Mourad Essalhi
email: mourad.essalhi@univ-orleans.fr

Stanislas Sizaret

Luc Barbanson

Yan Chen

Yannick Branquet

Dominique Panis

Pierre Camps

Pierre Rochette

Angels Canals

Track of fluid paleocirculation in dolomite host rock at regional scale by the Anisotropy of Magnetic Susceptibility (AMS): An example from Aptian

Keywords: AMS, carbonates, fluid flow, growth anisotropy, mineral texture. 1. Introduction

Track of fluid paleocirculation in dolomite host rock at regional scale by the Anisotropy of Magnetic Susceptibility (AMS): An example from Aptian carbonates of La Florida (Northern Spain)

Tracking hydrothermal circulation is one of the main challenges in investigations of metasomatism. Classic studies have used geochemical signature and megascopic hydrodynamic models (e.g., [START_REF] Wing | Magnitude and geometry of reactive fluid flow from direct inversion of spatial patterns of geochemical alteration[END_REF]. However, in these models fluid paths are not constrained by field observations. The method of Anisotropy of Magnetic Susceptibility (AMS) has been proposed to track flow circulation [START_REF] Hounslow | The crystallographic fabric and texture of siderite in concretions: implications for siderite nucleation and growth processes[END_REF][START_REF] Sizaret | Anisotropy of Magnetic susceptibility (AMS) and trace chemistry: a new approach to discriminate between hydrothermal and supergene processes. Application to the Ba-Fe-F deposit of Chaillac (Indre, France)[END_REF][START_REF] Sizaret | Magnetic fabrics and fluid flow directions in hydrothermal systems. A case study in the Chaillac Ba-F-Fe deposits (France)[END_REF]Sizaret et al., , 2006a;;[START_REF] De Wall | Oblique magnetic fabric in siderite-bearing pelitic rocks of the Upper Carboniferous Culm Basin, SW England: an indicator for paleo fluid migration?[END_REF]. This approach is based on crystal growth orientations [START_REF] Kessler | Direction of flow of mineralizing solutions at pine point[END_REF] and supported by the crystal growth theory [START_REF] Prieto | Formation of primary inclusions under influence of the hydrodynamic environment[END_REF]Sizaret et al., 2006b). These studies show a higher growth rate on crystal faces in upstream position which produces crystal elongation parallel to the direction of circulation. The orientation of this elongation can be measured using AMS method, and interpreted in terms of flow direction.

AMS, considerably developed in the last 30 years, was for a long time devoted to structural and rock petrofabric studies (e.g., [START_REF] Hrouda | Magnetic anisotropy of rocks and its application in geology and geophysics[END_REF][START_REF] Tarling | The magnetic anisotropy of rocks[END_REF][START_REF] Ferré | Theoretical models of intermediate and inverse AMS fabrics[END_REF], to granite pluton characterization (e.g., [START_REF] Jover | Magnetic mineralogy of some granites from the French Massif Central: origin of their low-field susceptibility[END_REF][START_REF] Bouillin | Granite emplacement in an extensional setting: an AMS study of the magmatic structures of Monte Capanne (Elba, Italy)[END_REF][START_REF] Talbot | Pull-apart emplacement of the Margeride granitic complex (French Massif Central). Implications for the late evolution of the Variscan orogen[END_REF] or magmatic flow description (e.g., [START_REF] Nomade | Paleomagnetic study of French Guyana Early Jurassic dolerites: hypothesis of a multistage magmatic event[END_REF], and to describe the rock deformation (e.g., [START_REF] Borradaile | The influence of deformation mechanisms on magnetic fabrics in weakly deformed rocks[END_REF][START_REF] Evans | Strain partitioning of deformation mechanisms in limestones: examining the relationship of strain and Anisotropy of Magnetic Susceptibility (AMS)[END_REF]. This technique is based on the directional variation of the magnetic susceptibility K on sample scale. The latter is a property of solids reflecting the capacity of a material to be magnetized in a given magnetic field (

H M K =
, M and H are respectively the induced and applied magnetic fields). In an anisotropic material, K can be described as a second rank tensor or an ellipsoid defined by three perpendicular oriented axes K 1 , K 2 and K 3 (the maximum, intermediate and minimum of the magnetic susceptibility, respectively). K 1 and K 3 are respectively considered as the magnetic lineation and the pole of the magnetic foliation.

Several studies were carried out on the relation between carbonate single crystals and their magnetic susceptibility [START_REF] Owens | The development of magnetic susceptibility anisotropy through crystallographic preferred orientation in a calcite rock[END_REF][START_REF] Rochette | Inverse magnetic fabric in carbonate bearing rocks[END_REF][START_REF] Shogenova | The influence of dolomitization on the magnetic properties of Lower Palaeozoic carbonate rocks in Estonia[END_REF][START_REF] Schmidt | Magnetic anisotropy of calcite at roomtemperature[END_REF]. In carbonates, magnetic susceptibility is controlled by intrinsic properties (such as crystallographic directions and chemical composition) and crystal shape.

So, a fluid migration occurring in these rocks and producing recrystallisation and/or cementation would introduce a modification in composition and/or shape of their constitutive minerals and, therefore, a remarkable variation of the magnetic fabrics. The latter can be measured and interpreted to infer the characteristics of circulating paleo-fluid [START_REF] Prieto | Formation of primary inclusions under influence of the hydrodynamic environment[END_REF]Sizaret et al., 2006b). As observed by [START_REF] Kessler | Direction of flow of mineralizing solutions at pine point[END_REF] and modelled by Sizaret et al. (2006b), this fluid circulation may be evidenced by a growth anisotropy. According to these authors, the thickest growth bands show the upstream, whereas the thinnest ones indicate the downstream of the flow. These results are fundamental to recognize the relationship between the carbonate crystal growth and their magnetic fabrics.

The main objective of this study is to link AMS data and mineral texture analysis to fluid migration in a carbonate environment, at a larger regional scale with respect to previous works [START_REF] Sizaret | Magnetic fabrics and fluid flow directions in hydrothermal systems. A case study in the Chaillac Ba-F-Fe deposits (France)[END_REF](Sizaret et al., , 2006a)). For this work it has been chosen to apply the method to study deposit in carbonate environment where large fluid migration is suspected.

The Zn-Pb mineralizations of Cantabrian mining district are located in Cretaceous basin with occurrence of salt dome (Fig. 1A). The ore is hosted in Urgonian carbonates and is associated with epigenetic dolomite [START_REF] Barbanson | Distribution à différentes échelles et chronologie relative des carbonates de l'Aptien de la Province de Santander: relation entre auréole ferrifère et minéralisations Zn-Pb du type Réocin[END_REF][START_REF] Barbanson | Les minéralisations Zn-Pb des systèmes biosédimentaires urgoniens du domaine Ouest-Santandérin (Nord de l'Espagne)[END_REF][START_REF] Barbanson | The carbonate hosted Zn-Pb deposit of West-Santanderin type (North of Spain): Tectonical control at regional and local scale[END_REF]. Recent study based on Br, Cl and Na concentration of the mineralising fluids suggest a general mixing involving halite saturated brine derived from halite dissolution suggesting a strong link with salt dome [START_REF] Grandia | Origin of ore-forming brines in sediment-hosted Zn-Pb deposits of the Basque-Cantabrian basin, Northern Spain[END_REF]. At La Florida mine this relation is also supported by a geochromatography of Organic matter suggesting migration from salt into the Urgonian plate form [START_REF] Hu | Hydrocarbon geochromatographic fractionation, water-washing, biodegradation and Zn-Pb ore genesis: the La Florida ore deposit (Spain)[END_REF]1998). Tracking mineralising flow direction on this site using the method based on AMS and texture analysis is the challenge of this paper.

Geological setting

General framework

The Zn-Pb mine of La Florida (Province of Santander, Spain) is located in the western part of a Cretaceous basin, which overlies the Asturian Paleozoic massif in the west and the Basque massif in the east (Fig. 1B). This basin is covered by the Vieja Castilla and the Ebro Tertiary deposits in its south and limited by the Bay of Biscay in its north. The meridian line of Santander forms a rough limit between an oriental domain more intensely folded during the Pyrenean orogeny and a west-Santanderian domain where this orogeny is weakly expressed.

This latter domain contains the La Florida mine where this study has been carried out. The eastern border of this mine is limited by Triassic evaporite diapirs (Fig. 1B).

The geological history of this basin starts at the Aptian and the Albian when a distensive folding of the Basco-Cantabric unit induces the development of a passive continental margin [START_REF] Rat | Subsidence et évolution des environnements sédimentaires sur la marge cantabrique (Espagne) du Crétacé[END_REF][START_REF] Rat | Les plates-formes carbonatées à Rudistes (dites urgoniennes) du Cretacé Inferieur et leur environnement[END_REF]. This event initiates the development of large Urgonian carbonate platforms in the west-Santanderian domain. [START_REF] Pascal | Evolution des systèmes biosédimentaires Urgoniens en Espagne du Nord[END_REF][START_REF] Pascal | Les systèmes biosédimentaire Urgoniens (Aptien-Albien) sur la marge nord-ibérique[END_REF] described the evolution of this Urgonian complex as the succession in time of three bio-sedimentary systems. The first two systems end up respectively by the lower and the upper rudist Urgonian platforms (Fig. 2A). The last bio-sedimentary system is characterised by an invasion of the basin by terrigenous sediments.

