|Domracheva, N.E.; Mirea, A.; Schwoerer, M.; Torre Lorente, L.; Lattermann, G.: Magnetic properties of poly(propylene imine)-copper dendromesogenic: an EPR study. , ChemPhysChem, 7(12), 2567-2577 (2006)|
Copper(II) complexes formed by coordination of the CuII ion with liq.-cryst. poly(propylene imine) dendrimer ligand (L) of the first (complex 1) and second (complex 2) generations with various CuII contents (x = Cu/L) have been studied by ESR (EPR) spectroscopy. The existence of a redox-active blue complex 1 (x = 1.9) and the copper(II) nitrate electron transfer assocd. with the valence tautomerism are revealed for the first time in copper-based dendrimers. It has been shown that the electronic structure of the blue complex 1 (x = 1.9) is adequately described as a mixed-valence dimer contg. d9- and diamagnetic d10-configurated copper ions, and an antiferromagnetically coupled NO3. radical arising on the nitratebridged counter ligand. The activation energy value found for the electron transfer is about 0.35 meV, which indicates a low-energy charge dynamic. The ability of the blue and green complexes 1 (x = 1.9) dissolved in isotropic solvents to orient themselves in the magnetic field was revealed by EPR spectroscopy. The degree of orientation of the mol. z axis (Sz) of these complexes in the magnetic field differs, depending on the type of copper(II)-complexing site in the dendrimer ligand, and can reach 0.76, which is close to Sz = 1 (completely aligned system). A combination of magnetic and orientational parameters indicates an NO4 environment of the CuII ion in green complex 1 (x = 1.9), and confirms the chain structure with intermol. CuII-NO3-CuII bridges between CuII centers in columns.