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 a hexamganesium-bis(heptamolybdate) compound viz. [Mg(H2O)6]3[Mg(H2O)5(Mo7O24)][(H2O)5Mg(µ2-Mo7O24)Mg(H2O)5]∙6H2O 1. Herein we report the crystal structure, spectral characteristics, thermal and electrochemical properties of 1. The all-inorganic 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 (h1) 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.