Peculiarities of crystal structures and magnetic properties of Cu(II) and Ni(II) mixed-ligand complexes on the 1,3-dithiole-2-thione-4,5-dithiolate basis

Mixed-ligand Cu(II) and Ni(II) complexes, [Cu(dmit)(bpy)](2) (I), [Ni(dmit)(phen)(2)] (II) and [Ni(dmit)(phen)(2)]center dot CH2Cl2 (III) (dmit=1.3-dithiole-2-thione-4.5-dithiolate, phen=1.10-phenantroline, bpy=2.2'-bipyridine) have been prepared by ligand exchange between phen or bpy and (Bu4N)(2)[M(dmit)(2)] (M=Ni, Cu) and characterized by elemental analysis, IR spectroscopy, single-crystal X-ray analysis and by investigation of magnetic and resonance properties. In complex I, the monomeric units form dimers in a head-to-tail arrangement by weak coordination bonds between copper and dithiolate sulfur atoms and pi-pi interactions between dmit and bpy from neighboring monomers. Dimers in I are further extended into chains by weak Cu-S(thione) contacts. In crystal packing of complex II and III, there exists a weak pi-pi interaction between two parallel phen molecules of the adjacent complexes. As a consequence, the magnetic and resonance characteristics of copper complex may be described in approximation of exchange-coupled pairs of Cu2+ ions with ion spin S=1/2. The nickel complexes are described by isotropic exchange model for single-site spin S=1. (C) 2011 Elsevier Ltd. All rights reserved.