The powder X-band electron paramagnetic resonance spectroscopy of septet pyridyl-2,4,6-trinitrene

The first X-band EPR spectrum containing only non-overlapping signals of septet pyridyl-2,4,6-trinitrene and triplet pyridylnitrenes is reported. This spectrum was recorded after photolysis of 2,4,6-triazidopyridine in solid argon at 5 K. The zero-field splitting (ZFS) parameters of this trinitrene as well as of intermediate triplet mononitrenes and quintet dinitrenes formed at early stages of the photolysis were determined using the combination of modern computer line-shape spectral simulations and density functional theory (DFT) calculations. It was found that septet pyridyl-2,4,6-trinitrene has the record negative parameter D-S = -0.1031 cm(-1) among all known to date septet pyridyl-2,4,6-trinitrenes and may be of interest as a model multi-qubit spin system for investigations of quantum computation processing

Structural relaxation features of spark plasma sintered Ni3Al samples

A study of the features of relaxation processes activation in Ni3Al samples obtained by ball milling and subsequent spark plasma sintering (SPS) was carried out. The effect of the duration of the preliminary high-energy ball milling (HEBM) on the activation of structural relaxation processes at temperatures above and below the SPS temperature was revealed. It was found that at temperatures above the synthesis temperature, the main relaxation processes are associated with the activation of primary recrystallization in the most defective regions, that consist of grains of submicron sizes. It was shown that the temperature of activation of high-defect states relaxation in SPS samples of Ni3Al decreases with an increase in the duration of the preliminary HEBM

Mathematical Modeling of Dielectric Permeability and Volt-Ampere Characteristics of a Semiconductor Nanocomposite Conglomerate

Mathematical computer models of the permittivity of silicon-based nanostructures upon interaction with electromagnetic radiation in a wide frequency range have been developed. To implement computer models for studying the electrophysical properties of the structures under study, algorithms and a set of programs have been developed. The results of the study of materials will not only provide fundamental information about the physical effects occurring in composite nanostructures but will also be useful for solving problems related to calculations for given electrophysical problems. For a nanocomposite based on ceramics and semiconductor oxides of zinc grains, resonant bursts of permittivity are observed within a wavelength of 300–400 nm; it has been found that this is due to the presence of electronic polarization of the nanocomposite core. The paper presents the results of modeling the current-voltage characteristics of a nanocomposite based on ceramics and semiconductor grains of zinc oxide. The obtained results show that the geometrical parameters, such as the number of layers and sample width, affect the CVC of the nanocomposite, and the operating point of the CVC shifts. This may be of interest in the development of materials with desired electrical characteristics for the creation of varistors

The Organic Ammonium Counterion Effect on Slow Magnetic Relaxation of the [Er(hfac)₄]⁻ Complexes

The first mononuclear anionic erbium complex [Er(hfac)4]− (hfac = hexafluoroacetylacetone) with an organic ammonium cation [(CH3)4N+] as the counterion was synthesized and structurally and magnetically characterized. The coordination geometries around the Er ions are square antiprisms with pseudo-D4d symmetry. The complex shows distinct field-induced slow magnetization relaxation, which is described by a combination of Orbach (Ueff/kB~28.54(8) K.) and direct mechanisms. Quantum chemical calculations were performed to analyze the magnetic properties of the complex under consideration

A Series of Field-Induced Single-Ion Magnets Based on the Seven-Coordinate Co(II) Complexes with the Pentadentate (N3O2) H2dapsc Ligand

A series of five new mononuclear pentagonal bipyramidal Co(II) complexes with the equatorial 2,6-diacetylpyridine bis(semicarbazone) ligand (H2dapsc) and various axial pseudohalide ligands (SCN, SeCN, N(CN)2, C(CN)3, and N3) was prepared and structurally characterizated: [Co(H2dapsc)(SCN)2]∙0.5C2H5OH (1), [Co(H2dapsc)(SeCN)2]∙0.5C2H5OH (2), [Co(H2dapsc)(N(CN)2)2]∙2H2O (3), [Co(H2dapsc)(C(CN)3)(H2O)](NO3)∙1.16H2O (4), and {[Co(H2dapsc)(H2O)(N3)][Co(H2dapsc)(N3)2]}N3∙4H2O (5). The combined analyses of the experimental DC and AC magnetic data of the complexes (1–5) and two other earlier described those of this family [Co(H2dapsc)(H2O)2)](NO3)2∙2H2O (6) and [Co(H2dapsc)(Cl)(H2O)]Cl∙2H2O (7), their theoretical description and the ab initio CASSCF/NEVPT2 calculations reveal large easy-plane magnetic anisotropies for all complexes (D = + 35 − 40 cm−1). All complexes under consideration demonstrate slow magnetic relaxation with dominant Raman and direct spin–phonon processes at static magnetic field and so they belong to the class of field-induced single-ion magnets (SIMs)

Heavy Atom Effect on Magnetic Anisotropy of Matrix-Isolated Monobromine Substituted Septet Trinitrene

