Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “paramagnetism”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 793 records · Page 44
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Half-Metallic Ferromagnetism Character in Cr-Doped CaS Diluted Magnetic Insulator and Semiconductor: an Ab Initio Study

The overall aim of this study is to investigate theoretically the structural, electronic, and magnetic properties of calcium sulfide (CaS) doped with chromium (Cr) impurity, in order to conduct a new search dilute magnetic semiconductors (DMS) suitable for different applications in electronics and spintronics. For measuring, the physical property of this compound is implemented using the first principles approach employed in WIEN2K code. The structural characteristics are optimized using the Generalized Gradient Approximation established by Perdew-Burk-Ernzerhof (PBE-GGA). We calculate and minimize the total energy of the three ternary compounds (Ca{sub 0.75}Cr{sub 0.25}S, Ca{sub 0.50}Cr{sub 0.50}S, and Ca{sub 0.25}Cr{sub 0.75}S) in the paramagnetic (PM), ferromagnetic (FM), and antiferromagnetic (AFM) phase. We find all compounds stable in (FM) structure, whereas the modified Becke and Johnson local density approximation (mBJ-LDA) functional has been employed to evaluate the electronic and magnetic properties. Based on our findings, indicate that this system revealed a half-metallic ferromagnetic behavior with half-metallic gap (HM) and 100% spin-polarized at the fermi level for all chromium (Cr) concentrations. This advantageous set of properties is due to the half-metallic behavior, where the majority spin and minority spin exhibit metallic and semiconducting behaviors respectively. The chromium atom is the most important source of the total magnetic moment in these compounds (4 μβ) by comparison with magnetic moments produced by Ca and S atoms, which have minor contribution. Finally, our prediction results require an experimental confirmation in the future.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Spin Glass Behavior in La{sub 0.7}Ca{sub 0.23}Sr{sub 0.07}MnO{sub 3} Nanofibers Obtained by Electrospinning

This work contributes to the development of new nanostructured mixed valence manganites and to explore and optimize their magnetic properties at 1-D level. Nanofibers of La{sub 0.7}Ca{sub 0.23}Sr{sub 0.07}MnO{sub 3} manganite were fabricated using the electrospinning method and three different heat treatments to determine how the nanostructure affects its thermomagnetic behavior. From scanning electron microscopy, nanofibers morphology was observed and average diameters of 75, 94, and 97 nm were identified after heat treatments of 973, 1073, and 1173 K, respectively. According to X-ray diffraction technique, a single-phase orthorhombic structure was defined for each sample. Average crystallite sizes were determined as 47, 49, and 58 nm. A ferromagnetic to paramagnetic transition with Curie temperatures of 297, 305, and 314 K were identified, respectively. Furthermore, a glassy state was induced by nanofibers agglomeration. The spin glass and irreversible temperatures diminished as the magnetic field was increased and a highly anisotropic state was evidenced for all samples. Thermomagnetic behavior in manganites showed to be significantly influenced by the one-dimensional structure and exposed how the dimensionality proportionated by the fabrication method can be used to adjust magnetic properties.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Studies of the Magnetocaloric and Electrical Properties of La{sub 0.7}Er{sub 0.05}Sr{sub 0.15}Ca{sub 0.1}Mn{sub 1−x}In{sub x}O{sub 3} (0 ≤ x ≤ 0.30)

We report on the study of In substitution for Mn on the magnetic and transport properties of layered manganese oxides La{sub 0.7}Er{sub 0.05}Sr{sub 0.15}Ca{sub 0.1}Mn{sub 1−x}In{sub x}O{sub 3} (0 ≤ x ≤ 0.30) synthesized via sol-gel method. For all the samples, all peaks are satisfactorily indexed in the rhombohedra structure with R 3-bar c space group. Magnetic data, under a magnetic field of 0.05 T, revealed that our compounds exhibit a continuous (second-order) transition from a ferromagnetic (FM) to a paramagnetic (PM) state upon decreasing the temperature. Also, magnetic entropy change and relative cooling power for magnetic field variation were predicted. Then, we have fitted the experimental data of resistivity using non-linear curve fitting, a typical mathematical function (Gauss function). This function can describe the carrier transport behavior of manganites as a function of temperature around the electrical phase transition. The obtained results were discussed. These predicted parameters agree with the experimental data.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Effect of Ca Doping on the Structure and Magnetic and Electronic Properties of La{sub 1 − x}Ca{sub x}Cr{sub 0.8}Cu{sub 0.2}O{sub 3} (x = 0~0.3)

