Single Crystal EPR Studies Research Articles

Analysis of electron paramagnetic resonance and optical studies of central metal ion (Cu2+) in lithium potassium phthalate single crystal

Molecular ion Cu2+ in lithium potassium phthalate (LiKP) single crystal has been grown at room temperature by slow evaporation process. Single crystal EPR study has been taken for the LiKP:Cu2+ crystal. Presence of two Cu2+ sites is reported from EPR data. Angular variation plot in the three planes is used to determine the principal g and A values. Spin Hamiltonian parameter values reveal that site A and site B exist as orthorhombic and axial crystal field symmetry around the impurity ion. Substitutional incorporation has occurred for site A and site B exists as interstitial position in the LiKP:Cu2+ crystal lattice. Using admixture coefficient terms, the ground state of the grown crystal has been calculated. Molecular orbital coefficients have been obtained from the principal g and A values. Optical absorption study was carried out at room temperature. Through optical absorption data, Dq, Ds, and Dt parameters have been evaluated, showing the tetragonally distorted octahedral symmetry of Cu2+ ion in LiKP lattice.

Single crystal EPR and X-ray studies of exchange interactions in Hexaaquocopper (II) picrylsulphonate tetrahydrate

Single crystal EPR and X-ray studies of exchange interactions in Hexaaquocopper (II) picrylsulphonate tetrahydrate

Synthesis, characterization, single crystal X-ray structure, EPR and theoretical studies of a new hybrid inorganic-organic compound [Cu(Hdien)2(H2O)2](pnb)4·4H2O and its structural comparison with related [Cu(en)2(H2O)2](pnb)2

A new hybrid inorganic-organic compound [Cu(Hdien)2(H2O)2](pnb)4·4H2O (1) (where pnb = p-nitrobenzoate), in which the tridentate ligand diethylenetriamine (dien) shows an unusual coordination behavior acting as a bidentate ligand when present in its monoprotonated form (Hdien+) has been synthesized by the reaction of copper(II) p-nitrobenzoate and slight excess of dien in methanol-water mixture (4:1v/v). Re-crystallization of the violet precipitated product from hot water gave single crystals suitable for X-ray diffraction studies. The newly synthesized compound 1 has been characterized by spectroscopic techniques (UV–Vis, FT-IR, EPR), and theoretical methods (DFT and MRCI/SORCI). Single crystal X-ray structure determination revealed the existence of the cationic species [Cu(Hdien)2(H2O)2]4+, four p-nitrobenzoate as counter anions and four water molecules are present as solvent of crystallization. Packing analyses of title compound as well as of the structurally similar [Cu(en)2(H2O)2](pnb)2,2 has shown similarities in the crystalline architecture that both hybrid inorganic-organic compounds is stabilized by various non-covalent interactions such as N-H⋯O, C-H⋯O, O-H⋯O etc.

Synthesis, Structure, and Properties of Al((R)bpy)3 Complexes (R = t-Bu, Me): Homoleptic Main-Group Tris-bipyridyl Compounds.

The neutral homoleptic tris-bpy aluminum complexes Al((R)bpy)3, where R = tBu (1) or Me (2), have been synthesized from reactions between AlX precursors (X = Cl, Br) and neutral (R)bpy ligands through an aluminum disproportion process. The crystalline compounds have been characterized by single-crystal X-ray diffraction, electrochemical experiments, EPR, magnetic susceptibility, and density functional theory (DFT) studies. The collective data show that 1 and 2 contain Al(3+) metal centers coordinated by three bipyridine (bpy(•))(1-) monoanion radicals. Electrochemical studies show that six redox states are accessible from the neutral complexes, three oxidative and three reductive, that involve oxidation or reduction of the coordinated bpy ligands to give neutral (R)bpy or (R)bpy(2-) dianions, respectively. Magnetic susceptibility measurements (4-300 K) coupled with DFT studies show strong antiferromagnetic coupling of the three unpaired electrons located on the (R)bpy ligands to give S = (1)/2 ground states with low lying S = (3)/2 excited states that are populated above 110 K (1) and 80 K (2) in the solid-state. Complex 2 shows weak 3D magnetic interactions at 19 K, which is not observed in 1 or the related [Al(bpy)3] complex.

