Cocrystal of Urea and Imidazolidone: Formation of an Unexpected 1-D Substructure in a Plausibly Predictable Cocrystal

The preparation and crystal structure of a new cocrystal between urea and imidazolidone is reported. An uncharacteristic structural motif of urea molecules was identified and found to be exhibited by only one other urea-containing structure in the Cambridge Structural Database. A comparison is made between the two cocrystals through the use of graph set analysis. The fact that the two structures are of molecules with different H-bonding functionalities did not alter the hydrogen bonding topology but was manifested in slight geometric alterations. The overall structure is structurally dominated by the formation of an identical extended one-dimensional substructure of urea molecules which pack slightly differently, the second component playing the role of a linker. The importance of examining the extended structure, as opposed to only cell constants and space group, when searching for structural similarity, is illustrated. Crystal data: triclinic space group P1̅, a = 5.112(3) Å, b = 7.944(4) Å, c = 9.247(5) Å, α = 85.62(1)°, β = 74.92(1)°, γ = 75.35(9)°, V = 350.8(3) ų, Z = 2, D_calc = 1.384 Mg/m³, μ = 0.112 mm⁻¹, F(000) = 156, θ_min = 2.28 to θ_max = 26.36°, R1 = 0.0491, wR1 = 0.1607 observed data (I > 2σI) = 999, total = 1850, R(int) = 0.023, GOF = 1.13 for 132 parameters.