging from 257.4(2) to 264.2(2) pm. All these distances reflect typical values among bromo-tungstenate cluster units of this type. a ] is displayed in Figure 4 and shows a -11 ≤ h ≤ 11, -15 ≤ k ≤ 15, -14 ≤ l ≤ 14

Table 2 .

 2 Atomic coordinates (x 10 4 ) and equivalent isotropic displacement parameters (pm 2 x 10 -1 ) of (BiBr 2 ) 2 [(W 6 Br 8 i )Br 6 a]. U eq is defined as one third of the trace of the orthogonalized U ij

	tensor.
	________________________________________________________________________
		x	y	z	U eq
	________________________________________________________________________
	Bi(1)	72(1)	8578(1)	998(1)	27(1)
	W(1)	5939(1)	6247(1)	40(1)	22(1)
	W(2)	3577(1)	5643(1)	505(1)	20(1)
	W(3)	5908(1)	4728(1)	1422(1)	20(1)
	Br(1)	5427(2)	6607(1)	1970(1)	29(1)
	Br(2)	8244(1)	5345(1)	956(1)	28(1)
	Br(3)	6441(1)	5850(1)	-1888(1)	27(1)
	Br(4)	3611(1)	7154(1)	-864(1)	26(1)
	Br(5)	7164(2)	8048(1)	29(1)	40(1)
	Br(6)	1572(2)	6481(1)	1228(1)	37(1)
	Br(7)	7080(2)	4312(1)	3444(1)	35(1)
	Br(8)	-786(2)	482(1)	1225(1)	39(1)
	Br(9)	-251(2)	8094(1)	2948(1)	41(1)

Table 3 .

 3 Selected bond lengths (in pm) of (BiBr 2 ) 2 [(W 6 Br 8 i )Br 6

	a ].
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	W -W: 261.94(7) -264.13(7)