¹⁷O and ¹⁸³W NMR diamagnetic and paramagnetic shifts in heterodecatungstates XW₁₀Oⁿ⁻₃₆ (X = Ln, Th, U) in aqueous solutions

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• 作者：Fedotov ; Martin A. ; Samokhvalova ; Elena P. ; Kazansky ; Leonid P.
• 刊名：Polyhedron
• 出版年：1996
• 出版时间：June, 1996
• 年：1996
• 卷：15
• 期：1
• 页码：3341-3351
• 全文大小：720 K

文摘

Heterodecatungstates of the general formula XW₁₀Oⁿ⁻₃₆ where X = Ce, Pr, Nd, Gd, Tb, Dy, Ho, Er, Th and U) have been studied by ¹⁷O and ¹⁸³W NMR spectroscopy. It is shown that the structure of the heteropolyanions, where X occupies a centre of a square antiprism formed by two W₅O₁₈ ligands and which was determined in the crystalline state, is retained in aqueous solution. Completely resolved ¹⁷O and ¹⁸³W NMR spectra for all atoms, even for the nearest oxygen atoms, have been recorded. From the analysis of the isotropic shifts, the contact and dipolar contributions have been estimated for all constituting atoms. The possible σ- and ρ-mechanisms of the spin transfer are considered. The negative spin density determines the dominant contact shift for the oxygen and tungsten nearest to X. The large pseudo-contact (ligand centred) contributions are estimated for the nearest oxygen and tungsten atoms. The positive spin density due to the σ-mechanism and large dipolar contribution gives rise to the observed chemical shift for the internal oxygen atom. The other oxygen atoms experience a mostly dipolar contribution with other terms probably cancelling each other. Temperature dependences of the chemical shifts are discussed.