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

A medium-nuclearity mixed-valence polyoxomolybdate [H2Mo16O52](10-) = {Mo-16} (1a) was synthesized using an approach that employed protonated hexamethylenetetramine (HMTAH(+)) as counter ion and yielded (HMTAH)(10) 1a.34 H2O(1). The {Mo-16} 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)(8)H-2 Mo16O52](6-) (M = Fe-II (2), Mn-II (3), Co-II (4)). The highly reactive nature of the {Mo-16} 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 [M-2(H2O)(9)Mo7O24](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.