A series of La{sub 1 − x}Ca{sub x}Cr{sub 0.8}Cu{sub 0.2}O{sub 3} samples were successfully prepared by sol-gel method, and their crystal structures were refined by using X-ray powder diffraction data. All samples had orthorhombic structure with a space group Pbnm. Two magnetic transitions were observed for all of samples, and the paramagnetism-antiferromagnetism transition temperature decreased, and the antiferromagnetism-ferromagnetism transition temperature increased with increasing Ca content. Moreover, Cu and Ca co-doping improved conductivity and active energy.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Superparamagnetic Behavior of Zn and Al Substituted Cobalt Nanoferrites

Nanostructured Zn- and Al-doped cobalt spinel ferrites Zn{sub x}Co{sub 1-x}Fe{sub 2-x}Al{sub x}O{sub 4} (0 ≤ x ≤ 1.0) with particle size in the range of 7–13 nm were synthesized by glycol-thermal reaction. XRD analysis confirmed single-phase cubic spinel structure with no impurity phases. The Mössbauer spectra for Zn- and Al-substituted fine powders could be resolved into two quadrupole doublets associated with {sup 57}Fe nuclei in paramagnetic spin phase. An unusual reducing magnetization with increasing particle size has been observed. The field cooled and zero field cooled magnetization measurements show superparamagnetic nanoparticles in the compounds investigated. The blocking temperatures (T{sub B}) are sensitive to particle size. Larger particles are blocked at higher temperatures compared to smaller particles at the same field.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Study of Critical Behavior and Magnetocaloric Effect in Nd{sub 1− x} Sr{sub x}MnO{sub 3} Compounds

In this paper, we have investigated the influence of substitution of Nd by Sr on the structural, magnetic, and magnetocaloric properties of Nd{sub 1 − x}Sr{sub x}MnO{sub 3} (x = 0.3 and x = 0.4). These compounds were prepared using the solid state method. The structural, morphological, and magnetic properties of our system were characterized by XRD, MEB techniques, and a magnetometer for magnetic characterization. The Rietveld refinement has revealed the coexistence of both Pnma orthorhombic and R-3c rhombohedral phases. The magnetic data indicate that the compounds exhibit a continuous paramagnetic (PM) to ferromagnetic (FM) phase transition. In addition, the critical behavior in both compounds associated with the magnetic phase transition has been studied by the magnetization isotherms. The critical exponents are deduced using various techniques such as the modified Arrott plot, Kouvel–Fisher plot, and critical isotherm technique. Finally, the results obtained of the magnetocaloric effect are in agreement with the reported values of previous researches. These results show that our samples can be used as a magnet refrigerant at room temperature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Multiple Magnetic Phase Transitions in Mn-deficient Co{sub 0.4}Ni{sub 0.6}Mn{sub 1−x}Ge Compounds

The structural and magnetic transition in Mn-deficient Co{sub 0.4}Ni{sub 0.6}Mn{sub 1−x}Ge was investigated by DC magnetization and temperature-dependent X-ray diffraction measurements. By introducing Mn vacancies in the stoichiometric Co{sub 0.4}Ni{sub 0.6}MnGe compound, multiple magnetic phase transitions and tunable martensitic transitions were observed. A paramagnetic martensite (Ni{sub 2}In-type structure) to ferromagnetic austenite (TiNiSi-type structure) transition was realized in Co{sub 0.4}Ni{sub 0.6}Mn{sub 0.98}Ge around 275 K. A large volume expansion of 2.6% accompanied this transition. In addition, a martensitic transition induced by the magnetic field was also observed near room temperature. Furthermore, a significant magnetic entropy variation of − 21.3 J/kg K at 263 K (∆B = 5 T) was obtained in the Co{sub 0.4}Ni{sub 0.6}Mn{sub 0.98}Ge compound.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Experimental Study of Structural and Magnetic Properties of LaNi{sub 5} and MmNi{sub 4.7}Al{sub 0.3} Hydrogen Storage Alloys

