O3LYP calculations were carried out to study the structures and properties of the alpha-Keggin-type vanadium(V)-substituted heteropolyanions [PVnMo12-nO40]((3+n)-) (n = 0-3) in an attempt to characterize their catalytic performance. Five alpha-Keggin [PV2Mo10O40](5-) (alpha-PV2) isomers are studied thorou Ofly. ill comparison with the two -Keggin isoniers of their Counterparts and three of the 13 isomers of [PV3Mo9O40](6-) (alpha-PN3). The d-orbital contribution of vanadium atom to the LUMO (DCVL) of the vanadium-substituted heteropolymolybdates is found to be a key factor in their catalytic performances. Based on this, the activity differences between the five alpha-PV2 isomers are predicted and rationalized. A linear correlation between the turnover numbers based oil the vanadium atom and the DCVLs is established for the benzene hydroxylation to phenol. The order of the catalytic activities is predicted as [PMo12O40](3-)(alpha-PV0) < alpha-PV3 < alpha-PV2 < [PVMo11O40](4-) (alpha-PV1). which is in good agreement with the reported experimental results. (c) 2006 Elsevier Inc. All rights reserved.