Bi- and Trifurcated Halogen Bonding M–C≡N···I in 1D, 2D, and 3D Supramolecular Network Structures of Co-Crystallized Diiodoacetylene C₂I₂ and Tetracyanonickelate [Ni(CN)₄]^2–

Abstract

The co-crystallization of square-planar tetracyanonickelate(II) [Ni(CN)4]2– with an excess of the strong halogen bond donor diiodoacetylene C2I2 in dichloromethane results in the formation of supramolecular network structures. Crystal structures of [PPh4]2[Ni(CN)4]·2 C2I2·3 CH2Cl2, [NBu4]2 [Ni(CN)4]·4 C2I2·2 CH2Cl2, and [PNP]2[Ni(CN)4]·6 C2I2 reveal that up to three iodine atoms can coordinate to one cyano ligand. Unexpectedly, C≡N···I angles in these structures are in the range of 95–160° and show a strong dependence of N···I distances. This trend is also reproduced by DFT calculations. Additionally, the crystal structure of C2I2 was redetermined.