Polymorphism in fuchsones

Abstract

Seven 2,6-disubstituted fuchsones (fuchsone = 4-(α,α-diphenylmethylene)-1,4-benzoquinone, R = H, Me, i-Pr, t-Bu, Ph, Cl, Br) were synthesized and crystallized from different solvents to find new polymorphs in this family of compounds. The chloro and isopropyl derivatives are dimorphic, methyl, and t-butyl compounds crystallized as trimorphs, but H-, Ph-, and Br-substituted compounds gave one crystal structure each. Polymorphism in a family of compounds is discussed for the first time with respect to different conformations adopted by the exodiphenylmethylene group at the 4-position of the benzoquinone ring. Depending on the acceptor availability of the fuchsone C=O and the conformation of the phenyl ring, different C-H···O interactions, and close packing motifs are optimized in these crystal structures. One polymorph of dichloro-fuchsone has Z' = 4 due to offset in the stacking of symmetry-independent molecules. Phase transition in dimethyl fuchsone showed the β polymorph to be stable at high temperature, whereas the a form dominates at room temperature, making it an enantiotropic cluster. The three experimental polymorphs of dimethyl fuchsone lie within the 10 lowest-energy predicted crystal structures. Fuchsones represent easy to synthesize compounds derived via a molecular engineering approach for the study of conformational polymorphism.