Investigating the electronic excitations in Polyoxoniobates: (Nb6O19)8-, (Nb10O28)6- and (XNb12O40)Y with (X = As, P, Si, Ge) and (Y=15-and 16-)

Polyoxoniobates are polyoxometalates with applications in catalysis, water splitting and organic reactions such as condensation of Knoevenagel and Cycloaddition of CO2. Actually, range-separated hybrids (RSHs) are being indicated for the description of electronic excitations within Time Dependent Density Func-tional Theory (TDDFT), mainly in systems presenting charge - transfer transitions. Here, this protocol is applied for studying ultraviolet - visible (UV/Vis) bands of polyoxoniobates in aqueous solution. Al-though the experimental data for comparison are scarce, the RSHs investigated were particularly suc-cessful, providing wavelength deviations usually smaller than 30 nm. Results indicate that wavelengths change slightly among all these compounds (22 - 35 nm), with the following sequence: [Nb10O28](6-) < [Nb6O19]8- < [SiNb12O40](16-) = [AsNb12O40](15-) = [PNb12O40](15-) < [GeNb12O40](16-). Atomic charges in internal oxygens and heteroatoms are nearly insensitive to these transitions. In addition, the largest elec-tronic charge transfer from oxygens to niobium occurs in [Nb6O19](8-) (0.39 e ), followed by [Nb10O28](6-) (0.31 e ), [SiNb12O40](16-) (0.27 e ), [PNb12O40](15-) (0.23 e ), [AsNb12O40](15-) (0.11 e ) and [GeNb12O40](16-) (0.06 e ). (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

Polyoxoniobates are polyoxometalates widely used in catalysis, water splitting, and organic reactions. Range-separated hybrids (RSHs) are successful in describing electronic excitations, with wavelength deviations usually smaller than 30 nm. There are slight variations in wavelengths among different compounds, with the largest electronic charge transfer occurring in [Nb6O19](8-).