Powder ESR Research Articles

Synthesis and magnetic properties of novel oxamido heterotrinuclear complexes Cu IIM IICu II (M = Mn and Cu)

Two novel trinuclear complexes have been synthesized, namely [Cu 2(oxae) 2(H 2O) 2Mn](ClO 4) 2 ( 1) and [Cu 2(oxae) 2Cu](ClO 4) 2 ( 2), where oxae denotes the N, N′-bis(2-aminoethyl)oxamido dianion. Based on IR, elemental analyses, conductivity measurements and electronic spectra, the complexes are proposed to have extended oxamido-bridged structures. The magnetic susceptibility of the complex 1 has been studied in the 4–300 K range and the observed data were fit by least-squares to a susceptibility equation derived from the spin Hamiltonian, H ̂ = −2J( S ̂ 1 S ̂ 2 + S ̂ 2 S ̂ 3)−2J′ S ̂ 1 S ̂ 3 . The exchange integrals, J and J′, were found to be equal to −18 and −0.38 cm −1. This procedure indicates the existence of an antiferromagnetic spin-exchange interaction between the adjacent metal ions. The powder ESR spectrum of complex 1 has been obtained and discussed.

Synthesis of a derivative of triangulene; the first non-kekulé polynuclear aromatic

The first synthesis of a non-Kekule polynuclear aromatic, a trioxy derivative of triangulene, has been achieved through a two-electron reduction of tetrabutylammonium 4,8-dioxo-4H,8H-dibenzo[cd,mn]pyren-12-olate 14. The single crystal X-ray diffraction structure of this precursor shows it to be essentially planar with a three-fold axis of symmetry. The trioxytriangulene produced when it is reduced also possesses a three-fold axis of symmetry and it has a triplet ground state. The powder ESR spectrum obtained is that for a uniaxial system fitted using the parameters |D/hc|= 0.0064 cm–1, |E/hc|= 0.0000 cm–1. It is stable at room temperature but very sensitive to sir oxidation.

ESR study of Cu(II)-indomethacin and its pyridine and DMF adducts

Powder ESR spectra of [Cu2(Ind)4](H2O)2 at room temperature show the presence of copper acetate like dimers characterized by a strong antiferromagnetic exchange interaction (J≈−338 cm−1). Two different monomeric species were evidenced in 40%Py+60%DMF solution absorbed on NaY zeolite: the Cu(Ind)2(DMF)2 with an elongated tetragonal-octahedral symmetry and the Cu(Ind)2(Py)2 with a CuN2O2 chromophore in atrans square-planar arrangement. Only one monomeric species Cu(Ind)2(Py)2 was identified in 20%Py+80%DMF and 20%Py+80% Chloroform solutions. The Cu(Py)42+ species of CuN4 chromophore occurs in pyridine Cu(II)-indomethacin solution suggesting a decomposition of the solvit compound.

Syntheses, properties and structures of copper and nickel complexes of 6,7‐dihydro‐5H‐1,4‐dithiepin‐2,3‐dithiolate

AbstractThe reaction of CuCl2·2H2O or NiCl2·6H2O with K2(C5H6S4) [potassium salt of 6,7‐dihydro‐5H‐1,4‐dithiepin‐2,3‐dithiolate] under nitrogen atmosphere resulted in the isolation of [Cu(C5H6S4)2]− or [Ni(C5H6S4)2]− as the tetrabutylammonium salt. Both complexes show characteristic IR and UV −Vis absorptions of transition metal dithiolenes. Cyclic voltammograms contain two waves indicating a two step electrochemical procedure [M(C5H6S4)2]0 = [M(C5H6S4)2]1‐= [M(C5H6S4)2]2‐ Single crystal structure study has been carried out on the nickel complex. Crystal of [Bu4N][Ni(C5H6S4)2] belongs to monoclinic space group P21/c with a=17.576(5), b=10.883(2), c=17.773(4) A, β=91.07(2)°, Z=4, and ρ(calcd.)=1.348 g/cm3. Final result is R=0.059 for 2959 reflections. The NiS4 core exhibits square planar coordination with average Ni—S bond length of 2.134(5) Å. There are not anion pairs in crystal. The anions stack along a and c axes while the cations intercalate in them. The nearest S—S contact is 4.429 Å. The solid powder ESR spectrum of the nickel complex shows three broadening signals at g1 =2.097, g2=2.042, g3=2.022. Magnetic susceptibility data for [Bu4N][Ni(C5H6S4)2] reveal enhanced anti‐ferromagnetic interaction.