Controlled generation of highly saddled (porphyrinato)iron(III) iodide, tri-iodide and one-electron oxidized complexes.

For the first time, three iron(III) porphyrinato complexes have been synthesized selectively by varying the iodine concentration in the reaction mixture which eventually forms both five and six coordinate complexes with iodide and/or tri-iodide as axial ligands. Combined analysis using single crystal X-ray structure determination, and Mössbauer, (1)H NMR and EPR studies as well as VT magnetic studies has revealed the admixed-intermediate (iodo complex), pure intermediate (tri-iodide complex) and high-spin (1e-oxidized complex) states of iron.

EPR Investigation Of Mn (II) Probe In Diaquamalonatozinc(II) Single Crystals - Usage In Enrichment Of Dental Cement

Single crystal EPR studies on Cu(II) and VO(II) doped Diaquamalonatozinc(II) are already studied and published. Inorder to understand the effect of Mn(II) in the host lattice Diaquamalonatozinc(II), single crstal EPR studies of Mn(II) doped Diaquamalonatozinc(II) are carried out at room temperature to identify the local structure of the host ion. Angular variation of Mn(II) hyperfine lines in the three orthogonal planes shows the presence of a two sites. The spin-Hamiltonian parameters calculated from the single crystal EPR spectra are: gxx = 1.989, gyy = 1.999, gzz = 2.023; Axx = 8.72, Ayy = 9.28; Azz = 9.34 mT, Dxx = -33.36, Dyy = -7.25, Dzz = 40.61 mT and E = 13.05 mT. The spin-Hamiltonian parameters calculated from the powder EPR spectrum are: g = 1.995, A = 9.25 mT, D = -53.6. The percentage of covalency obtained is around 8.5%.

Effect of VO(II) Doping on Structural and Optical Properties of Diaquamalonato(1,10-phenanthroline)zinc(II)

Single crystal EPR and optical studies of a mixed ligand zinc(II) complex doped with VO(II) ion is carried out to establish the structural properties. The angular variation of vanadyl hyperfine lines indicates a single site, with spin Hamiltonian parameters as: gxx = 1.985, gyy = 1.979, gzz = 1.943; Axx = 8.71, Ayy = 6.41 and Azz = 17.80 mT. By comparing the direction cosines of principal g and A values with the direction cosines of metalligand bonds, it has been confirmed that the vanadyl ion has entered the lattice interstitially. The exact interstitial position of VO(II) in host lattice has been calculated using the fractional coordinates of atoms in the host lattice out of many assumptions. The EPR and optical data have been confirmed to obtain various bonding parameters, from which the nature of the bonding in the complex is discussed. FT-IR confirms the formation of structure of host lattice.

Structural evaluation and position of the VO2+ ion in diaquacadmium(diaquabismalonato)cadmate: spectroscopic studies

Single crystal EPR, optical, FT-IR, and powder XRD studies of VO2+ ion-doped diaquacadmium(diaquabismalonato)cadmate were carried out at ambient temperature to ascertain the structural properties. In EPR, the angular variation of VO2+ ion hyperfine lines indicated a single site, with spin Hamiltonian parameters g and A values g xx = 1.979, g yy = 1.963, g zz = 1.939, A xx = 0.0074 cm−1, A yy = 0.0065 cm−1, and A zz = 0.0166 cm−1. The calculated results of the VO2+ ion-doped diaquacadmium(diaquabismalonato)cadmate indicate VO2+ substitutes the Cd2+ ion in the host lattice, and it has rhombic symmetry. The EPR and optical absorption data were corroborated to obtain various bonding parameters, from which the nature of bonding in the complex was discussed. FT-IR and powder XRD studies were used to observe the effect of dopant on structural parameters of the host lattice.

EPR and optical studies of Nickel(II) at 300 K

Single crystal EPR studies of Ni(II) in hexaimidazolecobalt(II) dichloride tetrahydrate have been carried out at ambient temperature to obtain g and zero-field tensors, making it one of the very few systems having room temperature EPR data. The results show rhombic distortion around the Ni(II) ion, with the ion being entered the lattice substitutionally in place of Co(II). The optical data suggest trigonally distorted electronic structure around Ni(II) and collaboration with EPR data provided a few bonding parameters.

