ja010820r_si_001.pdf (1.16 MB)
The Elusive Vanadate (V3O9)3-: Isolation, Crystal Structure, and Nonaqueous Solution Behavior
journal contribution
posted on 2001-12-11, 00:00 authored by Elizabeth E. Hamilton, Phillip E. Fanwick, Jonathan J. WilkerThe isolation, crystal structure, and nonaqueous solution characteristics of the first trinuclear
vanadate are presented. The crystal structure reveals a six-membered cyclic arrangement of alternating
vanadium and oxygen atoms for the anion of [(C4H9)4N]3(V3O9). The 51V NMR spectrum of this compound
in CD3CN exhibits multiple peaks. The relative intensities of each resonance can be altered by concentration
and temperature changes, the later of which are reversible. Addition of [(C4H9)4N]Br and NaClO4 also perturbs
the equilibria between species observed. Conductivity data for [(C4H9)4N]3(V3O9) in CH3CN as a function
of concentration display pronounced curvature and indicate formation of a neutral species in solution at
the highest concentrations studied. Stoichiometric mixtures of [(C4H9)4N]3(V3O9) with the known vanadates
[(C4H9)4N]3(HV4O12), [(C4H9)4N]3(V5O14), and [(C4H9)4N]3(H3V10O28) are prepared and examined by 51V NMR.
Equilibration between the various vanadates is observed and characterized. Resonances for these known
vanadates, however, cannot be used to identify the peaks found for [(C4H9)4N]3(V3O9), alone, in solution.
The existence of ion pairs in acetonitrile is the only interpretation for the solution behavior of [(C4H9)4N]3(V3O9) consistent with all data. As such, we can directly observe each possible ion pairing state by 51V
NMR: (V3O9)3- at −555 ppm, {[(C4H9)4N](V3O9)}2- at −569 ppm, {[(C4H9)4N]2(V3O9)}- at −576 ppm, and
[(C4H9)4N]3(V3O9) at −628 ppm. To the best of our knowledge, [(C4H9)4N]3(V3O9) presents the first case in
which every possible ion paired state can be observed directly from a parent polyion. Isolation and
characterization of this simple metal oxo moiety may now facilitate efforts to design functional polyoxometalates.