Metallogenic framework

La Florida Pb-Zn mine is located close to the well known Reocin mine (60 MT, 8%

Zn) in the western part of the Santander district in the Aptian Basque-Cantabrian basin. In this Fig. 1 district a number of similarities between Urgonian hosted Zn-Pb deposits of Cantabria allowed [START_REF] Barbanson | Les minéralisations Zn-Pb des systèmes biosédimentaires urgoniens du domaine Ouest-Santandérin (Nord de l'Espagne)[END_REF] to define a "west-Santanderian" sphalerite  galena ore deposit type in carbonated environment. Three main characteristics are common in these deposits: (i) mineralizations are located in ferroan dolomite host rock (Fig. 2A), (ii) these mineralizations occur mainly close to the synsedimentary faults controlling the Urgonian sedimentation, and (iii) in the ore, the paragenetic succession is split in two main mineralogical sequences: sphalerite  galena  Fe-rich dolomite and dolomite  marcasite (Fig. 2B). Geological observations suggest that synsedimentary and epigenetic mineralizations were formed during an Aptian-Early Cenomanian metallogenic epoch. It could be noted that ferroan dolomite host rock is affected by an Aptian emersion [START_REF] Barbanson | The carbonate hosted Zn-Pb deposit of West-Santanderin type (North of Spain): Tectonical control at regional and local scale[END_REF]. [START_REF] Barbanson | Les minéralisations Zn-Pb des systèmes biosédimentaires urgoniens du domaine Ouest-Santandérin (Nord de l'Espagne)[END_REF] recognize two genetic processes forming deposits of Cantabria (La Florida and other mining districts); the first is interpreted as a synsedimentary mineralization occurring in paleo-channels, whereas the second is an epigenetic mineralization observed in subterranean cavities. In both cases mineralizations display the same paragenetic succession as presented in figure 2B.

In the Cantabria district two main stages of dolomitization could be described. The first one consists in pervasive dolomitization affecting the Aptian limestone. The analysis of the δ 13 C PDB and δ 18 O SMOW on dolomite host rock of the Reocin deposit are interpreted by [START_REF] Velasco | Geology and geochemistry of the Reocin zinc-lead deposit, Basque-Cantabrian Basin, Northern Spain[END_REF] as "the result of the early circulation of hot Mg 2+ -rich fluids probably derived from the dewatering of basinal mudrocks". The second stage is dominated by a main iron rich dolomitization and the third stage corresponds to the saddle dolomite and Fedolomite crystals present in the ore. The mineralizing fluids have been studied and the homogenisation temperature measured in sphalerite of the Reocin mine is about 77°C, with a salinity of 25.5 wt percent NaCl equiv [START_REF] Grandia | Origin of ore-forming brines in sediment-hosted Zn-Pb deposits of the Basque-Cantabrian basin, Northern Spain[END_REF]. Moreover, analysis of Na, Cl and Br contents in fluid inclusion of sphalerite and dolomite associated to sphalerite at La Fig. 2 Florida and Reocin compared with other data measured in the mineralisation of the Basque-Cantabrian Basin suggest a precipitation by mixing of two fluids. "One of the end members could have been a highly evaporated brine and the second fluid could have been either an evaporated brine was not halite saturated or a diluted halite dissolution brine" [START_REF] Grandia | Origin of ore-forming brines in sediment-hosted Zn-Pb deposits of the Basque-Cantabrian basin, Northern Spain[END_REF].

At La Florida, Zn-Pb mineralizations are strictly associated with the ferroan dolomite host rock, which is enclosed in ordinary dolomite host rock, and the whole is involved in the Aptian limestone (Fig. 2A; [START_REF] Barbanson | Distribution à différentes échelles et chronologie relative des carbonates de l'Aptien de la Province de Santander: relation entre auréole ferrifère et minéralisations Zn-Pb du type Réocin[END_REF][START_REF] Velasco | Geology and geochemistry of the Reocin zinc-lead deposit, Basque-Cantabrian Basin, Northern Spain[END_REF]. Organic matter studies related to the mineralizations showed a geochromatographic fractionation toward West, which is more coherent with an epigenetic origin of mineralizations [START_REF] Hu | Hydrocarbon geochromatographic fractionation, water-washing, biodegradation and Zn-Pb ore genesis: the La Florida ore deposit (Spain)[END_REF][START_REF] Hu | Processus d'altération thermique, physico-chimique et biologique des constituants organiques et genèse des minéralisations sulfurées: le gîte Zn-Pb de La Florida (Cantabria, Espagne)[END_REF]. To track paleocirculation linked to dolomitization, the study is focus on the surrounding rocks with three types of simple mineralogical assemblage; Aptian biomicritic limestone locally dolomitized is constituted by calcite, whereas dolomite host rock and ferroan dolomite host rock are composed by anhedral crystals of dolomite and Fe-rich dolomite, respectively (Fig. 2B). Iron oxides are generally rare in limestone and dolomite host rock and are relatively more abundant in ferroan dolomite host rock (SEM observations).

Field structural observations

Pyrenean orogeny deformation is weakly marked in the studied zone by scarce styloliths and a few kilometer-scale folds. On the outcrop scale, the synsedimentary deformation is documented by NW-SE tilting that accommodates organic matter deposition. An observed hydroplastic slickenside lineation with direction of N110° reflects a deformation type developed in partially lithified sediments. Concerning the syndolomitization deformation, it appears in some N30° subvertical veins which are filled with baroque dolomite associated to the Zn-Pb mineralizations.

Textural analysis

Lattice Preferred Orientation

To better understand the relationship between crystallographic axis orientations of carbonates and their corresponding magnetic fabrics, measurements of lattice preferred orientation were realized by the Universal Goniometer UG 950 (Inel) on two dolomite host rock and two ferroan dolomite host rock samples to ensure representative results. The method is described by Schultz (1949aSchultz ( , 1949b)). The spatial orientations of a (h k i l) diffracting plane may be defined by records of X-rays diffracted by the rotating sample along two orthogonal axes. A spatial statistical analysis allows to infer the crystallographic preferential orientation.

Datum acquisition and treatment were described in [START_REF] Heizmann | Utilisation d'un détecteur courbe à localisation spatiale pour la mesure simultanée de plusieurs figures de pôles par les rayons X[END_REF]. To facilitate comparison and interpretation all samples were prepared according to their magnetic responses (i.e. in the K 1 K 2 or K 2 K 3 planes). All measurements were done with collimator window of 1x1 mm 2 ; sample was moved by steps on 15 mm. The (0006) diffraction peak was chosen because (i) the relation with ‹c› axes is trivial and (ii) in the diffractogram, the neighbouring of (0006) line is free of other diffraction peaks preventing overlapping by other diffraction lines.

Fig. 3 shows the measurements of lattice preferred orientation on all 4 dolomite host rock and ferroan dolomite host rock samples in tilt-corrected coordinates. We note that the ‹c› axes in dolomite host rock (Figs. 3A andB) and ferroan dolomite host rock (Figs. 3C andD) are well identified and grouped in a vertical position.

SPO statistics and growth bands studies in the (0001) isotropic plane

Thin sections from the same samples studied by texture goniometry were observed by Scanning Electron Microscope (SEM), to examine their mineralogical compositions and to Fig. 3 study the geometry of carbonate growth bands in the "isotropic" plane perpendicular to the ‹c› axes. Representative SEM images from studied thin sections are presented in Fig. 4.

In ferroan dolomite host rock we note the presence of two types of elongated ribbons whose limits cut across grain boundary (Fig. 4A). Within single crystal grains of Fe-rich dolomite two zones can be frequently distinguished: a pure dolomitic one hosting dark inclusions probably argillaceous and a Fe-dolomitic free of inclusions. The dark ribbons are made up of CaMg(CO 3 ) 2 whereas the bright ones are Ca(Mg,Fe)(CO 3 ) 2 in composition. Dark zones composed solely by pure dolomite correspond to the relic of initial rock (i.e. dolomite host rock). This difference between the two types of ribbons reflects a chemical flow that induced enrichment of some dolomite crystal zones by iron. To quantify the mean orientation of ribbons elongation, shape preferred orientation statistics [START_REF] Launeau | Fabric analysis using the intercept method[END_REF] has been carried out on microscopic images of a thin section. Results of image analysis are presented in Fig. 4B. The statistics were realized on four backscattered images taken in different places of the thin section; they give almost the same mean orientation. The result shows a well defined ENE-WSW elongation with a shape factor R of 1.387. The "nearest neighbor" statistics were also done with the same program on the relic of dolomite, they show an alignment according to the ENE-WSW direction with a shape factor R of 1.11 (Fig. 4C).

For dolomite host rock one note the presence of growth bands around triangular sections (i.e. isotropic plane) of single dolomite crystals (Figs. 4D andE). As shown by punctual analysis, the difference in grey intensities between the growth bands is due to slight departure

Magnetic analysis

Three hundreds and twenty-seven AMS oriented cores of thirty-four sites have been drilled in limestone, dolomite host rock and ferroan dolomite host rock located along four lateral transects on the northern flank of an E-W oriented anticline (Fig. 2A). This sampling scheme allows to compare the magnetic signals between mineralised rocks where fluid circulation occurred and their surrounding formations, and also to recognize spatial variation of the magnetic signal of each lithology. Sampling and measurement methods are described in [START_REF] Tarling | The magnetic anisotropy of rocks[END_REF]. Four oriented cores were at least taken from each site by a portable gasoline drill.