Single-crystal EPR study of three radiation-induced defects (Al–O2 3−, Ti3+ and W5+) in stishovite

Single-crystal electron paramagnetic resonance spectra of electron-irradiated stishovite, measured at temperatures from 3.5 to 294 K, reveal three S = 1/2 radiation-induced defects: an aluminum-associated oxygen hole center and two nd 1 centers (Ti3+ and W5+). The aluminum-associated oxygen hole center, characterized by an orthorhombic site symmetry, coaxial matrices of the electronic Zeeman g, nuclear hyperfine A(27Al) and nuclear quadrupole P(27Al), and the orientation of the g-minimum axis along an O–O direction and those of the unique A(27Al) and P(27Al) axes perpendicular to the O–O direction, is an Al–O2 3− center, with the unpaired electron equally distributed on two equatorial oxygen atoms of a substitutional Al3+ ion at the octahedral Si site. Fully optimized Al-doped structure, theoretical 27Al nuclear hyperfine and quadrupole coupling constants and directions, and 3D spin densities from periodic hybrid density functional theory calculations provide further support for this structural model. Spin Hamiltonian parameters of the Ti3+ and W5+ centers, which are confirmed by their diagnostic 47Ti, 49Ti and 183W hyperfine structures, arise from electron trapping on substitutional Ti4+ and W6+ ions at the octahedral Si site.

Substitutional location for a vanadyl ion in three water coordinated triaqua(1,10-phenanthroline-k2N,N′) (sulfato-kO)magnesium(II) complex: a rare observation

Vanadyl ion substitutes for the central ion, if the doped complex has at least four water molecules. However, the present EPR, XRD, FT-IR and optical absorption studies on vanadyl-doped triaqua(1,10-phenanthroline-k2N,N′)(sulfato-kO)magnesium(II) suggest a substitutional defective nature, which is a rare observation. Single crystal EPR studies in three mutually orthogonal planes indicate two chemically non-equivalent sites with different intensities. However, the lower intensity site could not be analysed due to its weaker intensity and overlap with other sites during crystal rotations. The spin Hamiltonian parameters obtained for the major site are as follows: g xx =1.973, g yy =1.972, g zz =1.930; A xx =7.15, A yy =6.77, A zz =18.92 mT. The direction cosines of principal g and A values suggest that the impurity has entered the lattice substitutionally, which is a very uncommon phenomenon. Admixture coefficients, Fermi contact, dipolar interaction and covalency of metal–ligand bonds have also been evaluated. Optical, FT-IR and powder XRD techniques confirm the structure of the complex.

An interplay between the spin density distribution and magnetic superexchange interactions: a case study of mononuclear [nBu4N]2[Cu(opooMe)] and novel asymmetric trinuclear [Cu3(opooMe)(pmdta)2](NO3)2·3MeCN