Synthesis and crystal structure determination of a one-dimensional end-to-end cyanate-bridged copper(II) compoun

The compound [{CuL(µ-NCO)}n][ClO4]n1(L =N, N, N′, N″, N″-pentamethyl-3-azapentane-1, 5-diamine) was synthesized and characterized. The crystal structure was determined by single-crystal X-ray analysis: orthorhombic, space group P21nb, a= 6.534(2), b= 10.945(3), c= 22.683(4)A, Z = 4. The magnetic behaviour was recorded between 290 and 2 K, showing antiferromagnetic coupling. The magnetic susceptibility data were fitted to the expression for a homogeneous S=½ linear chain, giving the parameters 2J=–1.26 cm–1and g= 2.10. Polycrystalline powder ESR spectra recorded at 4, 77, 180 and 298 K remained unchanged, showing axial distortion with g∥= 2.21 and g⊥= 2.06. The single-crystal ESR spectrum was also recorded at room temperature: g1= 2.059, g2= 2.055, g3= 2.21 3.

Synthesis, Characterization, Spectral, Magnetic, XRD and ESR Studies on Some Novel Trinuclear Copper(II) Tetrathiocyanatodiargentate(I) Complexes with Acyl Hydrazine and Hydrazone Bases

Abstract Copper(II) complexes of the type CuAg2(SCN)4˙L (where L = benzoylhydrazine (BH), p-hydroxybenzoylhydrazine (PHBH), salicyloylhydrazine (SH), isonicotinoylhydrazine (INH), anthraniloylhydrazine (AH) and their isopropanone derivatives viz., isopropanone benzoylhydrazone (IBH), -salicyloylhydrazone (ISH), -anthraniloylhydrazone (IAH), and -isonicotinoylhydrazone (IINH) have been synthesized and characterized with the help of elemental analyses, electronic and IR spectra and magnetic moment data. Electronic spectral bands and μeff values suggest a distorted octahedral environment around copper(II). SCN groups act as bridge between two metal centres while all the ligands are bi-coordinately bonded through >C=O and -NH2 or >C=N-groups, except in CuAg2 (SCN)4˙L (L = INH and IINH) where the ligands are coordinated through -NH2/-N=C< and pyridyl ring nitrogens. Powder ESR data suggest an isotropic nature of all the complexes except for CuAg2 (SCN)4.SH where an axial nature of copper(II) is observed. Presence of half field signal in CuAg2 (SCN)4.PHBH complex suggests its dimeric nature. Powder X-ray diffraction studies for CuAg2(SCN)4 and CuAg2 (SCN)4. IBH suggest the presence of orthorhombic and tetragonal crystal lattice respectively.

Electron spin resonance spectroscopy of free radicals

AbstractSolution and powder ESR spectra of the 4‐trifluoromethyl‐1,2,3,5‐dithiadiazolyl and 4‐pentafluorophenyl‐1,2,3,5‐dithiadiazolyl free radicals were analysed. Comparison of the ESR parameters with those obtained for the protonated equivalents shows that fluorination produces a drift of unpaired electron spin density away from the nitrogen 2px orbitals towards sulphur 3px orbitals (x is the direction perpendicular to the heterocyclic ring), consistent with an increase in electronegativity of the substituent. The fluorinated radicals dimerize more readily than their protonated counterparts.

Selective formation of specific alkyl radicals by gamma-irradiation of cis-decalin-d18/chloroalkane and bromoalkane systems at 77K a general method for obtaining powder ESR spectra of specific alkyl radicals

Irradiation of chloro- and bromoalkanes in solid cis-decalin-d18 results in the selective formation (as major paramagnetic species) of alkyl radicals that are specific or the haloalkane solute, in addition to matrix radicals. The method offers a convenient and universal technique for generating, specific alkyl radicals and for examining their powder ESR spectrum. Examples of the generation of chain-end, penultimate and interior alkyl radicals are given. Computer calculations, in which spectra of penultimate and interior radicals are added, clearly demonstrate that quite extensive amounts of interior radicals can be present in a radical mixture, without considerably affecting the composite spectrum.

