Recognition of a Novel Type X=N-Hal...Hal (X = C, S, P; Hal = F, Cl, Br, I) Halogen Bonding

The chlorination of the eight-membered platinum(II) chelates [PtCl sub(2){NH=C(NR sub(2))N(Ph)C(=NH)N(Ph)C(NR sub(2))=NH}] (R = Me (1); R sub(2) = (CH sub(2)) sub(5) (2)) with uncomplexed imino group with Cl sub(2) gives complexes bearing the =N-Cl moiety [PtCl sub(4){NH=C(NR sub(2))N(Ph)C(=NCl)N(Ph)C(NR sub(2))=NH}] (R = Me (3); R sub(2) = (CH sub(2)) sub(5) (4)). X-ray study for 3 revealed a novel type intermolecular halogen bonding =N-Cl...Cl super(-), formed between the Cl atom of the chlorinated imine and the chloride bound to the platinum(IV) center. The processing relevant structural data retrieved from the Cambridge Structural Database (CSDB) shows that this type of halogen bonding is realized in 18 more molecular species having X=N-Hal moieties (X = C, P, S, V, W; Hal = Cl, Br, I), but this weak =N-Hal...Hal super(-) bonding was totally neglected in the previous works. The presence of the halogen bonding in 3 was confirmed by theoretical calculations at the density functional theory (DFT, M06-2X) level, and its nature was analyzed.