Structure and Bonding in Dinuclear Oxoanions of V, Nb, Ta, Mo, and W

Abstract

The structure and bonding in [M2O7] n - anions of the early transition metals V, Nb, Ta, Mo, and W have been investigated by density-functional methods. Several molecular conformations have been tested in geometry optimizations, and systems with a linear M−O−M bridge have been the only structures obtained for V, Nb, and Ta, and the most stable configurations for Mo and W. Molecular-orbital analysis has indicated that multiple bonds are formed between the metal and both bridging (Ob) and terminal (Ot) oxygen atoms. However, it has been found that M−Ob interactions are characterized by bond lengths and bond orders that are typical of a single M−O bond. The results from population analysis (Mulliken charges and Mayer bond indices) have suggested that the repulsive interactions between the ends of the molecules may be a more important structural factor in determining the configuration of the bridge than M−Ob π bonding is.

Towards an understanding of the bonding in polyoxometalates through bond order and bond energy analysis

“…However, (relative) Mayer bond indexes and Mulliken charges can nonetheless provide valuable chemical information, if uniformity and consistency of basis set are maintained. 39 The Mulliken analysis is consistent with the internal structure of the molecular orbital formalism and we have shown 19 that the values it predicts for polyoxometalates are qualitatively consistent with those based on other schemes. We have shown previously 39 that for many bonds, such as those between a central atom and ligands, the bond order can be expressed as a sum over symmetry species G,…”

“…The developments and advances in density functional (DF) theory and effective core potentials or frozen cores have provided both the accuracy and computational economy necessary to model the structures and properties of polyoxometalates. Most of the first-principle studies related to polyoxoanions have been carried out by Poblet, Bénard and co-workers, [6][7][8][9][10][11][12][13][14][15][16][17] initially at the Hartree-Fock (HF) and latterly at density functional (DF) levels of theory, and by Bridgeman and Cavigliasso, [18][19][20][21][22][23][24][25][26][27] and Borshch and coworkers [28][29][30] at the DF level. This computational work has demonstrated that it is possible to accurately model many properties of polyoxometalates, including structures, vibrational spectra and aspects of reactivity such as redox behaviour and protonation sites.…”

“…In our studies [18][19][20][21][22][23][24][25][26][27] of the polyoxoanions of Mo and W, we have employed the combined approach based on population methods and bond energetics and have augmented the traditional analysis of orbital compositions and atomic charges with the calculation of bond orders and valency indexes. We have found the combination of bond and valency indexes with bond energies to be an extremely useful and transparent analytical and interpretative tool.…”

Computational Study of Solvent Effects and the Vibrational Spectra of Anderson Polyoxometalates

“…The agreement between the crystallographic and calculated bond lengths is reasonable at all levels. In keeping with previous computational studies of POMs, [24][25][26] bond lengths are over estimated particularly for terminal and heteroatom-oxygen bonds. The MoÀO 2c bond lengths are well reproduced at all levels.…”

“…The MoÀO 2c bond lengths are well reproduced at all levels. As we have noted previously, [6,25] the LDA approach appears best able to reproduce solid state bond lengths. This presumably reflects a compensation for the lack of the stabilizing crystal field in pseudo-gas phase calculations by the overbinding associated with the local density method.…”