2,4-dinitro-trans-cinnamic acid

2,4-Dinitrocinnamic acid [3-(2,4-dinitrophenyl)prop-2-enoic acid], C9H6N2O6, crystallizes as a normal centrosymmetrical carboxy dimer. O-H...O and C-H...O hydrogen bonds are found in the structure

Trimethyl isocyanurate and triethyl isocyanurate

The crystal structures of trimethyl isocyanurate, C6H9N3O3, (1) and triethyl isocyanurate, C9H15N3O3, (2) contain topologically similar C-H …O hydrogen-bonded networks. In (1), there are two symmetry-independent molecules and each forms its own layer structure. In (2), two of the ethyl groups point one way with respect to the heterocyclic ring while the third points in the opposite direction

4-(triphenylmethyl)phenol-triphenylphosphine oxide (1/1)

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Crystal engineering: some further strategies

Structural studies currently underway in our group are reported in this paper. Molecular symmetry is rarely carried over into the crystal, posing problems when high-symmetry networks are desired. This is illustrated by the low-symmetry structure of 2,4,6-trinitromesitylene. However, the involvement of the Cl<SUB>3</SUB> supramolecular synthon ensures a hexagonal network structure for 2,4,6-tris-(4-chlorophenoxy)-1,3,5-triazine. Arguments following from the equivalence between molecular and supramolecular synthons lead to the tetragonal network structure of the 1:1 complex of tetraphenylmethane and CCl<SUB>4</SUB>. With a similar reasoning, 4-(triphenylmethyl)benzoic acid is identified as a precursor of a supramolecular wheel-and-axle host substance. The study of novel and weaker intermolecular interactions is often useful. In N,N'-dibenzyl-1,4-cubanedicarboxamide, the acidity of the cubyl C-H groups leads to the formation of C-H&#183;&#183;&#183;O hydrogen bonds. Polymorphism is a difficult challenge for the crystal engineer and, in its most intriguing manifestation, two crystalline forms of a substance appear in the same crystallization batch. This is observed for 4,4-diphenyl cyclohexadienone. The ultimate frontier in the subject is an understanding of the phenomenon of crystallization, and the unexpected crystal structure of quinoxaline, with five symmetry-independent molecules, could possibly represent a case of arrested crystallization