Magnetic Behaviour of carbonates

It is well known that the magnetic susceptibility of carbonates is mainly controlled by the orientation of their crystallographic axes (e.g [START_REF] Nye | Propriétés physiques des cristaux[END_REF]. Studied carbonates display trigonal symmetry and the crystallographic cell can be described by four crystallographic axes. Three coplanar axes ‹a›, ‹b› and ‹t› are oriented at 120° each one to other, and the fourth axis ‹c› is perpendicular to the three formers. The four axes are such that ‹a› = ‹b› = ‹t› ≠ ‹c›.

The latter is parallel to the 3-fold axis of symmetry. In the case of a perfect single crystal of calcite for example, the absolute value of the magnetic susceptibility along the ‹c› axis is higher than those along the ‹a›, ‹b› and ‹t› axes, which have the same magnetic susceptibility

(K c = -1.38 x 10 -5 [SI], K a = K b = K t = -1.24 x 10 -5 [SI], after the "International Critical
Tables" in [START_REF] Nye | Propriétés physiques des cristaux[END_REF]. So, as it could be predicted from Neumann principle in terms of magnetic susceptibility, calcite and other trigonal carbonates are isotropic according to the (0001) plane containing ‹a›, ‹b› and ‹t› axes.

On the other hand, the anisotropy of magnetic susceptibility in carbonates was the subject of several studies [START_REF] Owens | The development of magnetic susceptibility anisotropy through crystallographic preferred orientation in a calcite rock[END_REF][START_REF] Rochette | Inverse magnetic fabric in carbonate bearing rocks[END_REF][START_REF] Hrouda | Problems in interpreting ams parameters in diamagnetic rocks[END_REF][START_REF] Schneider | Magnetic susceptibility variations in carbonates of the La Vid Group (Cantabrian zone, NW-Spain) related to burial diagenesis[END_REF][START_REF] Schmidt | Magnetic anisotropy of calcite at roomtemperature[END_REF]. AMS is controlled by the orientation of their crystallographic axes, their chemistry as well as the preferential orientation of their constitutive grains. According to [START_REF] Schmidt | Magnetic anisotropy of calcite at roomtemperature[END_REF], the ‹c› axes are parallel to K 3 axis (inverse fabric) in low iron-bearing carbonates (note that K 1 , K 2 and K 3 are classified according to their algebraic values, [START_REF] Hrouda | Magnetic anisotropy of rocks and its application in geology and geophysics[END_REF]. So, in trigonal diamagnetic carbonates as calcite and pure dolomite, the lower value of K is parallel to the ‹c› axis. In rich iron-bearing carbonates they are rather parallel to the K 1 axis (normal fabric). These behaviours are observed in our samples; as shown by the comparison between lattice preferred orientation measurements obtained by texture goniometry and AMS results performed on the same samples (Fig. 3). In Fe-poor dolomite host rock, the ‹c› axes are very well grouped and they are oriented parallel to the K 3 axis of the magnetic ellipsoid (Figs. 3A andB), while in ferroan dolomite host rock, they are also vertical but parallel to K 1 axis (Figs. 3C andD). This behaviour indicates hence that iron amount in carbonates controls their magnetic response.

Magnetic mineralogical identification

In addition to microscopic observations described above, four other methods were used to identify the magnetic susceptibility carrier(s) in studied rocks: bulk susceptibility Bulk susceptibility intervals for each lithology are plotted in Fig. 5A. A majority of limestone samples have low and negative magnetic susceptibilities; they contain thus principally diamagnetic minerals, but some samples show rather positive susceptibilities suggesting the presence of small quantities of para-and/or ferromagnetic (s.l.) minerals. The dolomite host rock and ferroan dolomite host rock samples have relatively low but positive magnetic susceptibilities; in this case the rocks are mainly constituted of paramagnetic minerals, with probably a small amount of ferromagnetic (s.l.) minerals.

Isothermal Remanent Magnetization (IRM) acquisition was carried out on one sample of each lithology: limestone (site L 3 ), dolomite host rock (D 4 ) and ferroan dolomite host rock (FD 2 ) (see Fig. 2A). Results illustrate that IRM of limestone shows a fast and total magnetic saturation for applied field values of 180 mT (Fig. 6A). This saturation value indicates a low coercivity ferromagnetic (s.l.) component which illustrates the presence of magnetite [START_REF] Dunlop | Rock magnetism: fundamentals and frontiers[END_REF]. For dolomite host rock (Fig. 6B) and ferroan dolomite host rock (Fig. 6C) we note, in addition to the low coercivity component corresponding to magnetite, a high coercivity component shown by a quasi linear increase of magnetization. That magnetic behaviour illustrates a probable existence of hematite or goethite with higher coercivities [START_REF] Dunlop | Rock magnetism: fundamentals and frontiers[END_REF]. It should be noted that values of remanent magnetization are very low (few mA.m -1 ); consequently, the quantity of ferromagnetic (s.l.) minerals is very weak in all studied samples.

The hysteresis measurements were done on samples coming from the same sites studied by IRM measurements, three apparatus with different precisions were used and give similar results, the most representative are showed in Fig. 6. The hysteresis curves are not perfectly Fig. 5 linear for all lithologies and they show a strong dominance of para-, dia-and antiferromagnetic fractions component in comparison with the hysteretic ferrimagnetic one.

The limestone curve has a negative slope (Fig. 6D); K is therefore negative and the main magnetic susceptibility carrier is a mixture between diamagnetic and ferromagnetic (s.l.) as seen before (Fig. 5A). Pure and ferroan dolomite host rock curves have a positive slope, signifying that K is positive and that the magnetic carriers in these rocks are mainly a mixture between paramagnetic and ferromagnetic (s.l.) minerals (Figs. 6E and6F). Saturation determined on the corrected curves, is reached at about 500-600 mT. At 180 mT (saturation value of magnetite), we have about 75% of saturation for limestone, 60% for dolomite host rock and about 55% for ferroan dolomite host rock. This result indicates that the ferromagnetic (s.l.) contribution is a mixture between minerals with soft and hard coercivities (magnetite and hematite/goethite, respectively).

Although the bulk susceptibility histogram (Fig. 5A) show a dominance of dia-and paramagnetic minerals in limestone and dolomites host rocks, respectively, but iron oxides were detected by microscopic observations, and contribution of ferromagnetic (s.l.) minerals is identified by IRM and hysteresis measurements. In limestone the IRM measurements show that the unique ferromagnetic mineral is the magnetite (Fig. 6A) but hysteresis ones suggest rather a mixture between magnetite and hematite/goethite (Fig. 6D). In the dolomite and ferroan dolomite host rocks, IRM (Figs. 6B and6C, respectively) and hysteresis (Figs. 6E and6F, respectively) curves show also a mixture between magnetite and hematite. However, it is very difficult to estimate the exact amount of each of them, because the overall hysteresis loop of bi-mineral mixture does not represent a simple sum of contributions corresponding to individual components, but is affected by interactions between magnetite and hematite grains [START_REF] Hejda | Analysis of hysteresis curves of samples with magnetite and hematite grains[END_REF]). On the other hand,

≥

, its amount in limestone, dolomite and ferroan dolomite host rocks is estimated below 2.1, 1.2 and 9.7 ppm, respectively. Considering these quantities of ferromagnetic minerals in studied samples and the magnetic susceptibility reported in the literature [START_REF] Rochette | Rock magnetism and the interpretation of the anisotropy of magnetic susceptibility[END_REF], the ferromagnetic minerals contribution to the magnetic susceptibility appears to be low. This is obvious for ferroan dolomite host rock that has a strong magnetic susceptibility. This point will be completed by the comparison of Anisotropy of Remanent Magnetization (ARM) and AMS measurements.

The possible existence of mixed fabrics (i.e. between dia and/or para and ferromagnetic (s.l.) minerals) should be clarified. The magnetic susceptibility carriers seem to be difficult to identify, so ARM measurements were carried out on samples of limestone (from site L 10 ), dolomite host rock (D 2 ) and ferroan dolomite host rock (FD 3 ). Measurements were carried out in three steps; (i) demagnetization of the sample with an alternating field (AF = 160 mT), (ii)

ARM acquisition with a bias direct field of 250 µT (and AF = 150 mT), (iii) measurement of the induced ARM values. These three steps are repeated for 9 positions. The remanent anisotropy is modelled by ellipsoid constructed from the axial measurements plus the off-axis remanence terms. In Fig. 7 are presented stereograms showing the relation between the orientation of ARM ellipsoid axes and the AMS ones. The dolomite host rock presents the same fabrics between ARM and AMS indicating thus that susceptibility carrier is mixed with contribution of ferromagnetic minerals (s.l.) and dia/paramagnetic ones in the magnetic fabric of dolomite host rock (Fig. 7B). For the ferroan dolomite host rock, the stereogram shows a significant difference between ARM and AMS, so the susceptibility magnetic carrier should not be ferromagnetic (s.l.) minerals but a paramagnetic one (Fig. 7C). In limestone, ARM and AMS ellipsoid axes orientation are comparable, though it is less obvious than in dolomite host rock (Fig. 7A), the carrier is probably a mixture between diamagnetic and ferromagnetic (s.l.) minerals (and perhaps paramagnetic ones).

