Building blocks and formation thermodynamics of α-Keggin-type [PW12O40]3− anion

The formation mechanism is a fundamental scientific issue for polyoxometalate chemistry. The structural characterization and the thermodynamic behavior of various possible intermediates in the formation of α-Keggin-type [PW12O40]3− anion in aqueous solution were analyzed by density functional method. Based on two proposed mechanisms (order of reaction with heteroatom), thermodynamic analysis indicates that [HPO4]2−, [WO3(OH)]−, [W2O7]2−, [W3O10]2−, [W4O13]2−, [W5O16]2−, and [PW2O9]− will be mainly involved in the polymerization processes of [PW12O40]3− anion. The starting reaction from isodimer has been determined through transition state search for the initial steps. Heteroatom has been introduced in the heterotrimer [PW2O9]− at the second step which experiences almost the same barrier with isotrimer [W3O10]2−. From geometric topology and thermodynamics, the defect structures are more suitable for building blocks.