Metal-Bound Nitrate Anion as an Acceptor for Halogen Bonds in Mono-Halopyridine-Copper(II) Nitrate Complexes

: Puttreddy R., Peuronen A., Lahtinen M., Rissanen K.

Publisher: AMER CHEMICAL SOC

: 2019

: Crystal Growth and Design

: CRYSTAL GROWTH & DESIGN

: CRYST GROWTH DES

: 19

: 7

: 3815

: 3824

: 10

: 1528-7483

: 1528-7505

DOI: https://doi.org/10.1021/acs.cgd.9b00284

Fifteen n-halopyridine-Cu(NO3)(2) complexes (n = 2, 3, 4) obtained from two different solvents, acetonitrile and ethanol, are investigated for C-X center dot center dot center dot O-N halogen bonds (XBs) in the solid state by single and powder X-ray diffraction. The nitrate anions bind copper(II) via anisobidentate modes and one of three oxygens act as an XB acceptor to halogens on the core pyridine rings. The N-metal coordination activates the electron-deficient pi-system and triggers even C2- and C4-chlorines in the corresponding [Cu(2-chloropyridine)(2)(NO3)(2)] and [Cu(4-chloropyridine)(2)(NO3)(2)(ACN)] complexes to form short C-Cl-2/Cl4 center dot center dot center dot O-N halogen bonds. Notably, the C2-Cl2 center dot center dot center dot O-N XBs with a normalized XB distance parameter (R-XB) of 0.89 is close to C2-I2 center dot center dot center dot O-N XBs [R-XB = 0.88] in the [Cu(2-iodopyridine)(2)(NO3)(2)] complex. In overall, the C-X center dot center dot center dot O-N halogen bonds in the studied complexes range from moderately short to roughly the van der Waals contact distance of the respective X center dot center dot center dot O atoms (R-XB = 0.88-0.99) and have a varying significance in governing the molecular packing respective of the complex. Among the studied complexes, two main coordination modes were observed distorted octahedral and distorted pentagonal bipyramid-of which the latter results from the coordination of acetonitrile to the Cu(II) ion. The crystal structures showed that the steric bulk of C2-halogens in 2-halopyridines prevent this, while in similar conditions the 3- and 4-halopyridine ligands yield acetonitrile bound Cu(II)-complexes.