Use of ESR for characterizing exchange-coupled polynuclear μ-oxo complexes of iron(iii)

ESR spectra of 13 bi-, tri- and tetranuclear -oxo complexes of Fe(III) were studied in the solid state and in solution. On the basis of the data obtained, the broad signal observed nearg=2 for all the complexes was interpreted as resulting from thermal populating of paramagnetic excited states.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 470–472, March, 1993.     

Synthesis and magnetic interaction of μ-2-chloroterephthalato binuclear iron (Ⅱ) complexes

Four μ-2-chloroterephthalato binuclear iron(Ⅱ) complexes, namely [Fe2 (CTPHA) L4]-(ClO4)2, where L stands for 4,4'-dimethyl-2,2'-bipyridine (Me2-bpy); 2,9-dimethyl-l, 10-phenanthro-line (Me2-phen); 5-chloro-l, 10-phenanthroline (Cl-phen); 4, 7-diphenyl-l, 10-phenanthroline (Ph2-phen), respectively, and CTPHA represents 2-chlorolerephthalate dianion, have been synthesized and characterized. Based on the elemental analyses, molar conductance measurements and spectroscopic studies, extended CTPHA-bridged structures consisting of two iron(Ⅱ) ions, each in a distorted octahedral environment, are proposed for these complexes. [Fe2 CTPHA)-(Me2-bpy)4] (ClO2 (1) and [Fe2(CT-PHA)·(Me2-phen)4](ClO4)2 (2) complexes were characterized by variable temperature magnetic susceptibility (4-300 K) measurements and the observed data were successfully simulated by the equation based on the spin Hamiltonian operator, H = - 2JS1 · S2 , giving the exchange integrals J = - 1.28 cm-1 for 1 and J = - 1.85 cm-1 for 2. These r     

The structure and EPR spectra of binuclear copper(II) complexes with acyldihydrazones of β-diketones

The synthesis and structure of binuclear copper(II) complexes with acyldihydrazones of some β-diketones are described. The molecular structure of the copper(II) complex [Cu₂L·4Py] with trifluoroacetylacetone succinyldihydrazone (H₄L) was determined by the single-crystal X-ray analysis. Central atoms are bridged by a chain of seven σ-bonds with a Cu...Cu distance of 8.750 Å. EPR spectra of copper(II) complexes with acyldihydrazones of trifluoroacetylacetone and lower dicarboxylic acids containing from one to four methylene groups in the aliphatic spacer show the seven-line HFS due to spin-spin coupling of unpaired electrons with the two equivalent copper nuclei (g = 2.110, a = (38.5–40.5)⊙10^?4 cm^?1). By extending polymethylene spacer, as well as by modifying starting β-diketone, an exchange interaction between paramagnetic centers is suppressed.     

Mössbauer spectra of bidentate and monodentate carbonyl-substituted pyridine complexes of iron(II) dichlorides

A number of complexes of iron(II) dichlorides with 2-, 3- and 4-position carbonyl-substituted pyridines, i.e. Fe(RCO-py)₂Cl₂ (R = CH₃, C₆H₅, H, OH and NH₂) have been prepared and characterized by means of Mössbauer, IR spectroscopy and magnetic measurements. These complexes have distorted octahedral structures. The quadrupole splittings (ΔE_O) for the 2-position substituted complexes are much larger than those of 3-, or 4-position substituted complexes, since the 2- and 3-, 4-derivatives do not coordinate in the same way. The 2-substituted complexes are bidentate and the 3- and 4-substituted complexes are monodentate. The ground state 3d orbital of the iron in the complexes was identified and the energy separation of the levels estimated. The effect on the isomer shift of substituent group(R) in the 2-position substituted complexes is discussed.     