Structure and magnetic exchange of an imidazolate-bridged copper dimer: [(dtma)Cu(im)Cu(dtma)]ClO 4·2.5H 2O

The compound of the formula [(dtma)Cu(im)Cu(dtma)]ClO 4·2.5H 2O (where dtmaH is 4-diethylenetriamineacetic acid and im is the imidazole anion) was synthesized and its crystal structure determined by X-ray diffraction methods. The structure consists of a dimeric complex bridged by the deprotonated imidazole. The geometries of the coordination polyhedron around the copper(II) ions are very near to tetragonal pyramid. The X-band ESR powder spectrum shows broad Δ M = 1 and weak Δ M = 2 absorptions. Variable-temperature (4.2–300 K) magnetic susceptibility data gave the antiferromagnetic interaction parameters J = −37 cm −1. This behaviour is best accounted for by a superexchange mechanism involving σ- and π-exchange pathways.

ESR spectroscopic investigation of some 4‐substituted 1,3,2‐dithiazolyl and 2,3,1‐dithiazolyl radicals

AbstractFurther information has been obtained on the electronic structure of 1,3,2‐dithiazol‐2‐yl radicals. The structure has been well characterized previously except for positions 4 and 5 in the equation image ring. We have obtained solution and powder ESR spectra of radicals substituted with 13C in both positions and of radicals substituted with nitrogen or phosphorus in the 4‐position. It is probably the first time that a compound has been prepared containing the equation image ring. Two especially interesting facts emerged from the ESR spectra of these 1,3,2‐dithiazolyl radicals: the 13C‐substituted radical has a considerable amount of p spin density in the plane of the ring and the phosphorussubstituted radical has a very low unpaired spin density at the phosphorus atom. It is known that 1,3,2,4‐dithiadiazolyl radicals isomerize readily by photolysis to the symmetrical 2,3,1,4‐dithiadiazolyl radicals; we attempted the same reaction with But equation image and a new radical was produced that we have been unable to identify.

Molecular design, synthesis, and magnetic characterization of poly(phenylacetylene) with pi‐toporegulated pendant nitronyl nitroxide radicals as models for organic superpara‐ and ferromagnets

AbstractThe present article describes the synthesis and magnetic properties of poly(phenylacetylene) (3) with pi‐toporegulated pendant stable 4,4,5,5‐tetramethylimidazolin‐3‐oxide‐1‐yloxyl radicals topologically participating in the pi‐conjugated system of poly(phenylacetylene). Polyradical 3 was prepared by the condensation reaction of poly(p‐ethynylbenzaldehyde) with 2,3‐bis(hydroxylamino)‐2,3‐dimethylbutane followed by oxidation with lead dioxide. The spin concentration of 3 determined by the ESR spectroscopic method was 1.1 × 1021 spins/g. This value approximately corresponds to 0.5 unpaired electron spin per the repeating unit. A powder ESR spectrum of 3 gave a 100% Lorentzian single line showing spin‐exchange narrowing. The vibrating sample magnetometer (VSM) measurement of 3 afforded a straight line with a positive slope, suggesting that 3 has predominant paramagnetic properties within an experimental error.

Spectroscopic studies on copper(II) halide complexes with isomeric benzoylpyridines: Electronic and electron spin resonance spectral evidence for five-coordinate copper(II) species in solution

Coordination compounds formed by copper(II) chloride and bromide with 2-, 3- and 4-benzoylpyridines (BOP)Cu(2-BOP)Cl 2 , Cu(3-BOP) 2 Cl 2 , Cu(4-BOP)Cl 2 , Cu(2-BOP) 2 Br 2 , Cu(3-BOP) 2 Br 2 and Cu(4-BOP) 2 Br 2 —have been characterized by elemental analyses, molar conductance, magnetic moments, electronic, IR and ESR spectral studies. It is suggested that Cu(2-BOP)Cl 2 is monomeric tetrahedral, Cu(3-BOP) 2 Cl 2 and Cu(4-BOP)Cl 2 are dimeric octahedral and tetrahedral structures, respectively, bridging through chlorines while all the bromo complexes are polymeric octahedral structures with bridging bromine atoms in the solid state. Powder ESR data reveal rhombic symmetry for all the chloro complexes. Cu(2-BOP) 2 Br 2 is suggested to have an axial symmetry while the other bromo complexes are isotropic in nature. Electronic and ESR spectral studies in DMSO solution suggest the interaction of solvent molecules with copper(II) ions in the axial plane. The solution spectral data are almost comparable suggesting same local symmetry for all the compounds consistent with five-coordinate square pyramidal geometry in each case. ESR spectra also suggest considerable CuCu interactions in Cu(3-BOP) 2 Cl 2 . Various Spin—Hamiltonian parameters calculated from ESR data indicate the presence of an unpaired electron in the d x 2 − y 2 orbital of the copper(II) ion in an axial symmetry.

