The Theoretical Study Of The Electronic Structures And Nonlinear Optical Properties Of Transition Metal Substituted Keggin-type Polyoxometalates And Its Analogous Species

Polyoxometalates(POMs) have the potential application in analytical and catalytic chemistry, and materials science because of their molecular structural diversity and unmatched physical and chemical properties. It is important for understanding of these kinds of compounds by using the electronic structures according to quantum chemical computations. However, the large sized POMs system with high negative charge and multiple metal atoms are very computationally demanding. Thanks much to the development of the density functional theory(DFT) and computer technology, there is a large improvement on the computational precision and speed for the POMs recently.In the present thesis, DFT has been employed to studies of the electronic structure, bonding feature, and nonlinear optical(NLO) properties of a series of transition-metal-substituted POMs, the aim of this thesis is that, (1) rationalization of the reactivity of high-valent metal nitrido derivatives of Keggin-type polyoxometalates ([PW11O39{MVIN}]4- (M=Ru, Os, Re)) in nitrogen transfer reaction. Simultaneously, a comparative analysis of nitrido ruthenium (VI) porphyrin and high valent ruthenium nitrido derivatives of Keggin typical polyoxometalate ([PW11O39{RuVIN}]4-) has been discussed. (2) Finding of the similarities and differences of the electronic structure, bonding feature and redox properties for the ruthenium derivatives of Keggin typical POM, [{PW11O39}RuIII(H2O)]4-, and its intermediates in different oxidation states. (3) Demonstration of donor-Ï€conjugated bridge-acceptor (D-Ï€-A) model of transition metal trisubstituted POMs, optimization of the second-order NLO properties of these POMs compounds.Part one of this thesis is the review of the basic properties of POMs and the recent developments of POMs chemistry, and the synopsis of DFT and time-depdent(TD)DFT. Part two of is the main body of this thesis, it contains four aspects:1. The ground states, excited states, and reduction states of Keggin-type POMs, [PW11O39{MN}]4- (M=Ru, Os, Re) have been investigated by using DFT and natural bond orbital(NBO) analysis methods. The results show that the ruthenium nitrido derivative has low-lying Ru-N antibonding orbitals with high RuN composition, this lead to the large increases of Ru-N bond in the excited and redox states of this POM complex. The substitution effects of central tetrahedron heteroatoms (XO4, X=Al, Si, P, As) of ruthenium derivative affect relative energy of the lowest unoccupied molecular orbital(LUMO), the relevant orbital energies increase in the order Al(III)