Kinetics of thermal decomposition of γ-irradiated and unirradiated complexes of mandelhydroxamic acid

The thermal decomposition of -irradiated and unirradiated complexes of mandel-hydroxamic acid (HMA), Co(HMA)₂.1/2H₂O, Mn(HMA)₂.2H₂O, Ba(HMA)₂.2H₂O and Cd(HMA)₂.2H₂O have been studied thermogravimetrically (under isothermal conditions). The thermal dehydration of each complex occurred in one step, while the decomposition of dehydrated complexes occurred in two steps. The kinetic parameters for dehydration were computed by different models. The thermal dehydration is regulated by random nucleation A₃ for Co-, Mn-, and Cd-complexes and by phase-boundary (R₃) for Ba-complex. The effect of -irradiation on the kinetic parameters of thermal decomposition is discussed. Radiation did not modify the mechanism of the reaction but accelarated the dehydration steps in the case of Mn- and Co-complexes.     

Electronic and resonance Raman spectra of iron(II)—tetraazamacrocyclic complexes containing N-heterocyclic ligands

The adducts of the meso-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-1,4,8,11-tetraene iron(II) complex with N-heterocyclic ligands exhibit three characteristic absorption bands in the ranges 690-640, 505-470 and 435-340 nm. Using excitation wavelengths coinciding with the low energy band, a selective enhancement of the Raman vibrational modes of the macrocyclic ligand is observed, supporting the assignment of a metal-to-diimine charge-transfer transition. The high energy band is strongly dependent on the nature and pK_a, of the axial ligands. Excitation at this band leads to the enhancement of the N-heterocyclic vibrational modes in the Raman spectra, indicating a metal-to-(N-heterocycle) charge-transfer transition. The intermediate band exhibits weak resonance Raman activity. Its intensity depends on the proximity of the high energy band and is consistent with the occurrence of an intensity stealing mechanism.     

ESR study of weak exchange interactions in binuclear copper(ii) complexes with acyldihydrazones of fluorinated β-diketones

A series of binuclear copper(ii) complexes with acyldihydrazones of aliphatic dicarboxylic acids (from malonic to adipic) and fluorinated -diketones (trifluoro- and hexafluoroacetylacetone) of composition Cu₂L·2Py (H₄L is acyldihydrazone) were studied by ESR spectroscopy. The ESR spectra of solutions of complexes with trifluoroacetylacetone acyldihydrazones have an isotropic signal with a seven-line hyperfine structure from two equivalent copper nuclei (g = 2.112, a _Cu = (39—40)·10^–4 cm^–1), which is indicative of weak exchange interactions between the paramagnetic centers due to spin density delocalization through a chain of the -bonds of the polymethylene bridge. On going to hexafluoroacetylacetone derivatives, the coupling is suppressed and the ESR spectra of solutions of such complexes show a signal with a four-line hyperfine structure (g = 2.121—2.131, a _Cu = (55—63)·10^–4 cm^–1) typical of mononuclear copper complexes.     

Chemistry of iron complexes—VI. ESR,spectroscopic and other studies of complexes of iron(III) perchlorate and isothiocyanate with bis(tertiary phosphine/arsine oxides)

A series of complexes of bis(tertiary phosphine/arsine oxides), Ph₂E(O) (CH₂)_nE(O)Ph₂ with iron(III) perchlorate and isothiocyanate, viz. [Fe(mdpo)₃] (ClO₄)₃·H₂O, [Fe(edpo)₂ (H₂O)₂] (ClO₄)₃, [Fe(hdpo)₂ (H₂O)₂] (ClO₄)₃, [Fe(edao) (O₂ClO₂)] (ClO₄)₂·H₂O, [Fe(bdao) (OClO₃)₂] (ClO₄)·H₂O, [Fe(bdpo) (ac)₂ (OClO₃)] (ClO₄)₂, [Fe(mdpo)₂ (NCS)₂] (NCS)·3H₂O, [Fe(bdpo) (NCS)₃]·H₂O], [Fe(L — L) (NCS)₃] (L — L) = edpo, edao, bdao and hdpo) [(L — L, n, E; mdpo, 1, P; edpo (or edao), 2, P (or As); bdpo (or bdao), 4, P (or As) and hdpo, 6, P], has been studied with the help of i.r., far i.r. and u.v.-vis, ESR spectra, magnetic moments, X-ray diffraction, TGA and conductance data. All the complexes are high-spin. Possible structures are suggested.     

