Magnetic properties of poly(propylene imine)-copper dendromesogenic complexes: An EPR study.
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.
Domracheva
Natalia
N
Zavoisky Kazan Physical-Technical Institute, Russian Academy of Science, 420029 Kazan, Russia. domracheva@mail.knc.ru
Mirea
Anisoara
A
Schwoerer
Markus
M
Torre-Lorente
Laura
L
Lattermann
Günter
G
D003300:Copper / Q000737:chemistry*; D050091:Dendrimers / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D006860:Hydrogen Bonding; D008024:Ligands; D008280:Magnetics; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D011126:Polypropylenes / Q000737:chemistry*; D012680:Sensitivity and Specificity; D013696:Temperature
D050091:Dendrimers; D008024:Ligands; D009942:Organometallic Compounds; D011126:Polypropylenes; C443641:poly(propyleneimine); D003300:Copper