From molecules to crystal engineering: supramolecular isomerism and polymorphism in network solids.

The hydrogen bond is the most important of all directional intermolecular interactions. It is operative in determining molecular conformation, molecular aggregation, and the function of a vast number of chemical systems ranging from inorganic to biological. Research into hydrogen bonds experienced a stagnant period in the 1980s, but re-opened around 1990, and has been in rapid development since then. In terms of modern concepts, the hydrogen bond is understood as a very broad phenomenon, and it is accepted that there are open borders to other effects. There are dozens of different types of X-H.A hydrogen bonds that occur commonly in the condensed phases, and in addition there are innumerable less common ones. Dissociation energies span more than two orders of magnitude (about 0.2-40 kcal mol(-1)). Within this range, the nature of the interaction is not constant, but its electrostatic, covalent, and dispersion contributions vary in their relative weights. The hydrogen bond has broad transition regions that merge continuously with the covalent bond, the van der Waals interaction, the ionic interaction, and also the cation-pi interaction. All hydrogen bonds can be considered as incipient proton transfer reactions, and for strong hydrogen bonds, this reaction can be in a very advanced state. In this review, a coherent survey is given on all these matters.

The hydrogen bond in the solid state.

Encoding and decoding hydrogen-bond patterns of organic compounds

Molecular self-assembly is the spontaneous association of molecules under equilibrium conditions into stable, structurally well-defined aggregates joined by noncovalent bonds. Molecular self-assembly is ubiquitous in biological systems and underlies the formation of a wide variety of complex biological structures. Understanding self-assembly and the associated noncovalent interactions that connect complementary interacting molecular surfaces in biological aggregates is a central concern in structural biochemistry. Self-assembly is also emerging as a new strategy in chemical synthesis, with the potential of generating nonbiological structures with dimensions of 1 to 10(2) nanometers (with molecular weights of 10(4) to 10(10) daltons). Structures in the upper part of this range of sizes are presently inaccessible through chemical synthesis, and the ability to prepare them would open a route to structures comparable in size (and perhaps complementary in function) to those that can be prepared by microlithography and other techniques of microfabrication.

https://science.sciencemag.org/content/sci/254/5036/1312.full.pdf

Molecular self-assembly and nanochemistry: a chemical strategy for the synthesis of nanostructures.

Molecular self-assembly and nanochemistry: A chemical strategy for the synthesis of nanostructures

Second order non-linear optical (NLO) effects, such as second harmonic generation, occur only in materials that are acentric. Finding ways to assure that a bulk material is acentric has been a serious hurdle in the design of new organic materials for non-linear optical uses.1 A trivial, albeit useful, solution to the symmetry problem is to use chiral molecules which necessarily crystallize in acentric structures.2 The general solution to the problem involves understanding how to promote self-assembly of molecules, regardless of their molecular symmetry, into acentric arrays. We have found a partial answer to the asymmetric self-assembly question using intermolecular hydrogen bonds.

Using Hydrogen Bonds to Design Acentric Organic Materials for Nonlinear Optical Users

Etude cristalline de deux formes polymorphes; dans les deux cas, les ions cyanine et oxonol forment des empilements avec les axes moleculaires des ions presque orthogonaux dans une forme, et paralleles dans l'autre

Solid-state chemistry and structures of a new class of mixed dyes. Cyanine-oxonol

Crystal structures of all available unblocked linear peptides with two to five residues were retrieved from the Cambridge Structural Database and their intermolecular contacts and packing modes studied using molecular graphics. This survey reveals that interactions between hydrophobic portions of the molecules are critically important in determining the overall features of their crystal packing patterns. Distinct hydrophobic columns or layers are observed in almost all crystal structures. Analyses of the relationships between these interactions and crystal growth properties of small peptides are given. It is suggested that needle growth is promoted by hydrophobic packing, usually along a short crystallographic axis (4.6-6.0 angstroms). Also contributing to these morphologic characteristics are entropic factors associated with hydrophobic aggregation as well as tightly bound water molecules on hydrophobic faces. The paper also provides a comprehensive overview of hydrogen bond patterns in acyclic peptide crystals. It is demonstrated that one of their primary roles is to provide a scaffolding within which hydrophobic groups can aggregate. Even though there is a high density of hydrogen bonds in the crystals, often with complex patterns and networks, certain motifs are found to recur in a number of structures indicating specific hydrogen bond preferences. Water, for example, is an integral part of the hydrogen bond networks in these crystals, usually acting as the primary donor for main-chain carboxylate groups in peptide hydrates.

Hydrogen bond connectivity patterns and hydrophobic interactions in crystal structures of small, acyclic peptides

Hydrogen-Bond Patterns in Several 2:1 Amine-Phenol Cocrystals

Hydrogen bond geometries as well as their stereochemical preferences have been compared for 255 small molecule carboxylate structures retrieved from the Cambridge Structural Database. A total of 974 independent hydrogen bonds were analysed. Hydrogen atoms cluster in the carboxylate lone-pair directions with no tendency to adopt a central, symmetric position between the two oxygens. The long, secondary H ⋯ O contacts of asymmetric syn hydrogen bonds do not affect either the overall geometries of the interactions or the total syn/anti distribution of accepted H-atoms, presumably due to very unfavourable CO ⋯ H angles. On this basis it is suggested that syn hydrogen bonds to carboxylates should be regarded most frequently as two-centre rather than three-centre (bifurcated) interactions. The statistical data also show that criteria traditionally used to infer three-centre hydrogen bonds are inadequate for carboxylate acceptors.

Margaret C. Etter

Papers

Using Hydrogen Bonds to Design Acentric Organic Materials for Nonlinear Optical Users

Solid-state chemistry and structures of a new class of mixed dyes. Cyanine-oxonol

Hydrogen bond connectivity patterns and hydrophobic interactions in crystal structures of small, acyclic peptides

Hydrogen-Bond Patterns in Several 2:1 Amine-Phenol Cocrystals

Hydrogen bonds to carboxylate groups. The question of three-centre interactions