EPR Spectra Of Compounds Research Articles

Novel Copper(II) Complexes with Dipinodiazafluorene Ligands: Synthesis, Structure, Magnetic and Catalytic Properties.

The reactions of CuX2 (X = Cl, Br) with dipinodiazafluorenes yielded four new complexes [CuX2L1]2 (X = Cl (1), Br (2), L1 = (1R,3R,8R,10R)-2,2,9,9-Tetramethyl-3,4,7,8,9,10-hexahydro-1H-1,3:8,10-dimethanocyclopenta [1,2-b:5,4-b’]diquinolin-12(2H)-one) and [(CuX2)2L2]n (X = Cl (3), Br (4), L2 = (1R,3R,8R,10R,1’R,3’R,8’R,10’R)-2,2,2’,2’,9,9,9’,9’-Octamethyl-1,1’,2,2’,3,3’,4,4’,7,7’,8,8’,9,9’,10,10’-hexadecahydro-1,3:1’,3’:8,10:8’,10’-tetramethano-12,12’-bi(cyclopenta [1,2-b:5,4-b’]diquinolinylidene). The complexes were characterized by IR and EPR spectroscopy, HR-ESI-MS and elemental analysis. The crystal structures of compounds 1, 2 and 4 were determined by X-ray diffraction (XRD) analysis. Complexes 1–2 have a monomeric structure, while complex 4 has a polymeric structure due to additional coordinating N,N sites in L2. All complexes contain a binuclear fragment {Cu2(μ-X)2×2} (X = Cl, Br) in their structures. Each copper atom has a distorted square-pyramidal coordination environment formed by two nitrogen atoms and three halogen atoms. The Cu-Nax distance is elongated compared to Cu-Neq. The EPR spectra of compounds 1–4 in CH3CN confirm their paramagnetic nature due to the d9 electronic configuration of the copper(II) ion. The magnetic properties of all compounds were studied by the method of static magnetic susceptibility. For complexes 1 and 2, the effective magnetic moments are µeff ≈ 1.87 and 1.83 µB (per each Cu2+ ion), respectively, in the temperature range 50–300 K, which are close to the theoretical spin value (1.73 µB). Ferromagnetic exchange interactions between Cu(II) ions inside {Cu2(μ-X)2X2} (X = Cl, Br) dimers (J/kB ≈ 25 and 31 K for 1 and 2, respectively) or between dimers (θ′ ≈ 0.30 and 0.47 K for 1 and 2, respectively) were found at low temperatures. For compounds 3 and 4, the magnetic susceptibility is well described by the Curie–Weiss law in the temperature range 1.77–300 K with µeff ≈ 1.72 and 1.70 µB for 3 and 4, respectively, and weak antiferromagnetic interactions (θ ≈ −0.4 K for 3 and −0.65 K for 4). Complexes 1–4 exhibit high catalytic activity in the oxidation of alkanes and alcohols with peroxides. The maximum yield of cyclohexane oxidation products reached 50% (complex 3). Based on the data on the study of regio- and bond-selectivity, it was concluded that hydroxyl radicals play a decisive role in the oxidation reaction. The initial products in reactions with alkanes are alkyl hydroperoxides.

Synthesis, crystal structure and spin exchange coupling in polynuclear carboxylates with {Li2(VO)2} metal core

Crystals of binuclear complex [(VO)2(µ-OH)(µ-Piv)2(bpy)2](OTf) (1) have been obtained by the reaction of [VO(H2O)5](OTf)2 (OTf=CF3SO3−, Piv=(CH3)3CCO2−) with 2,2′-bipyridine (bpy) and lithium trimethylacetate (pivalate), Li(Piv), in a ratio of 1:1:2 in MeCN. Change of the reagent ratio to 1:1:3 resulted in the bimetallic compound [Li2(VO)2(µ-Piv)6(bpy)2] (2), which was isolated in the form of 2·MeCN and 2·CH2Cl2 solvates. Replacement of Li(Piv) with lithium trifluoroacetate Li(Tfac) (Tfac=CF3CO2−) results in the bimetallic compound [Li2(VO)2(µ-Tfac)6(bpy)2] (3). A similar reaction with lithium trichloroacetate, Li(Tcac) (Tcac=CCl3CO2−), in ethanol gives the mononuclear complex [VO(Tcac)(bpy)2](OTf) (4). The structures of 1–4 were determined by single crystal X-ray diffraction. The magnetic properties (2–300K) and EPR spectra of compounds 1–3 have been studied. Using the ESEEM (electron spin echo envelope modulation) method it has been shown that the mononuclear cation [VO(Tcac)(bpy)2]+ of complex 4 has partial spin density transfer from the VIV atom to donor ligands (in particular, the bpy nitrogen atoms). According to EPR spectroscopy data and quantum-chemical calculations, a similar spin density distribution is observed for 2 and 3, though spin exchange in these compounds is hindered by lithium ions, which contain no spin density and block electron density delocalization in the bridging system between the “magnetic” vanadium ions. Electrochemical properties of compounds 2 and 3 confirm the vanadium(IV) oxidation state.

