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Magnetic Properties of Poly(propylene imine)–Copper Dendromesogenic Complexes: An EPR Study
Author(s) -
Domracheva Natalia,
Mirea Anisoara,
Schwoerer Markus,
TorreLorente Laura,
Lattermann Günter
Publication year - 2006
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.200600360
Subject(s) - electron paramagnetic resonance , chemistry , copper , crystallography , dimer , ligand (biochemistry) , ligand field theory , inorganic chemistry , ion , nuclear magnetic resonance , organic chemistry , biochemistry , physics , receptor
Copper(II) complexes formed by coordination of the Cu II ion with liquid‐crystalline poly(propylene imine) dendrimer ligand (L) of the first (complex 1 ) and second (complex 2 ) generations with various Cu II contents ( x =Cu/L) have been studied by electron paramagnetic resonance (EPR) spectroscopy. The existence of a redox‐active blue complex 1 ( x =1.9) and the copper(II) nitrate electron transfer associated 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 containing d 9 ‐ and diamagnetic d 10 ‐configurated copper ions, and an antiferromagnetically coupled NO 3 . radical arising on the nitrate‐bridged 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 molecular z axis ( S z ) 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 S z =1 (completely aligned system). A combination of magnetic and orientational parameters indicates an NO 4 environment of the Cu II ion in green complex 1 ( x =1.9), and confirms the chain structure with intermolecular Cu II –NO 3 –Cu II bridges between Cu II centres in columns.