According to above laboratory analyses on rock magnetism we conclude that the magnetic susceptibility carrier is paramagnetic carbonates (Fe-rich dolomite) in ferroan dolomite host rock and mixture between iron oxides (magnetite often) and carbonates (dolomite and calcite, respectively) in dolomite host rock and limestone.

Magnetic fabrics

The AMS measurements were carried out by KLY-3S kappabridge. For each site, the mean orientation of the principal axes of the ellipsoid of magnetic susceptibility is calculated by the "bivariate statistics" [START_REF] Henry | Application de l'extension bivariate de la statistique Fisher aux données d'Anisotropie de Susceptibilité Magnétique: intégration des incertitudes de mesure sur l'orientation des directions principales[END_REF]. Principal susceptibility axes and AMS parameters are calculated by SUSAR program (AGICO).

For diamagnetic minerals, [START_REF] Hrouda | Problems in interpreting ams parameters in diamagnetic rocks[END_REF] propose two models to explain the AMS signal for quartzite/evaporite and marble/limestone. He suggest the use of signed values (approach 1) for plotting principal directions and absolute values of K 1 , K 2 and K 3 (approach 2) to calculate T parameter in case of marble or limestone, because it is calculated from <c> axes distribution pattern (in opposite to the quartzite/evaporite model which propose to use the T parameter based on the signed principal susceptibilities (approach 1), because it describes the shape of the susceptibility ellipsoid of the ferro-/paramagnetic admixture fraction). This is the case here since SUSAR program used in our measurements utilizes signed negative values (approach 1) for plotting principal directions and absolute values (approach 2) for calculating all AMS parameters.

Fig. 7

Table 1 resumes the AMS data with their principal associated parameters and Fig. 5B shows a plot of the shape parameter (T) versus the corrected anisotropy degree (P') for the three studied lithologies. P' for diamagnetic samples has been calculated following the equation given in Table 1.

To limestone, the shape parameter T is mainly positive; the ellipsoid of magnetic susceptibility presents an oblate shape. A remarkable high P' values has been observed (Table 1 and group Y of Fig. 5B), however, this may be an artefact generated by an overlap of diamagnetic and paramagnetic susceptibilities. [START_REF] Hrouda | The effect of quartz on the magnetic anisotropy of quartzite[END_REF] has shown by an AMS study on quartzites that the interference of dia-and paramagnetic behaviours can bias anisotropy results and change P' values for certain susceptibility ranges. This phenomenon characterizes our samples as shown by Fig. 5C, the corrected anisotropy factor (P') versus bulk susceptibility (K v ). A fast increase of P' occurs when K v is close to 0. In this case, high P' values are not related to deformation and thus we consider that the AMS of limestone is characterised by oblate ellipsoid and probably low anisotropy. As limestone, the ordinary dolomite host rock show an oblate ellipsoid of AMS with a low anisotropy degree P'

suggesting the absence of significant deformation (Table 1 and group X of Fig. 5B) [START_REF] Tarling | The magnetic anisotropy of rocks[END_REF]. The ellipsoids of ferroan dolomite host rock sites are well distinct, the anisotropy degree P' is low ranging from 1.002 to 1.012 and the shape parameter T is negative; the magnetic fabrics are thus dominated by linear texture (Table 1 and group Z of Fig. 5B) [START_REF] Tarling | The magnetic anisotropy of rocks[END_REF]. This prolate shape of the ellipsoid of magnetic susceptibility characterizes the fabrics inherited from Fe-metasomatism. This process may be the principal cause to make a distinguishable difference on the magnetic fabrics between limestone-dolomite host rock and ferroan dolomite host rock due to the fluid migration in the later one.

Discussions

The AMS results show a significant difference between the surrounding rocks (limestone-dolomite host rock) and ferroan dolomite host rock. Two main fabrics could be characterized and associated each one to a geological genetic process: sedimentary and metasomatic.

The fabric observed in limestone is characterised by an oblate shape with a horizontal magnetic lineation. In dolomite host rock, scatter fabrics may be result from mixed magnetic minerals between carbonates and magnetite. The fabric occurring in ferroan dolomite host rock shows a prolate ellipsoid of magnetic susceptibility with a vertical magnetic lineation,

The sedimentary fabric is observed in limestone, but the magnetic response is complex as the susceptibility carrier is a mixture between para and ferromagnetic (s.l.) minerals (Fig. Table . 1 7A). This fabric corresponds to an oblate ellipsoid of magnetic susceptibility (Fig. 5B) with a horizontal magnetic lineation (e.g., Figs. 8B-h and j). Moreover, six sites of limestone display a well defined NW-SE magnetic lineation (e.g., Figs. 8B-c and i), that is coherent with the NW-SE sedimentary transport direction (N110°) observed on outcrop (see part 2.3.) (Fig. 9).

In dolomite host rock, the influence of fluid circulation is evidenced by the existence of anisotropic growth bands (Figs. 4D andE), however, the magnetic signal is difficult to interpret because of the variations of the magnetic susceptibility carriers and, particularly, of the amount of ferromagnetic (s.l.) minerals as shown by IRM, magnetic hysteresis and ARM results (Figs. 6B, F and 7B, respectively).

As discussed in Part 4.1, the absolute value of magnetic susceptibility in carbonates is more important according to ‹c› axis and it is relatively weak in the (0001) plane. According to the texture goniometry analysis, the relation between lattice preferred orientation is now well constrained; in ferroan dolomite host rock, results show a well defined correspondence between K 1 and ‹c› axes (Figs. 3C andD) with a vertical position (e.g., Figs. 8A-c, g ando).

The symmetry breakdown recorded by the crystal is revealed in the K 2 -K 3 "isotropic" plane.

Only one site does not show the same feature as described above and has a horizontal magnetic lineation (Fig. 8A-p); this site is also the unique one to show an oblate shape of the ellipsoid of magnetic susceptibility. This abnormal behaviour is very likely due to a mixture between para-and ferromagnetic minerals, probably including diamagnetic as well.

At millimetric scale, in ferroan dolomite host rock two zones are distinguished by SEM observations: dark grey ribbons corresponding to the relic of initial rock and clear grey ribbons indicating the enrichment of iron (Fig. 4A) (see [START_REF] Barbanson | Distribution à différentes échelles et chronologie relative des carbonates de l'Aptien de la Province de Santander: relation entre auréole ferrifère et minéralisations Zn-Pb du type Réocin[END_REF]. The difference in mineralogical composition reflects a chemical flux which enriched dolomite crystals by iron. These ribbons show well developed elongations and, according to SPO statistics, their orientations present a direction parallel to the intermediate axis of magnetic susceptibility K 2 (Fig. 4B). The "nearest neighbor" statistics show also an alignment slightly parallel to the K 2 axis (Fig. 4C). This orientation may be therefore considered as the fluid flow direction (e.g., Figs. 8A-d andh), K 1 showing the ‹c› axes orientation.

If we take texture analysis and AMS results into account, we can discriminate two circulation directions; the dominant NE-SW direction interpreted as the principal direction of the fluid circulation (e.g., Figs. 8A-c, d andh), and the secondary NW-SE direction corresponding probably to the bend of fluid trajectory (e.g., Figs. 8A-g andk). Statistically, the principal direction is well observed when we plot all AMS data of ferroan dolomite host rock in the same stereogram (Fig. 8A-q). AMS data allows thus to define indirectly the fluid flow direction.

The dominant NE-SW direction of fluid circulation obtained from this study may be interpreted as the consequence of metasomatic process probably related to diapirs underlying the eastern boundary of La Florida mining district (Figs. 1 and9). Previous geologic studies have illustrated the spatial and contemporal relations between the diapiric structures and mineralizations [START_REF] Barbanson | Distribution à différentes échelles et chronologie relative des carbonates de l'Aptien de la Province de Santander: relation entre auréole ferrifère et minéralisations Zn-Pb du type Réocin[END_REF][START_REF] Barbanson | Les minéralisations Zn-Pb des systèmes biosédimentaires urgoniens du domaine Ouest-Santandérin (Nord de l'Espagne)[END_REF][START_REF] Barbanson | The carbonate hosted Zn-Pb deposit of West-Santanderin type (North of Spain): Tectonical control at regional and local scale[END_REF][START_REF] Grandia | Origin of ore-forming brines in sediment-hosted Zn-Pb deposits of the Basque-Cantabrian basin, Northern Spain[END_REF]. So, we consider the metasomatic flow as responsible to the ferriferous metasomatism of the Urgonian carbonates. Moreover, as the mineralizations are associated in time and space with ferroan dolomite host rock, we conclude that the well defined principal direction corresponds to that of the mineralizing fluid. The block-diagram presented in Fig. 9 synthesises AMS observations and geological understanding.

