Desolvation Induced Conformational Transition in a Cryptophane Host: Crystal To Crystal Transformation

Cryptophanes show different conformations in solution and solid state depending upon various factors, such as the length of connecting linkers, medium, and nature of the incoming guest molecule(s). A cyclotriguaiacylenes (CTG) based cryptophane molecule was synthesized using click chemistry containing three triazole linkers and studied as well. This molecule shows two conformations, out-out crown-crown (CC), and out-in CC, in the presence or absence of guest molecule(s), as studied both in solution and solid state. The out-in CC, in which both CTG fragments are in crown conformation with one crown sitting above the other, could be obtained by slow escape of the trapped acetone molecules from out-out CC in solid state. This transformation could be obtained through a single-crystal-to-single-crystal (SCSC) transformation from a large volume out-out CC to a smaller volume out-in CC conformation which is also supported by density functional theory calculations.