Effects of Heteroatoms on Electronic States of Divanadium-Substituted 纬-Keggin-type Polyoxometalates

详细信息    查看全文

• 作者：Kazuhiro Uehara ; Takuya Miyachi ; Takahito Nakajima ; Noritaka Mizuno
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：April 7, 2014
• 年：2014
• 卷：53
• 期：7
• 页码：3907-3918
• 全文大小：667K
• 年卷期：v.53,no.7(April 7, 2014)
• ISSN：1520-510X

文摘

Effects of heteroatoms on electronic states of divanadium-substituted 纬-Keggin-type polyoxometalates (TBA)₄[纬-XV₂W₁₀O₃₈(渭-OH)(渭-OR)] (X = Ge, Si; R = Me, Et, n-Pr, H; TBA = tetra(n-butyl)ammonium) and (TBA)₄[纬-XV₂W₁₀O₃₈(渭-O)] (X = Ge, Si) were investigated, using a combination of nuclear magnetic resonance spectroscopy and density functional theory (DFT) calculations. Both the substitution of SiO₄ heteroatom units with larger GeO₄ ones and the introduction of more electronegative alkoxo groups in place of hydroxo groups resulted in deshielding of the vanadium nuclei. DFT calculations using the Def2-SVP basis set at TPSSh level of theory could well-reproduce the anionic moieties of a series of divanadium-substituted 纬-Keggin-type polyoxometalates, and the estimated chemical shifts approximately reproduced the experimental ones with the individual gauge localized orbital method (SO-IGLO) taking the spin鈥搊rbit interaction into account. The magnetic shielding (蟽) consists of 蟽_d + 蟽_p + 蟽_SD + 蟽_FC, where 蟽_d, 蟽_p, 蟽_SD, and 蟽_FC are diamagnetic, paramagnetic, spin-dipolar, and Fermi contact terms, respectively. The 蟽_p changed much among (TBA)₄[纬-XV₂W₁₀O₃₈(渭-OH)₂], (TBA)₄[纬-XV₂W₁₀O₃₈(渭-OH)(渭-OR)], and (TBA)₄[纬-XV₂W₁₀O₃₈(渭-O)], while 蟽_d, 蟽_SD, and 蟽_FC did not change much. Therefore, the 蟽_p largely contributed to the magnetic shielding. Moreover, 蟽_p consisted of the occupied鈭抩ccupied transitions (s-terms) and the occupied鈭抳irtual ones (u-terms), and the u-terms were predominant for 蟽_p. The most contributing occupied localized orbital consisted of the d_z² orbital of vanadium, the p_z orbital of terminal oxygen related to the V鈺怬 bond, and the p_z orbital of oxygen of the XO₄ unit, whereas the two virtual localized orbitals consisted of the d_yz orbital of vanadium and the p_y orbital of terminal oxygen. Analysis of the structural and electronic characteristics of a series of divanadium-substituted 纬-Keggin-type POMs revealed a linear correlation between both ⁵¹V{H} chemical shifts and the reciprocal values of the energy gaps between the corresponding XO₄-predominant orbital HOMOs-X and the LUMOs+X (X = 0, 1, or 2). All these results indicate that neighboring XO₄ units weakly interact with the addenda atoms and control the electronic states of polyoxometalates and the magnetic shielding of their addenda atoms.