Treatment of the diethyl ester of o-phenylenebis(oxamic acid) (opbaH(2)Et(2), 1) with 5/6 equivalent of MeNH(2) in abs. EtOH results in the exclusive formation of the ethyl ester of o-phenylene(N′-methyl oxamide)(oxamic acid) (opooH(3)EtMe, 2) in ca. 50% yield. Treatment of 2 with four equivalents of [Me(4)N]OH followed by the addition of Cu(ClO(4))(2)·6H(2)O gave [Me(4)N](2)[Cu(opooMe)]·H(2)O (3A) in ca. 80% yield. As 3A appears to be a hygroscopic solid, the related [(n)Bu(4)N](+) salts [(n)Bu(4)N](2)[M(opooMe)]·H(2)O (M = Cu (3B), Ni (4)) have been synthesized. By addition of two equivalents of [Cu(pmdta)(NO(3))(2)] to a MeCN solution of 3B the novel asymmetric trinuclear complex [Cu(3)(opooMe)(pmdta)(2)](NO(3))(2) (5) could be obtained in ca. 90% yield. Compounds 2, 3A, 3B, 4 and 5 have been characterized by elemental analysis and NMR/IR spectroscopy. Furthermore, the solid state structures of 3A in the form of [Me(4)N](2)[Cu(opooMe)]·MeOH (3A′), 3B in the form of [(n)Bu(4)N](2)[Cu(opooMe)] (3B′), 4 in the form of [(n)Bu(4)N](2)[Ni(opooMe)]·1.25H(2)O (4′) and 5 in the form of [Cu(3)(opooMe)(pmdta)(2)] (NO(3))(2)·3MeCN (5′), respectively, have been determined by single-crystal X-ray diffraction studies. By controlled cocrystallization, diamagnetically diluted 3B (1%) in the host lattice of 4 (99%) in the form of single crystals have been made available, allowing single crystal EPR studies to extract all components of the g-factor and the tensors of onsite (Cu)A and transferred (N)A hyperfine interaction. Out of these studies the spin density distribution of the [Cu(opooMe)](2-) complex fragment could be determined. The magnetic properties of 5 were studied by susceptibility measurements versus temperature. An intramolecular J parameter of -65 cm(-1) has been obtained, unexpectedly, as 5 should possess two different J values due to its two different spacers between the adjacent Cu(II) ions, namely an oxamate (C(2)NO(3)) and an oxamidate (C(2)N(2)O(2)) fragment. This unexpected result is explained by a summarizing discussion of the experimentally obtained EPR results (spin density distribution) of 3B, the geometries of the terminal [Cu(pmdta)](2+) fragments of 5 determined by X-ray crystallographic studies and accompanying quantum chemical calculations of the spin density distribution of the mononuclear [Cu(opooMe)](2-) and of the magnetic exchange interactions of trinuclear [Cu(3)(opooMe)(pmdta)(2)](2+) complex fragments.

Syntheses and Structures of Magnesium Complexes with Reduced α-Diimine Ligands

The reduction of neutral α-diimine ligands bearing different substituents on the N-aryl rings by different amounts of potassium metal and subsequent reaction with anhydrous MgCl2 in THF afforded a series of magnesium compounds, [(LiPr)2–Mg(THF)2]·THF (2), [(LMes)2–Mg(THF)3] (3), [(LiPr)−2Mg]·THF (4), [(LMes)−2Mg] (5), and [(LMes)2–2Mg(η6:η6-K(THF)2)][K(THF)6]·(THF)2 (6) (LiPr = [(2,6-iPr2C6H3)NC(Me)]2), LMes = [(2,4,6-Me3C6H2)NC(Me)]2). Complexes 2–6 have been characterized by single-crystal X-ray diffraction, elemental analysis, NMR spectroscopy, and EPR studies (for 4 and 5). The noninnocent α-diimine ligands exist as the dianionic form in compounds 2, 3, and 6 and as a monoanion in 4 and 5. Effects of the ligand substituents and the amount of the reducing agent on the structure of the product have been discussed.

A Vanadium (VO2+) Metal–Organic Framework: Selective Vapor Adsorption, Magnetic Properties, and Use as a Precursor for a Polyoxovanadate

The reaction of VOSO(4) with 2-carboxyethylphosphonic acid (H(2)-CEP) in presence of piperazine (PIP) produces a 3D inorganic-organic hybrid framework, {(H(2)PIP)(0.5)[VO(CEP)]·H(2)O} (1) with bidirectional channels occupied by the H(2)PIP cations and H(2)O molecules. The PO(3)(2-) unit of CEP connects three V(IV) centers to generate a 1D ladder, which is further linked to four such ladders by the CEP linkers to form a 3D hybrid framework. The dehydrated framework, {(H(2)PIP)(0.5)[VO(CEP)]} (1') shows selective and gated adsorption behavior with H(2)O but not with methanol and ethanol. Very interestingly, when 1 is treated with an aqueous solution of LiNO(3)/NaNO(3), the framework breaks down and results in a new polyoxovanadate (POV) cluster, [H(5)(H(2)PIP)(3)][V(V)(12)V(IV)(2)O(38)(PO(4))]·8H(2)O (2) at pH ≈ 2.1. The cluster has been characterized by single-crystal X-ray diffraction, (31)P NMR, EPR, and magnetic studies. The temperature-dependent magnetic susceptibility measurement suggests antiferromagnetic ordering in 1 with T(N) ≈ 3.8 K.

