LAUSR

Halogen bonding in self-complementary 1:2 metal-ligand complexes obtained from copper(II) bromide (CuBr2) and seven 2,5dihalopyridines are analyzed using single crystal X-ray diffraction. All presented discrete complexes form 1-D polymeric chains connected with C–X···Br–Cu halogen bonds (XB). In (2-chloro-5-Xpyridine)2·CuBr2 (X = Cl, Br and I), only the C5-halogen, and in (2bromo-5-X-pyridine)2·CuBr2 (X = Cl, Br and I) both, C2and C5halogens, form C–X···Br–Cu halogen bonds with the X acting as the XB donor and copper-coordinated bromide as the XB acceptor. The electron withdrawing C2-chloride in 2-chloro-5-X-pyridine-CuBr2 complexes has only a minor effect on the C5–X5···Br–Cu XBs, and the X5···Br distances follow expected order, I5 < Br5 < Cl5 in the RXB values of 0.91, 0.94 and 0.99, respectively. In 2-bromo-5-X-pyridineCuBr2 complexes, due to the polarization of both halogens, the C2– X2···Br–Cu and C5-X5···Br–Cu the RXB values are very similar [0.92 – 0.99] due to competition of C2and C5-halogens for XB formation. In addition to the classical halogen bonds the square planar Cu(II) complexes exhibit C2–X2···Cu (X = Cl and Br) contacts perpendicular to the Br–Cu–Br plane with shorter C2–Br2···Cu than C2–Cl2···Cu contacts. These interactions induce a pseudo-octahedral geometry for Cu(II) ions. Notably, C2–X2···Br–Cu halogen bonds and the additional C2–X2···Cu contacts are slightly enhanced by the C5halogen electronegativity.