Preparation, Crystal Structures, and Magnetic and ESR Properties of Molecular Assemblies of Ferrocenium Derivatives and Paramagnetic Polyoxometalates

The synthesis, X-ray crystal structures, and ESR and magnetic properties of the anhydrous salt Na 3 [Cr(OH) 6 Mo 6 O 18 ]·6(CH 3 ) 2 SO ( CrDMSO ) containing the Anderson−Evans polyanion, of two new molecular compounds based on this polyanion ([Fe(C 5 Me 5 ) 2 ] 3 [Cr(OH) 6 Mo 6 O 18 ]·20H 2 O [ FeCr(1) ], Na[Fe(C 5 H 5 ) 2 ] 2 [Cr(OH) 6 Mo 6 O 18 ]·3H 2 O [ FeCr(2) ]), and of another based on a Keggin polyanion, [Fe(C 5 Me 5 ) 2 ] 4 [HPCu(H 2 O)W 11 O 39 ]·6CH 3 CN ( FeCu ), are reported. CrDMSO: monoclinic, C 2/ c, a = 25.37(2) Å, b = 14.632(2) Å, c = 15.455(6) Å, β = 123.17(4)°, Z = 4. FeCr(1): triclinic, P 1̄, a = 12.489(3) Å, b = 14.113(3) Å, c = 15.662(4) Å, α = 101.55(2)°, β = 105.82(2)°, γ = 110.23(2)°, Z = 1. FeCr(2): monoclinic, P 2 1 / n, a = 10.015(2) Å, b = 7.722(6) Å, c = 25.137(5) Å, β = 90.626(9)°, Z = 2. FeCu: monoclinic, P 2 1 / n, a = 15.596(7) Å, b = 15.138(3) Å, c = 25.921(12) Å, β = 97.53(2)°, Z = 2. In the compound FeCr(1) the Fe(C 5 Me 5 ) 2 units are perpendicular to each other and form a centrosymmetrical group of three cations, which alternates with the planar [Cr(OH) 6 Mo 6 O 18 ] 3 - anion to form perpendicular mixed chains along the [211̄] and [2̄11̄] directions. In the compound FeCu, the decamethylferrocenium units form a polyhedral structure which encapsulates the Keggin polyanion. The magnetic properties indicate that the salts containing metallocenium radicals present weak antiferromagnetic interactions obeying the Curie−Weiss expression χ = C /( T − ϑ) with small negative values for ϑ ( FeCr(1), ϑ = −0.5, −0.4; FeCr(2), ϑ = −0.6; FeCu, ϑ = −0.8). The ESR spectra for compounds containing chromium atoms may reveal a zero field splitting of the central chromium atom of the Anderson−Evans polyanions, which is directly related to the local symmetry of the chromium in its octahedral site.