Successive Protonation of Decaniobate, [Nb10O28]6−: Electronic Properties and Spectra.

Decaniobate is a polyoxoniobate considered in photocatalytic studies lacking more detailed electronic transition data. Moreover, its stability in aqueous solution depends on the pH and little is known regarding the protonation of this polyanion. Hence, this electronic structure study based on Density Functional Theory calculations shows that initial protonations occur at specific external oxygen sites situated above and below the equatorial plane of the polyanion [Oe(A)]. Moreover, these Oe(A) protonations cause small perturbations to the inner core structural skeleton constituted by bonds between niobium and internal oxygen atoms via a trans effect. The ultraviolet/visible spectra are slightly affected by these protonations as well, exhibiting a general trend for formation of four main bands in the range from 150 to 250 nm with similar positions and relative intensity profiles. The nature of the lowest energy electronic transitions (231 to 249 nm) indicates that these are charge transfer bands mainly from bridging oxygen to niobium atoms, with an amount of electronic charge received by metal atoms nearly unaltered by the protonations (from 0.32 to 0.38 e). [ABSTRACT FROM AUTHOR]