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.