Synthese,Struktur und Phasenumwandlung von Se4(MoOCl4)2

Synthesis, Crystal Structure, and Phase Transition of Se₄(MoOCl₄)₂ Dark green, very air sensitive crystals of Se₄(MoOCl₄)₂ are formed from selenium and MoOCl₄ at 190°C in a sealed, evacuated glass ampoule in quantitative yield. The structure is built of nearly square planar Se₄²⁺ ions and centrosymmetric dimeric MoOCl₄^? ions which are linked by bridging Cl atoms. At ?21°C Se₄(MoOCl₄)₂ undergoes a reversible solid state phase transition of first order. Structure determinations at ?70°C and 23°C show that during the phase transition the structures of the ions remain unchanged, while the orientations of the ions with respect to each other change in such a way that in the low temperature form the Se₄²⁺ ions obtain a higher coordination number by Cl and O atoms of neighboring MoOCl₄^? ions.