Theoretical Study On Electronic Structures And Chiroptical Properties Of Chiral Polyoxometalate Derivatives

Polyoxometalates(POMs) constitute an immense class of compounds which are formed by early transition metals(VV, MoVI, WVI) and connected by oxygen atoms. Development of POM chemistry can be dated back to 1826, when Berzerius obtained a yellow precipitate phosphoric acid, ammonium molybdate, which was the first synthesis of heteropoly acids, 12-ammonium phosphomolybdate. Nowadays, POM chemistry is an important field that many scientists are interested in. Because of the structural unit-{MO4} and {MO6} in POMs, the functions and diversified structure of polyoxometalates are different. At the same time, many new compounds are synthetized which possess the unique physical and chemical properties in many areas of natural science. It is the reason why many scientists are interested in POMs that POM chemistry shows the application prospect, huge and vast chiral materials such as: catalysis, nano materials, electronic transmission material and so on. With the progress of science and technology, POMs on experimental studies rapidly develop and obtain significant results. Constantly developing with quantum chemistry calculation methods, theoretical researches have also obtained the substantial progress. Density functional theory(DFT) method has gradually become an important quantum chemistry calculation method applied to the caculation of POM compounds and their derivatives. According to POM compounds and their derivatives, the electronic properties, optical properties, reduction properties and catalytic mechanism have been successfully investigated by DFT methods. Recently, many excellent properties of chiral polyoxometalates and chiral POM derivatives are constantly designed and synthesised based on the structure of POMs. While in the theoretical studies on chiral polyoxometalates are few. There are three reasons: firstly, POMs are much larger systems. Secondly, many transition metal atoms are contained in the POM systems. Thirdly, POMs contain high negative charge. Due to above three points, the theoretical researches on POM compounds and their derivatives are relatively difficult.This thesis is investigated by quantum chemistry calculation method related to the electronic properties of two classes of chiral POMs. The calculations on electric circle dichroism(ECD) spectra are applied to analyze the chiroptical properties of chrial POMs and chiral origins. The work mainly includes the following two aspects:1. The geometrical strucutres, electronic structures, UV-Visible absorption(UV-Vis) and electronic circular dichroism(ECD) spectra of chiral polyoxometalates(POMs) [SeIVMo6O21(L-alanine)3]2-, [SbIIIMo6O21(L-alanine)3]3-, [BiIIIMo6O21(L-alanine)3]3- modified by L-O2CCHCH3NH3(L-alanine) have been explored using the density functional theory(DFT) method. The effect of heteroatoms on optical activities of studied compounds has been determined. The result indicates that the geometrical structures, UV-Vis spectra absorption intensity and peak shape are affected by heteroatoms. The rotational absorption direction and strength of the ECD spectra significantly change from SeIV, SbIII to BiIII. The UV-Vis and ECD spectra in the low-energy range are mainly ascribed to charge-transfer(CT) transitions from the p orbitals of O atoms to the d orbitals of Mo atoms in the POMs, and the both spectra in the high-energy range are mainly from the heteroatoms in the POMs and the p orbitals of the O atoms connecting with heteroatoms to the d orbitals of Mo atoms. These conclusions are significant for understanding the electronic structures and chiral spectroscopy properties of this kind of amino acids modifying POMs.2. The UV–Vis/ECD spectra of asymmetric chiral Waugh heteropolymolybdate, L-[Mn Mo9O32]6-, was systematically investigated using time-dependent density functional theory(TDDFT) method. The electronic circular dichroism(ECD) spectra of the L/D-[Mn Mo9O32]6- were produced over the range of 2.6-3.8 e V. The origins of the ECD bands are mainly ascribed to charge-transfer(CT) transitions not only from oxygen atoms to Mn atom and Mo atoms, but also from Mn atom to Mo atoms unusually. It makes Mn atom be the center of electron transfer that the center position in the structure and charge transfer properties.