Crystal Engineering最新文献

The solid state structures of the complexes of para-sulphonato-calix-[4]-arene with putrescine, cadaverine, cis-1,2-cyclohexanediamine and spermidine have been determined. Di- or triammonium cations are included in the calix-[4]-arene molecular cavity and are held in place by hydrogen bonds and hydrophobic interactions. In two of the compounds, diammonium cations are present external to the cavity and are clathrated in tubes formed by the para-sulphonato-calix-[4]-arene network. All four structures show the classic bilayer “organic clay” packing arrangement of opposing para-sulphonato-calix-[4]-arene molecules, with either capsules for the linear diammonium cations, or slipped pairs for the bulky cis-cyclohexane diammonium and triammonium cations.

Crystal engineering of gossypol using pyrazine as a complexing agent led to the discovery of new families of crystalline inclusion complexes on the basis of a mixed “gossypol–pyrazine” host. Depending on the H-bonding ability of the solvent guest molecules, different types of clathrates were formed. In these clathrates, pyrazine molecules incorporate gossypol molecules to relatively robust mixed host matrix through symmetrical H-bonds of the type O–H⋯N.

The single-crystal structures of 2,6-di-^tbutyl-4-nitrophenol (dbpH), guanidinium 2,6-di-^tbutyl-4-nitrophenolate, piperidinium 2,6-di-^tbutyl-4-nitrophenolate, 1,8-diazabicyclo-(5,4,0)-undec-7-enium 2,6-di-^tbutyl-4-nitrophenolate and 4-(dimethylamino)pyridinium 2,6-di-^tbutyl-4-nitrophenolate are reported. The structure of dbpH is non-centrosymmetric and an ungraded powder sample exhibits five times the second-order nonlinear optical intensity of an ungraded urea sample when irradiated with infrared light. The four salt co-crystals all associate via hydrogen-bonding interactions to the phenolate oxygen atom while two of these also involve hydrogen-bonding associations to the nitro oxygen atoms. The presence of the 2,6-disubstituted t-butyl groups hinder the rotation of the plane of the associated base molecules to >60° with respect to the plane of the phenolate ring, thus introducing limited controllability over the approach and association of these molecules.

The compounds 1-(2-fluorophenyl)-6,7-dimethoxy-2-phenyl-1,2,3,4-tetrahydroisoquinoline (1) and 5-(2-fluorophenyl)-6-phenyl-5,6,7,8-tetrahydro dioxolo[4,5-g]isoquinoline (2) have been studied via single crystal X-ray diffraction at 100.0(2) K. Compound 1 crystallizes in the space group $\text{P}\text{1}\text{̄}$ with two molecules in the asymmetric unit (Z=4), whereas compound 2 crystallizes in the space group P2₁/n. The two molecules of 1 in the asymmetric unit offer different modes of interactions via C–H…F and C–H…O resulting in altered molecular conformations. Compound 2 essentially packs via C–H…F interaction.

Nine molecular co-crystals containing 2,3-, 2,5-, 2,6- and (3,5-dichlorophenoxy)acetic acid have been prepared and studied using single-crystal X-ray diffraction techniques. The free acid structure of (2,3-dichlorophenoxy)acetic acid is also reported. The bases used to prepare the adducts were 2-aminopyrimidine, 2-amino-2-thiazoline, 2-amino-5-chlorobenzoxazole and 4,4’-dipyridine. The conformations of the phenoxyacetic acid molecules were found in all but one case to be either synclinal (twisted) or antiperiplanar (planar). The one exception was a molecule of (2,6-dichlorophenoxy)acetic acid whose conformation was assigned as anticlinal. General comments are given about the conformational aspects of these and previously reported adducts of phenoxyacetic acid derivatives and how they compare to their free acid structures.

Crystallographic studies of 2,6-bis(2,4,6-trimethylphenyl)-4-methyliodobenzene 1 and 2,6-diphenyl-4-methyliodobenzene 2 were performed and in both cases [CH₃···I] interactions were identified. Theoretical calculation of the dipole moment of 1 and the partial charges of the iodine and methyl hydrogens were performed. These charges, although small, suggest that they are large enough to encourage the formation of weak dipole-dipole interactions in the absence of other stabilizing forces

A Protein Data Bank (PDB) study was undertaken to investigate the role of C–X…π interactions (X=F, Cl, Br, I) in protein structures. From this analysis, it is evident that the propensity for the formation of C–X…π interactions is higher in case of fluorine than in other halogens. These results compare well with the recently reported C–X…π interactions in small molecules and depict the orientational dependence of these interactions.