Isomorphous Series of Pd<sup>II</sup>-Containing Halogen-Bond Donors Exhibiting Cl/Br/I Triple Halogen Isostructural Exchange
Alexander V. Buldakov, Mikhail A. Kinzhalov, Mariya A. Kryukova, Daniil M. Ivanov, Alexander S. Novikov, Andrey S. Smirnov, Галина Л. Старова, Nadezhda A. Bokach, Vadim Yu. Kukushkin
Abstract
Two isomorphous series including the adducts trans-[PdI2(CNC6H4-4-X)2]·2I2 [(1–3)·2I2; X = Cl 1, Br 2, I 3] and the complexes cis-[PdCl2(CNC6H4-4-X)(PPh3)] (4–6; X = Cl 4, Br 5, I 6) were characterized by X-ray crystallography. Inspection of the X-ray diffraction data allowed the identification of halogen-bonding C–X···I–I in (1–3)·2I2 and C–X···Cl–[Pd] in 4–6 thus providing a rare example of the triple Cl/Br/I exchange of σ-hole donating halogens. In accord with the conducted theoretical considerations, the strength of these XBs are in the range of 0.9–2.8 kcal/mol, and these contacts are of a noncovalent nature. The calculated maximum electrostatic potentials on the σ-hole donating X centers of CNC6H4-4-X on the 0.001 au molecular surfaces for both (1–3)·2I2 and 4–6 series are increased along with the decrease of relative XB lengths. These data are consistent with Politzer and co-workers conclusions that are based exclusively on theoretical ground.