2',5'-DIMETHOXYPHENYL)CYCLOBUTANE-1,2-DICARBOXYLIC ACID - ENGINEERED TOPOCHEMICAL SYNTHESIS AND MOLECULAR AND SUPRAMOLECULAR PROPERTIES

The title compound (1b), synthesized using the principles of crystal e ngineering, exhibits interesting molecular and supramolecular properti es. Diacid 1b crystallizes in the triclinic space group P1BAR, a = 8.1 50(1), b = 8.927(2), c = 17.894(4) angstrom; alpha = 98.91(1), beta = 97.60(1), gamma = 110.62(2)-degrees, and the structure was solved and refined to an R factor of 0.063 on 2910 nonzero reflections. Intramole cular charge transfer in 1b was studied spectroscopically. Through-bon d coupling (TBC) and the resultant C-C bond elongation are observed in lb to a moderate extent. A more general Cambridge Structural Database (CSD) study on 1,2-diphenylethanes provides clear evidence for the mo lecular attributes required for TBC. Diacid 1b forms a host-guest comp lex with toluene in which the orientation of the guest molecule is per fectly tuned to the steric and electronic requirements of the host. Th e toluene guest molecule induces a convergent supramolecular cage, whi le another divergent supermolecule results because of the zigzag hydro gen-bonded chains of carboxyl groups. A water molecule, seemingly inad vertently trapped in the carboxyl channels, is not involved in hydroge n bonding but is a mere space filler. A general analysis of the solvat ion properties of benzene, toluene, and water is presented.