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The ability to predict and control the assembly of molecular and ionic species into ordered networks is becoming an important target area in chemistry, biochemistry and materials science. In this context, the selectivity and directionality of the hydrogen bond have been instrumental in the preparation of distinctive structural aggregates, and the use of hydrogen bonding as a steering force is now emerging as the most important strategy in crystal engineering. A reliable supramolecular synthetic protocol also requires access to a wide range of reactions that are versatile, selective and give rise to high supramolecular yields. Through a systematic structural study we have examined three issues that are relevant to the development of transferable supramolecular synthesis; (a) structural invariance to molecular isomerism; (b) hierarchy of synthons based upon competition between intermolecular forces and (c) changes in supramolecular yield as a function of molecular substitution.

A new family of supramolecular reagents based upon [(benzimidazol-1-yl)methyl]-benzamides and geared toward the assembly of binary and ternary cocrystals have been synthesized and characterized. Single-crystal structure determinations of four of these compounds demonstrate that the carboxamide moieties engage in either dimeric or catemeric self-complementary hydrogen bonds, as well as in a N−H···N hydrogen bond involving the anti proton of the amide moiety (the hydrogen-bond donor) and a heterocyclic nitrogen atom (the hydrogen-bond acceptor). The crystal structures of two binary cocrystals illustrate that [(benzimidazol-1-yl)methyl]-benzamides are capable of coexisting within a crystalline lattice with a suitable partner, and this fact, coupled with their wide ranging solubility, makes them into versatile and, potentially, very useful supramolecular reagents.

A conformationally flexible tris-carboxylic acid has been employed in the construction of several co-crystals involving a variety of ditopic N-heterocyclic hydrogen-bond acceptors.

The supramolecular reactions between symmetric ditopic imidazoles/benzimidazoles and a variety of aliphatic and aromatic dicarboxylic acids produced molecular cocrystals 1−8 in high yields. Despite variations in molecular shape and substituent groups on the ditopic bases, each structure contained infinite 1-D molecular chains held together by robust, primary O−H···N hydrogen bonds. Secondary C−H···O interactions existed within these motifs as well as between neighboring chains, and it seems that intra- and interchain interactions are of equal structural importance based upon an analysis of the metrics displayed by each set of interactions. This study demonstrates that neutral hydrogen-bond interactions between imidazole/benzimidazoles (acting as the acceptor sites) and carboxylic acids (acting as the donor sites) provide sufficient driving force for the directed assembly of a wide range of binary cocrystals.

On the basis of a combination of new structural data (eleven single-crystal structure determinations are presented) and information from the Cambridge Structural Database, it has been shown that self-complementary hydrogen-bond based amide...amide dimers can be relied upon as effective supramolecular synthons for the assembly and organization of acac- and paddle-wheel complexes of a variety of metal(II) ions. The targeted molecular recognition event and intended extended one-dimensional motif appear with a supramolecular yield of 78% (a total of 28 structures were examined). Despite the fact that the hydrogen bonds that give rise to the R2(2)(8) motif can be disrupted by both carboxylate- and acac-ligands, as well as by solvent molecules, they remain remarkably resilient and therefore represent useful synthetic tools in inorganic crystal engineering.

A series of ligands that utilize five-membered N-heterocycles as coordination sites, and the self-complementarity of the carboxamide functionality, have been employed in the supramolecular synthesis of Ag(I)-based extended networks. The crystal structures of eight compounds are reported: bis[4-(2-methylbenzimidazol-1-yl)methylbenzamide]silver(I) tetrafluoroborate hydrate methanol, 1; bis[3-(2-methylbenzimidazol-1-yl)methylbenzamide]silver(I) tetrafluoroborate, 2; bis[4-(5,6-dimethylbenzimidazol-1-yl)methylbenzamide]silver(I) tetrafluoroborate, 3; bis[4-(2-methylbenzimidazol-1-yl)methylbenzamide]silver(I) hexafluoroarsenate methanol, 4; bis[3-(2-methylbenzimidazol-1-yl)methylbenzamide]silver(I) hexafluoroarsenate methanol(0.5), 5; bis[4-(5,6-dimethylbenzimidazol-1-yl) methylbenzamide]silver(I) hexafluoroarsenate, 6; bis[4-(2-methylbenzimidazol-1-yl)methylbenzamide]silver(I) hexafluoroantimonate, 7; and bis[3-(2-methylbenzimidazol-1-yl)methylbenzamide]silver(I) hexafluoroantimonate, 8. An analysis of motifs and structural patterns that result from the primary intermolecular interactions in these structures, reveals that this family of ligands is capable of providing quite reliable means for propagating the linear geometry of the complex ions into extended 1-D architectures via ligand-ligand, N-H...O, hydrogen-bond interactions.

The design and modular synthesis of three ternary co-crystals with desired connectivity, assembled using tailor-made pyridyl/benzimidazol-1-yl-based supramolecular reagents, are described.