Efficient syntheses of the complete set of compounds [{(OC)(5)M}(6)E-6](2-) (M = Cr, Mo, W; E = Ge, Sn) - Structure and redox behaviour of the octahedral clusters [Ge-6](2-) and [Sn-6](2-)

Improved syntheses of the known clusters [{(OC)(5)Cr}(6)Ge-6](2-)(1) and [{ (OC)(5)Cr}(6)Sn-6](2-) (4) are reported. The new synthetic procedures also allow for the preparation of the molybdenum and tungsten derivatives [{(OC) (5)M}(6)Ge-6](2-) (M = Mo: 2; M = W: 3) and [{(OC)(5)M}(6)Sn-6](2-) (M = Mo : 5; M = W: 6). Compounds 1-6 were obtained as crystalline [Ph4P] salts, wh ose structures were determined for the whole series 1-6 by single-crystal X -ray analyses. All six [Ph4P] salts crystallise in tetragonal space groups, with the site group symmetries of the cluster core ranging from C-4h to D- 4h The average octahedral symmetry of the cluster core in solution is evide nt from Sn-119 NMR spectroscopic data. Reversible one-electron oxidation of the dianions is suggested by cyclovoltammograms, while reduction is irreve rsible throughout. Electronic transitions which could be due to the cluster core were not found in the experimentally accessible energy range above 30 0 nm (below 4 eV). These findings indicate a high intrinsic stability of th e precise electron clusters [Ge-6](2-) and [Sn-6](2-).