Conclusion

Fig. 9 Flow direction of metasomatic process could be tracked by magnetic fabrics. However, the reasonable AMS interpretation in carbonate depends on the good understanding on the magnetic mineralogical composition and the correspondence between the lattice preferred orientation and the principal axes of magnetic susceptibility. The textural analysis is necessary to interpret magnetic signature of fluid flow. Coupled with texture goniometry and SEM observations as well as SPO statistics, the magnetic fabric study shows a significant difference between ferroan dolomite host rock hosting the Zn-Pb mineralizations and its surrounding rocks; a dominance of the NE-SW elongation deduced from K 2 magnetic axis in ferroan dolomite host rock is interpreted as the direction of fluid migration in studied Urgonian carbonates, and this regional-scale study enhances also a comprehensive understanding on the metasomatic process in the La Florida mining district. Therefore, coupling with textural analysis, AMS method can be considered as an efficient tool to track flow in metasomatic formations at a regional scale, even if the magnetic signal is low as in studied carbonates. ln ln ln ln ; ln ln ln ln ln ln 2 exp ' [START_REF] Barbanson | Distribution à différentes échelles et chronologie relative des carbonates de l'Aptien de la Province de Santander: relation entre auréole ferrifère et minéralisations Zn-Pb du type Réocin[END_REF]. Dots show AMS sampling sites. L: limestone, D: dolomite host rock, FD: ferroan dolomite host rock. (B) Evolution of the general paragenetic sequence in La Florida mining district (after [START_REF] Barbanson | Les minéralisations Zn-Pb des systèmes biosédimentaires urgoniens du domaine Ouest-Santandérin (Nord de l'Espagne)[END_REF]. average distance between "nearest neighbours" of these relics, both obtained by SPO statistics [START_REF] Launeau | Fabric analysis using the intercept method[END_REF]. (D and E) SEM backscattered images from thin sections of dolomite host rock (sample LFW-43); dotted lines outline the limits of growth bands. K 1 , K 2 and K 3 are respectively the maximum, intermediate and minimum semi axes of magnetic susceptibility ellipsoid. statistics [START_REF] Henry | Application de l'extension bivariate de la statistique Fisher aux données d'Anisotropie de Susceptibilité Magnétique: intégration des incertitudes de mesure sur l'orientation des directions principales[END_REF]. , and correspond to K 1 , K 2 and K 3 , respectively. Magnetic foliation is defined by the K 1 -K 2 plane, and the magnetic lineation corresponds to the K 1 axis. Projection was carried out in lower hemisphere in tilt-corrected coordinates. Curves around poles correspond to the interval of confidence at 95 per cent.

2 1 3 2 2 1 2 2 3 1 3 2 3 2 1 2 2 3 1 2 1 3 2 1 2 1 2 3 2 2 2 1 - = + + + + + = + + = - + - + - = k k k k T k k k k k k k k k k k k P k k k k k k k k k k P m m m m

  Fig.4

Fig. 8

 8 Fig.8presents the stereographic projections of AMS measurements in tilt-corrected

Fig. 8

 8 Fig.8

Fig. 1 :

 1 Fig. 1: Simplified geological map of the Cretaceous basin containing La Florida mining

Fig. 2 :

 2 Fig.2: (A) Geological section of La Florida mining district (after[START_REF] Barbanson | Distribution à différentes échelles et chronologie relative des carbonates de l'Aptien de la Province de Santander: relation entre auréole ferrifère et minéralisations Zn-Pb du type Réocin[END_REF].

Fig. 3 :

 3 Fig. 3: Lattice preferred orientation for the (0006) pole corresponding to ‹c› axes compared

Fig. 4 :

 4 Fig. 4: (A) SEM backscattered images from thin sections of ferroan dolomite host rock

Fig. 5 :

 5 Fig. 5: (A) Histogram of the bulk susceptibility for all samples of studied carbonates. (B)

Fig. 6 :

 6 Fig. 6: Isothermal Remanent Magnetization (IRM) acquisition curves of limestone (A),

Fig. 7 :

 7 Fig. 7: Stereogram comparing the principal axes ( : K 1 , : K 2 and : K 3 ) of ARM (grey)

Fig. 8 :

 8 Fig. 8: AMS responses for sites of ferroan dolomite host rock (A) and limestone/dolomite

Fig. 9 :

 9 Fig. 9: Block-diagram showing the principal direction of the fluid flow and that of sediments transport suggested by AMS results from this study.

  [START_REF] Peters | Magnetic identification of selected natural iron oxides and sulphides[END_REF]. An over-estimation of the magnetite component in studied carbonates is possible by using the saturation remanence Mrs. Thus; saturation remanence M rs is proportional to the magnetite concentration. Considering the M rs value of

	magnetite	M rs	. 10	m . A	2	/	Kg

s rs M M values in dolomite host rock (0.043) and ferroan dolomite host rock (0.19) indicate that there is a dominance of magnetite (Peters and Fig. 6

Acknowledgements

We thank the EGIDE program (PAI Programme Picasso n°10998VL) for its financial support. The first author benefits a scholarship grant from the French Minister of Education and Research. The authors would like to thank the Editor C. Jaupart and the three anonymous reviewers whose comments help to improve greatly this manuscript.

Yusta, I., Velasco, F., Herrero, J.M., 1998. Anomaly threshold estimation and data normalization using EDA statistics: application to lithogeochemical exploration in Lower Cretaceous Zn-Pb carbonate-hosted deposits, northern Spain. Appl. Geochem. 13, 421-439.

Table and figure captions

Table 1: AMS data and their associated parameters. L: limestone, D: dolomite host rock, FD: ferroan dolomite host rock, n: number of measured samples, P': corrected anisotropy degree, T: shape parameter [START_REF] Jelinek | Characterization of the magnetic fabric of rocks[END_REF], K v : bulk susceptibility, D: declination, I: inclination, K 1 , K 2 , and K 3 are respectively the axes of the maximum, intermediate and minimum of magnetic susceptibility.

(

) (


Wassim Maalej
email: maalej_wassim@hayoo.fr

Rim Jaballi

Asma Ben Rached

Philippe Guionneau

Nathalie Daro

Zakaria Elaoud

Supramolecular architectures of mononuclear nickel(II

come

Introduction

The structural chemistry of organometallic architectures continues to attract interest from scientists in crystal engineering, mainly due to the development of new phenomena and the potential applications of the resultant materials. [1][2][3][4][5][6] In supramolecular chemistry, in addition to the coordinate covalent bonding, hydrogen bonds are effective in establishing particular contacts which occur regularly, and play a significant and repetitive role in directing molecules during crystallization. [7][8][9][10] In this way, the interactions, such as hydrogen bonding and π…π stacking, may serve as additional forces sustaining the coordination networks, or as the forces interlinking discrete or low-dimensional coordination motifs into higher-dimensional architectures organic-inorganic hybrid materials. Among the non-covalent interactions, H-bonding is the most widely used synthons over other and can able to generate hybrid compounds, which are more elastic in nature. Among the other types of non-covalent interactions, π…π stacking between the aromatic rings are used in construction of hybrid compounds. [11][12][13][14][15] The characteristic features of these materials are the exceptional electrical and optical properties . 16- 23 Moreover, a large number of studies showed that postsynthetic functionalization or direct syntheses with ligands having suitable functionality can impart hydrogen bond capabilities to the organic-inorganic hybrid. 24,25 Besides, one of the most widely studied functional groups that have been used to impart hydrogen bonding capabilities to the hybrid is the amino, carbonyl, anhydride, cyano group, etc., [26][27][28][29][30] Even more recently, the self-assembly processes are sensitive to diverse synthetic conditions in some cases, change of reaction conditions such as the solvent, pH and temperature for a given set of organic ligands and metal ions can cause various supramolecular architectures. 31,32 In this regard, solvent molecules or counter-ions (CH3COO -, NO3, NO2, ClO4 -, etc) may also dramatically influence the overall solid-state architecture Please do not adjust margins Please do not adjust margins by participating in metal coordination and hydrogen bonding. On the basis of the aforementioned thoughts and as an expansion of our research on supramolecular architectures of the 5,5'-dimethyl-2,2'-bipyridine based salts, in which aromatic N play a key vital role in generating threedimensional (3D) networks through π…π stacking interaction. 33 In the present work, we report the synthesis, spectroscopic characterization and X-ray crystal structures of two new Ni(II) and Cu(II) coordination complexes as well as a deep analysis of their interesting crystalline architectures formed by supramolecular interactions.

Experimental General Procedures

The starting compounds including the 5,5'-dimethyl-2,2'bipyridine ligand, the nickel and copper perchlorate salts and the solvents were purchased from commercial suppliers (Sigma-Aldrich, Merck and others). All chemical reagents were used without further purification. Deionized water, acetonitrile and acetic acid was used as solvent in this work. C, H, and N microanalyses were carried out with a Perkin-Elmer system 2000 elemental analyzer and scanning electron microscopy (SEM). Infrared spectra (IR) was recorded on a PerkinElmer Spectrum TM 100 FT-IR spectrometer as KBr pellets in the range 4000-400 cm -1 . Differential thermal analysis (DTA) and thermogravimetric analysis (TGA) measurements were performed on our heating the sample in a platinum crucible from 300 to 700 K in a SETARAM thermal analyser (TG-ATD92) under air at a heating rate of 5 K min -1 . The UV-vis diffuse reflectance spectrum was measured at room temperature using a Shimadzu-type 3101 PC UV spectrophotometer equipped with a double beam monochromator covering the spectrum range from 200 nm to 1000 nm. Powder X-ray diffraction patterns (PXRD) were recorded using a PANalytical X'Pert Pro diffractometer (Cu Kα1, 1.5406 Å) and the Single crystal X-ray diffraction (SCXRD) data collection were run using an Apex-II Bruker diffractometer.

