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.

Nitrilotrismethylenetri-2-pyridinium perchlorate, C18H21N4(3+).3C1O4-, Mr = 591.74, cubic, P2(1)3, a = 13.289 (3) A, V = 2347 (2) A 3, Z = 4, Dx = 1.675 (2) g cm-3, lambda(Mo K alpha) = 0.71069 A, mu = 4.60 cm-1, F(000) = 1216, T = 189 (3) K, R = 0.056 for 1073 unique observed reflections with I greater than sigma(I). All four ions lie on threefold axes. The perchlorate ions are nearly regular tetrahedra. The bond lengths and angles in the ions are normal. As the name implies, the cation is protonated on the pyridine N atoms and not on the amine N atom. Each H atom attached to an N atom is part of a three-centered hydrogen bond in which the H-atom acceptors are O atoms on two different perchlorate ions.

Tris[(2-pyridinium)methyl]amine perchlorate.

Trichlorotricyanobenzene-mesitylene (1/1) is monoclinic, space group P21/n; at −88°Ca=10.509(3),b=14.863(7),c=11.518(3) A, β=99.38(2)0,V=1775(2) A3,D
 x
 =1.409(2) g cm−3,Z=4. Trichlorotricyanobenzene-benzene (1/3) is hexagonal, space group
 
$$P\bar 6$$

 ; at −99°Ca=17.3914(3),c=7.2673(1) A,V=1903.6(1) A3,D
 x
 =1.2844(1) g cm−3,Z=3. In both complexes there are stacks of alternating trichlorotricyanobenzene and hydrocarbon molecules. In both complexes there are sheets of molecules perpendicular to the stacks. In the mesitylene complex these sheets contain equal numbers of both kinds of molecules with the trichlorotricyanobenzene molecules arranged in tapes. In the benzene complex the sheets contain only one kind of molecule or the other. The sheets containing the trichlorotricyanobenzene molecules have approximately linear C−N...Cl−C intermolecular interactions with N...Cl distances about 3.02 a.

1,3,5-trichlorotricyanobenzene complexes with mesitylene (1/1) and benzene (1/3)

The title compound, C 12 H 12 N 2 O 3 , is composed of a nitroanilino moiety and a cyclic α,β-unsaturated ketone moiety. The nitro group is oriented anti to the carbonyl group and the cyclic ketone ring is in a puckered conformation with C9 as the out-of-plane atom. The shortened C11-N2 and C7-C12 bond lengths suggest that the amino group is conjugated with the α,β-unsaturated ketone group. Intermolecular hydrogen bonds between the carbonyl O atom and the amino group link the molecules into infinite chains [N-H 0.88(3), H...O i 1.98 (3), N...O i 2.858 (3) A, N-H...O i 175 (1)° ; symmetry code : (i) 1+x,y,z].

3‐(3‐Nitroanilino)cyclohex‐2‐en‐1‐one: an Unexpected Product from the Co‐Crystallization of m‐Nitroaniline with 1,3‐Cyclohexanedione

2,3,5,6-Tetra­chloro­benzene-1,4-dicarbonitrile forms alternate π-stacked 1:1 complexes with pyrene, C8Cl4N2·C16H10, and phenanthrene, C8Cl4N2·C14H10. These complexes are pseudo-isomorphs. Phenanthrene, disordered about a centre of symmetry, takes the position of the pyrene, which sits exactly on this centre of inversion. The tetra­chloro­benzene­di­car­bo­nitrile mol­ecules in each complex also sit on centres of inversion and are in similar positions within the unit cells in the two structures, except that the orientation of the nitrile groups differs between the two.

1:1 complexes of 2,3,5,6-tetrachlorobenzene-1,4-dicarbonitrile with pyrene and phenanthrene: pseudo-isomorphs.

The title crystals, C7H2I3N, are isomorphous. Both mol­ecules lie across two crystallographic mirror planes and a twofold axis. The principal supra­molecular inter­action is centric R22(10) CN/NC⋯I short contacts involving both ortho I atoms, with two contacts bis­ecting each cyano and iso­cyano group. These form ribbons along [010] and give rise to a planar sheet structure parallel to (100). All pairs of adjacent sheets have centric stacking, a mode not previously reported for sheets of this type. This study completes the series of homo-2,4,6-trihalobenzo­nitriles, in which I atoms give the strongest CN⋯X and NC⋯X inter­actions (X = F, Cl, Br, I).

https://journals.iucr.org/e/issues/2018/02/00/lh5864/lh5864.pdf

Doyle Britton

Papers

Tris[(2-pyridinium)methyl]amine perchlorate.

1,3,5-trichlorotricyanobenzene complexes with mesitylene (1/1) and benzene (1/3)

3‐(3‐Nitroanilino)cyclohex‐2‐en‐1‐one: an Unexpected Product from the Co‐Crystallization of m‐Nitroaniline with 1,3‐Cyclohexanedione

1:1 complexes of 2,3,5,6-tetrachlorobenzene-1,4-dicarbonitrile with pyrene and phenanthrene: pseudo-isomorphs.

Crystal structures of 2,4,6-triiodobenzonitrile and 2,4,6-triiodophenyl isocyanide

Doyle Britton

Papers

Tris[(2-pyridinium)methyl]amine perchlorate.

1,3,5-trichlorotricyanobenzene complexes with mesitylene (1/1) and benzene (1/3)

3‐(3‐Nitroanilino)cyclohex‐2‐en‐1‐one: an Unexpected Product from the Co‐Crystallization of m‐Nitroaniline with 1,3‐Cyclohexanedione

1:1 complexes of 2,3,5,6-tetrachlorobenzene-1,4-dicarbonitrile with pyrene and phenanthrene: pseudo-isomorphs.

Crystal structures of 2,4,6-tri­iodo­benzo­nitrile and 2,4,6-tri­iodo­phenyl isocyanide

Crystal structures of 2,4,6-triiodobenzonitrile and 2,4,6-triiodophenyl isocyanide