Push-pull ethylenes: the structures of 3-(2-imidazolidinylidene)-2,4-pentanedione (I), C₈H₁₂N₂O₂, and 3-(1,3-dimethyl-2-imidazolidinylidene)-2,4-pentanedione trihydrate (II), C₁₀H₁₆N₂O₂.3H₂O

Abstract

(I): M_r=168, triclinic, P1, Z=2, a=5.596 (2), b=6.938 (3), c=10.852 (4) Å, α=75.64 (3), β=93.44 (3), γ=95.47 (3)°, V = 406.0 ų, D_m=1.35 (by flotation using carbon tetrachloride and n-hexane), D_x=1.374 Mg m^-3, μ (Mo Kα, λ=0.7107 Å) =1.08 cm^-l, F(000)=180, T=293 K. (II): M_r= 250, triclinic, P1, Z=2, α=7.731(2), b=8.580(2), c=11.033 (3) Å , α = 97.66 (2), β = 98.86 (2), γ=101.78 (2)°, V=697.5 ų, D_m=1.18 (by flotation using KI solution), D_x=1.190Mg m^-3, μ (Mo Kα, β=0.7107 Å)=1.02 cm^-1, F(000)=272, T=293 K. Both structures were solved by direct methods and refined to R=4.4\% for 901 reflexions for (I) and 5.7% for 2001 reflexions for (II). The C=C bond distances are 1.451 (3) Å in (I) and 1.468 (3) Å in (II), quite significantly longer than the C=C bond in ethylene [1.336 (2) Å]. The twist angle about the C=C bond in (II) is 72.9(5)° but molecule (I) is essentially planar, the twist angle being only 4.9 (5)°.