A Potentially Limitless Chiral Pool via Conglomerate Crystallisation: Unidentified Spontaneous Resolution in the CSD.

Conglomerate crystallisation is the behaviour responsible for spontaneous resolution and the discovery of molecular chirality by Pasteur. The phenomenon of conglomerate crystallisation of chiral organic molecules has been left largely undocumented and offers synthetic chemists a potential new chiral pool not reliant on biological systems to supply stereochemical information. While other crystallographic behaviours can be interrogated by automated searching, conglomerate crystallisations are not identified within the Cambridge Structural Database (CSD) and are therefore not accessible by conventional means. By conducting a manual search of the CSD, a list of over 1,700 chiral species capable of conglomerate crystallisation was curated by inspection of the synthetic routes described in each publication. The majority of these are produced by synthetic chemists who seldom note and rarely exploit the implications this phenomenon can have on the enantioenrichment of their crystalline materials. We propose that this list represents a limitless chiral pool which will continually grow in size as more conglomerate crystals are synthesised and recorded.

The extensive solid-form landscape of sulfathiazole: geometrical similarity and interaction energies

A set of 96 crystal structures containing sulfathiazole (SLFZ) is presented, comprising 52 new crystal structures and 39 structures retrieved from the Cambridge Structural Database. The set comprises five polymorphs,...

Kilobytes of kilopascals: high-pressure depositions of the Cambridge Structural Database

The Cambridge Structural Database (CSD) is the largest repository of crystal structures of organic and metal–organic compounds, containing over 1.1 million entries. Over 3300 of the deposits are structures determined under high pressure, with the number being strongly affected by the experimental requirements of the high-pressure techniques. Nevertheless, it still presents a population sufficiently representative for statistical data mining. In this work, an in-depth analysis of this population is presented, showing where contributors of high-pressure depositions come from, which journals high-pressure structures are published in, and also providing information on some trends in high-pressure crystallography and how they have changed over the years elucidated from data collected in the CSD. The ultimate goal of this article is to bring the high-pressure crystallography content in the CSD to a wider audience of scientists.

Understanding distortions of inorganic substructures in chloridobismuthates(III)

The molar ratio variations of organic and inorganic reactants of chloridobismuthates(III) with N,N-dimethylethane-1,2-diammonium, [(CH3)2NH(CH2)2NH3]2+, and N,N,N′,N′-tetramethylguanidinium, [NH2C{N(CH3)2}2]+, cations lead to the formation of four different products, namely, tris(N,N-dimethylethane-1,2-diammonium) bis[hexachloridobismuthate(III)], [(CH3)2NH(CH2)2NH3]3[BiCl6]2 (1), catena-poly[N,N-dimethylethane-1,2-diammonium [[tetrachloridobismuthate(III)]-μ-chlorido]], {[(CH3)2NH(CH2)2NH3][BiCl5]} n (2), tris(N,N,N′,N′-tetramethylguanidinium) tri-μ-chlorido-bis[trichloridobismuthate(III)], [NH2C{N(CH3)2}2]3[Bi2Cl9] (3), and catena-poly[N,N,N′,N′-tetramethylguanidinium [[dichloridobismuthate(III)]-di-μ-chlorido]], {[NH2C{N(CH3)2}2][BiCl4]} n (4). The hybrid crystals 1–4, containing relatively large but different organic cations, are composed of four distinct anionic substructures. They are built up from isolated [BiCl6]3− octahedra in 1, from face-sharing bioctahedral [Bi2Cl9]3− units in 3, from polymeric corner-sharing {[BiCl5]2−} n chains in 2 and from edge-sharing {[BiCl4]−} n chains in 4. The distortions shown by the single [BiCl6]3− polyhedra in 1–4 are associated with intrinsic interactions within the anionic substructures and the organic...inorganic substructures interactions, namely, N/C—H...Cl hydrogen bonds. The first factor is the stronger, which is evident in comparison of the experimentally determined geometrical and calculated distortion parameters for the isolated octahedron in 1 to the more complex inorganic substructures in 2–4. The formation of N—H...Cl hydrogen bonds, in terms of their number and strength, is favoured for 1 and 3 containing relatively easily accessed hydrogen-bond acceptors of isolated [BiCl6]3− and [Bi2Cl9]3− units. The studies of the deviations from regularity of the [BiCl6]3− octahedra within inorganic substructures were supported by a survey of the Cambridge Structural Database, which confirmed the role played by different factors in the variations in geometry of the inorganic anions.