This study deals with an experimental investigation of structural and magnetic properties of LaNi{sub 5} and MmNi{sub 4.7}Al{sub 0.3} (Mm consists of 66.6 wt% Ce and 33.3 wt% La) hydrogen storage alloys. LaNi{sub 5} and MmNi{sub 4.7}Al{sub 0.3} alloys were prepared by vacuum induction melting method and then hydrogenated under 50 bar hydrogen gas pressure. The structure of the samples, before and after hydrogenation, was probed by X-ray diffraction (XRD) analysis which showed that all the samples have a single phase hexagonal crystal structure (CaCu5-type). Then X-ray fluorescence (XRF) measurement was used to investigate the chemical compound of the as-prepared samples. The study of the magnetic properties of samples indicated that the as-prepared alloys are weakly ferromagnetic or paramagnetic, while the hydrogenation process causes ferromagnetic behavior of samples to intensify. Honda-Arrott plot analysis exhibited that substitution of Al for Ni and Ce for La in the as-prepared samples reduces the magnetic susceptibility from 4.8 × 10{sup −6} to 3.06 × 10{sup −6} emu/gOe. Magnetic anisotropy of the hydrogenated samples in a high magnetic field was studied using the law of approach to saturation. The results indicated that the magnetic anisotropy and anisotropy field increase by the replacement of Ni and La with Al and Ce respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Magnetic Properties of Disordered Li{sub 2}Co{sub 2 – x}Ni{sub x}(MoO{sub 4}){sub 3} (0 ≤ x ≤ 2) System with a Lyonsite Structure

We report on the magnetic properties of disordered Li{sub 2}Co{sub 2 – x}Ni{sub x}(MoO{sub 4}){sub 3} (0 ≤ x ≤ 2) system with a lyonsite structure, where Li{sup +}, Ni{sup 2+}, and Co{sup 2+} ions are distributed in a disordered manner in the trigonal prism and octahedral sites. All compositions were found to exhibit paramagnetic behavior at high temperature; the magnetic susceptibility was described by the modified Curie-Weiss law. The experimental effective moments were explained by spin and orbital contributions of the Co{sup 2+} ions and only the spin contribution for Ni{sup 2+} ions. The negative Curie-Weiss temperature θ indicates the existence of antiferromagnetic coupling for all compositions. At low temperature, the compounds with Co{sup 2+} ions (x = 0, 1, 1.6, and 1.8) exhibit a weak ferromagnetic state below 4 K due to intrinsic canting of antiferromagnetically coupled lattices. The compound containing only Ni{sup 2+} ions, Li{sub 2}Ni{sub 2}(MoO{sub 4}){sub 3}, exhibits a pure antiferromagnetic behavior.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

AC Magnetic Susceptibility of Y{sub 3}Ba{sub 5}Cu{sub 8}O{sub 18} Substituted by Nd{sup 3+} and Ca{sup 2+} Ions