μ-phenoxo-bridged binuclear copper(II) complexes

Summary Two -phenoxo-bridged binuclear copper(II) complexes, [Fsal(GG)₂Cu₂Cl₃]·H₂O (1) containing an exogenous chloride-bridge and [Fsal(GG)₂Cu₂(OH)](ClO₄)₂·H₂O (2) containing an exogenous hydroxide-bridge, where {Fsal(GG)₂ = 2,6-bis[N-(acetylglycine)-imino-methylene]-4-methylphenol}, were synthesized. The complexes were characterized be several spectroscopic methods. According to variable temperature magnetic susceptibility measurements (4–300 K), the hydroxide-bridged complex (2) has a weak antiferromagnetic spin exchange integral (J =- 23.6 cm), while the chloride complex (1) has an unusual weak ferromagnetic spin exchange integral (J = + 30.9 cm); both complexes have similar optical spectra in the aqueous solutions.     

Synthesis and magnetic studies of phthalato-bridged oxovanadium(Ⅳ) binuclear complexes

Six new μ-phthalato binuclear oxovanadium(IV) complexes,namely [(VO)2(PHTH)-(L)2]SO4 (L denotes 2,2'-bipyridine (bpy);1,10-phenanthroline (phen);4,4'-dimethyl-2,2'-bipyridine (Me2bpy);5-nitro-1,10-phenanthroline (NO2-phen);5-chloro-1,10-phenanthroline (Cl-phen) and 5-methyl-l,10-phenanthroline (CH3-phen),where PHTH is the phthalate dianion),have been synthesized and characterized by elemental analyses,IR,electronic spectra,magnetic moments at room temperature and molar conductivity measurements.The temperature dependence of the magnetic susceptibility of complexes [(VO)2(PHTH)(Phen)2]SO4 (1) and [(VO)2(PHTH)(CH3-phen)2]SO4 (2) was measured in 4-300 K range and the observed data were successfully simulated by the equation based on the spin Hamiltonian operator,H--2JS1S2,giving the exchange integrals J=-12.8 cm-1 for 1 and J=-7.9 cm-1 for 2.This indicates an antiferromagnetic spin-exchange interaction between the metal ions within each molecule.     

Synthesis, structure and characterization of binuclear copper(Ⅱ) complexes

At room temperature, dibenzoyl peroxide undergoes oxidative addition reaction with metallic copper powder and pyridine N-oxide (triphenylphosphine oxide or 2,9-dimethyl-4,7-diphenyl-1,10-phenanthrolin) which affords the last products as binuclear copper(II) complexes, [Cu(C5H5NO)-(C6H5COO)2]2(1), [Cu(OPPh3)(C6H5COO)2]2(2) and [Cu(C6H5COO)(C26H2oN2)](3, C26H2oN2 is 2,9-dimethyl-4,7-diphenyl-1,10-phenanthrolin). The structure of the complexes were characterized by elemental analyses, IR spectra, TG-DTA and magnetic property. Crystals(1) are triclinic, space group P1,a=0.92617(36),b=1.06973(17), c=1.08813(29) nm, a=59.60(2)°, β=74.83(3)°,γ=72.80(2)°, V=0.880 nm3, Dc=1.520 g/cm3, Z=1, R=0.044, Rw=0.048, Mr=805.78, 3477 reflections with I > 3σ(I). Each copper(Ⅱ) ion is coordinated by two bridging bidentate benzoate ligands and one pyridine N-oxide or triphenylphosphine oxide to form dimeric binuclear molecules. The structure of the compound(1) shows a clear centre of symmetry.     

