Diamagnetic Solids Research Articles

Magnetism in d0 impurities doped CdTe: ab-initio calculations

In this work, using the ab-initio calculations, we have investigated the phantom magnetism when the diamagnetic solids, carbon and nitrogen with $$d^{0}$$ doped CdTe. We have applied in these calculations the combination between the Korringa–Kohn–Rostoker and coherent potential approximation method within the local density approximation and generalized gradient approximation (GGA). In this study, the doped compound presents a metallic behavior for both the approximations characterized by a small moment of about 0.299/0.326 and 0.249/0.266 $$\mu _{{\mathrm{B}}}$$ for 24% of C and N, respectively. The polarization has shown a low and decreasing value from 43.73/59.56 to 0.29/2.26% for 9% and 24% of C impurity concentration, respectively. Unlike for the case of N, this parameter varies from 76.7/72.86 to 85.29/83.63% for 9% and 24% concentration, respectively. In addition, we have determined the mechanism of ferromagnetic coupling for the C- and N-doped CdTe. Furthermore, the stability of the compound is investigated by comparing the energy difference between the spin glass and ferromagnetic states. It is found that below the percolation threshold, contrary to the case of doping by N except for 20% using GGA, the C impurities lead to the most ferromagnetic stable phase. While the system changes its stability above this threshold when doped by the C impurities. Finally, we have estimated and discussed the Curie temperature using the mean field approximation.

Microwave stimulation of dislocations and the magnetic control of the earthquake core

Microwave irradiation transforms the elasticity of solids into plasticity by controlling the dislocation mobility via magnetic interactions within the electron spin pairs on the dislocations. In ionic crystals, microwaves cause dislocations to accelerate and increase their mean free path, thus leading to a release of elastic energy; in covalent crystals, microwaves keep dislocations in place, thereby accumulating elastic energy and increasing the crystal strength. Microwave pumping at resonant Zeeman frequencies (in the magnetic resonance regime) is firm evidence of the concepts of electron spin pairs and of the magnetoplasticity phenomenon itself. However, the dominant contribution to the macroscopic transformation of elastic energy into plastic flow comes from nonresonant microwaves. These can be used to control the mechanics of diamagnetic solids, including, importantly, the earthquake focus. The observed correlation between magnetic events (such as magnetic storms and hydrodynamically generated high-power magnetic pulses) and their seismic and tectonic consequences (earthquake frequency and magnitude and deformations) indicates unambiguously that magnetically controlling the earthquake focus provides a realistic means to prevent a catastrophe by transforming large-magnitude earthquakes into weak, low-magnitude events.

Tetrafluoridonitridotechnetate(VI) – Reactions and Structures

Dissolution of the polymeric nitridotechnetic(VI) acid in aqueous HF results in the formation of the [TcNF4]– anion. The presence of the paramagnetic anion in such solutions can readily be confirmed by EPR spectroscopy. Addition of CsF or (NEt4)F gives orange‐yellow, diamagnetic solids of the compositions Cs3(NH4)[F4NTc(μ‐O)TcNF4] and (NEt4)3(NH4)[NF2Tc(μ‐O)2TcNF2]2, respectively.

Comment on “Synthesis, growth and characterization of a new metal–organic NLO material: Dibromo bis (l-proline) Cd(II)” [J. Mol. Struct. 1080 (2015) 37–43

The title paper by Boopathi and Ramasamy reports a study on the crystal growth and characterization of dibromobis(l-proline)cadmium(II) 1. Many points of criticism, concerning the crystal structure of 1 and the magnetic properties of 1, dibromobis(l-proline)zinc(II) 2 (J. Mol. Struc. 1033 (2013) 121–126) and diiodobis(2-aminopyridine)cadmium(II) 3 (J. Mol. Struc. 1042 (2013) 25–31) are described to show that compounds 1 to 3 are not soft magnets but instead diamagnetic solids.

