Structural refinement of T2Mo3O8 (T=Mg, Co, Zn and Mn) and anomalous valence of trinuclear molybdenum clusters in Mn2Mo3O8

Crystal structure of a series of mixed-metal oxides, T2Mo3O8 (T=Mg, Co, Zn and Mn; P63mc; a=5.7628(1) Å, c=9.8770(3) Å for Mg2Mo3O8; a=5.7693(3) Å, c=9.9070(7) Å for Co2Mo3O8; a=5.7835(2) Å, c=9.8996(5) Å for Zn2Mo3O8; a=5.8003(2) Å, c=10.2425(5) Å for Mn2Mo3O8) was investigated by X-ray diffraction on single crystals. Structural analysis, magnetization measurements, X-ray photoemission spectroscopy and cyclic voltammetry showed that the Mn ions at the tetrahedral and octahedral sites in Mn2Mo3O8 adopt different valences of +2 and 2+δ (δ>0), respectively. The formal valence of the Mo3 in Mn2Mo3O8 is 12−δ to retain electric neutrality of the compound. In contrast, the T ions and Mo3 in T2Mo3O8 (T=Mg, Co and Zn) adopt the valences of +2 and +12, respectively.