Reversible Luminescence Vapochromism and Crystal-to-Amorphous-to-Crystal Transformations of Pseudopolymorphic Cu(I) Coordination Polymers

Four solvent-responsive one-dimensional copper­(I) coordination polymers (CPs), namely, {[Cu4I4L(MeCN)2]­·CH2Cl2}n (1), {[Cu4I4L(MeCN)2]­·CHCl3}n (2), {[Cu4I4L(MeCN)2]­·0.5p-xylene}n (3), and [Cu4I4L­(MeCN)2]n (4), were prepared by reaction of CuI with N,N′-bis­[2-(cyclohexylthio)­ethyl]­pyromellitic diimide (L) via self-assembly under varying solvent conditions. CPs 1–4, which are pseudopolymorphic supramolecular isomers derived from solvent molecules, are composed of Cu4I4 cubane clusters. The ligands in CPs 1–3 adopted a syn-conformation, whereas in CP 4 they were observed in the anti-conformation. This occurred via syn to anti transitions upon heating, followed by exposure to MeCN vapor. In addition, a reversible anti to syn transition was achieved by agitating in mixed organic solvents. It was shown that ligand transition from the syn- to the anti-conformation occurred through crystal-to-amorphous-to-crystal transformations. Furthermore, CPs 1–3 exhibited reversible solvent exchange and crystal transformation by exposure to vapors from volatile organic compounds.