Morphological Change of Cocrystal Bis(8-Quinolinolato) Copper(II): 7,7,8,8-Tetracyanoquinodimethane Polymorphism

We studied cocrystal of bis(8-quinolinolato) copper(II) (CuQ₂) and 7,7,8,8-tetracyanoquinodimethane (TCNQ), which change dramatically crystal shape in a moment by adding press on crystal face. Single crystal was prepared by dissolving CuQ₂ and TCNQ in chloroform by evaporation of the solution at ambient conditions. We investigated about crystal structure and morphological change properties. We proclaim that this phenomenon is solid phase transition to Form I from Form II, it is caused by pressure on the crystal face (001) of Form II and the crystal expansion direction is the side face (100). We take note of the common structure between polymorph and explain that this transition occurs by the structure like dominoes falling. We obtained a correlation between molecular level structure change and macroscopic shape changes.