Synthesis, Structural Characterization, and Magnetic Properties of a New Charge-Transfer Salt Composed of Polyoxotungstate Acceptors [W^VW^VI ₅O₁₉]³⁻ and Cationic Ferrocenyl CpFe⁺Cp Donors

Abstract

The crystal structure of the charge-transfer slat (CpFe⁺Cp)₃[W^VW^VI ₅O₁₉] (CpFeCp=Fe(C₅H₅)₂), synthesized from the reaction of Na₂WO₄⋅2H₂O with ferrocene under acid conditions, has been determined by single-crystal X-ray diffraction. The crystal is of triclinic space group P(−1) with a=13.0374(3), b=15.0406(3), c=16.8239(1) Å, α=91.417(1), β=98.931(1), γ=115.294(1)°, V=2931.20(9) ų, Z=1, M _r =5895.57, F(000)=2652, μ=18.735 mm⁻¹, and D _c =3.340 g⋅cm⁻³. The final R factor is 0.0502 for 10173 (R _int=0.0563) unique reflections and 770 parameters. The structural analysis reveals that there are two crystallographically distinct [W^VW^VI ₅O₁₉]³⁻ polyoxoanions and six independent ferrocene cations per unit cell. Each polyoxoanion consists of six WO₆ octahedra with three types of W–O bond lengths. Interestingly, CpFe⁺Cp moieties are stacked to form octagonal channels that incorporate the polyanions. The closest Fe⋅⋅⋅Fe distances between the neighboring ferrocenyl cations are more than 6.49 Å, therefore, a good magnetic isolation between the iron centers is expected.