Theoretical and experimental characterization of pyrazolato-based Ni(ii) metal–organic frameworks

The structural, electronic, dielectric and vibrational features of two metal–organic frameworks with bispyrazolate ligands are investigated by combining ab initio periodic calculations and experimental techniques. UV-Vis spectroscopy has been used to study the electronic structure, while FTIR spectroscopy to obtain information about the vibrational features of the samples and their adsorptive properties. The examined MOFs contain square-planar Ni(II) nodes bridged either by the 4,4′-bispyrazolato (bpz) or by the 1,4-bis(4-pyrazolato)benzene (bpb) spacers. As expected, they are diamagnetic solids, with Ni(II) in low spin state. This has been confirmed through computations, other magnetic phases being predicted as remarkably less stable. Both materials possess a band gap of ∼3.4 eV and show interesting dielectric properties due to the microporous structure and the low dielectric constant. Although Ni(II) is coordinatively unsaturated, it does not show any specific interaction with the probe molecules tested, as evidenced by FTIR measurements. This unexpected behavior is explained on the basis of computed results. The high stability of the low spin state of Ni(II) in square-planar coordination and a reduced accessibility of the metal sites due to steric effects are considered to be the reasons for the absence of preferential interactions between the metal centers and the probe molecules adopted.

Magnetoplasticity and magnetic memory in diamagnetic solids

A mechanism for the depinning of dislocations pinned by a stopper is formulated. This mechanism includes the transfer of an electron from a dislocation to the stopper and the appearance of a spin two-electron nanoreactor that has no Coulomb interaction that would hold the dislocation at the stopper in the initial state. The spin dynamics in the nanoreactor is controlled by a magnetic field; therefore, it causes magnetoplasticity and short-term magnetic memory. Another origin of magnetoplasticity is the aggregation of diffusing paramagnetic ions (stoppers) into dimers, trimers, and clusters; this aggregation is also spin-selective and magnetically sensitive. The magnetic-field dependence of the structural evolution of the stoppers provides long-term magnetic memory in diamagnetic solids. Both mechanisms of magnetoplasticity and magnetic memory can coexist and be independent of or dependent on each other.

Efficiency of Magnetic Alignment Found in Various Paramagnetic and Diamagnetic Solids Detected by Simple Rotational Oscillation of Sample in Microgravity

Oscillation of magnetically stable-axis with respect to a static field below 20 kOe occurred for various solids without spontaneous magnetic moment. The oscillation was caused by anisotropy of magnetic susceptibility ΔΧ. According to theoretical consideration on the origin of diamagnetic and paramagnetic anisotropy, ΔΧ values of ordinary solid is expected to range over 6 orders of magnitude. These Δ Χ values can be obtained from period of the above-mentioned oscillation; small ΔΧvalues were detectable because effect of restoration torque of a fiber that suspended the sample was excluded in the measurement. ΔΧ above 1 x 10 -9 emu/g were detected at terrestrial gravity in a field below B = 20k0e. The fiber itself was excluded by floating a sample in microgravity, for the purpose of detecting Δ Χ below 1 × 10 -9 emu/g. Alignment of micron-sized crystals dispersed in fluid at room temperature is achieved below 2 Tesla for most of the solids since their ΔΧ value is above 1 x 10 -9 emu/g. Efficiency of magnetic alignment is enhanced considerably for ordinary oxide when resultant ΔΧ is increased by paramagnetic impurity ions up to level of 10 -5 emu/g.

Spin-lattice relaxation of heavy spin-1/2 nuclei in diamagnetic solids: A Raman process mediated by spin-rotation interaction

We present a theory for the nuclear spin-lattice relaxation of heavy spin-1/2 nuclei in solids, which explains within an order of magnitude the unexpectedly effective lead and thallium nuclear spin-lattice relaxation rates observed in the ionic solids lead molybdate, lead chloride, lead nitrate, thallium nitrate, thallium nitrite, and thallium perchlorate. The observed rates are proportional to the square of the temperature and are independent of magnetic field. This rules out all known mechanisms usually employed to model nuclear spin relaxation in lighter spin-1/2 nuclei. The relaxation is caused by a Raman process involving the interactions between nuclear spins and lattice vibrations via a fluctuating spin-rotation magnetic field. The model places an emphasis on the time dependence of the angular velocity of pairs of adjacent atoms rather than on their angular momentum. Thus the spin-rotation interaction is characterized not in the traditional manner by a spin-rotation constant but by a related physical parameter, the magnetorotation constant, which relates the local magnetic field generated by spin rotation to an angular velocity. Our semiclassical relaxation model involves a frequency-mode description of the spectral density that can directly be related to the mean-square amplitudes and mode densities of lattice vibrations in the Debye model.

