Catalytic oxidation performance of the α-Keggin-type vanadium-substituted heteropolymolybdates: A density functional theory study on [PVnMo12−nO40](3+n)− (n=0–3n=0–3)

O3LYP calculations were carried out to study the structures and properties of the α-Keggin-type vanadium(V)-substituted heteropolyanions [PVnMo12−nO40](3+n)− (n=0–3n=0–3) in an attempt to characterize their catalytic performance. Five α-Keggin [PV2Mo10O40]5− (α-PV2) isomers are studied thoroughly, in comparison with the two β-Keggin isomers of their counterparts and three of the 13 isomers of [PV3Mo9O40]6− (α-PV3). 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 α-PV2 isomers are predicted and rationalized. A linear correlation between the turnover numbers based on 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−(α-PV0)<α-PV3<α-PV2<[PVMo11O40]4−(α-PV0)<α-PV3<α-PV2<[PVMo11O40]4− (α-PV1), which is in good agreement with the reported experimental results.