Single Crystal ESR Research Articles

Synthesis and Catalytic Properties of Novel Ruthenacarboranes Based on nido-[5-Me-7,8-C2B9H10]2− and nido-[5,6-Me2-7,8-C2B9H9]2− Dicarbollide Ligands

The effect of methyl substituents in the lower belt of dicarbollide ligands on the redox potential of ruthenacarboranes based thereof, as well as the ability of the metallacarboranes obtained to catalyze radical polymerization with atom transfer were studied. For this purpose, a new approach to the synthesis of closo-ruthenacarboranes based on substituted dicarbollide ligands was developed and six new complexes 3,3-(Ph2P(CH2)4PPh2)-3-H-3-Cl-9-Me-12-X-closo-3,1,2-RuC2B9H9, 3,3,8-(Ph2P(CH2)4PPh-μ-(C6H4-o))-3-Cl-9-Me-12-X-closo-3,1,2-RuC2B9H8 and 3,3,4,8-(Ph2P(CH2)4P-μ-(C6H4-o)2)-3-Cl-9-Me-9-X-closo-3,1,2-RuC2B9H7 (X = H, Me) were synthetized and characterized by single crystal X-ray diffraction, NMR and ESR spectroscopy and MALDI TOF mass-spectrometry. Comparison of the values of the redox potentials of the synthesized ruthenium complexes in 1,2-dichloroethane with the values previously found for the corresponding ruthenacarboranes based on the parent dicarbollide anion showed that the introduction of methyl substituents into the carborane cage led to a decrease in the redox potentials of the complexes, which made them more preferable catalysts for ATRP. Test experiments on the polymerization of MMA showed that the synthesized ruthenacarboranes were effective catalysts for ATRP, the most active being the complex with two methyl groups and two ortho-phenylenecycloboronated fragments.

Cycloaddition versus Cleavage of the C=S Bond of Isothiocyanates Promoted by Digallane Compounds with Noninnocent α-Diimine Ligands.

Whereas the chemistry of single-bond activation by compounds of the main group elements has undergone some development in recent years, the cleavage of multiple bonds remains underexplored. Herein, the reactions of two digallanes bearing α-diimine ligands, namely, [L1 Ga-GaL1 ] (1, L1 =dpp-dad=[(2,6-iPr2 C6 H3 )NC(CH3 )]2 ) and [L2 Ga-GaL2 ] (2, L2 =dpp-bian=1,2-[(2,6-iPr2 C6 H3 )NC]2 C10 H6 ), with isothiocyanates are reported. Reactions of 1 or 2 with isothiocyanates in 1:2 molar ratio proceeded with [2+4] cycloaddition of the C=S bond across the C2 N2 Ga metallacycle with formation of C-C and S-Ga single bonds to afford [L1 (RN=C-S)Ga-Ga(S-C=NR)L1 ] (3, R=Me; 4, R=Ph) and [L2 (RN=C-S)Ga-Ga(S-C=NR)L2 ] (8, R=allyl; 9, R=Ph). In the cases of 8 and 9, this cycloaddition is reversible. The digallanes reacted with 2 equiv of PhNCS in the presence of Na metal or at high temperatures through a unique reductive cleavage of the C=S bond to yield the disulfide-bridged digallium species [Na(THF)3 ]2 [L1 Ga(μ-S)2 GaL1 ] (5), [L2 Ga(μ-S)2 GaL2 ] (10), and [Na(DME)3 ][L2 Ga(μ-S)2 GaL2 ] (11). Moreover, products 4 and 5 can further react with an excess of isothiocyanate, through cleavage of the C=S bond or cycloaddition, to give the bis- or mono-S-bridged complexes [Na(THF)2 ]2 [L1 (PhN=C-S)Ga(μ-S)2 Ga(S-C=NPh)L1 ] (6) and [L1 (PhN=C-S)Ga(μ-S)Ga(S-C=NPh)L1 ] (7). All the newly prepared compounds were characterized by elemental analysis, single-crystal X-ray diffraction, IR spectroscopy, NMR (3-9) or ESR spectroscopy (11), and DFT calculations.

Field-Induced Slow Magnetic Relaxation of GdIII Complex with a Pt-Gd Heterometallic Bond.

