Molecular Hume-Rothery compounds [M(ZnR)n] and [M(ZnR)a(GaR)b] (a + 2b = n ≥ 8): relations of coordination polyhedra and electronic structure.

The icosahedral complex [Mo(ZnMe)(9)(ZnCp*)(3)] is discussed as the prototype for a whole family of high-coordinate, metal-rich compounds [M(ZnR)(n)] and [M(ZnR)(a)(GaR)(b)] (a + 2b = n ≥ 8; for the same metal M). In contrast to other highly coordinate complexes of classic, monodentate (nonchelating) nonmetal atom ligator ligands, for the (weakly) bonding metal atom ligators ZnR and GaR, attractive ligand-ligand interactions play an important role. The structures of the compounds were evaluated by the method of continuous-shape measures, and the bonding situation of models (R = H) was analyzed on the density functional level of theory. The structures and coordination polyhedra of [M(M'R)(n)] (M' = Zn, Ga) turned out to be independent of the central metal or the nature of the metals M' in the ligand shell, and the resulting molecular orbital schemes vary only slightly as a result of the different symmetries, however resulting in the same coordination polyhedra (structures) for all complexes. This result may be viewed as a molecular representation for the situation in extended solid-state intermetallic phases of the Hume-Rothery type.