Can Electron-Rich Oxygen (O2–) Withdraw Electrons from Metal Centers? A DFT Study on Oxoanion-Caged Polyoxometalates

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2017-10, Vol.121 (40), p.7684-7689
• Main Authors: Takazaki, Aki, Eda, Kazuo, Osakai, Toshiyuki, Nakajima, Takahito
• Format: Article
• Language: English
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/acs.jpca.7b05950

The answer to the question “Can electron-rich oxygen (O 2– ) withdraw electrons from metal centers?” is seemingly simple, but how the electron population on the M atom behaves when the O–M distance changes is a matter of controversy. A case study has been conducted for Keggin-type polyoxometalate (POM) complexes, and the first-principles electronic structure calculations were carried out not only for real POM species but also for “hypothetical” ones whose heteroatom was replaced with a point charge. From the results of natural population analysis, it was proven that even an electron-rich O2–, owing to its larger electronegativity as a neutral atom, withdraws electrons when electron redistribution occurs by the change of the bond length. In the case where O2– coexists with a cation having a large positive charge (e.g., P5+(O2–)4 = [PO4]3–), the gross electron population (GEP) on the M atom seemingly increases as the O atom comes closer, but this increment in GEP is not due to the role of the O atom but due to a Coulombic effect of the positive charge located on the cation. Furthermore, it was suggested that not GEP but net electron population (NEP) should be responsible for the redox properties.