Divalent transition metal complexes of alkylpyridyl derivatized dmit ligands

The two new bis-alkylpyridyl substituted dmit ligands, 4,5-bis(2-pyridylmet hylsulfanyl) -1,3-dithiole-2-thione (bpmdmit) and 4,5-bis(2-pyridylethylsul fanyl) -1,3-dithiole-2-thione (bpedmit), and some of their transition metal complexes have been prepared. Two basic structural types for the complexes MX2L (M = Ni, Co, Cu, Pd; L = bpmdmit or bpedmit; X = Cl or Br) were deter mined by X-ray crystallography. The cobalt(II) and the nickel(II) complexes CoBr2(bpmdmit) and NiCl2(bpmdmit) show octahedral geometries around the me tal ions with coordination to the metal ions by the pyridyl nitrogen atoms and the thioether sulfur atoms of the ligand and cis coordination of the ha lide ions. By contrast, only the pyridyl nitrogen atom of the ligands in th e copper(II) and the palladium(II) complexes, CuCl2(bpedmit) and PdCl2(bped mit), are coordinated to the metal ions to give essentially square planar m etal environments. The copper complex was isolated as both green and purple crystals. However, the X-ray structures of both forms are similar, and sho w a dimeric arrangement with bis-mu-chloride bridges between the copper ion s in the dimeric units. The green crystals contain two molecules of acetoni trile in the unit cell, however these do not interact with the metal ions. The geometry of the copper ions in the green form deviates most from centro symmetric square planar geometry and this is consistent with the observed c olour. Apart from the colour, the solids can be distinguished in the solid state by EPR spectroscopy since they give different rhombic signals. UV-Vis and EPR spectroscopy show that in solution the structures of the purple an d green forms of CuCl2(bpedmit) are identical, as expected. (C) 2000 Elsevi er Science Ltd All rights reserved.