BIS[4-(2,6-DIMETHYLPHENYLIMINOMETHYL)-5-PYRAZOLETHIOLATO]NICKEL(II) COMPLEXES WITH AN UNUSUAL TRANS-PLANAR STRUCTURE

The nickel(II) complexes bis[1-phenyl-3-methyl-4-(2,6-dimethylphenyl)iminomethyl-5- pyrazolethiolato]nickel(II) (1) and bis[1,3-diphenyl-4-(2,6-dimethylphenyl)iminomethyl-5- pyrazolethiolato]nickel(II) (2), based on the 4-imino-methyl-5-thiopyrazole ligands containing a 2,6-xylyl substituent at the coordinating imino nitrogen atom, have been prepared and their structures investigated. Complex 1 is tetrahedral and high-spin in solution as indicated by its temperature-independent mu(eff), value of 2.75 BM whereas 2 displays magnetic behaviour and H-1 NMR spectra consistent with a fast planar (LS)-tetrahedral (HS) equilibrium (Delta H degrees=11.8 kJ mol(-1), Delta S degrees=34.6 J mol(-1) K-1). 1 and 2 are low-spin in the solid state. An X-ray diffraction study of 1 revealed a trans-square-planar coordination geometry which is unusual for bis-chelate N2S2 metal complexes, in comparison to cis-planar geometry.