Heterometallic Gd-Pt complexes ([Gd2 Pt3 (H2 O)2 (SAc)12 ] (SAc=thioacetate), [Y1.4 Gd0.6 Pt3 (H2 O)2 (SAc)12 ], and [Gd2 Pt3 (H2 O)6 (SAc)12 ]⋅7 H2 O have been synthesized. The crystal structures and DFT calculations indicated a Gd-Pt heretometallic bond. Single-crystal ESR spectra determined the direction of magnetic anisotropy as direction of the Gd-Pt bond. In other words, the Gd-Pt bond dictates the direction of magnetic anisotropy. The heterometallic Gd-Pt bond lowers the symmetry of the Gd ion, splitting the Kramers doublet in a dc field. Thus, we observed clear field-induced slow magnetic relaxation of [Y1.4 Gd0.6 Pt3 (H2 O)2 (SAc)12 ] up to 36 K. The relaxation process was determined to be a direct process.

ChemInform Abstract: A Novel Europium (III) Nitridoborate Eu3[B3N6]: Synthesis, Crystal Structure, Magnetic Properties, and Raman Spectra.

AbstractThe title compound is prepared from a 1:1 molar mixture of Eu3(BN2)2 and Br2 (1073 K, 12 h) and characterized by powder and single crystal XRD, ESR, Raman and Moessbauer spectroscopy, and DFT quantum chemical calculations.

Electronic instabilities and irradiation effects in the (TMTTF)2X series

The paper presents a single-crystal ESR study of a series of pristine and X-ray irradiated (TMTTF)2X salts, where TMTTF is tetramethyltetrathiafulvalene and X is either a centro-symmetrical (SbF6 and Br) or a non-centro-symmetrical (ReO4, ClO4, BF4, SCN and NO3) monovalent anion. Besides standard line-width and spin-susceptibility measurements, the analysis of the asymmetry of the ESR line shape allows to obtain simultaneous information on the electrical conductivity. This whole set of data is used to determine the charge and spin gaps related to the charge ordering (CO) and anion ordering (AO) ground states and their evolution as a function of X-ray irradiation damages. We show in particular that the sensibility of (TMTTF)2X salts to irradiation depends upon the nature of the anion X and that the CO ground state is drastically affected by irradiation damages at the difference of the AO ground state. We also present evidence of a CO transition and of a decoupling between the AO transition and the opening of a spin gap in (TMTTF)2NO3.

Magnetic superexchange interactions: trinuclear bis(oxamidato) versus bis(oxamato) type complexes.

The diethyl ester of o-phenylenebis(oxamic acid) (opbaH2Et2) was treated with an excess of RNH2 in MeOH to cause the exclusive formation of the respective o-phenylenebis(N(R)-oxamides) (opboH4R2, R = Me , Et , (n)Pr ) in good yields. Treatment of with half an equivalent of [Cu2(AcO)4(H2O)2] or one equivalent of [Ni(AcO)2(H2O)4] followed by the addition of four equivalents of [(n)Bu4N]OH resulted in the formation of mononuclear bis(oxamidato) type complexes [(n)Bu4N]2[M(opboR2)] (M = Ni, R = Me , Et , (n)Pr ; M = Cu, R = Me , Et , (n)Pr ). By addition of two equivalents of [Cu(pmdta)(NO3)2] to MeCN solutions of , novel trinuclear complexes [Cu3(opboR2)(L)2](NO3)2 (L = pmdta, R = Me , Et , (n)Pr ) could be obtained. Compounds have been characterized by elemental analysis and NMR/IR spectroscopy. Furthermore, the solid state structures of and have been determined by single-crystal X-ray diffraction studies. By controlled cocrystallization, diamagnetically diluted and (1%) in the host lattice of and (99%) (@ and @), respectively, in the form of single crystals have been made available, allowing single crystal ESR studies to extract all components of the g-factor and the tensors of onsite (Cu)A and transferred (N)A hyperfine (HF) interaction. From these studies, the spin density distribution of the [Cu(opboEt2)](2-) and [Cu(opbo(n)Pr2)](2-) complex fragments of and , respectively, could be determined. Additionally, as a single crystal ENDOR measurement of @ revealed the individual HF tensors of the N donor atoms to be unequal, individual estimates of the spin densities on each N donor atom were made. The magnetic properties of were studied by susceptibility measurements versus temperature to give J values varying from -96 cm(-1) () over -104 cm(-1) () to -132 cm(-1) (). These three trinuclear Cu(II)-containing bis(oxamidato) type complexes exhibit J values which are comparable to and slightly larger in magnitude than those of related bis(oxamato) type complexes. In a summarizing discussion involving experimentally obtained ESR results (spin density distribution) of and , the geometries of the terminal [Cu(pmdta)](2+) fragments of determined by crystallographic studies, together with accompanying quantum chemical calculations, an approach is derived to explain these phenomena and to conclude if the spin density distribution of mononuclear bis(oxamato)/bis(oxamidato) type complexes could be a measure of the J couplings of corresponding trinuclear complexes.

