Organically Functionalized Mixed-Valent Polyoxo-30-molybdate Wheel and Neutral Tetramolybdenum(V) Oxo Cluster.

The first organofunctionalized mixed-valent polyoxo-30-molybdate wheel, [Mo VI 18 Mo V 12 O 84 {AsO 2 (CH 3 ) 2 } 18 ] 18- ( Mo 30 ), was synthesized in aqueous, mildly acidic conditions, and upon further acidification, the neutral tetramolybdenum(V) oxo cluster [Mo V 4 O 8 {AsO 2 (CH 3 ) 2 } 4 ] ( Mo 4 ) was obtained. Single-crystal X-ray diffraction (XRD) revealed that Mo 30 comprises 18 Mo VI and 12 Mo V ions arranged in a cyclic fashion with alternating {Mo V 2 } and {Mo VI 3 } groups, which are capped by 18 dimethylarsinate ligands, resulting in a novel polyoxo-30-molybdate wheel with a central cavity of ∼1.5 nm. On the other hand, Mo 4 has a distorted-cubic structure, with the corners of the cube being occupied by alternating Mo V ions and oxo ligands. The compounds were characterized in solution by 1 H and 13 C NMR and UV-vis spectroscopy and in the solid state by X-ray photoelectron spectroscopy and powder XRD. Mo 30 represents a novel type of polyanionic cycle with manyfold possibilities regarding host-guest chemistry.