Polarized ethylenes: structures of (1,3-dimethyl-2-imidazolidinylidene)malononitrile and (1,3-dimethyl-2-perhydropyrimidinylidene)malononitrile

Abstract

Crystal structures of the title compounds, (I) and (II), have been determined by three-dimensional diffraction methods. Crystals of C₈H₁₀N₄ (I) are monoclinic, space group P2₁/a with Z=4, M_r=162, a=7.965 (1), b=16.232 (2), c=7.343 (1) Å , β=113.54 (1)° , V=890.7 ų, D,_n=1.218, D_x = 1.208 gcm^-3, μ (Cu Kα, λ=1.5418 Å)=6.47 cm^-1, F(000) = 344. The crystals of C₉H₁₂N₄ (II) are orthorhombic, space group P2₁cn, with Z=4, M_r=176, a = 7.983 (3), b=8.075 (2), c=14.652 (3) Å, V = 944.43 ų, D_m=1.219, D_x=1.237 g cm^-3, μ(Mo Kα, λ=0.7107 Å)=0.868 cm^-1, F(000)=376. Both structures were solved by direct methods and refined to R=5.8% for (I) and 5.3 % for (II). The C-C double-bond distances are 1.407 (3) in (I) and 1.429 (6) Å in (II), appreciably longer than normal. The steric and push-pull effects result in rotation about the C=C bond, the rotation angles being 20.2 (3) in (I) and 31.5 (6) o in (II).