Unusual Magnetic Behaviour of Polyferro(phenyl)siloxanes

Polyferro(phenyl)siloxanes are paramagnetic when the iron content is low, e.g. at a ratio Fe:Si<2.0, but when Fe:Si>2.0 the effective magnetic moment of the Fe^III atom increases with increase of the Fe:Si ratio and it also increases as the temperature decreases; this unusual magnetic behaviour may be explained in terms of spin frustration in polynuclear oxo-ferric polymer clusters.