STRUCTURAL AND SPECTROSCOPIC PROPERTIES OF ANTIFERROMAGNETICALLY COUPLED FE(III)MN(II) AND FE(II)MN(II) COMPLEXES

The heterobimetallic complexes Fe(III)Mn(II)BPMP(O2CCH2CH3)(2)](BPh(4))(2) (1), [Fe(III)MN(II)BPMP(O2CCH3)(2)](BPh(4))(2) (1'), and [Fe(II)Mn(II)BPMP(O2CCH2CH3)(2)](BPh(4)) (2), in which BPMP is the anion of 2,6-bis[(bis(2-pyridylmethyl)amino)methyl]-4-methylphenol, were synthesized and characterized by proton NMR, EPR, and magnetization measurements. The high-spin Fe(III) (S = 5/2) and high-spin Mn(II) centers (S = 5/2) in 1 and 1' are antiferromagnetically coupled, resulting in an S = 0 ground state in these complexes. Variable temperature magnetic susceptibility measurements show that J = 23 cm(-1) for 1' (H = JS(1).S-2). The solid state structure of the (FeMnII)-Mn-II complex (2) was determined by X-ray crystallography. Complex 2 crystallizes in the triclinic space group P1 with the following unit cell parameters: a 12.613(6) Angstrom, b = 15.037(13) Angstrom, c = 16.62(2) Angstrom, alpha = 82.070(5)degrees, beta = 81.180(5)degrees, gamma = 67.940(5)degrees, and Z = 2. Its structure contains a (mu-phenoxo)bis(mu-carboxylato)dimetal cluster 2) and high-spin Mn(II) (S = 5/2) ions are antiferromagnetically coupled affording an S = 1/2 ground state and an unusual EPR signal at 2.5 K. This resonance is broad with g(av) < 2 and exhibits EPR hyperfine features due to the nuclear spin of the Mn(II) ion (I = 5/2). At temperatures above 10 K, a second 5.8 which is ascribed to a doublet within the first excited S = 3/2 manifold. Variable temperature studies of both the ground and excited state EPR signals have yielded values of J = 8 cm(-1) and \D-Fe\ = 5 Cm-1, which approximately agree with the multifield, variable temperature magnetic susceptibility data on the polycrystalline material.