Dynamic Disorder and Fluxionality in M3(CO)12Clusters: Variable-Temperature X-ray Diffraction Studies on FenRu3-n(CO)12(n= 1, 2) and the Low-Temperature Phase of Fe3(CO)12

Abstract

The metal atom disorder in the crystalline clusters Fe2Ru(CO)12 (1) and FeRu2(CO)12 (2) has been shown to be dynamic in origin. At and below 313 K, 1 crystallizes in the noncentrosymmetric space group Pn with two independent molecules in the asymmetric unit, both molecules having approximate C2v symmetry with small C2 distortions. Above 313 K, crystals of 1 undergo a phase transition to the centrosymmetric space group P21/n, becoming isomorphous and isostructural with the room-temperature phase of Fe3(CO)12 (3). These reversible changes are accompanied by an increase in the metal atom disorder, from a completely ordered structure at 223 K to a statistically disordered (1:1) “Star of David” structure at 323 K. Crystals of 2 show similar behavior, belonging to the noncentrosymmetric space group C2cb below 228 K and undergoing a phase transition to the centrosymmetric space group Ccmb above this temperature. An increase in the extent of disorder is observed in 2, from an ordered structure at 173 K to the ext...