Supramolecular architecture of theophylline polymorphs, monohydrate and co-crystals with iodine: study from the energetic viewpoint

The regularities of crystal structure organization were thoroughly studied in all to date known polymorphic modifications of theophylline (THP) using an energetic approach. The monohydrate and a co-crystal of theophylline with one half equivalent of an iodine molecule were similarly investigated. The calculations of pairwise interaction energies have showed that the crystals studied can be divided into two groups according to their basic structural motifs: columnar-layered or columnar. The energetic approach also allows the role of different interactions in the crystal structure formation to be estimated. It was found that strong N-H⋯N, N-H⋯O hydrogen bonds and stacking interactions play the most important roles in polymorphic modifications of THP and the THP monohydrate. In the case of the co-crystal with iodine, N-H⋯O hydrogen bond participates in the dimeric building unit formation. However, instead of a stacking interaction the π⋯π interaction between carbonyl groups of neighboring molecules plays the highest role in the supramolecular architecture of this crystal. The lattice energies calculations in periodic conditions for polymorphic structures have shown that polymorph with the most anisotropic energetic structure may be considered as stable and all others forms metastable. In the polymorphic modification 1 of THP a zwitter-ionic resonance form is predominant, which affects significantly the solubility and the intermolecular interactions of this modification.

A third polymorph of the zwitterionic complex trichlorido-((dimethylphosphoryl)methanaminium-κO)zinc(II)

By the reaction of (dimethylphosphoryl)methanamine (dpma) with one equivalent of zinc(II) chloride in a concentrated hydrochloric acid solution and subsequent slow evaporation of the solvent, the title compound (dpmaH)ZnCl3 was obtained in quantitative yield. The primary reaction product mainly consists of larger brick-shaped colorless and smaller cuboide colorless crystals. Long-time storage over several months of these crystals in the mother liquor yielded a third polymorph (P21/n; a = 9.6639(1); b = 10.0271(1); c = 11.2446(1) Å; β = 98.964(1)°) of this compound. Similar to the two other modifications, its crystal structure consists of a zwitterionic dpmaHZnCl3 complex containing the cationic dpmaH+ ligand, which coordinates the zinc atom through its oxygen atom. Hydrogen bonds connect neighboring zwitterionic complexes to a layered structure. The motif of a hydrogen bonded dimer, similar to that found in the chain structure of polymorph I, is also present, but in the title structure these dimers form hydrogen bonds in two dimensions.

Revisiting 2-chloro-4-nitroaniline: analysis of intricate supramolecular ordering of a triclinic polymorph featuring a high Z value and strong second harmonic generation

A new polymorph of 2-chloro-4-nitroaniline is more stable than its 55 year-old antecedent.

The formation of the salt and neutral molecule cocrystal from equimolar solution of heliamine and bicyclo[2.2.1]hept-5-ene-endo-2,3-dicarboxylic acid

The possible interaction of 6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline (heliamine) with bicyclo[2.2.1]hept-5-ene-endo-2,3-dicarboxylic acid anhydride has been studied. Instead of the reaction with heliamine, the acid anhydride was hydrolyzed into the appropriate dicarboxylic acid. An equimolar mixture of unreacted heliamine and in-situ-generated dicarboxylic acid crystallized in space group P2₁/c. The comprehensive study of the obtained crystals shows that the peculiarities of the crystallization process lead to the formation of the salt-cocrystal structure where the dianion interacts simultaneously with two cations forming a chain as the primary structural motif. The neutral molecules of dicarboxylic acid link the dianions of the neighbouring chains, forming a layer as the secondary structural motif. As a result, the stronger hydrogen bonds formed by the neutral molecules play a secondary role in the crystal structure formation.

Intermolecular interactions in crystals of benzene and its mono- and dinitro derivatives: study from the energetic viewpoint

The weak intermolecular interactions and their role in mono- and dinitrobenzene crystal structure formation have been studied using quantum-chemical calculations.

Hydrogen bonding vs. stacking interaction in the crystals of the simplest coumarin derivatives: a study from the energetic viewpoint

Hydrogen bonded and stacked dimers have very close interaction energies in the crystals of the simplest coumarin derivatives according to the data of the crystal structure analysis based on the comparison of pairwise interaction energies.

Influence of substituents on the acceptor properties of the amino groups in the diaminobenzene analogues

The influence of substituents on the geometric parameters and acceptor properties of the amino group in the diaminobenzene analogues has been studied using quantum-chemical calculations and the study of crystal packing from the energetic viewpoint.