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1 Polish Journal of Chemistry

1 2006

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Characterization, Crystal Structure, and Solution Studies of a Proton Transfer Compound Obtained from 2,6-Pyridinedicarboxylic Acid and 1,4,10,13-Tetraoxa-7,16-diazacyclooctadecane

Moghimi A., Lippolis V., Aghabozorg H., Shokrollahi A., Shokrollahi A., Sheshmani S., Blake A.

Polish Journal of Chemistry

2006

Vol. 80, nr 8

1385-1396

The proton transfer compound, (DA18C6H2)(pydcH)2_0.25H2O, has been prepared from the reaction between 1,4,10,13-tetraoxa-7,16-diazacyclooctadecane, diaza-18-crown-6 (DA18C6), and 2,6-pyridinedicarboxylic acid, dipicolinic acid (pydcH2). The characterization was performed using 1H and 13C NMR, IR spectroscopy and single crystal X-ray diffraction analysis. The asymmetric unit consists of one (DA18C6H2)2+ cation adopting a sigmoidal conformation which interacts with two (pydcH)- anions via hydrogen bonds involving the protonated amine groups of the diazacrown ether. -COOHźźź-OOC- head-to-tail hydrogen bonds generate 2D undulating layers along [100] and [001] in the crystal lattice. The protonation constants of DA18C6 and pydcH2 and equilibrium constants for the reaction of the two reactants were determined by potentiometric pH titration. The solution studies supported the formation also in solution of (DA18C6H2)(pydcH)2 as the most abundant species at pH = 3.4.