Magnetic superexchange involving tetrahedral anions: One-dimensional antiferromagnetic interactions via sulfate anions in M(2,9-di-CH3-1,10-phenanthroline)SO4 (M = Mn,Fe, Co,Ni, Cu)

The magnetic susceptibilities of powder samples of the polymeric compounds M(dmp)SO₄ (M = Mn, Fe, Co, Ni, Cu; dmp = 2,9-di-CH₃-1,10-phenanthroline) have now been studied at temperatures between 1.5 and 305 K. There is clear evidence of one-dimensional, antiferromagnetic interactions in the Mn, Fe, Co, and Ni compounds: from $\text{T ? 300}\text{to}\text{1.7}\text{K}$, the magnetic moment decreases steadily from a value that is approximately the spin-only moment of the high-spin configuration to a value that is ～20% of the spin-only moment, and the susceptibility-vs-temperature curve contains a broad maximum atT ≤ 30 K. Cu(dmp)SO₄, however, exhibits almost perfect Curie-Weiss paramagnetism. These results when combined with the results of various spectroscopic studies lead to proposed molecular structures (chainlike polymers of cis-MN₂O₄ chromophores and bridging-chelating sulfates) and estimated energies of intrachain antiferromagnetic exchange ($\text{?0.5}\text{K}\text{≥}\text{J}\text{k}{}_{\mathrm{<mtext>B</mtext>}}\text{≥ ?10}\text{K}$).