Effect of Nd{sup 3+} and Ca{sup 2+} ion substitutions in Y{sub 3}Ba{sub 5}Cu{sub 8}O{sub 18} (Y-358) was studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), electrical resistivity, and ac magnetic susceptibility measurements. Superconducting samples of type Y{sub 3 − x}Nd{sub x}Ba{sub 5 − y}Ca{sub y}Cu{sub 8}O{sub 18} (with 0 ≤ x, y ≤ 0.4) were synthesized by the standard solid-state reaction technique. XRD patterns revealed that all the samples were mainly composed of Y-358 phase with orthorhombic structure. SEM micrographs showed that Nd{sup 3+} and Ca{sup 2+} ion substitutions had the ability to alter the grain morphology of Y-358 to irregular randomly oriented grains with smaller average grain sizes. The temperature-dependent electrical resistivity curves indicated that the superconducting transition temperature T{sub c} was decreased from 96.51 to 87.41 K as the substitution contents were increased from 0 to 0.4. Detailed AC magnetic susceptibility measurements were done using a quantum design physical property measurement system (PPMS) at different dc fields (B = 0.5–20 kG) and frequency of 1 kHz. A comparison between electrical resistivity and AC magnetic susceptibility data was performed. It was found that T{sub cs} obtained from AC magnetic susceptibility were much lower than those obtained from the resistivity measurements, for all studied samples. This was discussed in terms of filamentary paths that could produce sharp pronounced drops in diamagnetism. Generally, the depression in T{sub c} was attributed to the decrease in relative volume fraction of Y-358 or due to trapping of mobile holes or other mechanism connected with oxygen vacancy disorder. Werthamer–Helfand–Hohenberg (WHH) theory was employed to study the temperature dependence of the upper critical magnetic field B{sub c2}(T) for the samples. The relative importance of both orbital and paramagnetic effects in the suppression of superconductivity was described with the aid of Maki parameter (κ{sub M}). The estimated values of the upper critical magnetic field at 0 K, B{sub c2}(0), were found to decrease from 37.3 to 13.5 T as Nd{sup 3+} and Ca{sup 2+} contents were increased from 0 to 0.4. This decrement was attributed to the weak electron–phonon coupling and to the orbital as well as spin pair breaking mechanisms. Furthermore, Ginzburg–Landau coherence length ξ{sub GL} of Y{sub 3 − x}Nd{sub x}Ba{sub 5 − y}Ca{sub y}Cu{sub 8}O{sub 18} was found to increase with the increase of the Nd{sup 3+} and Ca{sup 2+} contents. Therefore, Nd{sup 3+} and Ca{sup 2+} ions play an important role in the pair-breaking mechanism and in suppressing superconductivity of the Y-358 phase.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

High-gradient magnetic filtration of UO 2 colloids from aqueous suspensions

Environmental samples often contain innocuous components that make trace actinide analysis difficult and expensive. Therefore, it is expedient to separate these materials from actinide particles. One characteristic of many actinides is that they are paramagnetic. High-gradient magnetic filtration (HGMF) is a non-destructive technique that selectively captures magnetic constituents from a matrix containing non-magnetic species. Here, in this work, a novel HGMF device made of a permanent magnet array was used to effectively separate UO 2 particles from undesirable soil species. Up to 88% of the UO 2 particles present in suspensions were effectively captured by HGMF, resulting in their enrichment and a substantial reduction in the concentrations of other constituents.

Actinide separations↗
DOE OSTI2019

Characterization of terbium containing cubic zirconia crystal for high power laser applications

A magneto-active terbium containing cubic zirconia crystal is an attractive material for creating Faraday isolators thanks to a high value of its Verdet constant and low absorption coefficient. The optical anisotropy parameter of this crystal which shows the distribution of orientations of the axes of thermally induced birefringence in a thermally loaded optical element has negative value. It means that there exists a dedicated orientation of crystallographic axes, at which the axes of thermally induced birefringence are arranged in the one direction and thermally induced depolarization may be reduced substantially. For assessing potential of this crystal for high-power applications we have investigated its temperature dependence of the Verdet constant that proved to correspond to the paramagnetic behavior. Thermo-optical characteristics are also of principal importance when operating with high-power laser radiation. We present results of measurements of thermo-optical characteristics Q and P which determines values of polarization and phase distortions of passing laser radiation. Measured values can be used to determine the characteristics of Faraday isolators based terbium containing cubic zirconia crystals in various implementations of their optical schemes for various parameters of laser radiation.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Chloride facilitates Mn(III) formation during photoassembly of the Photosystem II oxygen-evolving complex

