Carbon dioxide uptake by [Cu(bpca)]+: synthesis, crystal structure, and magnetic properties of {[Na(H2O)2][Cu2(bpca)2(CO3)(HCO3)]}n [Hbpca = bis(2-pyridylcarbonyl)amide]

Abstract

Herein we report on the preparation, spectroscopic and thermal characterization, structural study, and magnetic investigation of a new heterobimetallic coordination polymer (CP) of formula {[Na(H₂O)₂][Cu₂(bpca)₂(CO₃)(HCO₃)]}_n (1) [Hbpca = bis(2-pyridylcarbonyl)amide], which was isolated through the fixation of aerial carbon dioxide by the preformed [Cu(bpca)]⁺ complex in basic water/DMSO solvent mixtures. Compound 1 is made up of neutral heterobimetallic zigzag chains growing parallel to the crystallographic c axis where carbonate, bicarbonate, and bpca anions act as bridges with regular alternation of a pair of [Cu(bpca)]⁺ units and one [Na(H₂O)₂]⁺ fragment. The two crystallographically independent copper(II) ions (Cu1 and Cu2) are five-coordinate in somewhat distorted square pyramidal surroundings with three nitrogen atoms from the bpca ligand and either one bicarbonate-oxygen (Cu1) or a carbonate-oxygen (Cu2) in the basal plane and a shared carbonate-oxygen atom (Cu1 and Cu2) in the apical position. Each sodium(I) ion is also five-coordinate in a distorted trigonal bipyramidal environment, with two oxygen atoms from a bpca ligand and a water molecule building the trigonal plane and a bicarbonate-oxygen and another water molecule in the axial sites. The intrachain copper–copper separation across the bridging carbonate is 4.109(1) Å. The cryomagnetic study of 1 reveals the occurrence of a weak ferromagnetic interaction between the copper(II) ions through the bridging carbonate [J = +0.17(4) cm⁻¹, the spin Hamiltonian being defined as H = −JS_Cu1·S_Cu2]. Density functional theory (DFT) calculations on the [{Cu(bpca)}₂(μ-CO₃)] fragment of 1 in the gas phase and solid state were used to estimate the magnetic coupling constant (J = +0.42 cm⁻¹) and to describe the electronic structure and magnetic topology of the system.