Binuclear nickel(II) and copper(II) complexes containing an endogenous alkanethiolato-bridging sulphur atom and exogenous µ-pyrazolate (pz) group. Crystal structure of [Ni2L(pz)][L =NN′-3-mercaptopentane-1,5-diylbis(salicylideneiminate)(3–)]

Abstract

The first examples of binuclear nickel(II) and copper(II) complexes bonded to binucleating Schiff-base ligands containing an endogenous alkanethiolato-bridging sulphur atom have been synthesized. The complexes have the formula [M₂L(pz)](pz = pyrazolate) where L is the trianion of the pentadentate ligand NN′-3-mercaptopentane-1,5-diylbis(salicylideneimine). The pseudo-planar co-ordination spheres around M = Ni^II and Cu^II are completed by the N-donor atoms of an exogenous bridging µ-pyrazolate group. Crystals of [Ni₂L(pz)] are monoclinic, space group P2₁/c with a= 9.679(4), b= 8.860(4), c= 24.711(9)Å, β= 98.51(1)°, T= 20°C, Z= 4. The structure was solved by direct methods to R= 0.065 [I 3σ(I)]. Both the NiN₂OS chromophores are distorted from planarity and are not coplanar. The Ni ⋯ Ni distance is 3.507(3)Å and Ni–S distances are 2.165(4) and 2.182(3)Å. A Ni–S–Ni bonding angle of 107.5(1)° was observed and the S atom adopts a pyramidal bridging arrangement. The copper(II) complex represents one of the few known stable alkanethiolate species. Variable-temperature magnetic susceptibility measurements show a small decrease of µ_Cu with decreasing temperature indicative of weak antiferromagnetic exchange coupling. The analogous alcoholate O-bridged complex is much more strongly coupled due, primarily, to the (presumed) trigonal-planar geometry at the bridging oxygen atom.