Combined analysis of chemical bonding in a Cu^II dimer using QTAIM, Voronoi tessellation and Hirshfeld surface approaches

Interaction of 1-(1H-pyrazol-5-yl)ethanone oxime (H₂PzOx) with copper(II) chloride in the presence of pyridine afforded a binuclear discrete [Cu₂(HPz­Ox)₂Cl₂py₂] complex, which was characterized by Fourier transform–IR and electron paramagnetic resonance (EPR) spectra, magnetochemistry and high-resolution X-ray diffraction experiments. Multipole refinement of X-ray diffraction data and density-functional theory (DFT) calculations of an isolated molecule allowed charge and spin distributions to be obtained for this compound. Magnetochemistry data, EPR spectra and DFT calculations of an isolated molecule show antiferromagnetic coupling between copper(II) ions. The spin distribution suggests an exchange pathway via the bridging pyrazole ring in the equatorial plane of the CuN₄Cl coordination polyhedron, thus providing support for the classical superexchange mechanism; the calculated value of the magnetic coupling constant −2J is equal to 220 cm⁻¹, which compares well with the experimental value of 203 ± 2 cm⁻¹. Chemical connectivity was derived by Bader's `quantum theory of atoms in molecules' and compared with Voronoi tessellation and Hirshfeld surface representations of crystal space. All methodologies gave a similar qualitative and semi-quantitative description of intra- and intermolecular connectivity.

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