Isomorphous Series of PdII-Containing Halogen-Bond Donors Exhibiting Cl/Br/I Triple Halogen Isostructural Exchange

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 XRD 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 -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 noncovalent nature. The calculated maximum electrostatic potentials on the -hole donating X centers of CNC6H4-4-X on the 0.001 a.u. 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 coworkers conclusions that are based exclusively on theoretical ground.