The role of acid in the formation of hydrogen-bonded networks featuring 4,4′-dicarboxy-2,2′-bipyridine (H2dcbp): Synthesis, structural and magnetic characterisation of {[Cu(H2dcbp)Cl2]·H2O}2 and [Cu(H2dcbp)(NO3)2(H2O)]

Abstract

Reported herein are the synthesis, structural and magnetic characterisation of two hydrogen-bonded networks featuring the 4,4′-dicarboxy-2,2′-bipyridine (H₂dcbp) ligand: {[Cu(H₂dcbp)(Cl)₂]·H₂O}₂ 1 and [Cu(H₂dcbp)(NO₃)₂(H₂O)] 2. Compounds 1 and 2 result from the reaction of CuCl₂ and Cu(NO₃)₂, respectively, with H₂dcbp under hydrothermal conditions in the presence of either HCl or HNO₃. The acid ensures that H₂dcbp remains protonated and provides the anions required for charge balance irrespective of Cu(II) precursor. Within 1 and 2 the H₂dcbp ligand performs a dual role of Cu(II) coordination, via the 2,2′-bipyridine moiety, and propagates the formation of chains through hydrogen-bonding involving the peripheral 4,4′-dicarboxylic acid functionalities. Additional hydrogen bonding between the 4,4′-dicarboxylic acid groups, metal bound chloride and nitrate anions, in 1 and 2 respectively, and water molecules generate 3D networks. Variable temperature magnetic susceptibility measurements reveal very weak antiferromagnetic coupling between the Cu(II) centres across the chloride bridges in 1 (J = −3.02 cm⁻¹).