Spectrometric Investigation of Complexes of Copper(II) and anti-2-Aminobenzophenone Oximes, and Characterization of the syn and anti Forms

Abstract

Nine bivalent cations were examined spectrophotometrically for a color reaction with anti-2-amino-5-chlorobenzophenone oxime, using aqueous ethanol as solvent. Only Cu++ gave a positive color change owing to the formation of complexes. The syn isomer gave a negative result with all of the cations. This test also distinguished the two isomeric forms of eight additional pairs of analogous oximes. In the case of the anti-2-amino-5-chloro-derivative, the nature of the copper complexes in solution was explored; a crystalline complex, formulated as [(C13H11CIN2O)2Cu.H2O]2++2SO4−, was isolated. The proton-resonance signals given by the hydroxyl and amino groups for the whole set of oximes provide evidence for a significant structural difference between the two isomeric forms. The infrared spectra show lower symmetric NH stretching frequencies for the anti forms than for the syn forms. These differences are attributed to the presence of an intramolecular N-H…N=C hydrogen bond in the anti forms and to its absence in the case of the syn forms. The ultraviolet spectra of the anti forms show an increased intensity of absorption and a maximum at lower wavelength in the 220–250 mμ, range when compared to the syn forms. The situation is similar with regard to intensity, but there is a shift to a higher wavelength, for the broad absorption maximum in the 300–350 mμ range. It is concluded that these latter two regularities stem mostly from the differences in molecular geometry of the anti and syn isomers, with only a small contribution resulting specifically from the difference in hydrogen bonding.