The Mn 4 Ca oxygen-evolving complex (OEC) in Photosystem II (PSII) is assembled in situ from free Mn 2+ , Ca 2+ , and water. In an early light-driven step, Mn 2+ in a protein high-affinity site is oxidized to Mn 3+ . Using dual-mode electron paramagnetic resonance spectroscopy, we observed that Mn 3+ accumulation increases as chloride concentration increases in spinach PSII membranes depleted of all extrinsic subunits. At physiologically relevant pH values, this effect requires the presence of calcium. Here, when combined with pH studies, we conclude that the first Mn 2+ oxidation event in OEC assembly requires a deprotonation that is facilitated by chloride.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Glycerol Binding at the Narrow Channel of Photosystem II Stabilizes the Low-Spin S 2 State of the Oxygen-Evolving Complex

The oxygen-evolving complex (OEC) of photosystem II (PSII) cycles through redox intermediate states S i (i = 0–4) during the photochemical oxidation of water. The S 2 state involves an equilibrium of two isomers including the low-spin S 2 (LS-S 2 ) state with its characteristic electron paramagnetic resonance (EPR) multiline signal centered at g = 2.0, and a high-spin S 2 (HS-S 2 ) state with its g = 4.1 EPR signal. The relative intensities of the two EPR signals change under experimental conditions that shift the HS-S 2 /LS-S 2 state equilibrium. Here, we analyze the effect of glycerol on the relative stability of the LS-S 2 and HS-S 2 states when bound at the narrow channel of PSII, as reported in an X-ray crystal structure of cyanobacterial PSII. Our quantum mechanics/molecular mechanics (QM/MM) hybrid models of cyanobacterial PSII show that the glycerol molecule perturbs the hydrogen-bond network in the narrow channel, increasing the pK a of D1-Asp61 and stabilizing the LS-S 2 state relative to the HS-S 2 state. Here, the reported results are consistent with the absence of the HS-S 2 state EPR signal in native cyanobacterial PSII EPR spectra and suggest that the narrow water channel hydrogen-bond network regulates the relative stability of OEC catalytic intermediates during water oxidation.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

EPR studies of ferredoxin in spinach and cyanobacterial thylakoids related to photosystem I-driven NADP + reduction

Photosynthetic light-dependent reactions occur in thylakoid membranes where embedded proteins capture light energy and convert it to chemical energy in the form of ATP and NADPH for use in carbon fixation. One of these integral membrane proteins is Photosystem I (PSI). PSI catalyzes light-driven transmembrane electron transfer from plastocyanin (Pc) to oxidized ferredoxin (Fd). Electrons from reduced Fd are used by the enzyme ferredoxin-NADP + reductase (FNR) for the reduction of NADP + to NADPH. Fd and Pc are both small soluble proteins whereas the larger FNR enzyme is associated with the membrane. To investigate electron shuttling between these diffusible and embedded proteins, thylakoid photoreduction of NADP + was studied. As isolated, both spinach and cyanobacterial thylakoids generate NADPH upon illumination without extraneous addition of Fd. These findings indicate that isolated thylakoids either (i) retain a “pool” of Fd which diffuses between PSI and membrane bound FNR or (ii) that a fraction of PSI is associated with Fd, with the membrane environment facilitating PSI-Fd-FNR interactions which enable multiple turnovers of the complex with a single Fd. To explore the functional association of Fd with PSI in thylakoids, electron paramagnetic resonance (EPR) spectroscopic methodologies were developed to distinguish the signals for the reduced Fe-S clusters of PSI and Fd. Temperature-dependent EPR studies show that the EPR signals of the terminal [4Fe-4S] cluster of PSI can be distinguished from the [2Fe-2S] cluster of Fd at > 30 K. At 50 K, the cw X-band EPR spectra of cyanobacterial and spinach thylakoids reduced with dithionite exhibit EPR signals of a [2Fe-2S] cluster with g-values g x = 2.05, g y = 1.96, and g z = 1.89, confirming that Fd is present in thylakoid preparations capable of NADP + photoreduction. Quantitation of the EPR signals of P 700 + and dithionite reduced Fd reveal that Fd is present at a ratio of ~ 1 Fd per PSI monomer in both spinach and cyanobacterial thylakoids. Light-driven electron transfer from PSI to Fd in thylakoids confirms Fd is functionally associated (< 0.4 Fd/PSI) with the acceptor end of PSI in isolated cyanobacterial thylakoids. Furthermore, these EPR experiments provide a benchmark for future spectroscopic characterization of Fd interactions involved in multistep relay of electrons following PSI charge separation in the context of photosynthetic thylakoid microenvironments.