Extended hybrid architectures based on tetra-CoIIsandwiched polyoxotungstates

Three extended hybrid materials containing tetra-CoII sandwiched polyoxotungstates [Co(en)2(H2O)]2[Co(en)(H2O)]2[Co4(en)(SiW9O34)2]·2H2en·6H2O (1), [Co(Hen)(H2O)2]2[Co4(H2O)2(SiW9O34)2]·3H2en·28H2O (2) and [Co(enMe)2]4[Co(enMe)]2[Co4(H2O)2(SiW9O34)2]·22H2O (3) (en = ethylenediamine, enMe = 1,2-diaminopropane), have been hydrothermally synthesized and structurally characterized by IR spectra, UV-vis spectra, elemental analysis, thermogravimetric analysis, and single-crystal X-ray diffraction. Compound 1 is based on the tetra-Co-complex-supported clusters {[Co(en)2(H2O)]2[Co(en)(H2O)]2[Co4(SiW9O34)2]} through the linkage of en in an end-to-end fashion to form a 1-D linear chain, whereas compound 2 is constructed from [Co4(H2O)2(SiW9O34)2]12− building blocks and [Co(Hen)(H2O)2]3+ complexes with (3,6)-network topology. The novel 2-D structure of 3 consists of the building blocks [Co4(H2O)2(SiW9O34)2]12− decorated by two [Co(enMe)2]2+ groups and two types of cobalt complexes as double bridges, which was first observed in 2-D layered hybrid materials based on sandwich polyoxotungstates with a (4,4)-connected topology. Furthermore, at room temperature, the EPR spectra of compounds 1, 2 and 3 display broad signals due to the interaction within CoII ions. The values of the g tensor derived from the EPR spectra are ca. 2.57 for 1, ca. 2.20 for 2 and ca. 2.51 for 3, respectively, which are affected by the different coordination environments of CoII ions.

Versatile binding properties of a di-2-pyridyl ketone nicotinoylhydrazone ligand: Crystal structure of a Cu(II) complex

Six new copper complexes of di-2-pyridyl ketone nicotinoylhydrazone (HDKN) have been synthesized. The complexes have been characterized by a variety of spectroscopic techniques and the structure of [Cu(DKN) 2]·H 2O has been determined by single crystal X-ray diffraction. The compound [Cu(DKN) 2]·H 2O crystallized in the monoclinic space group P2 1 and has a distorted octahedral geometry. The IR spectra revealed the presence of variable modes of chelation for the investigated ligand. The EPR spectra of compounds [Cu 2(DKN) 2(μ-N 3) 2] and [Cu 2(DKN) 2(μ-NCS) 2] in polycrystalline state suggest a dimeric structure as they exhibited a half field signal, which indicate the presence of a weak interaction between two Cu(II) ions in these complexes.

EPR study of compounds in the LaAlO3-La0.67Sr0.33MnO3 system

The EPR spectra of compounds in the LaAlO3-La0.67Sr0.33MnyO3 system at a frequency of 9.4 GHz have been investigated at the temperatures T = 77 and 300 K as a function of the manganese concentration y (y = 0.015, 0.030, 0.080). It has been revealed that, in the paramagnetic state at y = 0.015, there exist isolated Mn2+ and Mn4+ ions, which has been confirmed by simulating the EPR spectra. The parameters of the EPR spectra have been determined. The effective magnetic moments μeff of the Mn2+ and Mn4+ ions have been calculated from the EPR spectra. It has been demonstrated that an increase in the Mn concentration leads to a decrease in the number of isolated ions and to the formation of new spin clusters. This manifests itself in the predominance of a broad line with weak traces of the hyperfine structure due to the isolated manganese ions.

