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CPP: Chemische Physik und Polymerphysik
CPP 12: Selforganized and supramolecular assemblies I
CPP 12.5: Vortrag
Montag, 7. März 2005, 10:45–11:00, TU C243
Orientation effects in EPR PPI Cu(II) - dendrimer complexes induced by a high magnetic field — •N. Domracheva1, A. Mirea2, M. Schwoerer2, G. Lattermann3, and L. Torre Lorente3 — 1Kazan Physical-Technical Institute of RAS, Kazan, 420029, Russia — 2Experimentalphysik II, Universität Bayreuth, D-95440 Bayreuth — 3Makromolekulare Chemie I, Universität Bayreuth, D-95440 Bayreuth, Germany
The poly (propylene imine) (PPI) dendrimers of the 1st and 2nd generations coordinated to Cu(II) and exhibiting liquid crystalline properties were studied by means of EPR for different copper content per dendrimer ligand L (0.3≤ Cu/L≤ 6.3). Orientation effect of a high magnetic field was used to obtain structural information for the metal ion complexed in the dendrimer. Using of this effect allowed us, for the first time, to resolve the anisotropic superhyperfine structure due to amide nitrogen ligands in dendrimers and to give the geometric information on the Cu(II) complex sites. At lowest content (Cu/L=0.3) the Cu(II) complexes have an approximately square-planar geometry, where each Cu(II) ion is bounded to two nitrogen and two carbonyl oxygen atoms from the amide groups in the outer core of the dendrimers. For intermediate concentrations, two kinds of Cu(II) complexation geometry exist: 1) a N2O2 pseudotetrahedral geometry (the distortion angle is γ = 56∘) with two amide nitrogen and two carbonyl oxygen coordination and 2) a five-coordinated, square-pyramidal geometry, presumably, N3O2 via additional bridging with a tertiary amine nitrogen from the dendrimer’s inner core. Higher Cu(II) "loadings" lead to the increase of exchange couplings between the sites.