Synthesis, crystal structures and spectroscopic characterization of two neutral heterobimetallic clusters MS4Cu4(pzMe2)6X2 (where M = Mo (1) or W (2), X = Cl (1) or disordered Cl/Br (2), and pzMe2=3,5-dimethylpyrazole)

The title complexes were synthesized in acetone by the reaction of [n-Bu4N](2)[MoS4Cu4Cl4] and pz(Me2) for compound 1, and n-Bu4NBr, [NH4](2)[WS4], 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 [MS4](2-) core are bridged by four copper atoms, giving a pentanuclear structure MS4Cu4(pz(Me2))(6)X-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 (mu(3)-S) atoms and two nitrogen atoms of pz(Me2) rings, giving a distorted tetrahedral CuS2N2 arrangement. The other two mutually trans Cu atoms are coordinated by two (mu(3)-S) atoms, one nitrogen atom of pz(Me2) and one terminal Cl or Br ligand, giving a distorted tetrahedral CuS2NX unit. In addition to being structurally studied by X-ray diffraction, the title compounds have been characterized by IR, UV-Vis and H-1 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 [MS4](2-) cores are coordinated through all four sulfur atoms in the complexes 1 and 2. (C) 2004 Elsevier Ltd. All rights reserved.