Structural identification of two differently coordinated heptamolybdate ligands in a hexamagnesium compound

Abstract

Dissolution of freshly prepared molybdenum trioxide in hot aqueous magnesium carbonate followed by crystallization results in the formation of an all-inorganic heptamolybdate compound viz. [Mg(H2O)6]3[Mg(H2O)5(Mo7O24)][(H2O)5Mg (µ2-Mo7O24)Mg(H2O)5]∙6H2O (1). The crystal structure, spectral characteristics, thermal and electrochemical properties of 1 are reported. Compound 1, which crystallizes in the acentric polar space group Cc, contains six unique Mg(II) ions. The two crystallographically independent heptamolybdate anions function as a monodentate (η1) and µ2-bridging bidentate ligand, respectively, forming the anionic [Mg(H2O)5(Mo7O24)]4− and [(H2O)5Mg(µ2-Mo7O24)Mg(H2O)5]2− species, which are charge balanced by three unique hexaaquamagnesium(II) cations. The electrochemical and conductivity studies of 1 reveal the presence of [Mg(H2O)6]2+ cations and uncoordinated (Mo7O24)6− anions in solution. Thermal decomposition of 1 leads to the formation of Mg2Mo3O11 via Mg6Mo14O48 and 3Mg2Mo3O11∙5MoO3.