Molecular structure and intra- and intermolecular magnetic interactions in chloro-bridged copper(II) dimers

Magnetic interactions in binuclear copper(II) complexes, [Cu2(apyhist)2Cl2](ClO4)2 (1) and [Cu2(2-pyhist)2Cl2](ClO4)2 (2) with tridentate diimine ligands and chloro-bridged groups (where apyhist=(4-imidazolyl)ethylene-2-amino-1-ethylpyridine and 2-pyhist=(4-imidazolyl)ethylene-2-aminomethylpyridine) were studied with the aim of better elucidating magneto-structural correlations in such species, both in solution and in solid state. X-ray analyses revealed that chloro-bridged ligands keep the copper(II) ion coordinated to adjacent unit, at Cu–Cl distances of 2.271 and 2.737 Å, and a Cu–Cl–Cu angle of 87.46° in compound 1. Each CuII atom is also coordinated to three N atoms from the imine ligand, in a distorted tetragonal pyramidal environment. Magnetic measurements carried out in temperatures from 0.8 to 290 K and in magnetic field up to 170 kOe indicated that besides the intramolecular magnetic coupling between the copper centers [J/k=−(1.93±0.05) K] further interactions between adjacent dimers [J′z/k=−(1.3±0.1) K] should be taken into account. Similar results were observed for compound 2, for which [J/k=−(4.27±0.05) K] and [J′z/k=−(3.7±0.1) K]. In solution, the interconversion of the dimer 1 and the related monomer species [Cu(apyhist)(H2O)2] (ClO4)2 (3) monitored by EPR spectra, was verified to be very dependent on the solvent.