Reversible Crystal Transformations and Luminescence Vapochromism by Fast Guest Exchange in Cu(I) Coordination Polymers

Abstract

Six Cu(I) coordination polymers (CPs)-[Cu₂I₂L₂]_n (1), {[Cu₂I₂L₂]·2MeCN}_n (2), [Cu₄I₄L₂]_n (3), {[Cu₄I₄L₂]·CH₂Cl₂}_n (4), {[Cu₄I₄L₂]·CHCl₃}_n (5), and {[Cu₄I₄L₂]·C₆H₆}_n (6)-were synthesized by self-assembly reactions of CuI and the flexible mixed N/S donor ligand 4-(2-(cyclohexylthio)ethoxy)pyridine (L). Single-crystal X-ray diffraction analyses reveal that these 1D CPs form sets of supramolecular isomers; 1 and 2 are based on Cu₂I₂ rhomboids, while 3-6 are based on cubane Cu₄I₄ clusters. Crystal-to-crystal transformations of CPs 1-6 were reversible under heat or in an appropriate solvent (acetonitrile, dichloromethane, chloroform, or benzene). In addition, crystal transformations between CPs 1 and 3 occurred through addition of L or CuI. Moreover, CPs 3-6 exhibited reversible guest exchange and crystal transformations on exposure to the vapor of volatile organic compounds and heat. Remarkably, a guest molecule was exchanged by other guest molecules in the vapor phase within very short times and without the use of acetonitrile as a solvent, which normally plays a key role in trapped solvent exchange experiments.