The crystal structures of two pyrazolinone azomethine dyes

Abstract

Pyrazolinone azomethine dyes are important as image formers in color photography. Usually these dyes are magenta in hue, but when they are overcrowded by suitable substituents, their absorption shifts bathochromically and they are cyan. The structures of two of these dyes the relatively uncrowded 4-(4-N,N-diethylaminophenylimino)-3-methyl-l-phenyl-2-pyrazolin-5-one (UPAD) and the highly hindered 4-(2,6-dimethyl-4-N, N-diethylaminophenylimino)-3-methyl-l-phenyl-2-pyrazolin-5-one (HPAD)have been determined from single-crystal X-ray diffraction data. UPAD is monoclinic, P21/n, with a= 11.840 ( ~ b = 12.748 (2), c= 11-982 (2) A, fl=93.02 (1) ° and Z=4; HPAD is triclinic, P1, with a=9-114 (1) , 13-657 (1), c=8-502 (1),~, e= 10319 (1), fl= 102-92 (1), y=9163 (1) , and Z= 2. The structures were solved by direct methods and refined by least squares. The hydrogen atoms were located from difference Fourier syntheses and were refined. The final R value for HPAD is 0.042 and for UPAD is 0.054. Neither dye is planar but HPAD deviates considerably more from planarity than UPAD. The dihedral angle between the pyrazolinone ring and the p-phenylenediamine ring is 13.9 ° for UPAD and 56.6 ° for HPAD. The bond lengths show that the unexcited canonical structure is the dominant contributor to the conjugation and that the quinoid form of the p-phenylenediamine part is more important for UPAD than for HPAD. A striking feature of the structure of UPAD is the presence of a definite intramolecular C-H. • • O hydrogen bond. The atomic separations are O. • • H = 2.03/~, O. • • C = 2.95/~. Infrared data show that the C=O stretch frequency is 24 cm -1 less for UPAD than for HPAD.