Theoretical studies on tricarbonyl metal derivatives of Lindqvist-type polyoxometalate complexes: electronic structures and nonlinear optical properties

Abstract

The density functional theory (DFT) method and natural bond orbital (NBO) analysis have been employed to investigate the electronic structures and second-order nonlinear optical (NLO) properties for tricarbonyl metal derivatives of a Lindqvist-type polyoxometalate, [Nb₂W₄O₁₉M(CO)₃]^3−/2− (M = Mn^I, Tc^I, Re^I, Fe^II, Ru^II and Os^II). The position of the tricarbonyl metal ligand and the substitution of different metal atoms M have an influence on the electronic absorption spectra and NLO responses of all complexes. Among the three isomers of [Nb₂W₄O₁₉Mn(CO)₃]³⁻, the β₀ value of isomer 1^a is the largest, which is 1.4 times and 2.3 times larger than those of isomers 1^b and 1^c, respectively. The β₀ value also depends on the tricarbonyl metal M, the β₀ value decreases in the order M = Ru > Re > Fe > Os > Mn > Tc. In addition, the analysis of the main transition orbitals shows that the tricarbonyl metal ligand acts as an electron donor in [Nb₂W₄O₁₉M(CO)₃]^3−/2− (M = Mn^I, Tc^I, Re^I, Ru^II and Os^II), while the [Fe(CO)₃]²⁺ ligand acts as an electron acceptor in [Nb₂W₄O₁₉Fe(CO)₃]²⁻.