The Neutron Structure at 116 K of the 1:1 Complex of Perdeuterated Parabanic Acid and Urea

Article abstract of DOI:10.1107/S0567740880005420

The perdeuterated 1:1 complex of parabanic acid (C3D2N2O3) and urea (CD4N2O) at 116 K is monoclinic, space group P2₁/c, with a=8.910 (3), b=5.597 (2), c=14.525 (6) Angstroem, β=108.39 (3) grad, and has four molecules of each kind per unit cell.The nuclear configuration has been determined from 2165 neutron intensities (sinθ/λ<0.76 Angstroem^-1, λ=1.0450 Angstroem) to give e.s.d.'s in apparent bond lengths and angles of 0.001 Angstroem and 0.1 grad, or less.The configurations of the two molecules are similar to those found in their separate crystal structures, but there are small differences, which appear to be related to the different hydrogen bonding .There is an unusually short hydrogen bond (N...O, 2.66 Angstroem) between parabanic acid N-D and urea O atoms.There are also short C...O distances (2.81, 2.86 Angstroem) between carbonyl groups of different parabanic acid molecules.The polar molecular interactions of parabanic acid are similar to those of the drug-active barbiturates.