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
Na3[Cr(OH)6Mo6O18]·6(CH3)2SO
(CrDMSO) containing the Anderson−Evans polyanion, of two
new molecular compounds
based on this polyanion
([Fe(C5Me5)2]3[Cr(OH)6Mo6O18]·20H2O
[FeCr(1)],
Na[Fe(C5H5)2]2[Cr(OH)6Mo6O18]·3H2O [FeCr(2)]), and of another based on a
Keggin polyanion,
[Fe(C5Me5)2]4[HPCu(H2O)W11O39]·6CH3CN
(FeCu), are reported. CrDMSO:  monoclinic,
C2/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, P1̄, 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,
P21/n, a =
10.015(2) Å, b = 7.722(6) Å, c
=
25.137(5) Å, β = 90.626(9)°, Z = 2.
FeCu:  monoclinic,
P21/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(C5Me5)2 units are
perpendicular to each other
and form a centrosymmetrical group of three cations, which alternates
with the planar
[Cr(OH)6Mo6O18]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.