title: Crystal structure of a chloride-bridged copper(II) dimer: piperazine-1,4-dium bis-(di-μ-chlorido-bis[(4-carboxypyridine-2-carboxyl-ato-κ2N,O2)chlorido-cuprate(II)].
abstract: Crystals of a new dimeric chloride-bridged cuprate(II) derived from pyridine-2,4-di-carb-oxy-lic acid were obtained solvothermally in the presence of piperazine and hydro-chloric acid. The crystal structure determination of the title salt, (C4H12N2)[Cu2(C7H4NO4)2Cl4], revealed one of the carboxyl groups of the original pyridine-2,4-di-carb-oxy-lic acid ligand to be protonated, whereas the other is deprotonated and binds together with the pyridine N atom to the CuIIatom. The coordination environment of the CuIIatom is distorted square-pyramidal. One of the chloride ligands bridges two metal cations to form a centrosymmetric dimer with two different Cu-Cl distances of 2.2632 (8) and 2.7853 (8) Å, whereby the longer distance is associated with the apical ligand. The remaining chloride ligand is terminal at one of the basal positions, with a distance of 2.2272 (9) Å. In the crystal, the dimers are linked by inter-molecular O-H⋯O hydrogen bonds, together with N-H⋯O and N-H⋯Cl inter-actions involving the centrosymmetric organic cation, into a three-dimensional supra-molecular network. Further but weaker C-H⋯O and C-H⋯Cl inter-actions consolidate the packing.
authors.affiliation: Inorganic Materials Chemistry Laboratory, Department of Pure and Applied Chemistry, University of Calabar, P.M.B. 1115-Calabar, Nigeria.
authors.forename: Bassey Enyi
authors.initials: BE
authors.lastname: Inah
authors.affiliation: Inorganic Materials Chemistry Laboratory, Department of Pure and Applied Chemistry, University of Calabar, P.M.B. 1115-Calabar, Nigeria.
authors.forename: Ayi Anyama
authors.identifier: https://orcid.org/0000-0002-4908-9929
authors.initials: AA
authors.lastname: Ayi
authors.affiliation: Department of Chemistry, Missouri University of Science and Technology, Rolla, MO 65409, USA.
authors.forename: Amit
authors.initials: A
authors.lastname: Adhikary
keywords: centrosymmetric dimer; coordination polymer; crystal structure; solvothermal synthesis