Theoretical Study Of Electronic Properties Of Polyoxovanadates And NLO Properties Of Hexamolybdate

Polyoxometalates (POMs) are a rich and diverse family of metal–oxygen clusters made up of early transitional metals with unique photonic, electronic, and magnetic properties and chemical reactivity that has promised dramatic applications in quite diverse disciplines, including catalysis, medicine, and materials sciences. Following the development of the computer technology, quantum chemistry calculation as a theoretical study method has been introduced to the field of POMs. In early time, the ab initio Hartree–Fock (HF) approximation provided a reasonable starting point for understanding the structural and electronic properties of POMs. However, it is necessary to analyze systematically molecular and electronic structures, redox, catalysis and optics of POMs, consequently these could direct synthesis and material preparation. In the last ten years, a few groups have been especially active and have made important progress in describing and rationalising the electronic and magnetic properties of POMs. But a combination of three factors—the large size of polyoxoanions, the presence of transition metal ions and the high negative charge—produce, in practice, important computational limitations. The ab initio and density-functional theory (DFT) modeling of polyoxoanions is still incipient.In this thesis, quantum chemistry calculations have been carried out to investigate electronic properties, stability, redox, and the second-order nonlinear optical (NLO) properties of a series of Keggin-type POM derivatives. The present work has been focus on the following two aspects:1. The electronic properties of the class of 1:13 polyoxovanadates [MV₁₃O_x]^n-,(M=Mn,Ni)(n=7,9) have been investigated, using density functional theory (DFT). The results show that for the [MV₁₃O₃₈]^7-, LUMO is mainly concentrated on the Ni in solvent, in other words Ni preferential obtain an additional electron. While for other system LUMO is mainly concentrated on the V, in gas and in solvent, so V preferential obtain an additional electron..2. DFT calculations have been carried out to investigate the nonlinear optical (NLO) response for D–π–A model of PNA-hexamolybdate derivatives and PNA–metal–carbonyl complexes. The bond length alternation (BLA) values decrease with lengthening ofπ–conjugated bridge, especially for PNA-hexamolybdate derivatives, which dramatically enhances the NLO response. In addition, the introduction of Mo≡N in PNA-hexamolybdate derivatives is expected to provide a better electron transition channel, consequently generating lower BLA values and outstanding NLO response than PNA–metal–carbonyl complexes. It is shown that the hexamolybdate acts as electron donor when incorporating metal carbonyl complexes into one molecule. All these behaviors reflect the superiority of hexamolybdate as donor moiety in D–π–A model to design potential NLO materials.