Form of the axially symmetrical EPR spectra of orientationally ordered solid systems

Konstantinov, V. N.; Овчинников, И. В.; Domracheva, N. E.

doi:10.1007/bf00747335

Cited by 5 publications

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“…Such moving lines, as proved theoretically and experimentally in the literature, [53,54,61] show that the direction of the principal magnetic and molecular z axis coincide. Figure 9 b shows EPR spectra for suspended green complex 1, simulated by using the distribution function of Equation (10) The question arises: what is the difference between the structure of the blue and green complexes 1?…”

mentioning

confidence: 79%

“…In the case of axial symmetry of the molecules (R x = R y = R), the distribution function given by Equation (10) transforms into the Kratky-Tanizaki function. [54,55] Figure 8 b shows the simulated EPR spectra for suspended blue complex 1. The spectra were calculated with the expo- nential distribution function defined as in Equation (9) and with the orientational parameters R x = R y = 2.5 and R z = 0, and magnetic parameters g z = 2.336, g x = 2.07, g y = 2.05, A z = 163.5 10 À4 cm…”

Section: Orienting Effect Of the Magnetic Fieldmentioning

confidence: 98%

“…So, for a qualitative analysis of its EPR spectra, we can use the theory developed for paramagnetic probes in oriented vitreous liquid crystals and in stretched polymers, which are analogous systems. [53,54] The EPR spectra were simulated by using a home-written program with algorithms described in the literature. [53,54] The shape of EPR spectra for an orientationally ordered system was calculated according to Equation (8) FðB,xÞ $ is the individual line shape, and y, f and w are Euler angles connecting the molecular coordinate system and the sample coordinate system (the latter is determined by the macroscopic director N).…”

Section: Orienting Effect Of the Magnetic Fieldmentioning

confidence: 99%

“…[53,54] The EPR spectra were simulated by using a home-written program with algorithms described in the literature. [53,54] The shape of EPR spectra for an orientationally ordered system was calculated according to Equation (8) FðB,xÞ $ is the individual line shape, and y, f and w are Euler angles connecting the molecular coordinate system and the sample coordinate system (the latter is determined by the macroscopic director N). Comparison of simulated and experimental spectra allows us to choose the type of orientational distribution of the molecular axes (x, y, z) with respect to N. For nematic liquid crystals the orientational distribution function has an exponential form and is expressed as Equation (9): [53,54] P n ðy,fÞ % exp ðÀR x sin 2 y sin 2 fÀR y sin 2 y cos 2 fÀR z cos 2 yÞ ð9Þ where R i (i = x, y, z) are the effective orientational parameters.…”

Section: Orienting Effect Of the Magnetic Fieldmentioning

confidence: 99%

“…The estimated values of the orientational parameters (R x = R y = 2.5, R z = 0) are in good agreement with those reported in literature for most monomeric, paramagnetic complexes oriented in liquid crystals, for which the analogous parameters are on the order of 2-4. [51,[56][57][58] If the orientational parameters are known, it is possible [53,54] to calculate the degree of orientation S i of the molecular axes (i = x, y, z) along the magnetic field. We obtained S z = 0.37.…”

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EPR Characterisation of Cu^II Complexes of Poly(propylene imine) Dendromesogens: Using the Orienting Effect of a Magnetic Field

et al. 2005

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Liquid-crystalline derivatives of poly(propylene imine)dendrimers of the 0th, 1st and 2nd generations, complexed with copper(II) ions, were studied by EPR spectroscopy. The structures of copper (II) complexes with different Cu(II) loadings x per dendrimer ligand L (x = Cu/L) were determined. At the lowest concentration, the Cu(II) ions form monomeric complexes with approximately square-planar N2O2 coordination of both carbonyl oxygen and amido nitrogen atoms. At higher copper content, two kinds of Cu(II) complex sites with different geometries exist. The orienting effect of a high magnetic field was used to investigate the structure and magnetic properties of the copper(II) complexes. This effect, for the first time in dendrimers, allowed the resolution of five nitrogen super-hyperfine lines on g(z) components with the unusual coupling constant of a(Nz)= 35.9 x 10(-4) cm(-1). The combination of the magnetic parameters and the orienting effect indicates the presence of a monomeric complex with pseudotetrahedral N2O2 coordination of the Cu(II) ion, as well as a "dimer" structure with fivefold coordination, presumably due to an N3O2 environment. Higher copper loadings lead to increased exchange coupling between the complex sites.

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mentioning

confidence: 79%

Section: Orienting Effect Of the Magnetic Fieldmentioning

confidence: 98%

Section: Orienting Effect Of the Magnetic Fieldmentioning

confidence: 99%

Section: Orienting Effect Of the Magnetic Fieldmentioning

confidence: 99%

mentioning

confidence: 99%

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EPR Characterisation of Cu^II Complexes of Poly(propylene imine) Dendromesogens: Using the Orienting Effect of a Magnetic Field

et al. 2005

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Magnetic Properties of Poly(propylene imine)–Copper Dendromesogenic Complexes: An EPR Study

et al. 2006

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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.

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Structural, Magnetic and Dynamic Characterization of Liquid Crystalline Iron(III) Schiff Base Complexes with Asymmetric Ligands

et al. 2011

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The iron(III) complexes that were formed by coordination of the Fe III ion with the asymmetric tridentate liquid crystalline Schiff base ligand (L), the water molecules and the different counterions [PF 6 -(1), NO 3 -(2), and Cl -(3)] were studied by electron paramagnetic resonance (EPR) spectroscopy. EPR spectroscopy demonstrated that each of the complexes investigated consists of two types of iron centers: S = 1/2 low-spin (LS) and S = 5/2 high-spin (HS). LS iron complexes 2, 3 and LS complex 1 in the temperature range 4. + X -, with X = PF 6 -as the counterion. The LS and HS iron centers of 1 are coupled together antiferromagnetically and form a dimer structure by means of the water molecules and the PF 6 -counterion. The second-type of LS and HS cen-

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Form of the axially symmetrical EPR spectra of orientationally ordered solid systems

Cited by 5 publications

References 4 publications

EPR Characterisation of Cu^II Complexes of Poly(propylene imine) Dendromesogens: Using the Orienting Effect of a Magnetic Field

EPR Characterisation of Cu^II Complexes of Poly(propylene imine) Dendromesogens: Using the Orienting Effect of a Magnetic Field

Magnetic Properties of Poly(propylene imine)–Copper Dendromesogenic Complexes: An EPR Study

Structural, Magnetic and Dynamic Characterization of Liquid Crystalline Iron(III) Schiff Base Complexes with Asymmetric Ligands

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Form of the axially symmetrical EPR spectra of orientationally ordered solid systems

Cited by 5 publications

References 4 publications

EPR Characterisation of CuII Complexes of Poly(propylene imine) Dendromesogens: Using the Orienting Effect of a Magnetic Field

EPR Characterisation of CuII Complexes of Poly(propylene imine) Dendromesogens: Using the Orienting Effect of a Magnetic Field

Magnetic Properties of Poly(propylene imine)–Copper Dendromesogenic Complexes: An EPR Study

Structural, Magnetic and Dynamic Characterization of Liquid Crystalline Iron(III) Schiff Base Complexes with Asymmetric Ligands

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EPR Characterisation of Cu^II Complexes of Poly(propylene imine) Dendromesogens: Using the Orienting Effect of a Magnetic Field

EPR Characterisation of Cu^II Complexes of Poly(propylene imine) Dendromesogens: Using the Orienting Effect of a Magnetic Field