Synthesis, crystal structure and spectroscopic properties of copper(II) complexes derived from 2-methylamino-5-pyridin-2-yl-1,3,4-oxadiazole

Two new complexes with the formulae [Cu(L)(oxalatoo)(H 2O)]·H 2O ( 1) and [Cu(L) 2(H 2O) 2](NO 3) 2 ( 2), where L=(C 8H 8N 4O)=2-methylamino-5-pyridin-2-yl-1,3,4-oxadiazole, have been synthesized and characterized. The structure of compound 1 contains monomeric entities in which the copper(II) ions exhibit five-coordinate square-pyramidal geometry. The oxadiazole bidentate ligand links to the metal ion through the N pyridine and one of the N oxadiazole atoms. Two oxygen atoms from the oxalato ligand complete the basal positions. The oxygen atom of a water molecule occupies the apical one. Solvation water molecules are also present in the lattice. The structure of compound 2 consists of monomeric distorted octahedral copper(II) species. The copper(II) ions are coordinated to both bidentate oxadiazole ligands in the equatorial plane, with the two oxygen atoms of both water molecules placed in the axial positions. Nitrate groups act as counterions. The presence of π–π stacking interactions interconnecting the monomeric entities in both complexes is discussed. The EPR spectra of compounds 1 and 2 show axial symmetries.

Binuclear Copper(II) Complexes with (1R*,4S*)-1-N-Morpholino-n-menth-8-en-2-one E-oxime: Synthesis, Structure, and Magnetic Properties

Copper(II) complexes with (1R*,4S*)-1-N-morpholino-n-menth-8-en-4-one (HL), namely, [Cu2(HL)2Cl4] (I) and [Cu2(HL)LCl3] · CH3CN (II), were synthesized and characterized by X-ray diffraction analysis, magnetic susceptibility, and EPR methods. The complexes have binuclear structures. In compound I, the coordination polyhedron of CuCl3N2 is a square pyramid in planar Cu2Cl2 metal cycle; the exchange couplings of unpaired electrons of Cu(II) ions are weak. Complex II incorporates polyhedra of CuCl2N2 (flattened tetrahedron) and of CuCl2N2O (trigonal bipyramid). The Cu2ClNO metal cycle is nonplanar with antiferromagnetic exchange coupling and exchange parameter –2J = 182 cm–1. The EPR spectrum of compound I are analyzed.

Synthesis and spectroscopic properties of copper(II) complexes derived from thiophene-2-carbaldehyde thiosemicarbazone. Structure and biological activity of [Cu(C 6H 6N 3S 2) 2

The synthesis, structure and spectroscopic properties on complexes with the formula [Cu(L III) 2] ( 1) and Cu(NO 3) 2(HL III) 2 ( 2), where HL III = thiophene-2-carbaldehyde thiosemicarbazone, have been developed. The molecular structure of compound 1 consists of monomeric entities. The copper(II) ions exhibit distorted square-planar geometry with both bidentate thiosemicarbazone ligands placed in a centrosymmetric way. Metal to ligand π-backdonation is proposed to explain several structural and spectroscopic features in these complexes. The EPR spectra of compound 1 show an orthorhombic g tensor indicating the presence of weak magnetic exchange interactions. The reaction of compound 1 with glutathione causes the reduction of the metal ion and the substitution of the thiosemicarbazone ligand by the thiol ligand. This mechanism seems to be related to the cytotoxicity of this complex against Friend Erithroleukemia cells (FLC) and melanome B16F10 cells.

Spectroscopic and magnetic properties of the pyridine-2-carbaldehyde thiosemicarbazonateiron(III) complexes: [Fe(C 7H 7N 4S) 2]X·ηH 2O (X = Cl, ClO 4, NO 3, PF 6). Crystal structure of the hexafluorophosphate compound

The [Fe(C 7H 7N 4S) 2]X·ηH 2O (X = Cl ( 1), ClO 4 ( 2), NO 3 ( 3), PF 6 ( 4); n = 0 ( 4), 1.5 ( 1), 0.5 ( 3)) compounds, where C 7H 8N 4S is pyridine-2-carbaldehyde thiosemicarbazone, have been synthesized and characterized. The crystal structure of compound 4 has been solved. It crystallizes in the monoclinic P/2 1 n space group with a = 13.099(2), b = 12.153(5), c = 13.710(1)Å, β = 102.56(1)°, V = 2130(1)Å 3, Z = 4. The framework consists of discrete monomeric cationic entities containing low-spin iron(III) ions in a distorted octahedral environment. The metal ion is bonded to one sulfur and two nitrogen atoms of each thiosemicarbazone molecule. The hexafluorophosphate molecules act as counterions. Extended Hu¨ckel MO calculations for complex 4 reveal a high delocalization and an important charge transfer contribution from the ligands to the metal. EPR spectra of compounds 1, 2, 3 and 4 show rhombic signals. Their main features, which can be expressed as a relatively low anisotropy in g values and a g 3 value which is greater than usual, are due to the low symmetry and the electronic delocalization.