Solid‐State NMR Spectroscopy of the Quadrupolar Halogens: Chlorine‐35/37, Bromine‐79/81, and Iodine‐127

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Solid-state NMR spectroscopy of the quadrupolar halogens: chlorine-35/37, bromine-79/81, and iodine-127

A thorough review of 35/37Cl, 79/81Br, and 127I solid-state nuclear magnetic resonance (SSNMR) data is presented. Isotropic chemical shifts (CS), quadrupolar coupling constants, and other available information on the magnitude and orientation of the CS and electric field gradient (EFG) tensors for chlorine, bromine, and iodine in diverse chemical compounds is tabulated on the basis of over 200 references. Our coverage is through July 2005. Special emphasis is placed on the information available from the study of powdered diamagnetic solids in high magnetic fields. Our survey indicates a recent notable increase in the number of applications of solid-state quadrupolar halogen NMR, particularly 35Cl NMR, as high magnetic fields have become more widely available to solid-state NMR spectroscopists. We conclude with an assessment of possible future directions for research involving 35/37Cl, 79/81Br, and 127I solid-state NMR spectroscopy.

Nitrido-ruthenium(VI) and -osmium(VI) complexes containing chelating multianionic (N, O) ligands. Synthesis, crystal structures and reactions with triphenylphosphine

A series of nitrido-ruthenium(VI) and -osmium(VI) complexes containing chelating di-, tri- and tetra-anionic ligands was synthesized by ligand substitution reaction in methanol under room conditions in the presence of 2,6-dimethylpyridine. All the newly prepared complexes are air-stable diamagnetic solids. The crystal structures of seven complexes have been established by X-ray crystallography. The RuN (1.615–1.594 A) and the OsN (1.612–1.621 A) bond distances are rather insensitive to the electron-donating power of the auxiliary ligands. All the nitridoruthenium(VI) complexes react spontaneously with triphenylphosphine, and the intermediate [RuIV(NPPh3)L1(py)Cl] has been isolated and characterized spectroscopically for the reaction with [RuVIN(L1)Cl]. However, for those nitridoruthenium(VI) complexes bearing the tri- (L2)3– and tetra-anionic (L3,4)4– ligands, the phosphiniminatoruthenium(IV) intermediate undergoes further reaction with pyrazole to generate a bis(pyrazole)ruthenium(IV) complex as the product.

A practical guide to solid-state NMR of half-integer quadrupolar nuclei with some applications to disordered systems

The practical aspects for obtaining useful NMR spectra of half-integer quadrupolar nuclei in diamagnetic solids are discussed in some detail. The general appearance of the Magic-Angle Spinning (MAS) line shape is described. The effects of a distribution in isotropic chemical shift and quadrupole interaction on the MAS line shape is shown. The necessity of fast MAS and short excitation pulses is demonstrated. The possibilities of 27Al MAS NMR at high fields is shown for some clay minerals. Techniques to obtain spectra free of quadrupolar broadening, such as DOuble Rotation (DOR), Dynamic Angle Spinning WAS) and Multiple-Quantum Magic-Angle Spinning (MQMAS), are discussed with some emphasis on the newly developed MQMAS method. The latter is used to describe structural details of phosphorus-impregnated alumina and aluminosilicate sol-gel materials. These examples give a good indication of the capabilities of this new technique.

A Bis(azo−imine)palladium(II) System with 10 Ligand π Electrons. Synthesis, Structure, Serial Redox, and Relationship to Bis(azooximates) and Other Species

The first azo-imine chelate system, Pd(N(H)C(R)NNPh)(2) (Pd(RA)(2)), has been isolated in the form of diamagnetic solids by the 6e(-)-6H(+) reduction of bis(phenylazooximato)palladium(II), Pd(N(O)C(R)NNPh)(2) (abbreviated Pd(RB)(2)), with ascorbic acid in a mixed solvent (R = Ph, alpha-naphthyl). Selected spectral features are described. The X-ray structures of Pd(PhA)(2) and Pd(PhB)(2) have revealed trans-planar geometry consistent with metal oxidation state of +2. Bond length trends within the chelate rings are rationalized in terms of steric and electronic factors. In Pd(PhA)(2) a total of 10 ligand pi electrons are present, each formally monoanionic ligand contributing five. Model EHMO studies have revealed that the filled HOMO (a(u)) in Pd(RA)(2) is a bonding combination of two ligand pi orbitals with large azo contributions. The LUMO (b(g)) is roughly the corresponding antibonding combination. The outer pi-electron configuration of Pd(RA)(2) is (a(u))(2)(b(g))(0). Four successive voltammetric responses, two oxidative and two reductive, are observed. The E(1/2) range is -1.3 to +0.8 V vs SCE for Pd(PhA)(2) in a 1:9 MeCN-CH(2)Cl(2) mixture (Pt electrode). EPR and electronic spectra of the electrogenerated one-electron-oxidized complex Pd(PhA)(2)(+) are described. The azo-imine system is compared with imine-imine and azo-azo systems. Crystal data for the complexes are as follows. Pd(PhA)(2): crystal system monoclinic; space group C2/c; a = 18.167(5) Å, b = 7.420(3) Å, c = 16.527(6) Å; beta = 92.70(3) degrees; V = 2225(1) Å(3); Z = 4; R = 2.61%, R(w) = 3.58%. Pd(PhB)(2): crystal system monoclinic; space group P2(1)/n; a = 5.735(5) Å, b = 10.797(6) Å, c = 18.022(11) Å; beta = 97.73(6) Å; V = 1105(1) Å(3); Z = 2; R = 3.37%; R(w) = 3.40%.

