Different crystal forms of a rich hydrogen bond acceptor compound resulting from alternative C–H⋯O and orthogonal CO⋯CO molecular interaction patterns

Abstract

The racemic compound 2,4,6,8-tetracarbomethoxybicyclo[3.3.0]octa-2,6-diene-3,7-diol 3 is known to form a solvent-free crystal structure (Polymorph I) through repetition of a centrosymmetric dimeric unit that is constructed by concave face to concave face association of two shallow dish-shaped tetraester 3 molecules. Compounds employing such awkwardly shaped repeat units are known to be prone to yielding more than one crystal form. Systematic screening has now revealed a second solvent-free crystal form (Polymorph II), and also a family of essentially isostructural lattice inclusion compounds (Inclusion form I), of 3. The X-ray crystal structures of Polymorph II, and the p-xylene and cyclohexanol compounds of the inclusion crystal form, are described. The predominant weak interactions in all three crystal forms comprise C–H⋯O and orthogonal CO⋯CO attractive forces and their different arrangements are compared and contrasted.