New bond-delocalized dianions: The crystal structure of 1,3-bis (dicyanomethylene) croconate salt (C11N4O3K2 2H2O)

C 11 N 4 O 3 K 2 · 2H 2 O crystallizes in the triclinic space group P 1 ¯ with a = 8.568(2), b = 9.105(4), c = 9.818(4)Å, α = 103.61(3), β = 107.63(3), γ = 101.58(3)°; Z = 2, ρ calc = 1.716, ρ obs = 1.72(2)g cm -3 (flotation). The structure was solved by direct methods and was refined by full-matrix least-squares procedures to a final R of 0.074 for 1989 observed reflections. The five-membered ring is planar and pentagonal. The two = C(CN) 2 groups define separate planes which form angles of 3.36 and 6.30° with the plane of the five-membered ring. The dianions form stacks along the a-axis. In a given stack, there is an alternating sequence of perpendicular distances (3.32, 3.42Å) between the planes defined by the ring atoms.