Electron paramagnetic resonance and quantum-mechanical analysis of binuclear niobium clusters in lithium–niobium phosphate glasses

Rakhimov, R.R.; Turney, V.J.; Jones, D.E.; Dobryakov, S.N.; Borisov, Y.A.; Prokof’ev, A.I.; Aleksandrov, A.I.

Авторы: Rakhimov R.R., Turney V.J., Jones D.E., Dobryakov S.N., Borisov Yu A., Prokof’ev A.I., Aleksandrov A.I.
Журнал: Journal of Chemical Physics
Том: 118
Номер: 13
Год издания: 2003
Издательство: AIP Publishing
Местоположение издательства: United States
Первая страница: 6017
Последняя страница: 6021
DOI: 10.1063/1.1556752
Аннотация: Electron paramagnetic resonance ~EPR! spectra of Nb41 ions in Li2O– Nb2O5 – P2O5 glasses withdifferent composition of oxide components have been investigated. The EPR spectrum shapeanalysis of Nb41 ~electron configuration 4d1, electron spin S51/2) reveals the formation of tripletniobium binuclear complex ~total electron spin S51) in glasses. The amount of Nb41 ions inglasses reversibly changes with temperature and is explained via the mechanism of electron hoppingbetween niobium ions in clusters. The dependence of the amount of Nb41 ions upon Li2O contenthas a maximal character, which implies that small amounts of Li1 ions stabilize the Nb41 pairs, butcause their disproportionation at higher concentrations of Li1 ions in the glass. Quantummechanical analysis of electronic and spin states of binuclear niobium clusters has been performedon model binuclear complexes, (HO)3Nb– O– Nb(OH)3 , @(HO)3Nb– O– Nb(OH)3#Li1, and@(HO)3Nb– O– Nb(OH)3#(Li1)2 that exhibit the reversible disproportionation reactionNb41 – O– Nb41⇔Nb31 – O– Nb51. Triplet states of these complexes ~total electron spin S51)have lower energies than singlet states (S50), and Li1 ions stabilize the binuclear niobiumcomplex. We have found that electron spin densities on niobium ions change depending upon theshift of the bridging oxygen atom. Application of this theoretical modeling to the analysis of theexperimental EPR spectrum in Li2O– Nb2O5 – P2O5 glass concludes noncentrosymmetric structureof binuclear niobium complex with ;0.1 Å offset of the bridging oxygen atom towards one Nbatom.
Добавил в систему: Александров Алексей Иванович

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Electron paramagnetic resonance and quantum-mechanical analysis of binuclear niobium clusters in lithium–niobium phosphate glassesстатья

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