Synthesis, magnetochemistry, and spectroscopy of heterometallic trinuclear basic trifluoroacetates [Fe2M(μ3-O)(CF3COO)6(H2O)3]·H2O (M = Mn, Co, Ni)

Three new mu(3)-oxo(trifluoroacetato) complexes [(Fe2MII)-M- III(mu(3)-O)(CF3COO)(6)(H2O)(3)].H2O [M = Mn (1), Co (2), Ni (3)] have been prepared. Compounds 1 and 2 crystallize in the monoclinic space groups C2/c [a = 22.002(5), b = 13.647(3), c = 24.767(4) Angstrom, beta = 98.23(3)degrees] and C2/m [a = 21.426(4), b = 15.100(2), c = 14.815(3) Angstrom, beta = 117.99(2)degrees], respectively. The coordination spheres of the metal ions are essentially octahedral, with the Fe-O distances [1.870(5) Angstrom] falling in the usual range for these systems. Magnetochemical studies reveal the presence of antiferromagnetic exchange in the isosceles triangular skeletons of the polynuclear species. Application of the isotropic spin Hamiltonian H = -2J(FeM)[SFe1SM + SMSFe2] - 2J(FeFe)[SFe1SFe2] gives the fitting parameters: g(Fe) = g(Mn) = 2.00, J(Fe-Fe) = -56.50(7) and J(Fe-Mn) = -16.23(4) cm(-1) (1), g(mol) = 2.09(1), J(Fe-Fe) = -42.8(3.5) cm(-1), J(Fe-Co) = -17.8(1.4) cm(-1) (2) and g(Fe) = 2.00, g(Ni) = 2.215(2), J(Fe- Fe) = -45.60(1) and J(Fe-Ni) = -16.96(2) cm(-1) (3). A Mossbauer investigation confirms that no electron transfer from Mn-II or Co-II to Fe-III occurs during the syntheses of these complexes. (C) Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002