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The Importance of Weak C−H···O Bonds and π···π Stacking Interactions in the Formation of Organic 1,8-Bis(dimethylamino)naphthalene Complexes with Z‘ > 1

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posted on 01.02.2006, 00:00 by Gary S. Nichol, William Clegg
Reaction in methanol or water of the organic base 1,8-bis(dimethylamino)naphthalene (often called “proton sponge”, PS) with four simple chemically related organic acids (HA), namely, violuric acid (VIH), cyanuric acid (CYH), barbituric acid (BAH), and orotic acid (ORH), gave rise to four new organic salts, 14, respectively, with very different crystal structures. Crystallographic problems (including disorder, weak diffraction, and rapid dissolution at ambient temperatures) were encountered with all four compounds and were successfully resolved in each case. Analysis of the crystal packing shows that weak C−H···O and π···π stacking interactions are important in maintaining the integrity of the structures. All four compounds have asymmetric units containing more than a single ion pair PSH+A- (i.e., Z > 2); for the chemically simple compound PS+VI-·MeOH (1), Z = 1 and Z = 3, but for the more complicated compound PS+OR- (4), Z = 8 and Z = 16 (counting only the species that have been modeled with discrete atoms and ignoring others that are highly disordered in “voids” of the structure) with an extensive network of weak intermolecular interactions holding the structure together.