UNUSUAL TYPES OF LAYERED ORGANIC CRYSTAL HYDRATES

In molecular crystalline hydrates with a high content of crystallization water infinite H2O...OH2 nets or finite fragments of such nets are formed. As a rule, these nets contain 5- and 6-membered cycles (H2O)n. Brand new topological types of layered organic crystal hydrates among the structures included in the Cambridge Structural Database in 2009–2019 were found and investigated. The discovered nets were deposited to the Topological Types Database. Topological characteristics of new nets are described, in particular, the maximum possible symmetry, information indices, vertex, edge and face transitivity of the nets

Zinc(II) and nickel(II) complexes of 3,5-dimethyl-1-(pyridin-2-yl)-1H-pyrazole: relationship between fluorescence and crystal packing

Two novel coordination complexes, namely, dichlorido[3,5-dimethyl-1-(pyridin-2-yl-κN)-1H-pyrazole-κN 2]zinc(II), [ZnCl2(C10H11N3)], 1, and aquachloridobis[3,5-dimethyl-1-(pyridin-2-yl-κN)-1H-pyrazole-κN 2]nickel(II) chloride monohydrate, [NiCl(C10H11N3)(H2O)]Cl·H2O, 2, have been synthesized. The crystal structure analyses revealed that complexes 1 and 2 are mononuclear and have ZnN2Cl2 distorted tetrahedral and NiN4OCl distorted octahedral structures, respectively. Complex 1 displays a dimer in the crystal structure, while complex 2 forms a chain along the [010] direction. The fluorescence properties of both complexes were also investigated. A search of the Cambridge Structural Database for other complexes of the ligand 3,5-dimethyl-1-(pyridin-2-yl)-1H-pyrazole (L) shows that there exist different coordination polyhedra with different arrangements as monomers, dimers and polycyclic structures. Here it has also been demonstrated that there is a relationship between the crystal packing and the fluorescence properties of ZnII and CdII complexes of L.

A survey of thermal expansion coefficients for organic molecular crystals in the Cambridge Structural Database

Typical ranges of thermal expansion coefficients are established for organic molecular crystals in the Cambridge Structural Database. The CSD Python API is used to extract 6201 crystal structures determined close to room temperature and at least one lower temperature down to 90 K. The data set is dominated by structure families with only two temperature points and is subject to various sources of error, including incorrect temperature reporting and missing flags for variable-pressure studies. For structure families comprising four or more temperature points in the range 90–300 K, a linear relationship between unit-cell volume and temperature is shown to be a reasonable approximation. For a selected subset of 210 structures showing an optimal linear fit, the volumetric expansion coefficient at 298 K has mean 173 p.p.m. K−1 and standard deviation 47 p.p.m. K−1. The full set of 6201 structures shows a similar distribution, which is fitted by a normal distribution with mean 161 p.p.m. K−1 and standard deviation 51 p.p.m. K−1, with excess population in the tails mainly comprising unreliable entries. The distribution of principal expansion coefficients, extracted under the assumption of a linear relationship between length and temperature, shows a positive skew and can be approximated by two half normal distributions centred on 33 p.p.m. K−1 with standard deviations 40 p.p.m. K−1 (lower side) and 56 p.p.m. K−1 (upper side). The distribution for the full structure set is comparable to that of the test subset, and the overall frequency of biaxial and uniaxial negative thermal expansion is estimated to be < 5% and ∼30%, respectively. A measure of the expansion anisotropy shows a positively skewed distribution, similar to the principal expansion coefficients themselves, and ranges based on suggested half normal distributions are shown to highlight literature cases of exceptional thermal expansion.