ChemInform Abstract: Molecular Magnetism of M6 Hexagon Ring in D3d Symmetric [(MCl)6(XW9O33)2]12‐ (M: CuII and MnII, X: SbIII and AsIII).

AbstractThe ferromagnetic compound (III) and antiferromagnetic compound (VI) are characterized by single crystal XRD, ESR spectroscopy, and magnetic measurements.

Postsynthetic modification of a coordination compound with a paddlewheel motif via click reaction: DOSY and ESR studies

Postsynthetic strategy based on organic coupling reactions has been explored for the synthesis of novel coordination complexes with larger dimensions. A discrete coordination species with a paddlewheel motif, dicopper(II) tetracarboxylate Cu2(OOC-C6H4-N3)4(quinoline)2 (SBU1), was covalently modified with methyl propiolate via “Click” reaction to generate a new coordination compound Cu2(OOC-C6H4-C2N3H-COOCH3)4·(quinoline)2 (1). The combination of single-crystal X-ray diffraction, diffusion NMR and ESR has confirmed the success of covalently modifying SBU1 and the retention of the structural integrity after the postsynthetic modification.

New approach to synthesis of nitronyl and imino nitroxides based on SNH methodology

It is shown that SN H approach opens new possibilities in the synthesis of polyfunctional nitronyl and imino nitroxides. It is found that the interaction of 4,4,5,5-tetramethyl-4,5-dihydro-1Himidazol-3-oxide-1-oxyl lithium salt Li1 with 3,6-diaryl-1,2,4-triazines leads to formation of the corresponding triazines bearing nitronyl nitroxide or imino nitroxide substituent at position 5 of the heterocycle. The reaction of Li1 with pyridazine-N-oxide gives rise to nitroxide with buten3-ynyl substituent 5. Spin-labeled 5 could be readily transformed by the use of 1,3-dipolar and nucleophilic addition reactions, as well as oxidative coupling, that gives a large group of new paramagnets: 2-(1H-pyrazol-5-yl)vinyl-, 2-ethynylcyclopropyl-, 2-(3-(ethoxycarbonyl) isoxazol5-yl)vinyl-, 1-(pyrrolidin-1-yl)but-3-ynyl-substituted nitronyl nitroxide and a diradical – 2,2′((1E,7E)-octa-1,7-dien-3,5-diyne-1,8-diyl)bis(4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-3oxide-1-oxyl). The new nitroxides were characterized by X-ray single crystal data, ESR and static magnetic susceptibility measurements.

Hydrothermal synthesis and crystal structure of a tungstovanadate: [4,4′-bipyH2][4,4′-bipyH]2[VW12O40] · 4,4′-bipy · 7.5H2O

An organic-inorganic hybrid Keggin compound, [4,4′-bipyH2][4,4′-bipyH]2[VW12O40] · 4,4′-bipy · 7.5H2O (bipy-bipyridine) (1), has been prepared under hydrothermal conditions and characterized by IR spectroscopy, single crystal X-ray diffraction, thermal analysis, and ESR spectroscopy. 1 crystallized in the monoclinic space group P21/c with a = 18.7350(15) A, b = 14.0253(12) A, c = 26.434(2) A, β= 105.0810(10)°, V = 6706.6(10) A3 and Z = 4. The crystal structure of 1 consists of diprotonated and monoprotonated 4,4′-bipyridine cations, free 4,4′-bipyridine molecule, lattice water molecules, and a typical Keggin-type polyoxoanion [VW12O40]4−. The polyoxoanion is constructed by four {W3O16} trinuclear groups, each of which is made up of three edge-sharing {WO6} octahedra, and the {VO4} tetrahedron is in the center of the cage.

