Reactions of a {Mo16}-type polyoxometalate cluster with electrophiles: a synthetic, theoretical and magnetic investigation

Abstract

A medium-nuclearity mixed-valence polyoxomolybdate [H₂Mo₁₆O₅₂]¹⁰⁻ = {Mo₁₆} (1a) was synthesized using an approach that employed protonated hexamethylenetetramine (HMTAH⁺) as counter ion and yielded (HMTAH)₁₀1a·34 H₂O (1). The {Mo₁₆} cluster anion exhibits significant nucleophilicity and traps electrophiles such as divalent transition metal ions, resulting in a family of isostructural compounds based on {Mo₁₆M₂}-type anions [M(H₂O)₈H₂Mo₁₆O₅₂]⁶⁻ (M = Fe^II (2), Mn^II (3), Co^II (4)). The highly reactive nature of the {Mo₁₆} system is also revealed by rearrangement and decomposition reactions of 1 to either slowly form a sodium-bridged heptamolybdate-based chain compound (5) when left in the reaction solution or, in the presence of very high concentrations of electrophiles, to heptamolybdate-based cluster compounds [M₂(H₂O)₉Mo₇O₂₄]²⁻ of the {M₂Mo₇}-type (M = Fe^II (6), Mn^II (7)). Compounds 1–7 were characterised by single crystal X-ray diffraction, elemental analysis, IR spectroscopy, magnetic susceptibility measurements, and density functional theory calculations.