A New Heptanuclear Cobalt(II) Cluster Encapsulated in a Novel Heteropolyoxometalate Topology: Synthesis, Structure, and Magnetic Properties of [Co<sub>7</sub>(H<sub>2</sub>O)<sub>2</sub>(OH)<sub>2</sub>P<sub>2</sub>W<sub>25</sub>O<sub>94</sub>]<sup>16-</sup>
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The synthesis and the structural and magnetic characterization of a novel heptanuclear cobalt cluster encapsulated in a heteropolyoxotungstate is reported. This complex shows how it is possible to control the nuclearity of the Co clusters formed in a tungstate solution by slightly changing the synthetic conditions, and the relevance of pH in this regard. This heptanuclear complex [Co7(H2O)2(OH)2P2W25O94]16- (Co7) crystallizes in the triclinic space group P1̄ (a = 12.3403(6) Å, b = 22.5966(11) Å, c = 23.2645(12) Å, α = 68.7830(11)°, β = 83.7981(12)°, γ = 78.5423(13)°, V = 5922.4(5) Å3, Z = 2) and is formed by six CoO6 octahedra from two Co3 trimers sustained by Keggin trivacant fragments held together by the bridge [CoW7O26(OH)2], which contains one tetrahedral CoO4 unit. The magnetic properties of the complex are discussed on the basis of the coexistence of ferro- and antiferromagnetic interactions and fitted according to an anisotropic exchange model in the low-temperature regime.
