Abstract
The dissociation constants of ampicillin and the formation constants of complexes with cobalt(II), copper(II), nickel(II), iron(III), zinc(II), lead(II), mercury(II) and cadmium(II) were evaluated at different temperatures (20-45°C) by potentiometric measurements in the presence of different percentages of ethanol-water. Two polymorphs of the degradation product 3-oxo-2-phenyl-pyrazine-5-carboxylic acid ethyl ester have been isolated from the reaction of copper chloride with ampicillin in aqueous ethanol. In the crystal structure of both polymorphs, molecules related by a center of symmetry form a dimer by coupling of the N-H ··· O hydrogen bonds resulting in the
(8) supramolecular synton. The π-π contacts indicate strong stacking interactions in both polymorphs.