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A new coordination synthon, Zn···NO2 recognition, is used in the synthesis of a layered porphyrin coordination polymer (Zn-5,15-di(4-nitrophenyl)-10,20-di(p-tolyl)-porphyrin, 1-Zn) with 44 topology. This solid is thermally stable and incorporates nitrobenzene molecules between the layers to form 1-Zn−PhNO2. The Zn···NO2 recognition exists in 1-Zn and 1-Zn−PhNO2; it is formed by coordination bonding between a Zn2+ ion embedded in a porphyrin core and one of the O-atoms of the nitro group. The structure of 1-Zn−PhNO2 is also layered and contains 44 networks such as those found in 1-Zn. The two structures, however, differ significantly in several intra- and interlayer parameters. Despite these differences, removal of nitrobenzene from the crystals of 1-Zn−PhNO2 yields crystalline 1-Zn. When soaked in nitrobenzene, these desolvated 1-Zn crystals yield crystalline 1-Zn−PhNO2. These reversible solid-to-solid transformations demonstrate the robustness of Zn···NO2 recognition in holding the 44 networks together i...

A new supramolecular crystal engineering approach toward quadratic nonlinear optics is inferred from an acentric cocrystalline template made of two different bi-dimensional octupolar molecules: tr...

Single-crystal X-ray diffraction analyses of α,ω-alkanedicarboxylic acids (HOOC−(CH2)n-2−COOH, n = 2−10) have been carried out at 130 and 298 K. Dimorphism is prevalent in odd carbon members, and the crystal structures of α- and β-forms of C7-diacid have been determined. Diacids show an alternation in their melting points with members containing an even number of carbon atoms exhibiting systematically higher melting points compared to odd ones. On the contrary, the solid-state densities of odd members with Cn ≥ 5 are higher than those of even members. Closest packing is therefore not the reason for alternating melting points in diacids. Diacids with Cn ≥ 5 show distinct packing regularities within even series and also within α- and β-series of odd members. The gross structural features are similar in even and (both forms of) odd diacids: (a) carboxy groups form hydrogen bonded dimers at both ends of the molecules, leading to infinite chains, and (b) methylene chains stack into columns through hydrophobic...

The structural details of a,w-alkanediols and a,w-alkanediamines which are characterized by H bonding and hydrophobic interactions. These systems represent a balance between structural simplicity and interaction complexity, which makes the study of interference between interactions a feasible exercise. The anal. of the crystal structures of diols and diamines revealed the interplay between 2 important intermol. interactions that are possible in these amphiphilic compds., namely, H bonding and hydrophobic interactions. While H bonding and hydrophobic interactions operate in consonance in even members, and therefore culminate in dense packing, they run into geometrical conflicts in odd members, leading to looser packing. Accordingly, the odd members of the diol and diamine series have relatively lower densities and m.ps. than the even members.

a,w-Alkanedithiols show an alternation in their m.ps. with even members exhibiting systematically higher m.ps. than odd members. Single crystals of the 1st nine members of a,w-alkanedithiols (HS-(CH2)n-SH, n = 2-10) were grown in situ using a miniature zone melting procedure, and their x-ray crystal structure analyses were performed. The structural similarities and differences between even and odd members were analyzed based on the packing arrangements of hydrocarbon chains and SH functionalities. Whereas the hydrocarbon chains maintain an intergrooving pattern, the SH groups assoc. in an antiparallel fashion in both the members. The SH groups do not form H bonds. In the even members the mols. are offset along their length, whereas such an offset is not obsd. in the odd members. The densities of even members are systematically higher than those of odd members and show an alternating trend. Using a simple geometrical model, describing even and odd members as modified parallelograms and trapezoids, resp., the d. features of the packing patterns in both the members are illustrated. The m.p. alternation in dithiols is attributed to the geometry allowed or forbidden mol. offset toward a higher packing d.

γ-Hydroquinone (1) and its tetrafluoro, tetrachloro and tetrabromo derivatives (2), (3) and (4) adopt crystal structures that have an almost invariant system of O—H...O hydrogen bonds. However, within this O—H...O framework, the four structures display variations that are characteristic of the C—H, C—F, C—Cl and C—Br groups. In the parent compound (1) aromatic rings are packed with a herringbone geometry, whilst in the halogenated derivatives (3) and (4), polarization-type halogen...halogen contacts are optimized. The fluoro derivative (2) is exceptional in that neither of the above possibilities is adopted, even though the O—H...O scaffolding does not per se prohibit either of them geometrically.

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 Cl3 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 CCl4. 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···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.

The principles of crystal engineering have been used to design a family of structures with potential as octupolar nonlinear optical (NLO) materials. The major aim in such an exercise, a carry-over of molecular symmetry into the crystal, is possible with a retrosynthetic approach. An appropriate choice of precursor trigonal molecules leads from the concept of the dimeric Piedfort unit. The crystal structures and NLO properties of a series of 2,4,6-triaryloxy-1,3,5-triazines, 1−6, are reported. These compounds consistently form quasi-trigonal or trigonal networks that are two-dimensionally noncentrosymmetric. Substitutional variations on the phenyl moieties that were expected to maintain or to perturb this trigonal network have been explored. Molecular nonlinearities have been measured by Harmonic Light Scattering (HLS) experiments. Among the compounds studied, 2,4,6-triphenoxy-1,3,5-triazine, 1 adopts a noncentrosymmetric crystal structure with a measurable SHG powder signal. All these crystal structures a...

