Synthesis, crystal structures and spectroscopic characterization of two neutral heterobimetallic clusters MS 4Cu 4(pz Me2) 6X 2 (where M = Mo ( 1) or W ( 2), X = Cl ( 1) or disordered Cl/Br ( 2), and pz Me2 = 3,5-dimethylpyrazole)

Abstract

The title complexes were synthesized in acetone by the reaction of [ n-Bu 4N] 2[MoS 4Cu 4Cl 4] and pz Me2 for compound 1, and n-Bu 4NBr, [NH 4] 2[WS 4], CuCl and pz Me2 for compound 2. X-ray diffraction studies of 1 and 2 demonstrate that four of the six edges of the tetrahedral [MS 4] 2− core are bridged by four copper atoms, giving a pentanuclear structure MS 4Cu 4(pz Me2) 6X 2 (M = Mo, W) with the five metal atoms essentially coplanar. The four Cu atoms exhibit two different coordination modes. Each of one pair of mutually trans Cu atoms is coordinated by two (μ 3-S) atoms and two nitrogen atoms of pz Me2 rings, giving a distorted tetrahedral CuS 2N 2 arrangement. The other two mutually trans Cu atoms are coordinated by two (μ 3-S) atoms, one nitrogen atom of pz Me2 and one terminal Cl or Br ligand, giving a distorted tetrahedral CuS 2NX unit. In addition to being structurally studied by X-ray diffraction, the title compounds have been characterized by IR, UV–Vis and 1H NMR spectroscopy. The IR results, which include low-frequency M–S b stretching bands, are consistent with the X-ray structural analysis and confirm that the [MS 4] 2− cores are coordinated through all four sulfur atoms in the complexes 1 and 2.