Synthesis of new dithiolate complexes of transition metals

Peter Herich¹, Jozef Kožišek¹, Jiři Kameníček²

¹Department of Physical Chemistry, Slovak Technical University, Bratislava, Slovakia.

²Department of Inorganic Chemistry, Palacky University, Olomouc, Czech Republic

Coordination compounds of transition metals in the oxidation state M(III) are quite unusual. The series of several dithiolate complexes of general formula R[M(bdt)₂] with benzene-1,2-dithiol (bdt), M = Ni, Co and Cu as the central atom and various ammonium (phosphonium) derivatives R = Me₄N⁺, Et₄N⁺, Pr₄N⁺, Me₃PhN⁺, MePh₃P⁺, Ph₄P⁺ , were prepared [1]. A wide range of technical applications (e.g. superconductors, resins, polarization filters, vulcanization accelerators) of the dithiolate complexes, as well as their biological activity (anticholinesterase activity, pesticides) makes them interesting subjects for the research. Our previous attempt to study the electronic structure of these complexes from diffraction data was not successful due to large anisotropic displacement parameters (ADPs) [2]. In order to reduce the thermal motion in the complex, chloro-substituted ligand, 3,6-dichloro-1,2-benzenedithiol (bdtCl₂) was used for the synthesis.

Preparation of (Me(Ph)₃P)[Cu(bdtCl₂)₂]: Solution of Na (0.08 g, 3.3 mmol) in MeOH (10 cm³) was added to 3,6-dichloro-1,2-benzenedithiole (bdtCl₂, 95%) (0.34 g, 1.6 mmol). To this mixture, CuCl₂·2H₂O (98%) (0.13g, 0.76 mmol) in MeOH (10 cm³) was added. Finally, Methyltriphenylphosphonium bromide (Me(Ph)₃PBr, 99%) (0.57 g, 1.6 mmol) in MeOH (10 cm³) was added. The resulting solution was stirred for 24 hours. The complex was precipitated by the slow addition of water, with vigorous stirring. The green crystalline powder was filtered off, washed with diethyl ether, and then recrystallized from acetone/methanol solution (40:5) (yield 99%). Crude product was purified by column chromatography using eluent mixture toluene/methanol (10:1). The same procedure was used for preparation of complexes (Me(Ph)₃P)[Ni(bdtCl₂)₂]; NiCl₂·6H₂O (98%) (0.18g, 0.76 mmol) and (Me(Ph)₃P)[Co(bdtCl₂)₂]; CoCl₂·6H₂O (98%) (0.18g, 0.76 mmol). After crystallization a single crystal suitable for X-ray analysis was selected. All solvents were products of LACHEMA Brno and mikroCHEM.The chemicals of analytical grade were purchased from Sigma-Aldrich.

X-ray data collection for (Me(Ph)₃P)[Cu(bdtCl₂)₂]; (Me(Ph)₃P)[Ni(bdtCl₂)₂] and (Me(Ph)₃P)[Co(bdtCl₂)₂] were performed on an Oxford Diffraction Gemini R four circle k-axis diffractometer equipped with a Ruby CCD detector and a graphite monochromator, using Mo-Kα radiation at 293(2)K and 100(2)K. CrysAlis program package (Oxford Diffraction, 2011) was used for data reduction [3]. The structure was solved by direct methods using SHELX [4, 5] and refined anisotropically for all non-hydrogen atoms by full-matrix least-squares. All hydrogen atoms were found from the Fourier map and were refined isotropically. DIAMOND was used for drawing[6].

The three prepared complexes are found to be isostructural, crystallizing in the space group P21/c. The structures consist of two complex anions and one molecular cation. The central atom is coordinated by two dithiolates ligands. The X-ray structure analysis of (MePPh3)[Ni(bdtCl₂)₂], (MePPh₃)[Co(bdtCl₂)₂] and (MePPh₃)[Cu(bdtCl₂)₂] confirmed a square-planar geometry of S₂MS₂ chromophore. The M-S bond lengths are for Ni: 2.1390(6)-2.1508(6)Å, for Co: 2.1570(6)-2.1640(6)Å and for Cu: 2.1720(6)-2.1761(5)Å which are significantly shorter then the usual published values for metal(II) complexes (Ni: 2.17-2.18 Å [7], Co: 2.28 Å [8] and Cu: 2.27 Å [9]); this fact also supports the assumption of a metal(III) oxidation state in these compounds. The appropriate bond angles around central atoms (Ch1,Ch2°)-(Ch1,Ch2°) are (87.33(2), 87.74(2)°)-(92.67(2), 92.26(2)°) for NiS₄, (87.66(2), 88.14(2)°)-(92.34(2), 91.86(2)°) for CoS₄ and (87.10(2), 87.57(2)°)-(92.90(2), 92.43(2)°) for CuS₄ chromophore. The structures of these complexes are stabilized by interaction of H27A-Cl1 (dist.: 2.905Å) for Ni complex, (dist.: 2.896Å) for Co complex and (dist.: 2.912Å) for Cu complex. The basic idea of this work was to obtain suitable M(III) compounds for study of electronic structure. The chloro-substituted ligand was used to eliminate disorder (Figure1). The elimination of disorder was successful. After purification the high quality crystals were prepared for the study of electronic structures.

This work has been supported by Slovak Grant Agency APVV (APVV-0202-10) and VEGA (1/0679/11).

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