A dinuclear vanadium compound with 24-membered macrocycle generated via formation of S–C bonds

A dinuclear vanadium 24-membered macrocycle with double-ring, [V 2O 2L 2(μ-CH 3COO)] − (H 2L = 3,3′-(1,3,4-thiadiazole-2,5-diyl)bis(sulfane-diyl) bis(4-hydroxypent-3-en-2-one)), was prepared in high yield from the reaction of VO 2(acac) with 2,5-dimercapto-1,3,4-thiadiazole dipotassium salt (K 2SSS) and acetylacetone (Hacac) at room temperature. Its closure of 24-membered macrocycle has resulted from the formation of U-shape units via S–C bonding between original SSS 2− and acac − ligands, while the bridging CH 3COO − has created from an unexpected decomposition of Hacac. The obtained two products were characterized by single crystal X-ray diffraction, XRD, ESR, TGA and magnetism analyses. A possible mechanism for formation of the bimetal 24-membered macrocycle has been discussed.

Tetranuclear pyrophosphate-bridged Cu(II) complex with 2,2′-dipyridylamine: Crystal structure, spectroscopy and magnetism

Use of pyrophosphate, 2,2′-dipyridylamine (hdpa) with Cu(NO 3) 2 · 3H 2O has enabled to synthesize a novel tetranuclear copper(II) complex, [Cu 4(hdpa) 4(μ-P 2O 7) 2] · 11H 2O 1, which was characterized by single crystal X-ray diffraction, IR, ESR spectrum, and variable-temperature magnetic susceptibilities (4.2–300 K). Extensive π–π stackings and H-bonding water clusters resulting from 11 free water molecules join Cu 4 units to make a 3D network. According to the molecular structure, the experimental data were fitted to the expressions derived from the Hamiltonian H = - 2 J 12 S ^ 1 S ^ 2 - 2 J 13 ( S ^ 1 S ^ 3 + S ^ 2 S ^ 4 ) - 2 J 14 ( S ^ 1 S ^ 4 + S ^ 2 S ^ 4 ) showing dominant antiferromagnetic behaviors.

Anisotropic conductivity and charge ordering in(TMTTF)2Xsalts probed by ESR

Single crystal ESR data on ${(\mathrm{TMTTF})}_{2}X$ salts are presented. Taking advantage of the large dimensions of the crystals, skin effect is studied through the asymmetry of the ESR resonance lines. When the microwave magnetic field is perpendicular to the stacking axis, a very rich temperature dependence of this asymmetry is found although the three components of the conductivity tensor often exhibit a semiconducting behavior. In particular, we show that anomalies are present when the TMTTF chains experience a Mott localization or a charge ordering. The whole set of data is discussed theoretically in relation with the anisotropy of the electrical conductivity. We show that the crystal orientation and crystal shape are crucial parameters in explaining the experimental results. More precisely, we found that at the charge ordering transition, the largest conductivity anomaly occurs along the transverse $b$ direction, and we provide evidence, through ESR measurements of the conductivity in this direction, of a charge ordering transition at about $50\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ in ${(\mathrm{TMTTF})}_{2}\mathrm{Br}$. With the same method, we also show that irradiation kills the charge ordering transition, while deuteration enhances its critical temperature.

Determining the Geometry and Magnetic Parameters of Fluorinated Radicals by Simulation of Powder ESR Spectra and DFT Calculations: The Case of the Radical RCF2CF2• in Nafion Perfluorinated Ionomers

