J. Appl. Cryst.の発刊に際して

The halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. In this fairly extensive review, after a brief history of the interaction, we will provide the reader with a snapshot of where the research on the halogen bond is now, and, perhaps, where it is going. The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design.

The Halogen Bond

Publisher Summary This review is concerned with the neglected class of inorganic compounds, which contain ions of the same element in two different formal states of oxidation. Although the number of references cited in our review show that many individual examples of this class have been studied, yet they have very rarely been treated as a class, and there has never before, to our knowledge, been a systematic attempt to classify their properties in terms of their electronic and molecular structures. In the past, systems containing an element in two different states of oxidation have gone by various names, the terms “mixed valence,” nonintegral valence,” “mixed oxidation,” “oscillating valency,” and “controlled valency” being used interchangeably. Actually, none of these is completely accurate or all-embracing, but in our hope to avoid the introduction of yet another definition, we have somewhat arbitrarily adopted the phrase “mixed valence” for the description of these systems. The concept of resonance among various valence bond structures is one of the cornerstones of modern organic chemistry.

Mixed Valence Chemistry-A Survey and Classification

Crystal polymorphism is encountered in all areas of research involving solid substances. Its occurrence introduces complications during manufacturing processes and adds another dimension to the complexity of designing materials with specific properties. Research on polymorphism is fraught with unique difficulties due to the subtlety of polymorphic transformations and the inadvertent formation of pseudopolymorphs. In this report, a summary of thermodynamic, kinetic and structural considerations of polymorphism is presented. A wide variety of techniques appropriate to the study of organic crystalline polymorphism and pseu-dopolymorphism is then surveyed, ranging from simple crystal density measurement to observation of polymorphic transformations using variable-temperature synchrotron X-ray diffraction methods. Application of newer methodology described in this report is yielding fresh insights into the nature of the crystallization process, holding promise for a deeper understanding of the phenomenon of polymorphism and its practical control.

Crystalline Polymorphism of Organic Compounds

Dendrimers in Supramolecular Chemistry: From Molecular Recognition to Self-Assembly.

The title compound, C7H3F2N, packs with slightly puckered molecular sheets [mol­ecules tilted by 8.1 (1)° with respect to the sheets]. Two of the H atoms in the mol­ecule are in contact with N atoms in adjacent mol­ecules, while the remaining H atom is in contact with two F atoms in adjacent molecules.

3,5-Di­fluoro­benzo­nitrile

p-Di­cyano­benzene and p-diiso­cyano­benzene are not isomorphous. The title compound, C8H4N2, is isomorphous with p-di­cyano­benzene. The mol­ecule lies on a center of symmetry and is end-for-end disordered. The bond lengths and angles lie within normal ranges, but the precise values are obscured by the disorder.

p‐Iso­cyano­benzo­nitrile

p-Decyl­phenyl isocyanide, p-C10H21–C6H4–NC or C17H25N, and p-decyl­benzo­nitrile, p-C10H21–C6H4–CN or C17H25N, are isomorphous. The mol­ecules lie in mirror planes, with the C6 rings perpendicular to the mirror. The packing of both mol­ecules includes an aliphatic region, with close to ideal packing of the C10H21 chains, and an aromatic region, with phenyl ring–CN interactions. In addition, the CN ends of the mol­ecules are also involved in a CN⋯NC dipolar interaction.

p-Decylphenyl isocyanide and p-decylbenzonitrile: isomorphous isonitrile/nitrile isomers.

2,6-Difluorobenzonitrile packs in slightly puckered molecular sheets (mol­ecules tilted 4.1 (2)° with respect to the sheets). All of the H atoms in the mol­ecule are in contact with N and F atoms in adjacent mol­ecules in the sheet.

2,6-Difluorobenzonitrile

4,4′-Di­cyano­bi­phenyl, C14H8N2, has a normal structure with a twist angle of 31.8 (2)°. The mol­ecules stack with overlapping π systems and form chains held together by antiparallel C—N⋯C—N interactions. In addition, there are a number of C—H⋯N interactions.

Doyle Britton

Papers

3,5-Difluorobenzonitrile

p‐Isocyanobenzonitrile

p-Decylphenyl isocyanide and p-decylbenzonitrile: isomorphous isonitrile/nitrile isomers.

2,6-Difluorobenzonitrile

4,4′-Dicyanobiphenyl

Doyle Britton

Papers

3,5-Di­fluoro­benzo­nitrile

p‐Iso­cyano­benzo­nitrile

p-Decylphenyl isocyanide and p-decylbenzonitrile: isomorphous isonitrile/nitrile isomers.

2,6-Difluorobenzonitrile

4,4′-Dicyanobiphenyl

3,5-Difluorobenzonitrile

p‐Isocyanobenzonitrile