Synthesis, structure and properties of a hexarubidium heptamolybdate with bridging aqua ligands

Abstract

The synthesis, single crystal structure, spectral, thermal and electrical properties of a hexarubidium heptamolybdate [Rb₆(H₂O)₄(Mo₇O₂₄)] 1 is reported. The bridging binding modes of the unique (Mo₇O₂₄)^6- ion and the four crystallographically independent coordinated water molecules results in coordination numbers ranging from 8 to 10 for the six unique Rb(I) ions in 1. Thermal decomposition of 1 results in the formation of an anhydrous residue of composition 7MoO₃·3Rb₂O. The cyclic voltammogram of an aqueous solution of 1 exhibits a single redox event characteristic of (Mo₇O₂₄)^6- anion. Solution conductivity studies reveal the presence of hydrated Rb⁺ cations and uncoordinated (Mo₇O₂₄)^6- anions. A comparative study of several alkali-metal heptamolybdates reveals a rich structural chemistry in terms of the binding modes of the (Mo₇O₂₄)^6- anion.