The ESR spectrum of the chain-end radical RCF2CF2* detected in Nafion perfluorinated membranes exposed to the photo-Fenton reagent was accurately simulated by an automatic fitting procedure, using as input the hyperfine coupling tensors of the two F alpha and two F beta nuclei as well as the corresponding directions of the principal values from density functional theory (DFT) calculations. An accurate fit was obtained only for different orientations of the hyperfine coupling tensors for the two F alpha nuclei, indicating a nonplanar structure about the C alpha radical center. The fitted isotropic hyperfine splittings for the two F beta nuclei in the Nafion radical, 24.9 and 27.5 G, are significantly larger than those for the chain-end radical in Teflon (15 G), implying different radical conformations in the two systems. The excellent fit indicated that the geometry and electronic structure of free radicals can be obtained not only from single-crystal ESR spectroscopy, but also, in certain cases, from powder spectra, by combination with data from DFT calculations. The optimized structures obtained by DFT calculations for the CF3CF2CF2CF2* or CF3OCF2CF2* radicals as models provided additional support for the pyramidal structure determined from the spectral fit. Comparison and analysis of calculated and fitted values for the hyperfine splittings of the two F beta nuclei suggested that the radical detected by ESR in Nafion is ROCF2CF2*, which originates from attack of oxygen radicals on the Nafion side chain. The combination of spectrum fitting and DFT is considered important in terms of understanding the hyperfine splittings from 19F nuclei and the different conformations of fluorinated chain-end-type radicals RCF2CF2* in different systems, and also for elucidating the mechanism of Nafion fragmentation when exposed to oxygen radicals in fuel cell conditions.

A novel sandwich polyoxometalate linked by mixed RE/TM interlayer: [Fe(phen) 3] 2[As 2W 18Fe 2{Y(OH 2) 2} 2O 68]·6.5H 2O

A novel sandwich polyoxometalate, [Fe(phen) 3] 2[As 2W 18Fe 2{Y(H 2O) 2} 2O 68]·6. 5H 2O 1, (phen = 1,10-phenanthroline), has been hydrothermally synthesized and characterized by elemental analyses, IR(25 ∼ 650 °C), single-crystal X-ray diffraction, ESR spectroscopy and thermal analyses (TG-DTA). The crystallographic analysis reveals that the dimeric polyanion, [As 2W 18Fe 2{Y(OH 2) 2} 2O 68] 6−, are constructed from two [ B-AsW 9O 34] 9− fragments linked by two Y 3+ ions and two Fe 3+ ions. The ESR spectra exhibit that the high spin state and the low spin state of Fe(III) coexist in the title compound.

Tuning of Electronic Structures of Quasi-One-Dimensional Halogen-Bridged Ni–Pd Mixed-Metal Complexes, [Ni1−xPdx(chxn)2X]X2 (X = Cl, Br) with Strong Electron Correlation

Abstract This article describes the tuning of the electronic structures in a series of quasi-one-dimensional halogen-bridged Ni–Pd mixed-metal complexes, [Ni1−xPdx(chxn)2X]X2 (chxn = 1R,2R-diaminocyclohexane; X, Y = Cl or Br). In these compounds, planar [M(chxn)2] units are bridged by halogen ions (X), forming linear chain M–X–M structures. Therefore, their electronic structures are 1D and are composed of hybridization between the dz2 orbitals of the metal ions and pz orbitals of the bridging halogens. In this system, electron-correlation on the Ni sites and electron–phonon interaction on the Pd sites should compete with each other. Their electronic structures have been investigated by means of the single-crystal reflectance, ESR and IR spectroscopies, electrical conductivities, and X-ray diffuse scattering. Moreover, their local electronic structures have been directly observed by scanning tunneling microscopy (STM) using single-crystals at room temperature and under ambient pressure. As a result, while the oxidation state of the Ni sites is +3 in all mixing ratios in these compounds due to strong electron-correlation, the conversion from the PdIII Mott–Hubbard states to the PdII–PdIV mixed-valence states is observed around x ≈ 0.90 for Br and x ≈ 0.85 for Cl. Interestingly, the spin-soliton in Ni0.05Pd0.95(chxn)2Br3 was directly observed by STM for the first time.

Ferromagnetic Exchange Interactions for Cu612+and Mn612+Hexagons Sandwiched by Two B-α-[XW9O33]9-(X = AsIIIand SbIII) Ligands inD3d-Symmetric Polyoxotungstates