Ni(II) and Cu(II) schiff base complexes with an extended H-bond network

Reaction of the hydroxy-rich Schiff base Hsaladhp = Ph(OH)CHNC(CH 3)(CH 2OH) 2 with CuCl 2·4H 2O or NiCl 2·4H 2O. gave mononuclear complexes CuCl[Ph(O)CHNC(CH 4)(CH 2OH) 2]·H 2O ( 1). Ni[Ph(O)CHNC(CH 3)(CH 2OH) 2] 2 ( 2) and Ni[Ph(O)CHNC(CH 3)(CH 2OH) 2] 2·(C 5H 5N)·2H 2O ( 3). The complexes were characterized by spectroscopic methods and by single crystal X-ray structure determination. 1 crystallizes in the orthorhombic space group Pcab, with a = 10.638(1), b = 27.584(2), c = 8.818(1) A ̊ and D cale = 1.665 g cm −3 for Z = 8; 2 crystallizes in the triclinic space group P 1 , with a = 14.637(2), b = 10.912(1), c = 8.794(1) A ̊ , α = 74.444(3), β = 112.579(3), γ = 87.138(3)° and D cale = 1.393 g cm fro Z = 2: 3 crystallizes in the monoclinic space group P2 1/ c, with a = 10.166(1), b = 12.65(1), c = 25.960(2), β = 97.232(3)° and D cale = 1.342 g cm for Z =4. The EPR spectra of compound 1 in the solid state give features characteristics for the presence of an S = 1 triplet state due to the presence of the extended H-bond network.

Synthesis, characterization and properties of two novel octanuclear heterometallic molecules consisting of two triangular molybdenum clusters bridged by oxochromium ligands: M 2[Mo 3O 4(O 2CEt) 8Cr 2(O 2CEt) 8O 4Mo 3] · n(HO 2CEt) (M = K, n = 2; M = Li, n = 0)

Two novel octanuclear mixed-metal clusters M 2[Mo 3O 4(O 4CEt) 8Cr 2(O 2CEt) 8O 4Mo 3] · n(HO 2CEt) [M = K, n = 2 ( 1); M = Li, n = 0 ( 2)] have been synthesized and characterized by X-ray crystallographic structure determinations. Compound 1 is soluble in EtOH and N,N′-dimethylformamide solution, while compound 2 is insoluble. Both compounds contain a novel cyclic anion formed by two triangular trinuclear molybdenum cluster anions [Mo 3O 4(O 2CEt) 8] 4− and two chromium atoms as bridges connecting the two triangular molybdenum cluster anions. The potassium atom in compound I is coordinated to six oxygen atoms, including one oxygen atom from a weakly bound terminal HO 2CEt ligand. The lithium atom in compound 2 is five-coordinate. The weakly bound terminal ligand is responsible for the solubility of compound 1. Cyclic voltammetry shows a quasireversible redox couple for compound 1 at −0.97/−0.75 V/SCE and an irreversible oxidation peak at −0.52 V/SCE. The EPR spectrum of compound 1 suggests strong delocalization of electrons in this compound.

EPR studies of some vanadium oxyfluoro anionic complexes

Abstract The EPR of Vanadium (IV) in natural abundance of KVO2F20.5H2O[A], K2VO2F30.5H2O[B], K3VO2F4[C], and K3VOF6[D], prepared by a solid state route, was studied at different temperatures in the range 77-573K. The spectra of compounds A and B are nearly temperature independent and are characteristic of a rigid anion. Only in compound B, the 19F super hyperfine structure can be seen well resolved on one of the perpendicular components even at room temperature. The EPR spectra of compounds C and D are characterised by the presence of discrete anionic species, and, depending on the temperature, some of the anions are in rigid state while the others are in re-orienting state. EPR and DSC studies indicate the occurrence of a first order phase transition in these two compounds.