Synthesis of [Ni(dmbpy)2(CH3COO)]ClO4 (1)

A mixture of 5,5'-dimethyl-2,2-bipyridine (10 mmol, 1.84 g) and nickel (II) perchlorate hexahydrate (5 mmol, 1.28 g) were dissolved in 35 ml of H2O (1.5 ml), MeCN (10 ml) and AcOH (10 ml) to give a blue solution. The mixture was then introduced into a 125 ml autoclave, which was sealed and heated under autogenous pressure at 130°C for 72 h. After cooling to room temperature the products, shiny blue crystals were washed with distilled water, ethanol, and acetone followed by drying in air. Elemental analysis (%) calcd: C, 53.32; H, 4.61; N, 9.56. Found: C, 52.26; H, 3.79; N, 9.18.

Synthesis of [Cu2(dmbpy)4(CH3COO)3]ClO4 (2)

The compound (2) was prepared by the hydrothermal treatment of a mixture of 5,5'-dimethyl-2,2-bipyridine (10 mmol, 1.84 g), copper (II) perchlorate hexahydrate (5 mmol, 1.31 g), H2O (1.5 ml), MeCN (10 ml) and AcOH (10 ml) were placed in Teflon-lined stainless steel vessel. The sample was heated at 130°C for 3 days and then cooled to room temperature. After washed by ethanol, and acetone, light yellow crystals were obtained with a yield of 45 % based on Cu. Elemental analysis (%) calcd: C, 46.66; H, 4.27; N, 7.25. Found: C, 45.21; H, 3.37; N, 6.94. The reaction scheme followed for the synthesis of Ni(II) and Cu(II) complexes is shown in Fig. 1. PXRD was used to demonstrate the phase purity of nickel(II) and copper(II) complexes. As shown in Fig. 2, the experimental PXRD patterns of complexes are well-matched with the calculated patterns obtained from their single crystal data, demonstrating the phase purity of complexes.

IR spectra of the complexes

FT-IR spectra of the two compounds are similar (Fig. S1) and the absorption bands can be assigned on the basis of the literature. Several main peaks were detected, due to functional group vibrations. In all cases, a series of weak peaks in the region ca. 3700-2940 cm -1 were observed, corresponding to C-H stretching vibrations of the aromatic ring and C-H alkyl (methyl) group. 34 In the complexes (1) and ( 2 FIG. 2 X-ray diffraction patterns obtained directly from the experiment for the powder (blue) and derived from the single-crystal analysis (red) for ( 1) and (2).

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Please do not adjust margins Please do not adjust margins bands in the region 1550-1600 cm -1 corresponds to υ(COO)sym frequency, respectively, are associated to the acetate ligand. At lower frequency range, the bands observed at 1240 in (1) and 1301 cm -1 in (2) can be ascribed are (COO) symmetric deformation modes. 35,36 The bands in the range 1673-1413 cm - 1 are characteristics for the skeletal vibrations of the aromatic rings. The (dmbpy) ligand has some characteristic vibrational bands of the ν(C=C) and ν(C=N) groups at 1650 1430 cm -1 , respectively. 37,38 The C-H in-plane bending and C-H out-of-plane bending vibrations sort out in the range of 1410-1150 cm -1 and 820-660 cm -1 respectively. 37 Furthermore, the presence of bands at 1093, 1039, 834 and 616 cm -1 for complex (1) and the bands at 1080, 1046, 842 and 626 cm -1 in complex (2), indicate a Td symmetry of ClO4 -, suggest the presence of perchlorate ion outside the coordination sphere. [39][40][41] Finally, the coordination of ligands is substantiated by a band in the range 540-421 cm -1 for all of the complexes corresponding to M-O and M-N stretching vibrations. 42,43

Thermogravimetric analysis

To estimate the stability of the coordination compounds, thermogravimetric analysis (TGA) and differential thermogravimetric analysis (DTA) were carried out. As shown in Fig. S2, the thermogram of mononuclear nickel (1) indicates the stability of the compound up to 549 K but the homobinuclear copper compound (2) shows the decomposition in 520 K. The Cu(II) complex exhibits single decomposition stage at the temperature range of 500-650 K which corresponds to the removal of one 5,5'-dimethyl-2,2'-bipyridine and two acetate moieties, are related by exothermic effect in 550 K (found 39.54%, calculated 39.14%) Fig. S3. In the case of nickel complex, the TG curve shows that the complex exhibits the continuous weight loss because another reaction starts before the one of decomposition reactions ends in the temperature range of 520-840 K. Therefore, it is difficult to distinguish the reactions from each other. The total weight loss in this temperature range is 62.42% corresponds to the removal of one 5,5'-dimethyl-2,2'-bipyridine and 1 acetate and 1 perchlorate moieties (calculated 58.51%), with three exothermic peaks observed on the DTA curve at 620.65, 678.69 and 740.06 K.

X-ray crystal structure determination

Suitable single crystals of complexes (1) and ( 2) were mounted on a APEX-II Bruker diffractometer equipped with a graphitemonochromated Mo-Kα radiation (λ = 0.71073 Å) at 298 K. All absorption corrections were performed using the SADABS program. The two structures were solved by the direct methods and refined by full-matrix least-squares fitting on F 2 by SHELXTL-97 [START_REF] Sheldrick | Crystal structure refinement with SHELXL[END_REF] through the WinGX program suite. [START_REF] Farrugia | WinGX and ORTEP for Windows: an update[END_REF] All non-hydrogen atoms were refined with anisotropic thermal parameters. Hydrogen atoms were located at geometrically calculated positions and treated by a mixture of independent and constrained refinement. Crystallographic data and structural refinements for compounds Ni and Cu are summarized in Table 1. The selected bond lengths parameters of the compounds 1 and 2 are summarized in Tables S1 andS2, respectively.

Hirshfeld surface analysis

Known to be very efficient to describe the intermolecular contact in molecular crystals, notably in view of structureproperties relationships, 46,47 Hirshfeld surfaces 48 were generated using Crystal Explorer 17.5 based on the results from X-ray studies. Directions and strengths of intermolecular interactions within the crystal were mapped onto the Hirshfeld surfaces using the descriptor dnorm, which is a ratio encompassing the distances of any surface point to the nearby interior di (the distance from a point on the surface to the nearest atom inside the surface) and exterior de (the distance Please do not adjust margins Please do not adjust margins from a point on the surface to the nearest atom outside the surface) atoms and the van der Waals radii of the atoms, given by the equation ( 1). Associated plots of di vs. de, referred to as fingerprint plots (FP), are given, which are useful in identifying and comparing different kinds of interactions. 49 The value of dnorm is negative (red colour) or positive (blue colour) when intermolecular contacts are shorter or longer than van der Waals separations, respectively. Additionally, the combination of di and de in the form of a 2D fingerprint plot 50,51 provides summary of intermolecular contacts in the crystal. 2D FP are considered unique for a molecule in a given molecular environment, hence shapes, area and symmetry of those plots can be used for an assessment and comparison of supramolecular properties of related molecules. (Fig. 4b).

On the other hand, the perchlorate anions are also involved in Hbonding. the three oxygen atoms, namely O3, O4 and O6 of the ClO4 - moiety, There are five C-H•••O interactions between noncoordinated oxygen atoms of the perchlorate groups as acceptor and Fig. 3 ORTEP view of the asymmetric unit of 1 with displacement ellipsoid at 50% probability. Please do not adjust margins Please do not adjust margins Thus anion•••π interaction together form a chain zig-zag of noncovalent interactions which stabilize the 3D supramolecular network of [Ni(dmbpy)2(CH3COO)]ClO4, as shown in Fig. 8. The geometrical parameters of these intermolecular interactions are collected in Table 1.

Crystal structures of complex [Cu2(dmbpy)4(CH3COO)3]ClO4 (2)

In order to understand the details of the crystal structure of (2), single-crystal X-ray diffraction data were collected at 293 K. The analyses indicate that (2) crystallizes in the triclinic crystal system with the space group P-1. The molecular structure of copper (II) complex consists of homobinuclear [Cu2(dmbpy)4(CH3COO)3] + complex cations that is balanced by ClO4 -counter ions. The molecular structure of ( 2) is shown in Fig. 9a, selected bond lengths and angles are given in Table S2. Each copper atom is surrounded by a 5.5'dmbpy bidentate ligand through two N-donor atoms and three acetate groups coordinated differently to copper ions; two bidentate groups (CH3COO -) are linked to two Cu 2+ ions via four oxygen atoms [(Cu1-O1 = 1,932 (6) Å, Cu2-O2 = 1,942 (6) Å, Cu1-O3 = 1,950 (6) Å and Cu2-O4 = 2,217 (6) Å], and a third monodentate group is coordinated with the two copper ions only by the oxygen atom [Cu1-O5 = 2.172 (5) Å and Cu2-O5 = 1.992 ( 5) Å]. The O5 atom acts as a bridge between the two copper ions (Cu1 and Cu2). It occupies an axial position of the intermediate geometry of Cu1 and an equatorial position in the pyramidal environment with a square base of Cu2. The axial Cu2-O4 bond parameter is 2.217 (6) Å. The four short Cu-N bond lengths are in the range from 1.999 (6) to 2.030 (6) Å. These results are comparable to those found for similar compounds. 55 Within this structure, each copper ion is in a five-coordinated CuN2O3 environment with geometries swing between the ideal square pyramidal and trigonal bipyramidal structures, this is justified by the trigonal parameter τ, τ = (β -α)/60: where α and β are the largest angles around the Cu2 + ion. We noticed that τ = 1 corresponds to a trigonal bipyramidal geometry and τ = 0 to a square pyramidal geometry. As regard to the Cu1 center, the value of τ = 0.47, indicating that its geometry is intermediate between the ideal square pyramidal and trigonal bipyramidal prisms. 56 The geometric parameters of the coordination sphere of Cu1 are collected in Table S2, revealing an axial elongation of the intermediate along the direction Cu•••O5. The axial distance Cu1-O5 is longer than the other equatorial bonds Cu-O1, O2, N3, N4 (Fig. 9éb). In addition, the values of the angles N/O-Cu1-O/N are ranged between 80.3 (3) and 169.1 (2) °.

