The isocyanide trans-[PdBr2(CNC6H4-4-X′)2] (X′=Br, I) and nitrile trans-[PtX2(NCC6H4-4-X′)2] (X/X′=Cl/Cl, Cl/Br, Br/Cl, Br/Br) complexes exhibit similar structural motif in the solid state, which is determined by hitherto unreported four-center nodes formed by cyclic halogen bonding. Each node is built up by four Type II C−X′⋅⋅⋅X−M halogen-bonding contacts and include one Type I M−X⋅⋅⋅X−M interaction, thus giving the rhombic-like structure. These nodes serve as supramolecular synthons to form 2D layers or double chains of molecules linked by a halogen bond. Results of DFT calculations indicate that all contacts within the nodes are typical noncovalent interactions with the estimated strengths in the range 0.6–2.9 kcal mol−1.
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- Organic Chemistry