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°.