(V₂O₅)<i>_n</i> Gas-Phase Clusters (<i>n</i> = 1−12) Compared to V₂O₅ Crystal: DFT Calculations

Abstract

Stable structures of neutral (V2O5)n clusters (n = 1−5, 8, 10, and 12) are determined by density functional calculations (BP86 functional with a double-ζ (V)/triple-ζ (O) valence basis set augmented by polarization functions). Comparison is made with calculations for the periodic structure of solid V2O5. The most stable structure of the smallest cluster is doubly O-bridged, OV−O2−VO2, and by 184 kJ/mol VO2.5 less stable than the periodic bulk structure. From the tetrahedral V4O10 structure on (41 kJ/mol VO2.5 above the crystal energy) polyhedral cage structures are the most stable isomers: trigonal prism (V6O12), cube (V8O20), pentagonal prism (V10O25), 16-hedron (V16O40), dodecahedron (V20O50), and truncated octahedron (V24O60). The polyhedra have vanadyl groups at the apexes and bridging oxygen atoms on the edges. Differently from the crystal structure, vanadium is 4-fold coordinated and 3-fold coordinated oxygen is avoided. The energies relative to the periodic solid are 22.1, 12.4, 9.4, 5.5, 3.3, and 3.4 kJ/mol VO2.5, respectively. Structures that correspond to fragments cut out of the crystal structure (examined up to n = 8) are significantly less stable. The IR spectra of cage-type structures will show bands in the 1040−1080 cm-1 and in the 800−925 cm-1 regions (terminal VO(1) and bridging V−O(2)−V, respectively), but not between 650 and 750 cm-1 or around 500 cm-1 (V−O2(2)−V double bridges and triply coordinated oxygen, respectively).