EPR and Optical Absorption Study of VO2+-Doped Lithium Hydroxylammonium Sulphate

ABSTRACT Single-crystal and powder EPR studies of VO2+-doped lithium hydroxylammonium sulphate (LiNH3OHSO4) were carried out at room temperature. The results indicate the presence of two magnetically inequivalent VO2+ sites. The VO2+ ion takes up a substitutional position in the host lattice. The angular variation of EPR spectra in three mutually perpendicular planes were used to determine the spin Hamiltonian parameters, and the values obtained were the following: For Site 1, gx = 2.0249 ± 0.0002, gy = 1.9698 ± 0.0002, gz = 1.9552 ± 0.0002, Ax = (51 ± 2) × 10−4 cm−1, Ay = (93 ± 2) × 10−4 cm−1, and Az = (165 ± 2) × 10−4 cm−1; and for Site 2, gx = 2.0267 ± 0.0002, gy = 1.9743 ± 0.0002, gz = 1.9213 ± 0.0002, Ax = (40 ± 2) × 10−4 cm−1, Ay = (80 ± 2) × 10−4 cm−1, and Az = (155 ± 2) × 10−4 cm−1. The optical absorption spectrum recorded at room temperature shows four bands. From the optical and EPR data, various molecular coefficients are evaluated, and the nature of bonding in the crystal is discussed.

Molecular structure identification and position of a dopant ion in diaqua(2,2′-bipyridine)malonatozinc(II) by spectroscopic studies – II: VO(II)

Single crystal EPR, optical, FT-IR and powder XRD studies of VO(II) ion doped diaqua(2,2′-bipyridine) malonato zinc complex were carried out at room temperature to ascertain the structural properties. In EPR, the angular variation of vanadium hyperfine lines indicated a single site, with spin Hamiltonian parameters as: g xx = 1.968, g yy = 1.964, g zz = 1.928, A xx = 7.54 mT, A yy = 6.36 mT and A zz = 18.81 mT. In addition, the dopant had entered the lattice in an interstitial position and the position had been identified with the help of atom positions of the host lattice. The EPR and optical data was corroborated to obtain various bonding parameters, from which the nature of the bonding in the complex was discussed. FT-IR and powder XRD studies were used to observe the effect of dopant on structural parameters of the host lattice.

Single crystal EPR study at 95 GHz of a large Fe based molecular nanomagnet: toward the structuring of magnetic nanoparticle properties

A W-band single-crystal EPR study has been performed on a molecular cluster comprising 19 iron(III) ions bridged by oxo- hydroxide ions, Fe(19), in order to investigate magnetic nanosystems with a behavior in between the one of Magnetic NanoParticles (MNP) and that of Single Molecule Magnets (SMM). The Fe(19) has a disk-like shape: a planar Fe(7) core with a brucite (Mg(OH)(2)) structure enclosed in a "shell" of 12 Fe(III) ions. EPR and magnetic measurements revealed an S = 35/2 ground state with an S = 33/2 excited state lying ∼ 8 K above. The presence of other low-lying excited states was also envisaged. Rhombic Zero Field Splitting (ZFS) tensors were determined, the easy axes lying in the Fe(19) plane for both the multiplets. At particular temperatures and orientations, a partially resolved fine structure could be observed which could not be distinguished in powder spectra, due to orientation disorder. The similarities of the EPR behavior of Fe(19) and MNP, together with the accuracy of single crystal analysis, helped to shed light on spectral features observed in MNP spectra, that is a sharp line at g = 2 and a low intensity transition at g = 4. Moreover, a theoretical analysis has been used to estimate the contribution to the total magnetic anisotropy of core and surface; this latter is crucial in determining the easy axis-type anisotropy, alike that of MNP surface.

