Magnetic properties of iron(II) near the 5T2–1A1 crossover

Abstract

A series of iron(II) complexes which lie near the high spin–low spin crossover (FeL₂X₂,nH₂O, where X is NCS or NCSe and L is a ring-substituted analogue of 1,10-phenanthroline or 2,2′-bipyridyl) have been prepared and their magnetic and spectroscopic properties investigated. Small modifications in the molecules are found to produce starting effects on the properties, and the various members of the series illustrate many kinds of ‘crossover’ behaviour. Some of the complexes have nearly equienergetic high spin and low spin states, both of which are thermally populated while some exhibit complete transitions between the two spin states within very narrow temperature ranges; the behaviour of some of the complexes falls in between these two extremes, while others have temperature independent moments, intermediate between high and low spin values, attributable to a triplet ground state.