Intercalation of ferrocenylalkylammonium cations into the layered lattice of VOPO4

Some ferrocenylalkylammonium iodides, [FeII(C5H5){C5H4(CH2)nNR2R′}]+I–(n= 1 or 2; R,R′= H or Me), benzyldimethyl- and benzyltrimethyl-ammonium iodides reacted with VvOPO4·H2O·EtOH suspended in ethanol to afford intercalation compounds of VOPO4·H2O with 0.45[FeII(C5H5)(C5H4CH2NHMe2)]+, 0.20[FeII(C5H5)(C5H4CH2 NMe3)]+, 0.43[FeII(C5H5)(C5H4CH2 CH2NH3)]+, 0.17[FeIII-(C5H5)(C5H4 CH2CH2NMe3)]2+, 0.54PhCH2NHMe2+ and 0.45PhCH2NMe3+. Ferrocenylalkylammonium chlorides, [FeII(C5H5)(C5H4CH2 NHMe2)]+Cl– and [FeII(C5H5)(C5H4CH2 CH2NH3)]+ Cl–, were also intercalated to give compounds of VOPO4·H2O with 0.29[FeIII(C5H5)(C5H4 CH2NHMe2+Cl–)]+ and 0.18[FeIII(C5H5)(C5H4 CH2CH2NH3+Cl–)]+. The intercalation compounds comprise layered VOPO4 moieties having both the vanadium-(IV) and -(V) states and the ferrocenylalkyl-, benzyldimethyl-, and benzyltrimethyl-ammonium cations as well as ferrocenium-substituted alkylammonium chlorides, [FeIII(C5H5)(C5H4CH2 NHMe2+Cl–)]+ and [FeIII(C5H5)(C5H4CH2 CH2NH3+Cl–)]+, in the interlayer space, producing VOPO4–interlayer spacings of 9.8–21.0 A. The molecular arrangements of these alkylammonium-substituted ferrocene and ferrocenium species in the interlayer space and the electronic states of the guest and host moieties are discussed on the basis of powder X-ray diffraction patterns, and IR, ESR and X-ray photoelectron spectra.

Synthesis, crystal structure and magnetic properties of di-µ-hydroxo-bis[(2,2′-bipyridine)(trifluoromethanesulfonato-O)-copper(II)

The compound [Cu2(bipy)2(OH)2(CF3SO3)2](bipy = 2,2′-bipyridine) has been synthesised and its crystal structure determined by X-ray crystallographic methods. Crystals are triclinic with a= 8.165(2), b= 14.265(2), c= 18.748(5)Å, α= 93.10(1), β= 100.58(2), γ= 99.17(1)°, space group P, and Z= 3. Least-squares refinement of 5872 reflections with I 3σ(I) and 679 parameters gave a final R′= 0.042. The structure consists of discrete centrosymmetric and non-centrosymmetric di-µ-hydroxo-copper(II) dimers with 2,2′-bipyridine as outer ligand and semi-co-ordinated CF3SO3– anions. Intramolecular copper–copper distances are 2.920(1) and 2.8917(7)Å for the centrosymmetric and non-centrosymmetric dimers respectively. The co-ordination geometry around each copper ion is square pyramidal with the bridging hydroxo groups and two nitrogen atoms of the bipyridine ligand comprising the basal plane, and the apical site occupied by an oxygen atom of the CF3SO3– group. Coupled variable-temperature powder ESR spectral and magnetic susceptibility data demonstrate that the copper(II) ions within both dimeric molecules are ferromagnetically coupled (Jc= 17, Ja= 158 cm–1, g 2.09 and 2.10, with J= singlet–triplet energy gap and subscripts c and a denoting the centrosymmetric and asymmetric dimers). The nature and strength of the exchange interaction is discussed on the basis of the structural features and correlated with previously reported magnetostructural data for other di-µ-hydroxo-bis[2,2′-bipyridine)copper(II)] complexes.

Studies on salicylaldehyde-2-aminobenzophenone-2-thenoylhydrazone complexes with 3d metal ions

Salicylaldehyde-2-aminobenzophenone-2-thenoylhydrazone (Hsabth) complexes of OV(IV), Mn(II), Ni(II), Ni(II), Cu(II) and Zn(II) having 1∶2 metal-ligand stoichiometry have been prepared and characterized by elemental analyses, molar conductance, magnetic susceptibility, electronic, ESR, infrared, NMR (1H and13C) and X-ray powder diffraction studies. Square pyramidal geometry around oxovandium(IV) and octahedral geometry around the rest of the metal ions have been proposed on the basis of magnetic and spectral studies.

