DIRECTIONALITY OF NON-BONDED INTERACTIONS IN SOLVATED MOLECULAR CRYSTALS H. Oswaldo Aldas-Palacios and Raymond E. Davis. Department of Chemistry and Biochemistry, The University of Texas at Austin, Austin, TX 78712-1167, USA

The correlation between the molecular electrostatic potential (MEP) of solvent molecules and the geometrical preferences of their non-bonded interactions with electrophilic and nucleophilic species in molecular crystals is examined. Pyridine and benzene solvents are chosen due to their similar size and shape, but different electrostatic characteristics.

The crystal structures used in this study were obtained from the Cambridge Structural Database (CSD). Structures with no disorder and with R values less than 15% were selected for the study. The environment of each solvent molecule was studied at distances ranging from 2.0 to 4.2 Å from its non-hydrogen atoms. Non-hydrogen atoms within this contact range were found and characterized as to their chemical identity. Contact atom locations and functional group orientations with respect to the solvent molecule were determined.

Ab initio calculations using the Gaussian 92 computer programs were performed, with the geometry optimization at the 6-31 level, and the MEP calculation, corresponding to the location of each non-bonded atomic contact, at the 6-311** level. The MEP was stored incrementally on a grid with its origin at the centroid of the solvent molecule. Computer programs were then used to analyze geometrical preferences and the correlation of the MEP with the directionality of the intermolecular interactions.

Supported in part by the Robert A. Welch Foundation, Grant F-233