Synthesis, Detailed Characterization, and Theoretical Understanding of 
Mononuclear Chromium(III)-Containing Polyoxotungstates [CrIII(HXVW7O28)2]13– (X 
= P, As) with Exceptionally Large Magnetic Anisotropy

Liu, Wenjing; Christian, Jonathan H.; Al-Oweini, Rami; Bassil, Bassem S.; van Tol, Johan; Atanasov, Mihail; Neese, Frank; Dalal, Naresh S.; Kortz, Ulrich

doi:10.1021/ic501385r

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Synthesis, Detailed Characterization, and Theoretical Understanding of Mononuclear Chromium(III)-Containing Polyoxotungstates [Cr^III(HX^VW₇O₂₈)₂]^13– (X = P, As) with Exceptionally Large Magnetic Anisotropy

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Atanasov, Mihail
Research Department Neese, Max Planck Institute for Chemical Energy Conversion, Max Planck Society;
Institute for General and Inorganic Chemistry, Bulgarian Academy of Sciences;

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Neese, Frank
Research Department Neese, Max Planck Institute for Chemical Energy Conversion, Max Planck Society;

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Citation

Liu, W., Christian, J. H., Al-Oweini, R., Bassil, B. S., van Tol, J., Atanasov, M., et al. (2014). Synthesis, Detailed Characterization, and Theoretical Understanding of Mononuclear Chromium(III)-Containing Polyoxotungstates [Cr^III(HX^VW₇O₂₈)₂]^13– (X = P, As) with Exceptionally Large Magnetic Anisotropy. Inorganic Chemistry, 53(17), 9274-9283. doi:10.1021/ic501385r.

Cite as: https://hdl.handle.net/21.11116/0000-0007-A3A9-2

Abstract

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]·47H₂O (1) and Na₁₃[Cr^III(HAs^VW₇O₂₈)₂]·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 4–295 K temperature fully support the magnetization results and show that D = +2.4 cm^–1, 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– model complexes allowed to unravel the crucial role of the second coordination sphere of Cr^III 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.