A Mixed‐Valence, Hexadecamolybdenum Cluster With an Mo VI Cubane “Jewel” in a “Setting” of Five Molybdate VI ‐Linked Dinuclear Mo V Units

The hexadecanuclear, mixed‐valence cluster [Mo 16 O 42 (OH) 2 (3‐ i PrC 3 H 3 N 2 ) 12 ] ⋅ n  H 2 O ( 1 ), has been synthesized and characterized by X‐ray crystallography, IR spectroscopy and mass spectrometry. The C 2 ‐symmetric complex consists of a cubane Mo VI 4 O 4 “jewel” held in a 10‐point “setting” comprised of five dinuclear Mo V units tethered together by two tetrahedral Mo VI centers. The dinuclear units are ligated by twelve 3‐isopropylpyrazole units that interact with the MoO framework through a network of hydrogen bonds. Structural parameters, charge requirements, and bond valence sum analyses support the assignment of +5 and +6 oxidation states to the dinuclear and cubane/tetrahedral Mo centers, respectively. Space filling models reveal that the pyrazole groups coat much of the surface of the molecule, apart from a number of oxo‐rich seams that trace a chiral pattern across the surface. Complex 1 exhibits a unique structure that combines moieties generally atypical of polyoxometalates, viz., a Mo cubane containing only two terminal oxo ligands, and three distinct Mo V 2 units (including a 5‐coordinate Mo center) tethered into a 10‐point “setting” by tetrahedral Mo VI centers.