Intramolecular dynamics of the C 4H 8NH radical cation. An application of the anisotropic exchange theory for powder ESR lineshapes

The temperature variation of ESR spectra attributed to the heterocyclic radical cation C 4H 8NH + stabilised in a CFCl 3 matrix is shown to be due to intramolecular dynamics of the ring. Two new methods for simulating anisotropic exchange broadened ESR spectra, the secular and nonperturbative, were utilised to investigate the dynamics of C 4H 8NH +. The powder ESR lineshape exhibits overall anisotropic features and a differentiated broadening with respect to the nuclear spin quantum numbers, which could be explained by simultaneously including the g- and hyperfine tensor anisotropies in the model for the dynamical motion. The motion was described by an interconversion of the ring between two isodynamic twisted structures having C 2 symmetry. It was concluded that the major changes of the ESR lineshape were governed by the exchange of the isotropic hyperfine coupling constants. The anisotropic interactions were shown to account for the overall anisotropic features and the differentiated broadening of the spectra.

ESR and optical absorption spectra of vanadyl ion in magnesium maleate dihydrate single crystals

Abstract ESR and optical absorption spectra of VO2+] ions doped in single crystals of magnesium maleate dihydrate have been studied between 300 K to 120 K. The spin-Hamiltonian parameters are determined from single crystal ESR data and also from powder ESR data. The g and A tensors are found to be axially symmetric. Two distinct vanadyl complexes at substitutional sites (Mg2+]) have been identified. From the optical and ESR data the molecular orbital bonding coefficients have been evaluated.

Studies on 2-Acetylfuran-2-Thenoylhydrazone Complexes of Some Bivalent Metal Ions

Abstract 2-Acetylfuran-2-thenoylhydrazone, C4H3SC(O) NHNC(CH3)C4H3O (Hafth) yields the complexes VO(Hafth)2SO4, M(Hafth)2Cl2 [M = Mn(H), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II)] and M(afth)2(H2O)2 [M = VO(IV), Mn(II), Co(II), Ni(II), Cu(II) and Zn(II)] depending on the pH of the reaction medium. The complexes have been characterized by elemental analyses, molar conductance, magnetic susceptibility, electronic and photoacoustic, esr, ir, nmr (1H and 13C) and X-ray powder diffraction studies. Square pyramidal geometry for the OV(IV) complexes and octahedral geometry for the remaining complexes have been proposed.

Studies of mixed-valence states in three-dimensional halogen-bridged gold compounds, Cs2Au I Au III X6(X = Cl, Br or I). Part 1. Synthesis, X-ray powder diffraction, and electron spin resonance studies of CsAu0.6Br2.6

A new non-stoichiometric mixed-valence compound CsAu0.6Br2.6 has been prepared, and its powder X-ray diffraction profile, ESR spectra, and electrical conductivity determined. From its empirical formula the average valence of Au is + 2.67. Powder diffraction data indicate that the compound has a cubic perovskite structure [cubic lattice, space group Pm3m, a= 5.462(2)A]. This means that the AuBr6 octahedra are crystallographically equivalent. ESR measurements show the existence of a +II formal oxidation state for Au. The conductivity is four orders of magnitude higher than that of the AuI–AuIII mixed-valence compound Cs2Au2Br6.

Crystal structure and spectroscopic properties of a copper(II) complex with a chain arrangement: [Cu(pymep)Cl(H 2O)](PF 6)

A novel complex of copper(II) with the tridentate ligand N-[2′-(6-methyl)pyridyl]methylene-2-(2′-pyridyl)ethylamine (pymep), of formula [Cu(pymep) Cl(H 2O)](PF 6), has been synthesized and its X-ray crystal structure determined. The structure consists of [Cu(pymep)Cl(H 2O)] + cations and hexafluorophosphate anions. The copper complex is stacked to make a chain arrangement orientated in the [010] direction. The geometry of the coordination polyhedron around the copper(II) ion is close to tetrahedrally distorted square pyramidal (SP th). One broad, unresolved band centred at 13,800 cm −1 is observed in the diffuse reflectance spectrum. The X-band ESR powder spectrum shows an orthorhombic signal with g 1 = 2.219, g 2= 2.210 and g 3 = 2.047.