Structural and Spectroscopic Properties of Antiferromagnetically Coupled FeIIIMnII and FeIIMnII Complexes

Theodore R. Holman, Zhigang Wang, Michael P. Hendrich, Lawrence Que

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The heterobimetallic complexes [FeIIIMnIIBPMP(O2CCH2CH3)2](BPh4)2 (1), [FeIIIMnIIBPMP(O2CCH3)2](BPh4)2 (1′), and [FeIIIMnIIBPMP(O2CCH2CH3)2](BPh4) (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 = JS1·S2). The solid state structure of the FeIIMnII 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) Å, b = 15.037(13) Å, c = 16.62(2) Å, α = 82.070(5)°, α = 81.180(5)°, γ = 67.940(5)°, and Z = 2. Its structure contains a (μ-phenoxo)bis(μ-carboxylato)dimetal cluster with an iron-manganese distance of 3.360(4) Å. Complex 2 is remarkably rich in spectroscopic characteristics. The high-spin Fe(II) (S = 2) and high-spin Mn(II) (S = 5/2ions are antiferromagnetically coupled affording an S = 1/2 ground state and an unusual EPR signal at 2.5 K. This resonance is broad with gav < 2 and exhibits hyperfine features due to the nuclear spin of the Mn(II) ion (I = 5/2). At temperatures above 10 K, a second resonance signal appears at g = 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 |DFe| = 5 cm−1, which approximately agree with the multifield, variable temperature magnetic susceptibility data on the polycrystalline material.

Original languageEnglish (US)
Pages (from-to)134-139
Number of pages6
JournalInorganic chemistry
Issue number1
StatePublished - Jan 1 1995


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