Supramolecular hydrogen-bonding networks constructed from copper(II) chlorobenzoates with nicotinamide: Structure and EPR

Abstract

Nicotinamide (nia) has been employed as a supramolecular reagent in the synthesis of four copper(II) chloro- and dichlorobenzoate (Clbz/Cl2bz) complexes. The structures of the compounds [Cu(2-Clbz)2(nia)2(H2O)2] (1), [Cu(4-Clbz)2(nia)2(H2O)2] (2), [Cu(3,5-Cl2bz)2(nia)2(H2O)2] (3), and [Cu(2,5-Cl2bz)2(nia)2(H2O)]·H2O (4) were determined. All the investigated compounds 1–4 reveal water molecules as coordinated. Their structures show distorted octahedral chromophores CuIIN2O2O′2, though some are better described as square-planar or square-pyramid due to a large deviation of the axial ligand away from the octahedral z-axis along with different Cu⋯O(axial) lengths. The equatorial positions are occupied in all four cases by two nitrogen (nia-py) atoms and two carboxylate oxygen atoms of two Clbz/Cl2bz ligands, while the axial positions are occupied by water molecules. The EPR spectra reveal for all 1–4 compounds a spin state of S = ½, mostly with axial symmetry of the spectra. Their resolution is clearly dependant to the crystal symmetry related equivalence of the magnetic sites. The coordination molecules of all compounds are connected by N–H⋯O and O–H⋯O H-bonds from nicotinamide NH2 groups, carboxylate anions and/or water molecules, which create supramolecular chains or further H-bonded into 2D sheets. Steric hindering of the chlorine atoms of the Clbz/Cl2bz, especially seen at the coordination of the water molecules, demonstrates its role at the coordination sphere appearance. Despite this influence, the water molecules in 1–4 always assist at the similar supramolecular H-bonded network, almost at the same manner.