Crystal structures and vibrational spectra of biuret co-crystals with cyanuric and glutaric acids, discussion of hydrogen bonding involving carbonyl groups

Abstract

Abstract The title structures of biuret-cyanuric acid (2/2) monohydrate, C10H18N12O11, 1 [P1̅, Z=2, a=8.2598(4) Å, b=10.8795(5) Å, c=11.9138(6) Å, α=67.036(1)°, β= 79.842(2)°, γ=69.859(2)°, V=924.38(8) Å3], and of biuret-glutaric acid (1/1), C7H13N3O6, 2 [P1̅, Z=2, a=5.0044(3) Å, b=7.0832(3) Å, c=14.9803(10) Å, α=102.860(4)°, β= 91.899(3)°, γ=102.202(4)°, V=504.20(5) Å3], show usual features both in constitution and intermolecular contacts except for a slightly longer C=O bond length in one of the carbonyl groups in 2. The biuret molecules have conformations with anti-parallel arrangement of the carbonyl groups. In each structure O–H…O and N–H…O hydrogen bonds of the moderate strength are present. The new results are compared with other structures which contain biuret molecules. The influence of the hydrogen bonding on the bond length of the carbonyl group C=O in the fragment NH2-(C=O)-NH with amine and hydroxyl donors has also been investigated. It transpires that the C=O…H angle of about 120° favors a slight elongation of the C=O bond length. The elongation of the C=O bond is more susceptible to the relative orientation of the C=O group with regard to amine over hydroxyl groups. This is the likely explanation why one of the C=O bonds in 2 is slightly longer than usual because this carbonyl group is simultaneously involved in two hydrogen bonds where C=O…H–O and C=O…H–N satisfy the 120° condition. Vibrational spectra of the title structures were also recorded and assigned.