The first coordination compound of deprotonated 2-bromonicotinic acid: crystal structure of a dinuclear paddle-wheel copper(II) complex

Abstract

A copper(II) dimer with the deprotonated anion of 2-bromonicotinic acid (2-BrnicH), namely, tetrakis(μ-2-bromonicotinato-κ2 O:O′)bis[aquacopper(II)](Cu—Cu), [Cu2(H2O)2(C6H3BrNO2)4] or [Cu2(H2O)2(2-Brnic)4], (1), was prepared by the reaction of copper(II) chloride dihydrate and 2-bromonicotinic acid in water. The copper(II) ion in 1 has a distorted square-pyramidal coordination environment, achieved by four carboxylate O atoms in the basal plane and the water molecule in the apical position. The pair of symmetry-related copper(II) ions are connected into a centrosymmetric paddle-wheel dinuclear cluster [Cu...Cu = 2.6470 (11) Å] via four O,O′-bridging 2-bromonicotinate ligands in the syn-syn coordination mode. In the extended structure of 1, the cluster molecules are assembled into an infinite two-dimensional hydrogen-bonded network lying parallel to the (001) plane via strong O—H...O and O—H...N hydrogen bonds, leading to the formation of various hydrogen-bond ring motifs: dimeric R 2 2(8) and R 2 2(16) loops and a tetrameric R 4 4(16) loop. The Hirshfeld surface analysis was also performed in order to better illustrate the nature and abundance of the intermolecular contacts in the structure of 1.