Synthesis, Detailed Characterization, and Theoretical Understanding of Mononuclear Chromium(III)-Containing Polyoxotungstates [CrIII(HXVW7O28)2]<

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• 作者：Wenjing Liu ; Jonathan H. Christian ; Rami Al-Oweini ; Bassem S. Bassil ; Johan van Tol ; Mihail Atanasov ; Frank Neese ; Naresh S. Dalal ; Ulrich Kortz
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：September 2, 2014
• 年：2014
• 卷：53
• 期：17
• 页码：9274-9283
• 全文大小：487K
• ISSN：1520-510X

文摘

Two monochromium(III)-containing heteropolytungstates, [Cr^III(HP^VW₇O₂₈)₂]^13- (1a) and [Cr^III(HAs^VW₇O₂₈)₂]^13- (2a), were prepared via simple, one-pot reactions in aqueous, basic medium, by reaction of the composing elements, and then isolated as hydrated sodium salts, Na₁₃[Cr^III(HP^VW₇O₂₈)₂]路47H₂O (1) and Na₁₃[Cr^III(HAs^VW₇O₂₈)₂]路52H₂O (2). Polyanions 1a and 2a comprise an octahedrally coordinated Cr^III ion, sandwiched by two {PW₇} or {AsW₇} units. Both compounds 1 and 2 were fully characterized in the solid state by single-crystal XRD, IR spectroscopy, thermogravimetric and elemental analyses, magnetic susceptibility, and EPR measurements. Magnetic studies on 1 and 2 demonstrated that both compounds exhibit appreciable deviation from typical paramagnetic behavior, and have a ground state S = ³/₂, as expected for a Cr^III ion, but with an exceptionally large zero-field uniaxial anisotropy parameter (D). EPR measurements on powder and single-crystal samples of 1 and 2 using 9.5, 34.5, and 239.2 GHz frequencies and over 4鈥?95 K temperature fully support the magnetization results and show that D = +2.4 cm^鈥?, the largest and sign-assigned D-value so far reported for an octahedral Cr^III-containing, molecular compound. Ligand field analysis of results from CASSCF and NEVPT2-correlated electronic structure calculations on Cr(OH)₆^{3鈥?/sup> model complexes allowed to unravel the crucial role of the second coordination sphere of CrIII for the unusually large magnetic anisotropy reflected by the experimental value of D. The newly developed theoretical modeling, combined with the synthetic procedure for producing such unusual magnetic molecules in a well-defined and essentially magnetically isolated environment, appears to be a versatile new research area.}