Two novel Cu6 and Mn6 hexagon sandwiched polyoxometalates, [(CuCl)6(AsW9O33)2]12- (1a) and [(MnCl)6(SbW9O33)2]12- (2a), have been synthesized and characterized by X-ray single-crystal analysis and magnetic measurements. These complexes are D3d symmetric and were isolated as [n-BuNH3]+ salts from aqueous solutions: (n-BuNH3)12[(CuCl)6(AsW9O33)2].6H2O (1), rhombohedral, R, a = 20.33(1) A, c = 26.35(2) A, Z = 3 and (n-BuNH3)12[(MnCl)6(SbW9O33)2].6H2O (2). Six Cu (or Mn) atoms, each of which shows 5-fold coordination, make an approximately equatorial hexagon with a first-neighboring Cu...Cu (Mn...Mn) distance of 2.913(2) A (3.248(1) A) and a Cu-O-Cu (Mn-O-Mn) bond angle of 94.5(2) degrees (100.4(2) degrees ). The magnetic behavior investigated by magnetic susceptibility measurements shows the ferromagnetic exchange interactions with J/k = +12.7 K (J/hc = +8.82 cm(-1)) and a S = 3 ground state for 1 and J/k = +0.20 K (J/hc = +0.14 cm(-1)) and a S = 15 ground state for 2, when only J refers to the isotropic magnetic-exchange interactions for first-neighbor atoms of the approximately equilateral Cu6(12+) and Mn6(12+) hexagons. The single-crystal ESR spectroscopy of 1 under the orientation of the magnetic field along a Cu6 hexagon's nearly 6-fold axis equal to the c axis on the variation of temperature supports the S = 3 ground state and allows an estimate of the zero-field (fine-structure) energy separation between Sz = 0 and Sz = +/-1 of D = -0.182 K to be obtained.

Hydrothermal syntheses, crystal structures, and properties of two polyoxometalates [Cd(2,2′-bpy)3]2[PMoVMoVI 11O40] and [H3PMo12O40]·3(4,4′-bpy)·4H2O

Two Keggin-type phosphododecamolybdate compounds [Cd(2,2′-bpy)3]2[PMoVMoVI 11O40] (1) and [H3PMo12O40]·3(4,4′-bpy)·4H2O (2) (bpy=bipyridine) were prepared by the hydrothermal method for the first time and characterized by elemental analyses, X-ray single-crystal diffraction, ESR spectra, and IR spectra, showing that compound 1 consists of a mixed valence Keggin polyanion [PMoVMoVI 11O40]4− and two isolated coordinated cations [Cd(2,2′-bpy)3]2+, while compound 2 is an intermolecular compound based on organic substrate 4,4′-bpy and heteropoly acid unit H3PMo12O40. Furthermore, both the compounds show strong photoluminescence properties in the solid state at room temperature. The catalytic activities of the two compounds were also determined by the oxidation of benzaldehyde to benzoic acid using H2O2 as oxidant in a liquid–solid triphase system.

A new mixed molybdenum–vanadium polyoxometalate double-supporting transition metal complex: {[Co(phen)2]2-C2O4} {H2PO44[Co(phen)2(H2O)]2}·7H2O

The new polyoxometalate double-supporting transition metal complexes, {[Co(phen)2]2C2O4} {H2PO44[Co(phen)2H2O]2}·7H2O (1) (phen = 1,10-phenanthroline) have been hydrothermally synthesized and characterized by single crystal X-ray analysis, IR, XPS, ESR and elemental analysis. Compound 1 is composed of a highly reduced tetra-capped pseudo-Keggin polyoxoanion supporting two transition metal complexes, a binuclear cobalt complex cation and lattice water. The magnetism and third-order non-linear optical properties of 1 have also been studied.

ESR of copper-doped sodium citrate

Single crystal ESR spectra of Cu 2 + ion doped in sodium citrate are reported at room temperature. The observed spectra are fitted to a spin-Hamiltonian of rhombic symmetry with g x = 2.1076 ± 0.002 , g y = 2.1289 ± 0.002 , g z = 2.4454 ± 0.002 , A x = ( 40 ± 2 ) 10 - 4 cm - 1 , A y = ( 62 ± 2 ) 10 - 4 cm - 1 and A z = ( 78 ± 2 ) 10 - 4 cm - 1 . It is found that Cu 2 + enters the lattice as a substitutional impurity replacing an Na + ion. The ground state wave function of Cu 2 + ion in this lattice is also determined from the spin-Hamiltonian constants obtained from ESR results. It is found that the ground state is predominantly | x 2 - y 2 〉 . With the help of the optical absorption study, the nature of bonding in the complex has also been discussed.