Halogen bonds in 2,5-dihalopyridine-copper(II) chloride complexes

: Puttreddy R, von Essen C, Peuronen A, Lahtinen M, Rissanen K

Publisher: ROYAL SOC CHEMISTRY

: 2018

: CrystEngComm

: CRYSTENGCOMM

: 20

: 14

: 1954

: 1959

: 6

: 1466-8033

DOI: https://doi.org/10.1039/c8ce00209f

Ten coordination complexes obtained through a facile reaction between 2,5-dihalopyridines and copper(n) chloride (CuCl2) are characterized using single crystal X-ray diffraction. Two series of dihalopyridine complexes based on 2-chloro-5-X-pyridine and 2-bromo-5-X-pyridine (X = F, Cl, Br and I) were prepared to analyze the C-X2/X5 center dot center dot center dot Cl-Cu halogen bonds (XB). The influence of X2- and X5-substituents on the respective interactions was examined by comparing them to the X2/X3 center dot center dot center dot Cl-Cu XBs found in mono-substituted halopyridine complexes, (n-X-pyridine)(2)center dot CuCl2 (n = 2, 3 and X = Cl, Br and I). Varying the X5-halogens in (2,5-dihalopyridine)(2)center dot CuCl2, the C5-X5-O-Cu XBs follow the order F5 < Cl5 < Br5 < 15 for X2 = Cl and Cl5 < Br5 < I5 for X2 = Br. The C2-X2 center dot center dot center dot Cl-Cu XB distances did not follow any particular trends, and are slightly longer compared to corresponding distances in (2-halopyridine)(2)center dot CuCl2 complexes due to the competition of X2 and X5-halogen based halogen bonds. The C3-X3 center dot center dot center dot Cl-Cu contacts in (3-halopyridine)(2)center dot CuCl2 have RxEl values > 1 and they cannot be considered as halogen bonds. This proves the polarization effect of X2- to X5-rather than X5- to X2-halogen, and the introduction of second halogen substituent in para-position to X5-triggers C2-X2 center dot center dot center dot Cl-Cu and C5-X5 center dot center dot center dot Cl-Cu XB interactions.