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

A copper(II) dimer with the deprotonated anion of 2-bromo-nicotinic acid (2-BrnicH), namely, tetrakis(μ-2-bromonicotinato-κ :')bis[aquacopper(-II)](-), [Cu(HO)(CHBrNO)] or [Cu(HO)(2-Brnic)], (), was prepared by the reaction of copper(II) chloride dihydrate and 2-bromo-nicotinic acid in water. The copper(II) ion in has a distorted square-pyramidal coordination environment, achieved by four carboxyl-ate O atoms in the basal plane and the water mol-ecule 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] four ,'-bridging 2-bromo-nicotinate ligands in the - coordination mode. In the extended structure of , the cluster mol-ecules are assembled into an infinite two-dimensional hydrogen-bonded network lying parallel to the (001) plane strong O-H⋯O and O-H⋯N hydrogen bonds, leading to the formation of various hydrogen-bond ring motifs: dimeric (8) and (16) loops and a tetra-meric (16) loop. The Hirshfeld surface analysis was also performed in order to better illustrate the nature and abundance of the inter-molecular contacts in the structure of .