Single-crystal neutron diffraction analyses of 2- and 3-aminophenols have been performed. In addition to O−H···N and N−H···O hydrogen bonds, both these structures contain previously unidentified N−...

The crystal structure of the title compound, C 24 H 21 N 3 , is stabilized by C-H...N and C-H...π interactions. Its crystallization in a lower symmetry space group highlights an important problem in crystal engineering, that is the failure of symmetry carry-over from the molecule to the crystal.

Carboxy terminated alkanethiol self-assembled monolayers promote the face-selective nucleation of the P-monoclinic polymorph of carbamazepine; the type of face nucleated depends on the parity of the alkyl chain.

Single crystal x-ray diffraction analyses of the 2:1 complexes of phenazine with hydroquinone and 1,5-dihydroxynaphthalene and the 3:1 complex of phenazine with 4,4'-dihydroxybiphenyl were performed. In these complexes and also in the 3:1 complex of phenazine with 5,10-dihydrophenazine, phenazine forms a host framework consisting of 1-dimensional channels. The variation of guest mols. and attendant variations in the H bond patterns, and the reproducibility of phenazine mol. stacks are described. Crystallog. data are given.

Crystal structures of methyl-, 2,3-, 2,5- and 2,6-dimethyl-, and trimethylpyrazine (2–6) have been determined by X-ray diffraction analysis. Four of these compounds (2–4 and 6) are liquids and their single crystals have been grown in situ on the diffractometer using a miniature zone melting procedure. These structures are analysed together with those of pyrazine (1) and tetramethylpyrazine (7) in the context of C–H···N interactions. Compounds 1–7 were chosen because they contain only C, H and N atoms, and also C–H groups of variable acidity. This facilitates the comparison of C–H···N geometries with respect to the C–H group acidity. Compounds 1 and 2 are dominated by sp2 C–H groups in their molecules and their supramolecular structures are generated by sp2 C–H···N. On the other hand the domination of sp3 C–H groups at the molecular level in 6 and 7 results in crystal structures that are governed by sp3 C–H···N. A balance of sp2 and sp3 C–H groups in the dimethyl derivatives 3–5 leads to a situation where both kinds of C–H groups play a structure directing role. While the sp2 C–H groups form C–H···N, the sp3 C–H groups are involved in C–H···π interactions. Thus the C–H group interactions follow a property unique to hydrogen bonds—stronger donors interact with stronger acceptors while weaker donors approaching weaker acceptors. Inter-structural comparison revealed that H···N distances decrease with increasing C–H acidity and therefore C–H···N interactions could be considered as weak hydrogen bonds.

Phenazine (1) and 5,10-dihydrophenazine (2) form not only a 1:1 complex (3), as expected from N–H···N hydrogen bond requirements, but surprisingly also a 3:1 complex (4). Single crystal X-ray analyses of compound 2 and complexes 3 and 4 have been carried out. While the overall packing in complex 3 is as efficient as in pure 1 and 2, acidic C–H groups, which contribute actively to the structural assembly in pure 2, are not involved in hydrogen bonding in 3. It is shown that the quest for hydrogen bonding by these C–H groups steers the formation of complex 4 with an unprecedented N–H···N and C–H···N hydrogen bond mediated tape structure.

The ability of CH3 groups to form helical chains of C–H‥π interactions with phenyl rings leads to polar stacking of trigonal octupolar networks in a substituted triazine, and therefore to three-dimensional non-centrosymmetry.

Ethynylpyridines show straight and zigzag chain patterns formed by ⋮C−H···N hydrogen bonds; cross-stitching of zigzag chains by C−H···N hydrogen bonds leads to two-dimensional networks with predictable topology in 5-ethynylpyrimidine.

The existence and nature of C−H···F−C interactions in crystalline fluorobenzenes 1−3 and 7−10 are discussed. These compounds were chosen because they contain only C, H, and F atoms; this is necessary in the evaluation of the weak acceptor capabilities of the C−F group. All of these compounds are liquids at room temperature, and single crystals for X-ray diffraction were grown in situ. The analysis of the C−H···F interactions that are found in all of these crystal structures takes the form of comparisons with related C−H···O/C−H···N analogues. Fluorobenzene, 1, bears a close relationship to pyridinium fluoride, pyridine 1-oxide, and benzonitrile at the level of individual interactions, showing that the character of the structure-determining intermolecular interactions in these four crystal structures are the same. Similarly, 1,4-difluorobenzene, 3, and 1,4-benzoquinone are related, the C−H···F interactions in the former playing the same structural role as the C−H···O interactions in the latter. A compariso...

The title compound has a C–H···O hydrogen bond-mediated trigonal network structure that leads to octupolar NLO behaviour in the solid state.

Trimethylisocyanurate 2 and 1,3,5-trinitrobenzene 3 form a hexagonal C–H ⋯ O mediated 1:1 complex wherein distinct molecular layers are formed, the molecular symmetry of the components being retained in the crystal.