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

Successive protonation of Lindqvist hexaniobate, [Nb6O19]8−: electronic properties and structural distortions

“…Sum of QTAIM charges for atomic categories (Sq) achieved at the ground state (GS) and at the excited states (ES) along with their respective variation under excitation (Dq) obtained for [Nb 6 O 19 ] 8À and for the protonated species (in e)8À to ES a (233 nm) is clearly an electronic charge transfer from O b to Nb, where the niobium atoms receive a total of 0.38 e and these oxygens lose 0.45 e. Hence, the external oxygens also gain a small fraction of electronic charge in this process, 0.07 e. These values are in nice agreement with our previous investigation for this case 21. The excitation to the next state, ES b , is mainly an electronic charge transfer from O b to O e atoms, where the first ones lose 0.61 e and the last atoms receive 0.49 e. Niobium atoms also gain a small fraction of electronic charge in ES b , 0.12 e. Finally, the CT character of the highest energy transition is less pronounced, with some electronic charge being donated from O e (0.18 e) to Nb (À0.07 e) and, mainly, O b atoms (À0.12 e).…”

“…These values are in nice agreement with our previous investigation for this case. 21 The excitation to the next state, ES b , is mainly an electronic charge transfer from O b to O e atoms, where the first ones lose 0.61 e and the last atoms receive 0.49 e . Niobium atoms also gain a small fraction of electronic charge in ES b , 0.12 e .…”

“…20 In addition, to contribute to a more detailed understanding of electronic structure changes driven by such excitations, we also simulated the UV-vis spectra of several non-protonated Nb-POMs (Lindqvist, decaniobate and Keggin) in water with recently developed exchange-correlation Quantum Theory Project (QTP) functionals containing long-range corrections and the charge transfer process caused by the electronic transitions was quantitatively evaluated. 21 Thus, an electronic charge transfer process was observed again along the transitions from the ground to the excited states of all these Nb-POMs, which takes place from bridging oxygens (O b ) to niobium atoms. Moreover, this charge transfer process was more prominent in isopolyanions, mainly in [Nb 6 O 19 ] 8À , than in heteropolyanions.…”

“…31 Next, the time-dependent density functional theory (TDDFT) [32][33][34][35][36][37][38] formalism was considered in order to achieve UV-vis data for the previous equilibrium structures, which was done by using the CAM-QTP-01 functional 39 with LANL2DZ (Nb) and cc-pVDZ basis sets (H and O) because of the good performance of this method in a previous related study with Nb-POMs. 21 In addition, 300 states are required in these TDDFT calculations to achieve the high energy region of the UV/vis spectra. Again, the PCM 30 model is used with water to include solvent effects.…”

Soluble Complexes of Cobalt Oxide Fragments Bring the Unique CO2 Photoreduction Activity of a Bulk Material into the Flexible Domain of Molecular Science

“…These crystallographic and computational results show that the hexaniobate clusters serve as largely “innocent” oxo-donor ligands for the Co 3 O 4 -like cores. This is consistent with the photochemical properties of hexaniobate anions for which UV-light-promoted ligand-to-metal charge transfer from O to Nb requires an energy input of 5.2 eV, − much larger than the energies of the visible-light-driven d–d transitions of mixed-valent cobalt oxides.…”