Strong metal atom motion anomaly in iron-organometallics

Temperature-dependent Fe-57 Mossbauer effect studies have been carried out over the range 90 less than or equal to T less than or equal to 350 K on a number of ring-substituted ferrocenes and reveal that in the presence of ce rtain molecular level architectural features, the recoil-free fraction (as monitored by the area under the resonance curve) declines very sharply some 200 K below the melting point of the neat solid. DSC measurements confirm the endothermic nature of this effect. Glassy solid and chemical modificati on experiments support the intra-molecular origin of these observations.