Cobalt analogue of ferroverdin: Synthesis and geometric structure

Tris(4- R-1,2-benzoquinato)cobalt(III), [Co(RL) 3] (R = Me, Cl, Br), complexes have been synthesized in high yields as dark coloured diamagnetic solids by the reaction of [Co(OCOCH 3) 2]·.4H 2O with ligands (HRL) in methanol. The 1H NMR spectra of equilibriated solutions reveal that these complexes are mixtures of facial (∼ 64%) and meridional(∼ 36%)isomers. The difference between [CO(RL) 3] and [Fe(RL) 3] − (exclusively fac) is assigned to interchelate steric interactions. The [Co(RL) 3] complexes are simpler versions of the cobalt(III) analogue of ferroverdin, a green pigment liberated by a species of streptomyces.

Organometallic nitrosyl chemistry. 43. Synthesis, characterization, and physical properties of unusual cyclopentadienyl bis(benzyl) nitrosyl complexes of molybdenum and tungsten

Treatment of either the dichloro or diiodo nitrosyl precursors Cp'M(NO)X 2 (Cp'=Cp (η 5 -C 5 H 5 ) or Cp* (η 5 -C 5 Me 5 ); M=Mo or W; X=Cl or I) in THF/Et 2 O with 2 equiv of a benzyl Grignard reagent, Ph'CH 2 MgCl (Ph'=C 6 H 5 or 2,4,6-Me 3 C 6 H 2 ), at 0°C affords the corresponding bis(benzyl) nitrosyl complexes, Cp'M-(NO)(CH 2 Ph')2, isolated yields typically being 50-65%. All the bis(benzyl) nitrosyl complexes are relatively high melting (143-163°C), orange-red, diamagnetic solids that are soluble in most common organic solvents

T1 Measurements for 13C with magic-angle spinning in iron (II) spin-crossover complexes. Evidence of an increase in spin diffusion with MAS

3C T 1 measurements have been made for two spin-crossover complethe low-spin region using “magic-angle spinning.” For 30% enriched [Fe(1,10-phenanthroline) 2 (N 13CS) 2] the decay to equilibrium of the spin magnetization was found to be exponential in time t, which is different from the decay found for the same sample when it is not spinning. In this case the decay was exponential in √ t. This change in rate law must result from a marked increase in the spin diffusion of 13C when the sample is spun. This increase in spin diffusion is large enough to produce T 1 values for 13C that are one-fifth the static T 1 values found for protons in the same sample. Measurement of T 1 values in [Fe (2,2′-bi-2-thiazoline) 2 (NCS) 2] (natural abundance) also shows a decay exponential in t for all ligand resonances when the sample is subjected to magic-angle spinning. Application of present theories for T 1 in diamagnetic solids having paramagnetic impurities, to the results found here, reveals several inconsistencies that may require revision of the theories as they apply to 13C NMR.

Calcified intracranial lesions: detection with gradient-echo-acquisition rapid MR imaging.