Molecular-topological structure of γ-irradiated polytetrafluoroethylene

The molecular-topological structure of polytetrafluoroethylene (PTFE) has been studied in the range of ?100 to +450°C by thermomechanical spectrometry. Revealed in this temperature range is a fourblock topological structure composed of one amorphous (T _g = 16°C) and three crystalline (low-melting (T _m = 315°C), intermediate (T _m ¹ = 355°C), and high-melting (T _m ² = 388°C)) polymorphs. At a dose of 1 kGy, the long-range orientation of chains in the intermediate and high-melting crystalline blocks of PTFE is replaced by short-range orientation of the cluster association structure. At doses of 100?C500 kGy, the latter structure transitions to the amorphous state and the irradiated samples acquire a semicrystalline structure of the two-block type. The molecular-mass distribution function of interjunction chains of the pseudo-network of the amorphous block is bimodal in character and its maxima are noticeable shifted toward lower masses with an increase in the radiation dose. As the dose increases, the crystallinity decreases and the molecular mobility of amorphized chains is enhanced. As a result, both the glass transition and the molecular flow onset temperatures of the polymer are reduced.     

Luminescent properties of γ-irradiated NaCl

Exposure of alkali halide crystals to high-energy radiation makes the crystals coloured and also causes them to glow. The luminescent behaviour of γ-irradiated NaCl crystals at room temperature is studied and results are presented on the correlation of known types of colour centres to the afterglow.     

Thermal Stability of γ-irradiated Tolbutamide

The thermal stability of tolbutamide before and after exposure to various γ-radiation doses was investigated. The data were followed by studying DTA, X-ray diffraction, IR, and UV absorption spectra before and after γ-irradiation. The results obtained were promising, and were explained, and discussed on the basis of γ-enhanced stabilization through recombination of free radicals. This revised version was published online in August 2006 with corrections to the Cover Date.     

Analysis of the ESR spectra of the ~ CF2CFCF2~ macroradical trapped in a γ-irradiated polytetrafluoroethylene matrix at 77 K

The Β-fluorine atoms in the ~CF₂CFCF₂~ radical trapped in γ-irradiated polytetrafluoroethylene (PTFE) were found to be nonequivalent and, hence, responsible for a doublet-triplet-triplet ESR spectral pattern. The conformational angle between the axis of the unpaired-electron orbital and the projection of C_Β-C_γ bond is equal to 60‡. The hyperfine coupling constants for α- and Β-fluorine atoms were determined. The hyper-fine splitting constants for two equivalent Β-fluorine atoms were found to be 7.2 mT. The corresponding value for the two other equivalent fluorine atoms is 1.8 mT, whereas the hyperfine splitting due to α-fluorine atom is 23.8 mT.     

ESR spectra studies of Cu(Ⅱ) 2,4-dihydroxybenzaldehyde tyrosine complex

A novel Schiff base derived from 2,4-dihydroxybenzaldehyde and tyrosine and its copper(Ⅱ)complex have been synthesized and characterized.The composition of the complex is K[CuL] H2O,where L=H11C16NO5.ESR spectra of the copper(Ⅱ)complex were investigated at different temperatures and in various solvents.The second order effect and the relaxation effect were observed in the solution spectrum at room temperature,which was satisfactorily explained by spin Hamiltonian.The bonding parameters of copper(Ⅱ)complex were calculated using spectral parameters from ESR spectra at low temperature.Its bonding characterization and stability were disscussed.The result shows that the in-plane a-bond and the in-plane π-bond in the complex all play an important role.     

Metal site electronic structure of μ-dithioterephthalato copper(II) binuclear complexes

The preparation and spectroscopic study of three homobinuclear complexes of Cu(II) with dithioterephthalic bisanion. DTTA, formulated as [(μ-DTTA)Cu₂(am)₂](ClO₄)₂, where am=aromatic diamine, is discussed. The instability of the compounds and the results of the spectral studies are in support of a polymeric structure with a local planar CuN₂S₂ chromophore.     

Molecular-topological structure of γ-irradiated ftorlon polytetrafluoroethylene

Six topological structures (an amorphous and five crystalline blocks) have been detected in a polytetrafluoroethylene film with a pseudo-network structure. During the Γ-irradiation of the polymer in air, the crystalline fractions degrade and gradually convert into amorphous and cluster states with the increasing radiation dose. After irradiation at a dose of 90 kGy, the polymer loses its capability for crystallization and forms a completely amorphous topological structure. However, regardless of dose in the range of 3–90 kGy, the topological structure of the polymer irradiated in a vacuum remains unchanged and consists of amorphous, cluster, and crystalline blocks.