A Million Crystal Structures: The Whole Is Greater than the Sum of Its Parts

The founding in 1965 of what is now called the Cambridge Structural Database (CSD) has reaped dividends in numerous and diverse areas of chemical research. Each of the million or so crystal structures in the database was solved for its own particular reason, but collected together, the structures can be reused to address a multitude of new problems. In this Review, which is focused mainly on the last 10 years, we chronicle the contribution of the CSD to research into molecular geometries, molecular interactions, and molecular assemblies and demonstrate its value in the design of biologically active molecules and the solid forms in which they are delivered. Its potential in other commercially relevant areas is described, including gas storage and delivery, thin films, and (opto)electronics. The CSD also aids the solution of new crystal structures. Because no scientific instrument is without shortcomings, the limitations of CSD research are assessed. We emphasize the importance of maintaining database quality: notwithstanding the arrival of big data and machine learning, it remains perilous to ignore the principle of garbage in, garbage out. Finally, we explain why the CSD must evolve with the world around it to ensure it remains fit for purpose in the years ahead.

Synthesis, crystal structure and properties of Cd(NCS)2 coordination compounds with two different Cd coordination modes

Reaction of Cd(NCS)2 with 4-methoxypyridine leads to the formation of four new compounds, of which one crystallizes in two different polymorphs. In Cd(NCS)2(4-methoxypyridine)4·(4-methoxypyridine)2 (1) and Cd(NCS)2(4-methoxypyridine)4 (2-I and 2-II) discrete complexes are found, in which the Cd cations are octahedrally coordinated by four 4-methoxypyridine co-ligands and two terminally N-bonded thiocyanate anions. For the polymorphs 2-I and 2-II no single crystals are available and therefore, the corresponding Mn(II) compound (2-I-Mn) was prepared, which is isotypic to 2-I, as proven by a Rietveld refinement. The crystal structure of 2-II was solved and refined from XRPD data. In [Cd(NCS)2(4-methoxypyridine)2] n (3), the Cd cations are also octahedrally coordinated but linked into linear chains by pairs of thiocyanate anions with all ligands in trans-position. {[Cd(NCS)2]3(4-methoxypyridine)5} n (4) also consists of chains but two different Cd coordination modes are observed. Two of the three crystallographically independent Cd cations show an octahedral coordination with a trans- or cis-arrangement of the N and S atoms of the anionic ligands, whereas the third one is in a distorted square-pyramidal coordination, with cis-coordination of the thiocyanate N and S atoms. Measurements using simultaneous thermogravimetry and differential scanning calorimetry of 2-I and 2-II show different heating rate dependent mass steps, in which the co-ligands are removed. In some of the residues obtained after the respective TG steps compound 3 was detected but no phase pure samples could be obtained.

Syntheses, crystal structures, magnetochemistry and catechol oxidase activity of a tetracopper(ii) compound and a new type of dicopper(ii)-based 1D coordination polymer

One phenoxo–hydroxo bridged tetranuclear cluster and one phenoxo-µ_1,1-azido-µ_1,3-azido bridged one-dimensional coordination polymer of copper(ii) derived from a Schiff base ligand are described.