Electron paramagnetic resonance↗
DOE OSTI2017

Quantum chemical study of binuclear adducts of cobalt azomethine complexes with pyrene-4,5,9,10-tetraimine

A computer simulation of 2 : 1 adducts of cobalt azomethine complexes with pyrene-4,5,9,10-tetraimine was carried out within the framework of the density functional theory (DFT B3LYP*/6-311++G(d,p)). It was shown that the variation of the substituents at the nitrogen atoms of cobalt bischelates, as well as the annulation of the five-membered ring to the azomethine fragment, considerably affects the relative energies of the isomers with different spin states. Compounds, which can manifest one- and two-step redox-isomeric rearrangements, accompanied by the migration of paramagnetic centers, were revealed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Multinuclear compounds of s-elements with sterically hindered о-semiquinonates and catecholates

Alkali metals form mutinuclear compounds with redox-active singly and doubly reduced derivatives of sterically of hindered о-benzoquinones. Complexes [Na{sub 6}(Cat){sub 3}(THF){sub 7}]•4THF, [Na{sub 5}(Cat){sub 2}(SQ)(THF){sub 5}], [Na{sub 4}(SQ){sub 4}(THF){sub 4}]•THF•C{sub 6}H{sub 14}, [Na{sub 4}(3,5-SQ){sub 4}(THF){sub 4}], [K{sub 4}(SQ){sub 4}(THF){sub 4}]•4THF and [Li{sub 3}(SQ){sub 3}(THF){sub 3}]•THF (Cat is catecholate, SQ is semiquinonate) possessing high sensitivity to atmospheric oxygen were synthesized and their structures were determined. Magnetochemical measurements and quantum chemical calculations revealed that variation of the alkali metal and/or change in the structure of the polymetallic core significantly affect the energy of exchange interaction between the unpaired electrons of the paramagnetic ligands framing the polynuclear metal core formed by s-elements.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Reactivity of an aluminum hydride complex with a redox-active diimine ligand

The reaction of the hydride [(dpp-bian)Al(H)Cl] (1) containing the 1,2-bis[(2,6-diisopropylphenyl) imino]acenaphthene (dpp-bian) radical anion with MeLi affords the compound [(dpp-bian)Al(H)Me] (2). The reaction of complex 1 with two equivalents of PhC≡CNa involves the replacement of chlorine along with oxidative substitution of hydrogen accompanied by the reduction of dpp-bian to the dianion to form the compound [(dpp-bian)Al(C≡CPh){sub 2}Na(Et{sub 2}O){sub 2}] ({sn3}). This reaction gives the complex [{dpp-bian(H)}Al(C≡CPh){sub 3}Na(Et{sub 2}O){sub 2}] (4) as the second product, which is apparently generated in the reaction of compound 3 with PhC≡CH. The reaction of compound 1 with Cp*Na (Cp* is pentamethylcyclopentadiene) in dimethoxyethane is also accompanied by the reduction of redox-active dpp-bian to the dianion, giving the complex [(dpp-bian)Al(H)Cl][Na(DME){sub 3}] (5). Diamagnetic derivatives 3–5 were characterized by {sup 1}H NMR spectroscopy; paramagnetic compound 2, by EPR spectroscopy. The molecular structures of compounds 2–5 were determined by X-ray diffraction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