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.

We have synthesized [Pt(CN-iso-C3H7)4][M(CN)4] (M = Pt, Pd) and studied their reversible hydration and sorption properties with UV−vis, FT-IR spectroscopy, and X-ray diffraction. Powder diffraction studies show that anhydrous [Pt(CN-iso-C3H7)4][Pt(CN)4] and [Pt(CN-iso-C3H7)4][Pd(CN)4] crystallize in a tetragonal space group with nearly identical lattice constants. Gravimetric studies reveal that variable guest−host stoichiometries occur when solid [Pt(CN-iso-C3H7)4][Pt(CN)4] sorbs the guest at room temperature from the gas phase [water, 12.1(1) molecules per formula unit, chloroform 6.0(1), methanol 8.0(1), and trifluoroethanol 4.1(1)]; these sorption processes are reversible. The unit cell distances in the tetragonal ab-plane expand dramatically when the solvent guests are sorbed, but changes along the c-axis (the M−M direction) are minimal. Crystallization of [Pt(CN-iso-C3H7)4][Pt(CN)4] from water gives monoclinic crystals of a hexadecahydrate [Pt(CN-iso-C3H7)4][Pt(CN)4]·16H2O. This salt consists of alt...

Structural Investigations of Vapochromic Behavior. X-ray Single-Crystal and Powder Diffraction Studies of [Pt(CN-iso-C3H7)4][M(CN)4] for M = Pt or Pd

To test the approach of combining both ionic and hydrogen-bonding
interactions for the design of non-linear optical (NLO) materials, a
number of phenol–pyridine co-crystals have been synthesized and
their NLO properties investigated. The co-crystals are characterized by
second harmonic generation measurements as well as the more conventional
methods of melting point measurements, infrared and nuclear magnetic
resonance spectroscopy. To investigate whether the phenol co-crystals are
organic salts, the 2-methoxy-4-nitrophenol–4-(dimethylamino)pyridine
(2:1) co-crystal 6 and the
2-methoxy-4-nitrophenol–4-pyrrolidinylpyridine–water (1:1:1)
co-crystal 8 are further characterized by X-ray single-crystal
diffraction. Crystal structure analyses reveal that both 6 and 8 are ionic
co-crystals (or organic salts) composed of a phenoxide anion, a pyridinium
cation and a neutral molecule. In the two co-crystals, the phenoxide,
pyridinium and neutral molecules are held together by ionic attractions as
well as hydrogen-bonding interactions. Both 6 and 8 crystallize in
non-centrosymmetric structures [Pna2
 1
 (orthorhombic),
a=6.880(4), b=38.40(1), c=8.454(3) A,
Z=4, D
 c
=1.369 g cm
 -3
 and
R=0.051 for 6 and Cc (monoclinic), a=7.302(3),
b=23.518(2), c=9.940(1) A,
β=107.12(2)°, Z=4, D
 c
=1.365
g cm
 -3
 and R=0.036 for 8]. In addition to X-ray
structure determination, it is possible to predict whether
phenol–pyridine co-crystals are organic salts based on the
ΔpK
 a

[pK
 a
(pyridine)-pK
 a
(phenol)]
and stoichiometric ratio of the co-crystals. Preliminary results suggest
that this type of co-crystals, particularly for the ionic co-crystals, may
have a higher chance of forming non-centrosymmetric structures than the
normal achiral organic compounds.

A novel class of phenol–pyridine co-crystals for secondharmonic generation

differences are more reasonable since the detailed shapes of the chains are considerably different. Some of the distances between non-bonded atoms are shown in Figs. 1-3. There are no unusually short distances between chains; the short (3.6-3.8 A) CH3. .CH3 distance along the vertical axis in the lower view in each figure is not short if C. • • H and H. • • H distance are considered rather than using an average radius for the methyl group. The one non-bonded distance that is slightly short is the 3.68 A distance between CH3 groups on adjacent acetylacetonate rings; this short distance plus the longer 2.95 A T1. . . O distances suggest that steric crowding might be beginning to be important in the geometry of the polymer. It was this observation that led us to look at the dibenzoylmethide where the ring methyl groups are replaced by phenyl groups. As described in the Experimental section the structure of dimethylthallium dibenzoylmethide was not studied in detail. It was carried to the point where the thallium atoms were exactly located and the light atoms were approximately located. The thallium atoms occur in pairs about 4-1 A apart, i.e. about the same distance apart as in the polymer chains in the other structures. This indicates that molecules occur as dimers rather than as infinite polymers. There are two independent dimer molecules in the unit cell. The light atom positions, except for the phenyl ring orientations, are about the same in both dimers, and are about the same as they are in a dimeric fragment of the acetylacetonate structure. It is clear from looking at the latter structure (Fig. 3) that the replacement of methyls by phenyls should block polymerization beyond the dimer.

The crystal structures of dimethylthallium tricyanomethide and dimethylthallium dicyanamide

A new synthetic procedure developed recently in our laboratories has made possible the synthesis of variety of new complexes of CuCN with diamines. Synthesis was effected by adding the ligand to a ...

Crystal Structures of a Series of Complexes Produced by Reaction of Copper(I) Cyanide with Diamines.

The syntheses and crystal structures of a family of silver cyanide complexes of thiourea and substituted thioureas are reported. The sulfur ligands include thiourea (tu), 1-methyl-2-thiourea (mtu), 1,3-dimethyl-2-thiourea (dmtu), 1,1,3,3-tetramethyl-2-thiourea (tmtu), and 2-imidazolidinethione (N,N‘-ethylenethiourea, etu). Synthesis was effected by dissolving AgCN in an aqueous solution of ligand. Two different complexes were obtained by the reaction of AgCN with tu. Complex 1a:  (AgCN)(tu), monoclinic, P21/c, a = 9.3851 (6) A, b = 8.2782 (5) A, c = 7.1178 (5) A, β = 94.591 (1)°, and Z = 4. Complex 1b:  (AgCN)(tu)2, triclinic, P1, a = 7.9485 (14) A, b = 9.431 (2) A, c = 12.771 (2) A, α = 85.695 (3)°, β = 81.210 (4)°, γ = 77.987 (2)°, and Z = 4. Complex 2:  (AgCN)(mtu), triclinic, P1, a = 4.113 (2) A, b = 9.472 (4) A, c = 9.679 (4) A, α = 113.918 (5)°, β = 98.188 (6)°, γ = 97.725 (6)°, and Z = 2. Complex 3 (AgCN)2(dmtu)2, monoclinic, P21/m, a = 7.1482 (7) A, b = 14.776 (2) A, c = 7.3366 (7) A, β = 92.418...

Doyle Britton

Papers

Structural Investigations of Vapochromic Behavior. X-ray Single-Crystal and Powder Diffraction Studies of [Pt(CN-iso-C3H7)4][M(CN)4] for M = Pt or Pd

A novel class of phenol–pyridine co-crystals for secondharmonic generation

The crystal structures of dimethylthallium tricyanomethide and dimethylthallium dicyanamide

Crystal Structures of a Series of Complexes Produced by Reaction of Copper(I) Cyanide with Diamines.

Crystal Structures of a Family of New Copper(I) Cyanide Complexes of Thiourea and Substituted Thioureas.