Syntheses, Structures, and Properties of New Niobium Cluster Complexes with Terminal Formate Ligands: ­[AI(CH3OH)n]4­[Nb6Cl12(OCHO)6] (AI = Na, K, Rb, Cs; n = 1, 2)

Four examples of the first hexanuclear niobium cluster complexes with formate ligands, [AI(CH3OH)n]4[Nb6Cl12(OCHO)6] (AI = Na, K, Rb, Cs; n = 1, 2) were prepared. They are obtained from the reaction of [Nb6Cl14(CH3OH)4]·6CH3OH with alkali metal formates in absolute CH3OH. Their structures were determined by single‐crystal X‐ray diffraction. They crystallize in the triclinic space group P$\bar{1}$ and contain isolated cluster anions with formate ligands, which occupy the exo sites of the hexanuclear cluster units. Four AI ions form tetranuclear cationic units, interconnected by oxygen atoms of methanol molecules and of the formate ligands. All compounds comprise network structures of interconnected cluster and complex cation units. Whereas the K, Rb, and the Cs salt contain planar rectangular arrangements of the AI cations, in the Na salt this unit is bent along one diagonal. Electrochemical measurements indicate the possibility of two one‐electron oxidations of the cluster units and possibly one reduction step. The cluster compounds were further characterized by elemental analyses, NMR‐, IR‐, and UV/Vis spectroscopy.