Seventeen patients with partially calcified intracranial lesions, as documented by CT, were evaluated with MR imaging at 1.5 T. All patients were imaged with both conventional spin-echo techniques and reduced flip-angle gradient-echo-acquisition (GEA) sequences, during which a signal is acquired in the absence of a 180 degrees radiofrequency pulse. GEA parameters were implemented so that T2* effects were maximized on these scans. In all 17 patients GEA images showed marked hypointensity throughout the entire area of calcification, matching the calcified region as seen on CT. In contrast, spin-echo findings in the calcified portions of the lesions were extremely variable, precluding confident identification of calcification on these images. The depiction of regions of calcification as marked hypointensity on GEA images can be ascribed to T2* shortening from static local magnetic field gradients at interfaces of regions differing in magnetic susceptibility, a phenomenon that is well documented in vitro, when various diamagnetic solids are placed in aqueous suspension. However, we cannot exclude the possible additional role of accompanying paramagnetic ions, which sometimes are present with diamagnetic calcium salts in various intracranial calcifications. Since the hypointensity due to calcification on GEA images is not specific, noncontrast CT could be used to confirm its presence. Although this lack of specificity and the artifacts that emanate from diamagnetic susceptibility gradients at or near air-brain interfaces somewhat limit the application of GEA techniques, we suggest that rapid MR imaging using GEA sequences can consistently demonstrate intracranial calcification, and that this technique thus seems to be a useful adjunct to conventional spin-echo imaging.

Carbon-13 spectral line broadening in paramagnetic solids

Sensitivity enhancement by cross-polarization and resolution enhancement by dipolar decoupling and magic-angle sample spinning has become an increasingly important method for structural and dynamic characterization of solid materials (I). Paramagnetic compounds, with several notable exceptions (24, have resisted characterization using line-narrowing methods. A common assumption about the failure of this experiment is that an efficient nuclear electron dipolar relaxation mechanism, modulated by the rapid electron relaxation times, r,, and Th, can render the relaxation times of the observed carbon nucleus, fi and T$ , sufficiently short that an unusually broad carbon spectrum results. Our experiments on several compounds demonstrate that this assumption is incorrect, at least among the paramagnetic lanthanide systems studied. Short carbon relaxation times as a source of the line broadening may be tested by measuring the carbon relaxation times in question, fi and E. We have previously reported the spin-lattice relaxation times for the carbon atoms of praseodymium acetate monohydrate and find that the carboxyl and methyl carbons have T, values of 125155 and 600 ms, respectively (3). These times predict a linewidth less than 3 Hz, far narrower than those observed in the MASS spectra of this compound, about 280 Hz for the carbonyl. A convenient and efficient method for estimating the transverse relaxation times for the carbon atoms is to take the Fourier transform of the echo train (5, 6) accumulated on the paramagnetic compound. The resulting spectrum consists of a series of sharp lines the intensity of which maps the powder pattern and the width of which correspond to the linewidth implied by the decay time of the whole echo train. The width of these lines is typically about 25 Hz for the carbonyl lines, far narrower than the MASS lines or the single crystal lines. Thus, the width of the carbon lines in these paramagnetic solids is not determined by the spin-lattice or spin-spin relaxation times at the carbon atoms. The limiting linewidths of diamagnetic organic solids have been considered by VanderHart, Earl, and Garroway (7) and by Alla and Lippmaa (8). The broadening in both the static and MASS spectra may be attributed to the anisotropy of the diamagnetic susceptibility in the aromatic compounds. The situation is aggravated by paramagnetic materials where the anisotropy of the magnetic susceptibility may be far larger (9-11). Following Alla and Lippmaa (8) the bulk effects are demonstrated in Fig. 1, which shows the spectrum of adamantane and adamantane in samples where praseodymium

Affinity separation of enzymes from mixtures containing suspended solids

Agarose beads containing immobilized enzymes or affinity ligands have been made magnetically responsive by adsorbing freshly precipitated magnetite on their surface. These beads are used for affinity adsorption of proteins from complex mixtures containing suspended solids. The magnetically responsive beads and the unwanted (diamagnetic) solids are then separated by magnetic filtration. This magnetic adsorption scheme for direct affinity separation of enzymes from mixtures containing suspended solids is compared with a similar, but nonmagnetic, scheme in which the affinity matrix is supported on fiberglass cloth. The enzyme is allowed to adsorb in this matrix, and the matrix is simply removed physically from the suspension to achieve separation from the unwanted solids. The two methods seem comparable in their ability to separate a desired enzymatic activity. The magnetic methods are technically the more complex of the two, but are significantly the more rapid. The efficiency of separation of diamagnetic and ferrimagnetic solids in these biological systems by high gradient magnetic filtration is good.

Experiments on magnetic materials

The construction and use of a simple apparatus to measure the magnetization density and magnetic susceptibility of ferromagnetic, paramagnetic, and the diamagnetic solids and liquids are described. The apparatus is valuable in demonstrations, student laboratories, and undergraduate research.