Magnetic properties of poly(propylene imine)-copper dendromesogenic complexes: An EPR study
| Autor: | N. E. Domracheva, Anisoara Mirea, Günter Lattermann, Markus Schwoerer, Laura Torre-Lorente |
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| Rok vydání: | 2006 |
| Předmět: |
Dendrimers
Stereochemistry Dimer chemistry.chemical_element Ligands Polypropylenes Sensitivity and Specificity Ion law.invention Electron transfer chemistry.chemical_compound Magnetics law Organometallic Compounds Physical and Theoretical Chemistry Electron paramagnetic resonance Valence (chemistry) Molecular Structure Electron Spin Resonance Spectroscopy Temperature Hydrogen Bonding Tautomer Copper Atomic and Molecular Physics and Optics Crystallography chemistry Diamagnetism |
| Zdroj: | Chemphyschem : a European journal of chemical physics and physical chemistry. 7(12) |
| ISSN: | 1439-4235 |
| Popis: | 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 d9- and diamagnetic d10-configurated copper ions, and an antiferromagnetically coupled NO3* 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 NO4 environment of the Cu(II) ion in green complex 1 (x = 1.9), and confirms the chain structure with intermolecular Cu(II)-NO3-Cu(II) bridges between Cu(II) centres in columns. |
| Databáze: | OpenAIRE |
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