Cobaloximes as Building Blocks in Halogen-Bonded Cocrystals

Isothiocyanate Sulfur Atom as an Acceptor Site for Halogen-Bonded Cocrystallization of Werner Ni(II) Coordination Compounds and Perfluorinated Iodobenzenes

We explore the halogen bond acceptor potential of the isothiocyanate sulfur atom in the synthesis of cocrystals involving metal-organic building blocks by using Werner Ni(II) coordination compounds whose pendant isothiocyanate group enables halogen bonding. A series of 14 cocrystals involving octahedral Ni(L)4(NCS)2 coordination compounds (L = pyridine or 4-methylpyridine) has been prepared by both crystallization from solution and liquid-assisted grinding. The effectiveness of this strategy is demonstrated by the assembly of a large family of cocrystals involving five perfluorinated iodobenzenes. For both coordination compounds, we generally obtained one cocrystal with each donor; in one case, we obtained an additional two stoichiomorphs, and in another, we obtained three additional solvates. Single-crystal X-ray diffraction experiments revealed that building units in all cocrystals are connected via S···I halogen bonds involving the donor iodine atom and the isothiocyanate sulfur atom, which is an acceptor of two and, in some cases, even three halogen bonds. Consequently, both coordination compounds act as multitopic acceptors that can form multiple halogen bonds leading to the formation of one-, two-, and three-dimensional halogen-bonded architectures. The relative shortenings of S···I distances are from 7 to 15%, while the S···I-C angles are in the range from 160 to 180°.

Combination of Hydrogen and Halogen Bonds in the Crystal Structures of 5-Halogeno-1H-isatin-3-oximes: Involvement of the Oxime Functionality in Halogen Bonding

Various functional groups have been considered as acceptors for halogen bonds, but the oxime functionality has received very little attention in this context. In this study, we focus on the analysis of the hydrogen and halogen bond preferences observed in the crystal structures of 5-halogeno-1H-isatin-3-oximes. These molecules can be involved in various non-covalent interactions, and the competition between these interactions has a decisive influence on their self-organization. In particular, we were interested to see whether the crystal structures of 5-halogeno-1H-isatin-3-oximes, especially bromine- and iodine-substituted ones, are characterized by the presence of halogen bonds formed with the oxime functionality. The oxime group proved its ability to compete with the other strong donor and acceptor sites by participating in the formation of cyclic hydrogen-bonded heterosynthons oxime∙∙∙amide and Ooxime∙∙∙Br/I halogen bonds.

Crystal engineering strategies towards halogen-bonded metal–organic multi-component solids: salts, cocrystals and salt cocrystals

This highlight presents an overview of the current advances in the preparation of halogen bonded metal–organic multi-component solids, including salts and cocrystals comprising neutral and ionic constituents.