These results indicate that the Jahn-Teller effect is involved in the coordination sphere of the copper Cu1 center which the environment is described as a geometric ranging from the square pyramidal to the trigonal bipyramidal structure. The second copper ion is surrounded in the equatorial plane by the atoms O2, O5, N1

D-H•••A a,b D-H/Å H•••A/Å D•••A/Å D- H•••A/° C13-H13

ARTICLE | 7

Please do not adjust margins Please do not adjust margins and N2 (Fig. 9c). The value of τ = 0.20, this value highlights the presence of a square pyramidal geometry. The cisoid and transoid bond angles fall in the regions 80.6 (3)-101.7 (3) ° and 157.4 (3)-169.7 (3) °, respectively, indicating the distorted SP geometry. This can be justified by the Jahn-Teller effect, which is engaged in the coordination sphere of copper (4 + 1). The deviations from the leastsquares plane through the CuN2O2 atoms in Cu1 and Cu2 are 0.418 and 0.236 respectively. The distance between two copper is of the order of Cu1-Cu2 = 3.38 (2) Å. This distance is shorter than binuclear Cu (II) complexes. 57 This value of the intermetallic distance will prompt us to think about studying the magnetic properties of this material. 58 The crystal structure of (2) reveals that the crystal packing of the polymorphs are stabilized through different hydrogen bonding interactions. Given that the lack of acidic protons on the (dmbpy) ligands and acetate anion, no classical hydrogen bond interaction is expected to play a prominent role in the crystal packing. 3.

D-H•••A a,b D-H/Å H•••A/Å D•••A/Å D-H•••A/° C13-H13•••O1 0.
(i) -x+1, -y+2, -z+1; (ii) -x, -y+1, -z+2. π•••π interactions, Cg•••Cg distance/Å Cg1•••Cg2 iii 3.761(7) Cg2•••Cg2 iv 3.747(9) Cg3•••Cg3 v 3.654(8) b Symmetry codes: (iii) 1-X,2-Y,1-Z; (iv) -x,2-y,1-z ; (v) 1-x,1-y,

Hirshfeld surfaces

The Hirshfeld surfaces of two Ni(II) and Cu(II) compounds are illustrated in Fig. 13 showing the surfaces that have been mapped over dnorm (-0.32 to 1.56 Å), shape index (-1.0 to 1.0 Å) and curvedness (-4.0 to 0.4 Å). The surfaces are shown as transparent to allow visualization of molecules, in a similar orientation for all of the structures, around which they were calculated. We have considered the asymmetric unit among the entire unit cell for all of the compounds. It is clear that the information present in the hydrogen bonding tables is summarized effectively in these spots, with the large circular depressions deep red visible on the dnorm surfaces and is marked as (A) indicative of hydrogen bonding contacts (the oxygen atoms one near to groups CH3COO -and another on the perchlorate anions), and other light red spots labelled (B) are due to H•••H contacts (π•••π interactions). The small extent of area marked as (C) and light color on the surface indicates other weaker and longer contacts are due to H•••C contacts (C-H••• π interactions) (Figure 13a). Furthermore, the Hirshfeld surfaces were mapped with shape index and curvedness functions to evaluate the presence of C-H•••π stacking interactions, which are clearly visible in the analysis of the crystal structure. In the shape index diagram of both compounds (Figure 13b), inspection of the adjacent red and blue triangles on the shape index surface shows the existence of π-stacking interactions in the structure of both compounds, involving the 2,2'-bipyridine ring. The interaction is almost identical in the two crystal structures. i.e. blue triangles represent convex regions due to ring carbon atoms of the molecule inside the surface, while red triangles represent concave regions due to carbon atoms of the 5,5'-dimethyl-2,2'bipyridine stacked molecule above it. The curvedness mapped on the Hirshfeld surface (Fig. 13c) shows that the largest region of flat curvedness appears for compound 2. This analysis is conforming to the structural results. Indeed, in the crystal packing of both compounds, π•••π interactions are clearly visible in the analysis of the section crystal structures, with Cg1•••Cg2 distances of 3.775 for (1) and 3.761 Å for (2). These interactions are also noticeable as relatively large and green flat regions delineated by the red circle on the curvedness surfaces of both compounds.

The full 2D fingerprint plots of the main intermolecular interactions of the compounds Ni(II) and Cu(II) are depicted in Figure 14 1) and (2) (Fig. S4). All the above considerations are based on intramolecular distances and angles, it would be very interesting to convert those experimental parameters into true interaction energies; but the latter is still a challenge in molecular crystals though some results have been recently obtained on metal coordination complexes that are to some extend similar to the present ones. 62

Optical properties

The UV-Vis absorption properties of (1) (d 8 , mononuclear) and (2) (d 9 , homobinuclear) have been examined in the solid state at room temperature. As shown in Fig. 16, (1) exhibits absorption peaks at 239 nm along with a broad absorption consisting of two peaks with the maximum at 498 nm. (2) features a new absorption at 398 nm except for two comparable absorptions at 235, and 693 nm but with a noticeable red-shift compared to (1). The first ones well resolved bands are assignable to intraligand transitions, π→π* (LLCT) in ( 1) and ( 2). The intense band at 394 nm appear for copper(II) complex is primarily due to a ligand-metal charge transfer (MLCT) associated with the nitrogen and oxygen donors. 63,64 In addition to these bands, in the visible region, bands are assigned to the d-d transitions of the metal ions, present in the title compounds. With this in mind, observed absorption peaks at 407-701 nm region for compound (1) can be attributed to d-d transitions with the modes of 3 A2g → 3 T1g(P) and 3 A2g → 3 T1g(F), which are well matched with the results observed in other octahedral Ni(II) coordination compounds. 65,66 In homobinuclear compound (2), relatively weak intensity the band in 701 nm characteristic of to the 𝐝 𝐱 𝟐 -𝐲 𝟐 → 𝐝 𝐳 𝟐 as expected for distorted squar-pyramidal and distorted square-planer copper(II) complexes with confirming the 𝐝 𝐱 𝟐 -𝐲 𝟐 based ground state and elongation of the axial bonds. Such types of absorption bands between Cu(II)-Cu(II) homobinuclear copper(II) complexes were observed in homobinuclear complexes reported in the literature. 8,67- 69 The optical band gap energy was calculated according to the equation Tauc: αhν = A(hν-Eg) n where A is a constant, hν is the incident photon energy, and Eg is the optical band gap material, n was considered to be equal to ½ in the equation for calculating the band gap of the complexes. 70 For this compounds the gap energy is of direct type because the absorption band used for the energy calculation is located outside the visible range (239 nm in (1) and 235 nm in (2)). 71 The band gap energy was estimated to be 4.17 eV and 4.32 eV for (1) and ( 2) respectively (Fig. 17), which falls in the UV region (< 3.1 eV for visible region). These values clearly classify these materials among the semiconductor materials. 72,73 Fig. 15 Relative contributions of various intermolecular contacts to the Hirshfeld surface area in 1 and 2. Please do not adjust margins Please do not adjust margins

Conclusions

In summary, both new complexes [Ni(dmbpy)2(CH3COO)]ClO4 (1) and [Cu2(dmbpy)4(CH3COO)3]ClO4 (2) were characterized by means of single-crystal X-ray diffraction, elemental analysis, IR spectroscopy, TGA/DTA and UV-Vis spectroscopy. Both compounds similarly crystallize in the triclinic system, with the centrosymmetric space group P-1. In each case, 5,5'-dimethyl-2,2-bipyridine molecules play the role of hydrogen bonding linkages between the acetate and perchlorate oxygen atoms in (1) and (2). In compound (1) the formation of multiple hydrogen bonding, C-H⋯π and π⋯π stacking interactions can act as primary tools for constructing 3D supramolecular architectures. For (2), C-H•••O hydrogen bonds lead to the stacking of 1D (pseudo-)chains into a 2D network. Intermolecular interactions were visualized and quantified using Hirshfeld surfaces with two dimensional fingerprint plots. These analyses put in light the effective role of H⋯H, O⋯H, C-H⋯π and π⋯π contacts in the cohesion of the crystal packing of ( 1) and ( 2). The 2D fingerprint plots indicate the more or less identical contributions of interactions in the complexes arising from their structural similarity. The optical properties show that the samples have a semiconducting character.

