Apparently anomalous magnetism in low spin iron(II) complexes

Abstract

A systematic investigation of some iron(II) complexes which might be expected to lie near the high spin - low spin crossover, shows that the complexes are actually low spin, and previously reported anomalous magnetic moments are found to arise essentially from paramagnetic impurities. The temperature independent paramagnetism (χ *) expected for iron(II) in the low spin ( 1A 1) state is calculated and the utility of comparison with available results of electronic absorption and Mössbauer Effect spectroscopy measurements discussed. The approximations involved in calculations of χ * are discussed in detail, and the maximum value of χ * that could reasonably be expected is estimated at 3 × 10 −4 c.g.s.e.m.u. This estimate is supported by experimental magnetic susceptibility measurements which may be reasonably explained in terms of a value of χ * less than 3 × 10 −4 c.g.s.e.m.u., together with, in some cases, a contribution from a paramagnetic impurity with normal Curie-Weiss behaviour. Where applicable, the magnitude of the contribution from paramagnetic impurities is estimated.