Vapochromic Behavior of a Chair-Shaped Supramolecular Metallacycle with Ultra-Stability

A new discrete supra­molecular metalla­cycle functionalized with an alkynyl­platinum­(II) bzimpy moiety was successfully prepared via coordination-driven self-assembly, and it displayed a reversible color change in the solid state between yellow and red, triggered by CH2Cl2 vapor or mechanical grinding. Notably, unlike many known vapo­chromic systems, the obtained vapo­chromic metalla­cycle exhibits ultra-stability, with the red color remaining unchanged in air for several months at room temperature or even under vacuum for >1 week. Further investigation revealed that the chair conformation of the metalla­cyclic scaffold, which was thought to prevent inter­molecular steric repulsion between the alkyl chain and triethyl­phosphine, favored close molecular stacking through inter­molecular Pt···Pt and π–π stacking interactions, thus allowing such vapo­chromic behavior with ultra-stability.