FIG. 1

 1 FIG.1Scheme of synthesis and SEM image of complexes 1 and 2.

FIG. 1

 1 FIG. 1 Chemical scheme and single-crystals morphologies for (1) and (2).

  Crystal structures of complex [Ni(dmbpy)2(CH3COO)]ClO4 (1)The single crystal X-ray diffraction results indicate that (1) crystallizes in the triclinic space group P-1 consisting of one Ni(II) ions, two (dmbpy) ligands, one acetate ion and one isolated ClO4 -tetrahedral. The asymmetric unit of (1) is shown in Fig.3. The Ni ion is six-coordinated in a distorted octahedral coordination sphere, including four N atoms (Ni-N1 = 2.053 (5) Å, Ni-N2 = 2.047 (4) Å), Ni-N3 = 2.059 (4) Å, Ni-N4 = 2.064 (4) Å) from two (dmbpy) ligands as well as two oxygen atoms (Ni-O1 = 2.104 (3) Å, Ni-O2 = 2.115 (4) Å) coming from one CH3COO -ion. The cisoid and transoid bond angles fall in the regions 62.6(1) -102.6(2)° and 162.3(2) -177.5 (2)°, respectively, indicating the octahedral coordination to be distorted. The isolated ClO4 - tetrahedra are slightly distorted and exhibit a range of 109.0 (3)-110.2 (3)° for the O-Cl-O angles, with an average Cl-O distance of 1.436 (10) Å. In the absence of chemical entities capable of establishing strong Hbonding, the molecules are assembled solely by a combination of weak C-H•••O and intramolecular π•••π stackings. The oxygen atom (O1) of the acetate anion are the strongest hydrogen bond acceptors and aromatic C-halogen groups are the strongest H bond donors in the system. However, the most significant hydrogen bond interaction is the intermolecular hydrogen bonds observed between C7•••H with O1 i [C7•••O1 = 3.194 (6) Å, H7•••O1 = 2.33 (1) Å, C7-H7•••O1 = 155 (1)°] which leads to the formation of the centrosymmetric a hydrogen bonded dimer with Ni(1)•••Ni(1) (1-x , 1-y, 1-z) separation of 7.429(3) Å (Fig. 4a). The hydrogen bonded ring motifs, in the formalism of graph-set analysis of hydrogen-bond patterns, 52 that are found for [Ni(dmbpy)2(CH3COO)] + are the 𝐒 𝟏 𝟏 (𝟓) and the common 𝐑 𝟐 𝟐 (𝟏𝟐) motifs consisting of 12 atoms, with 2 donors and 2 acceptor

Fig. 4 5

 45 Fig. 4 (a) Crystal packing of the molecules in 1 projected onto the (011) plane, and detail of the hydrogen bonding showing the centrosymmetric dimers (thermal ellipsoids represent 50% probability). (b) The hydrogen-bonding motif in the (101) plane.

Fig. 5

 5 Fig. 5 (a) C-H•••O6 hydrogen bonds (red lines) for 1 showing R 4 4 (18) the graph-set motif. (b) Formation of 1D tape in complex 1 through association of [Ni(dmbpy)2(CH3COO)]ClO4 through C-H•••O1 hydrogen bonds.

Fig. 6

 6 Fig. 6 The C-H⋯O3 interactions (a) The infinite 1D helix chain along b axis in 1 (b) The illustration of the 2D layer of 1•in the bc plane.

Fig. 7

 7 Fig. 7 (a) A view of the π•••π stacking for compound 1. (b) A viewof the C-H•••π interactions in 1 (c) The formation of the O•••π interactions by cations and ClO4 -for compound 1.

Fig. 9

 9 Fig. 9 (a) ORTEP view of the asymmetric unit of 2 with displacement ellipsoid at 50% probability. Cu1O3N2 (a) and Cu2O3N2 (b) square pyramidal formed by the oxygen atoms from four two bidentate acetate ligands completed by one monodentate acetate oxygen and two (dmbpy) nitrogen atom for Cu1 and Cu2, respectively.

Fig. 8

 8 Fig. 8 3D supramolecular structure induced by intermolecular interactions in 1 complex.

  However, several kinds of weak hydrogen bonds involving the carbon bound hydrogen atoms are observed in compound 2. Consequently, two weak C13-H13•••O1 (3.227 (3) Å) and C1-H1•••O2 (2.914 (10) Å) hydrogen bonds are found between the (dmbpy) ligand and the (CH3COO -) anion, forming an intramolecular bond with the motif S 1 1 (5). In addition, the C4 atom, which belongs to the [Cu2(dmbpy)4(CH3COO)3] + cation acts as a hydrogen bond donor to O4 atom of acetate group forming a centrosymmetric a hydrogen bonded R 2 2 (12) dimeric ring centred at (½, 0, ½), with Cu(1)•••Cu(1) and Cu(2)•••Cu(2) separation of 13.235 (4) Å and 7.501(2) Å, respectively (Fig. 10a). Furthermore, the two C19 and C30 carbon atoms acts as donor to the perchlorate oxygen atom O7 in the molecule, so generating centrosymmetric a R 4 4 (20) dimeric ring centred at (½, ½, 0,), with Cu(1)•••Cu(1) = 9,316 (6) Å (Fig. 10b). The combination of two types of R 2 2 (12) and R 4 4 (20) ring motif leads to the formation of one-dimensional (1D) parallel chains are arranged into sheets lying parallel to the crystallographic bc diagonal. (Fig. 10c). Such types of hydrogen bonds have already been investigated by earlier workers 13,59-61 . In addition, within this structure there are significant weak π•••π intermolecular interactions between the pyrimidine rings of (dmbpy) ligands from neighboring chains, which are almost parallel to each other, with a Cg1•••Cg2 and Cg2•••Cg2 distance of 3.761 (7) Å and 3.747(9) Å, respectively, Fig. 11. Concurrently, C-H•••π interactions were also observed between bridged CH3-groups of the 5,5'-dimethyl-2,2'-bipyridine or the acetate molecules act as hydrogen bond donors towards the Cg of pyrimidine rings of (dmbpy) to form C12-H12B•••Cg1, C23-H23B•••Cg4, C28-H28A•••Cg4 and C30-H30A•••Cg4 interactions, with are distances 3.393, 3.176, 3.531 and 3.440 Å, respectively. π•••π stacking and C-H•••π interactions occur between the 1D chains along [100] direction. Further investigation of the packing structure showed that the assembly of the 0D of (2) into a 2D supramolecular architecture is also accomplished via C-H•••O hydrogen bonds, π•••π and C-H•••π involving the (dmbpy) and acetate ligands Fig. 12. The corresponding interactions of 2 are summarized in Table

Table 3 Fig. 10

 310 Fig. 10 The hydrogen-bonding motif for compound 2 (a) R 2 2 (12) ring motif (b) R 4 4 (20) ring motif. (c) View of the 1D supramolecular chain by intermolecular C-H•••O in 2.

Fig. 11

 11 Fig. 11 View of the 1D supramolecular layered by intermolecular π•••π

Fig. 12

 12 Fig. 12 3D supramolecular structure induced by intermolecular interactions in (2), view along a. Fig. 13 Hirshfeld surfaces mapped with dnorm (a), shape index (b), and curvedness (c) for compounds 1 and 2.

Fig. 14 9

 149 Fig. 14 Fingerprint plots for compounds 1 and 2.

Fig. 16

 16 Fig. 16 UV-vis Absorption spectra of compounds 1 and 2.

Fig. 17

 17 Fig.17 Tauc plots analysis of compounds 1 and 2.

  Fig.17 Tauc plots analysis of compounds 1 and 2.

Table 1

 1 Crystallographic data and details of refinements for complexes 1 and 2

	Identification code	(1)	(2)
	formula	[Ni(dmbpy)2(CH3COO)]ClO4	[Cu2(dmbpy)4(CH3COO)3]ClO4
	Mr (g.mol -1 )	583.68	772.14
	Crystal system	Triclinic	Triclinic
	Space group	P-1	P-1
	a (Ǻ)	8.6159 (3),	8.019 (5)
	b (Ǻ)	10.8313 (3)	11.557 (5)
	c (Ǻ)	15.8252 (4)	18.735 (6)
	 (°)	98.300 (8	76.096 (7)
	 (°)	102.502 (8)	86.625 (7)
	 (°)	110.712 (9)	73.857 (8)
	Volume(Å 3 )	1308.57 (11)	1618.9 (13)
	Z-space group	2	2
	F (000)	303	396
	calc (mg m 3 )	1.486	1.584
	µ( mm -1 )	0.89	1.46
	Data/restraints/params 2634/0/344	7456/0/424
	GOF on F 2	1.19	1.10
	R1 (I = 2(I))	0.052	0.084
	R2 (all data)	0.114	0.241
	w	=1/[σ 2 (Fo 2 )+0.0334P 2 ]+ 2.9081P	=1/[σ2(Fo2)+0.0477P2]+ 24.2284P
		where P = (Fo2 + 2Fc 2 )/3	where P = (Fo2 + 2Fc2)/3
	Δρmax, Δρmin (e Å -3 )	0.36/-0.42	1.67/-1.63
	CCDC no.	2085397	2085398

Table 2

 2 Hydrogen bond, C-H•••π and π•••π stacking interactions in 1.

Acknowledgements

The authors thank the University of Sfax-Tunisia for financial support. The X-ray diffraction is performed at the XRD center of ICMCB.

Author Contributions

All authors contributed equally

Conflicts of interest

There are no conflicts to declare.

Supplementary information

CCDC numbers of 2085397 and 2085398 are corresponded to the supplementary crystallographic data for this paper. These data are available free of charge at http://www.ccdc.cam.ac.uk/conts/retrieving.html.