A comparative investigation of structure and bonding in Mo and W[TeM6O24]6- and [PM12O40]3- heteropolyanions

The structure and bonding in [TeM6O24](6-) (Anderson) and [PM12O40](3-) (alpha-Keggin) heteropolyanions have been investigated by density-functional methods. Various molecular-orbital and population approaches have been employed in the analysis of the structural and electronic properties. Good agreement between computational and experimental or bond-valence results for bond parameters has been obtained. The M-O interactions have been found to be largely of Md-Op character, whereas the orbital nature of Te-O and P-O bonding can be predominantly characterized as Tesp or Psp and Osp. The interactions between the [TeO6] or [PO4] fragments and the [MpOq] cages have been explored by a decomposition approach to the polyanion structure. The results obtained have suggested that the molecular-orbital structure of the Te-O and P-O bonds is not significantly different in the presence or absence of the metal-oxygen cages but that there is nonetheless some covalent character in the bonding of the [TeO6] and [PO4] fragments to the surrounding clusters.