Antioxidant and anticancer activities of supramolecularly controlled magnetostructural halo-oximes of lawsone

Crystal engineering based on halogen bonding together with host–guest interactions of water molecules via H-bonding, stabilizing supramolecular architecture in chloro 1, bromo 2 and iodo 3oximes of lawsone, is discussed. 1 and 2 crystallize in orthorhombic, non-centrosymmetric space group Pna21 while 3 crystallizes in monoclinic P21/n space group. Non-covalent competitive interactions of asymmetric solvation and halogen bonding can have a large influence on the spin distribution in 1, 2 and 3 derivatives of spin carrier lawsone live polymer as revealed by single crystal X-ray and EPR studies. The significant C3–Cl/Br⋯O, C3–Cl/Br⋯H, O–H⋯OC, C–H⋯π and π⋯π interactions have been identified in the molecular assemblies leading to net magnetostructures of halo-oximes. Dimer-of-dimer-type tetrameric radical assembly of 3 and interacting bi- and monoradical chain on 21 axis in 1 and 2 have been identified. The proton-coupled electron transfers possibly govern the antioxidant nature in halooximes of spin carrier lawsone in terms of oxygen reduction to water molecules. Such activity is found to be directly proportional to the spin (radical) concentrations in 1 to 3 and increases in order 1 < 2 < 3 according to halogen bonding effect. The antioxidant chemical DPPH assays for scavenging of such free radicals result in similar trend of increasing order like 1 < 2 < 3, but the chemical in vitro as well as ex vivoSOD antioxidant activities and biological anticancer activity on MCF-7, Hela and HL-60 cell lines show the increasing order 3 < 2 < 1 according to H-bonding effect. This probably could be attributed to the conversion of superoxide radical ions into H2O2, which leads to greater oxidative stress leading to apoptosis.

Determination of the relevant magnetic interactions in low-dimensional molecular materials: the fundamental role of single crystal high frequency EPR

A new one-dimensional copper(II) complex with formula [Cu(hfac)(2)(N(3)TEMPO)](n) (hfac = hexafluoroacetylacetonate and N(3)TEMPO = 4-azido-2,2,6,6-tetramethylpiperidine-1-oxyl) has been synthesized and investigated by X-ray crystallography, magnetometry and multifrequency single crystal EPR. The system crystallizes in the P1 space group with two non equivalent copper(II) ions in the unit cell, the two nitroxide radicals being coordinated to Cu(1) in axial positions. The copper(II) ions are bridged by N(3)TEMPO radicals resulting in a zig-zag chain structure. The magnetic susceptibility data were at first satisfactorily modeled assuming an alternating spin chain along the monodimensional covalent skeleton, with a ferromagnetic interaction between Cu(1) and the nitroxide moieties and a weaker antiferromagnetic interaction between these and Cu(2) (J(1) = -13.8 cm(-1), J(2) = +2.4 cm(-1)). However, single crystal EPR studies performed at the X- and W-band clearly demonstrate that the observed magnetic monodimensional character of the complex is actually due to the intermolecular contacts involving N(3)TEMPO ligands. This prompted us to fit the magnetic data using a consistent model, pointing out the fundamental role of single crystal EPR data in defining a correct model to describe the magnetic properties of molecular low dimensional systems.

Structural elucidation of transition metal complex by single crystal EPR study

Single crystal EPR studies of Mn(II) doped hexaaquazincdiaquabis(malonato) zincate [Zn(H 2O) 6][Zn(mal) 2(H 2O) 2] have been carried out at room temperature using X-band spectrometer to identify the location of the dopant. Single crystal rotations along the three orthogonal axes show more than 30 line pattern EPR spectra indicating the presence of two types of dopant ions in the host lattice, with intensity ratio of 6:1. However, the latter could not be followed due to its low intensity during crystal rotations. The spin-Hamiltonian parameters, estimated from the three mutually orthogonal crystal rotations are: g xx = 1.972, g yy = 2.000, g zz = 2.023, A xx = 8.95, A yy = 9.48, A zz = 9.93 mT, D xx = −34.49, D yy = −3.26, D zz = 37.74 mT and E = 15.6 mT. The direction cosines of one of the principal values of g match with that of Zn–O bond in the host lattice, suggesting that the Mn(II) ion entered the lattice substitutionally. The large value of E is indicative of low symmetry of the substitutional site, in accordance with the crystal structure of the isomorphous [Zn(H 2O) 6][Cu(mal) 2(H 2O) 2]. Covalency of Mn–O bond, estimated from Matamura’s plot, is 9%. Various admixture coefficients, bonding and optical parameters have also been calculated.