The results of atomic dynamics of ultrafines clusters of iron hydroxide and Fe2O3 with average size 1–3nm are shown. The clusters were synthesised after chemical reaction in solution in micropores of sorbents and in topochemical reactions of thermal decomposition salts. Moessbauer spectroscopy studies are applicated. The effect of Surface Active Substance(SAS) on dynamics of clusters is observed. Thermodynamics and phemonologic models of dynamic state of cluster are considered and the probability of the coexistans solid-liquid state of cluster is discussed.