The fourfold disordered structures of p-chloro-N-(p-methylbenzylidene)aniline and p-methyl-N-(p-chlorobenzylidene)aniline

Abstract

p-Chloro-N-(p-me thylbenzylidene) aniline, MeCI, and pmethyl-N-(p-chlo robenzylidene)an iline, CIMe, are isostructural, both C~4H~2C1N, Mr = 229.6, differing only in the disposition of a -----CHIN-- linkage joining two phenyl-ring systems, one with a p-C1 atom attached, the other with a p-methyl group attached. A nondisordered prototype structure would have the space group P21/n, Z = 4. MeCI: a = 5.965 (2), b = 7.423 (3), c = 27.420 (3) A,, /~= 99.22(1) °, V = 1198(1)A, 3, Dx = 1.28Mgm -3, T = 295K,/x = 24.5 cm -1, CuKot, A = 1.5418/~; C1Me: a = 5.971 (2), b = 7.411(3), c= 27.462 (3) A, /~ = 99.13(1) °, V = 1200(1)A, 3, Dx = 1.27 Mgm -3, T = 295K,/z = 24.3 cm -1, CuKc~, A = 1.5418/~. The molecules have pseudo-mmm symmetry, but no real symmetry. Four pseudoequivalent orientations occur in the disordered structure. If inversion-related orientations are equally populated, then 1 odd data are unobserved and the average disordered structure has the space group P21/a, with a' = a, b' = b, c' = c/2, Z = 2. This was the case for the CIMe crystal studied, but not for MeC1. For the crystals studied, occupation ratios for the reference-, inversion-, mirror- and twofold rotation-related orientations were 0.543:0.189 (3):0.095 (3):0.173 (3) for MeCI and 0.351:0.351:0.14 9:0.149(3) for C1Me. A * Author to whom correspondence should be addressed.