Hexa- and nona-nuclear heterometallic clusters based on mercury-capped MCo3(M = Fe or Ru) tetrahedral units

Abstract

The reactions of tetrahedral mixed-metal clusters K[MCo₃(CO)₁₂](M = Fe 1a or Ru 1b) with HgBr₂ afforded the pentanuclear clusters [MCo₃(CO)₁₂(HgBr)](M = Fe 2a or Ru 2b) together with hexanuclear clusters [MCo₃(CO)₁₂{µ₃-HgCo(CO)₄}](M = Fe 5a or Ru 5b) in which the mercury atom caps the Co₃ face of the precursor. Complexes 5a and 5b were most effectively prepared in dichloromethane by the reaction of 2a or 2b with Na[Co(CO)₄]. The reactions with Na[Mo(CO)₃(cp)](cp =η-C₅H₅) similarly afforded [MCo₃(CO)₁₂{µ₃-HgMo(CO)₃(cp)}](M = Fe 6a or Ru 6b). The syntheses of the nonanuclear sandwich clusters [µ₆-Hg{MCo₃(CO)₁₂}₂](M = Fe 7a or Ru 7b) are also described. All the complexes have been characterized by IR and UV/VIS spectroscopy. The crystal structure of [FeCo₃(µ-CO)₃(CO)₉{µ₃-HgMo(CO)₃(cp)}]6a has been determined by X-ray diffraction methods. Crystals are monoclinic, space group P2₁/c, with a= 28.123(9), b= 8.400(5), c= 25.290(8)Å, β= 114.72(2)° and Z= 8. The structure was solved by direct and Fourier methods and refined by full-matrix least squares to R= 0.0596 for 3016 observed reflections. In the asymmetric unit two crystallographically independent, but essentially identical complexes are present. The complex exhibits a FeCo₃ tetrahedron in which the Co₃ face is capped by a HgMo(CO)₃(cp) fragment such that the FeCo₃Hg metal core forms a trigonal bipyramid with the Hg and Fe atoms at the apices. Each Co–Co edge is bridged by an almost symmetrical carbonyl ligand. In addition, three terminal carbonyls are bonded to the Fe atom, and two to each Co atom. The Hg atom has a severely distorted tetrahedral co-ordination involving the three Co atoms and the Mo atom. The structure of 6a is compared with those of 5b and 7b, previously reported.