Crystalline-State Photochromism of a Newly Synthesized Rhodium Dithionite Complex with Inflexible Cyclo-Pentyl Groups

A rhodium dinuclear complex having inflexible cyclo-pentyltetramethylcyclopentadienyl (CpCyPen = η5-C5Me4cyclo-C5H9) and photoresponsive dithionite (μ-O2SSO2) ligands, [(CpCyPenRh)2(μ-CH2)2(μ-O2SSO2)] (1CyPen), was newly synthesized. Crystalline-state photochromism between 1CyPen and the corresponding μ-O2SOSO complex (2CyPen) was successfully investigated by performing time-dependent X-ray diffraction experiments. Without any degradation of the crystal, type-T inverse photochromic reaction based on the μ-O2SSO2 ligand proceeded within the rigid reaction cavity formed by the inflexible CpCyPen ligands.