Natural bond orbital studies on quasi-aromaticity of polyoxoanion (M_6O_(19))~(Z-) (M= Mo, W, Z = 2;M = V, Nb, Z = 8)

The natural bond orbitals and McWeeny bond orders for polyoxoanions (M6O19)Z- (M = Mo, W, Z = 2; M = V, Nb, Z = 8) have been calculated in terms of Weinhold' s natural bond orbital theory using DV-SCC-Xa method. It is shown that all polyoxoanions possess quasi-arornaticity. They are compared with other aromatic systems.