A DFT Study On The Electronic Properties And Stability Of Organoimido-polyanion Hybrid Material

Among various polyoxometalates (POMs) compounds, the hybrid organoimido-POMs derivatives have become a new focus of investigation. And a great number of lindqvist structural arylimido-POMs have been synthesized in experiment successively by Peng and Maatta, et al.. In recent years, lots of works have confirmed that density functional theory (DFT) methodology is the optimal choice for the complicated transition metal systems besides POMs. In this thesis, the electronic properties and stabilities of organoimido-polyanion hybrid materials[α-PMo₁₂O₃₉NC₆H₅]^3- and [W₅MoO₁₈NC₈H₉]^n- (M=Mo, n=2; M=V, Nb, n=3) isomers are investigated using DFT method. The important summarizations and conclustions are as following, (1) Triple-ξ plus polarization Slater basis sets were carried out in the calculation of Keggin structural [α-PMo₁₂O₃₉NC₆H₅]^3-. Geometry optimization by Cs symmetry shows the central tetrahedron PO4 slightly deforms and shifts to molybdenum linking to phenylimido group. The natural bond orbital (NBO) analysis confirms that there exists a Mo≡N triple bond. Mulliken population analysis shows Mo1 atom transfers 38.3% of its valence electrons to the neighbouring N and O atoms, which reveals the significant covalent character of Mo-N interaction. In addition, the highest occupied molecular orbital (HOMO) represents significant delocalized character. The Ï€-bonding interaction between organic delocalized Ï€-electrons and inorganic polyanion cluster d electrons brings exciting synergistic effect, which makes the hybrid phenylimido-phosphomolybdate [α-PMo₁₂O₃₉NC₆H₅]^3- stable. (2) Triple-ξ plus polarization Slater basis sets were also carried out in the calculations of Lindqvist structural [W₅MoO₁₈NC₈H₉]^n- (M=Mo, n=2; M=V, Nb,n=3) isomers. The optimized geometries confirm that for [W₅MoO₁₈NC₈H₉]^3- and [W5NbO18NC8H9]3- the W-N bonds are weaker than for [W5MoO18NC8H9]2-. The HOMO-LUMO energy gap reveals that for four [W₅MoO₁₈NC₈H₉]^2- isomers the redox ability of system 1f is weaker than 1g, 1h and 1i; for four [W₅MoO₁₈NC₈H₉]^2- isomers, 2f and 2g are superior to 2h and 2i; for [W₅MoO₁₈NC₈H₉]^2-isomers, 3f is superior to anyone of the other three 3g, 3h, 3i. The investigations on electronic properties reveal that the highest occupied molecular orbital (HOMO) of each system represents significant delocalized character. In addition, bonding energy analysis favors that the stability comparision should be 1f > 1i > 1h > 1g; 2g > 2h > 2f > 2i; 3f > 3g > 3h > 3i.