The Density Functional Study On Properties Of Linquist-, Stranberg- And Keggin-Polyoxometalate Derivatives

Polyoxometalates (POMs) constitute an immense class of compounds that are formed by early transition metals. POMs have potential applications in many fields including medicine, catalysis, multifunctional materials, and chemical analysis as they have determined structures, multiple components and remarkable chemical and physical properties. The electronic, redox and bonding properties, isomer stabilities, as well as optical properties those originate from the POMs , which have charge transfer have been receiving increasing attention.In the present work, three types POMs properties have been investigated by quantum chemistry calculations. The investigation includes the electronic, bonding, stability and nonlinear optical (NLO) properties of Linquist-type organoimido derivatives, the electronic properties of Stranberg-type polyoxometalates and their derivatives, as well as the influence of heteratom on the POMs, and the electronic and redox properties of high-valent metal nitrido fictionalized Keggin-type polyoxometalate. Our work has been focus on the following four aspects:1. The electronic properties, bonding character and stability of 2,6-dimethylaniline molybdate derivatives [Mo₆O₁₈R]^2- and [MO₆O₁₇R₂]^2- were investigated by density functional theory (DFT). The strong interaction of organoimido delocalized Ï€ electron with the d electrons of molybdate polyanion brings excellent synergistic effect. The Mo=N triple bond could be formed through the N→Mo c-donation and N←Mo Ï€-back-donation in the formation of the organoimido derivative. The total energy and bonding analysis showed that the favorable orthogonal [MO₆O₁₇R₂]^2- is formed. Comparing with the [MO₆O₁₉]^2-, organoimido modified the occupied orbitals of organoimido molybdate derivatives. The highest occupied molecular orbital (HOMO) of organoimido molybdate derivative concentrates on the arylimido and imido-bearing Mo atom. The centre oxygen atom O_c is closer to the imido-bearing Mo atom in the organoimido derivatives and is responsible for stabilizing the cluster.2. The orbital analysis of hexamolybdate organoimido derivatives present that the large charge transfer will come into being under the external electronic field. The mono- and di-substituted hexamolybdate organoimido derivatives, the dimer of mono-substituted hexamolybdate organoimido derivative and the derivative that is extended by increasing benzene via C=C extended were investigated in order to understand the charge transfer character and NLO origin. As for mono- and di-substituted hexamolybdate organoimido derivatives, charge transfer origins from organoimido to polyanion, however the charge transfer becomes more complex when the organoimido was lengthened or anotherorganoimido polyanion was introduced. The organoimido to polyanion charge transfer may be responsible to the NLO properties of this kind of compounds. The lengthening of organoimido Ji-conjugation or increasing organoimido polyanion is helpful to enhance the P value. Hartree-Fock method underestimated the hyperpolarizabilities of the systems and DFT methods used in this paper made significant improvements. The present investigation gives insight into the NLO properties of organoimido ployanion and makes trying to reveal the origin of the NLO properties of this family of cluster compounds, which are interesting and important in design and synthesis of new promising NLO material.3. DFT calculations were carried out on Strandberg anions [X2MO5O23]11" (X = Pv, SVI, Asv, SeVI) and [(RP)2Mo5O2i]4' ( R = H, CH3, C2H5). The heteroatoms X and the organic groups that are bonded to a phosphorus heteroatom have significant influence on the geometrical structures of Strandberg anions. The molecular orbital analysis indicate that the LUMOs in this kind of anions concentrate on the d orbitals of the metal atoms and/? orbitals of the terminal oxygen atoms. The Mo-0 bond has the Mo^Opantibonding character. The present calculations suggest that the energy gap between the HOMO and LUMO in the anions depends on the nature of the heteroatom X and therefore the redox properties of Strandberg anions depend on the heteroatom X. At the same time, the organic groups alter the redox properties of Strandberg anions. The Strandberg anion in which the heteroatom is bonded to the organic group is difficult to reduce.4. The high-valent metal nitrido functionalized Keggin-type tungstate [PWnO39(ReN)]n (n=3, 4, 5) and [PWiiO39(OsN)]2 were calculated by DFT. The results suggested that the strong Re=N and Os^N triple bond were formed between Re or Os and N atom. The strong interaction is helpful to consitute three demension net structure. The Re and Os nitrido modified the frontier molecular orbital of tungstate, Re and Os mainly changed the LUMOs of [PWnO39(ReN)]3 and [PWnO39(OsN)]2^. [PWnO39(ReN)]3ⁱs more powerful oxidizing agent than the corresponding tungstate. The [PWnO39(ReN)]3 will be preferentially reduced in the Re center when the one and two electrons are introduced into the polyanion.