Building blocks and formation thermodynamics of alpha-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 alpha-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. (C) 2012 Elsevier B.V. All rights reserved