The heavy atom effect on the magnetic anisotropy of septet trinitrenes is reported. Septet 1-bromo-3,5-dichloro-2,4,6-trinitrenobenzene (<b>S-1</b>) was generated in a solid argon matrix by ultraviolet irradiation of 1,3,5-triazido-2-bromo-4,6-dichlorobenzene. This trinitrene displays an electron spin resonance (ESR) spectrum that drastically differs from ESR spectra of all previously studied septet trinitrenes. The zero-field splitting (ZFS) parameters, derived from the experimental spectrum, show the parameter |<i>D</i>| = 0.1237 cm^–1 and the unprecedentedly large ratio of <i>E</i>/<i>D</i> = 0.262 that is close to the rhombic limit <i>E</i>/<i>D</i> = 1/3 for high-spin molecules. The CASCI (based on state-averaged CASSCF) and DFT methods were applied to calculate the ZFS tensor focusing on the heavy (bromine) atom effects on the spin–orbit term. These calculations show that the multiconfigurational ab initio formalism and the CASCI method are the most successful for accurate predictions of the spin–orbit term in the ZFS tensor of high-spin nitrenes containing heavy bromine atoms. Due to the presence of the bromine atom in <b>S-1</b>, the contribution of the spin–orbit term to the total parameter <i>D</i> is dominant and responsible for the unusual orientation of the easy <i>Z</i>-axis lying in the molecular plane perpendicular to the C–Br bond. As a result, the principal values <i>D</i>_<i>XX</i>, <i>D</i>_<i>YY</i>, and <i>D</i>_<i>ZZ</i> of the total tensor <i>D̂</i>_Tot have such magnitudes and signs for which the ratio <i>E</i>/<i>D</i> is close to the rhombic limit, and the total parameter <i>D</i> is large in magnitude and positive in sign

Effect of Ligand Substitution on Zero-Field Slow Magnetic Relaxation in Mononuclear Dy(III) β-Diketonate Complexes with Phenanthroline-Based Ligands

Herein, we report the synthesis, structure and magnetic properties of two mononuclear complexes of general formula [Dy(acac)3(L)], where L = 2,2-dimethyl-1,3-dioxolo[4,5-f][1,10] phenanthroline (1) or 1,10-phenanthroline-5,6-dione (2), and acac− = acetylacetonate anion. A distorted square-antiprismatic N2O6 environment around the central Dy(III) ion is formed by three acetylacetonate anions and a phenanthroline-type ligand. Both complexes display a single-molecule magnet (SMM) behavior at zero applied magnetic field. Modification of the peripheral part of ligands L provide substantial effects both on the magnetic relaxation barrier Ueff and on the quantum tunneling of magnetization (QTM). Ab initio quantum-chemical calculations are used to analyze the electronic structure and magnetic properties

Zero-Field Slow Magnetic Relaxation in Binuclear Dy Acetylacetonate Complex with Pyridine-N-Oxide

A new complex [Dy(C5H7O2)3(C5H5NO)]2·2CHCl3 (1) has been synthesized by the reaction of pyridine-N-oxide with dysprosium (III) acetylacetonate in an n-heptane/chloroform mixture (1/20). X-ray data show that each dysprosium atom is chelate-like coordinated by three acetylacetonate ligands and the oxygen atom from two bridging molecules of pyridine-N-oxide, which unite the dysprosium atoms into a binuclear complex. Static (constant current) and dynamic (alternating current) investigations and ab initio calculations of the magnetic properties of complex 1 were performed. The complex was shown to exhibit a frequency maximum under alternating current. At temperatures above 10 K, the maximum shifts to a higher frequency, which is characteristic of SMM behavior. It is established that the dependence of ln(τ) on 1/T for the relaxation process is nonlinear, which indicates the presence of Raman relaxation mechanisms, along with the Orbach mechanism

The first photochromic bimetallic assemblies based on Mn(III) and Mn(II) Schiff-base (salpn, dapsc) complexes and pentacyanonitrosylferrate

International audienceFour cyano-bridged bimetallic complexes, \[Mn(salpn)](2)[Fe(CN)(5)NO]\(n) (1), \[Mn(salpn)(CH3OH)](4)[Mn(CN)(5)NO]\[C(CN)(3)]center dot 3H(2)O (2), \[Mn(dapsc)][Fe(CN)(5)NO]center dot 0.5CH(3)OH center dot 0.25H(2)O\(n) (3) and \[Mn(salpn)(CH3OH)](4)[Fe(CN)(5)NO]\(ClO4)(2)center dot 4H(2)O (4), where salpn(2-) = N, N'-1,3-propylene-bis(salicylideneiminato) dianion and dapsc = 2,6-diacetylpyridine-bis(semicarbazone), have been synthesized and structurally characterized by single crystal X-ray diffraction. In 1, the nitroprusside anion [Fe(CN)(5)NO](2-) coordinates with four [Mn(salpn)](+) via four co-planar CN- groups, whereas each [Mn(salpn)](+) links two [Fe(CN)(5)NO](2-) ions, which results in a two-dimensional network. The structure of 3 contains two independent neutral infinite chains \[Mn(dapsc)][Fe(CN)(5)(NO)]\(infinity) consisting of alternating cationic [Mn-II(dapsc)](2+) and anionic [Fe-II(CN)(5)(NO)](2-) units connected through cyanide bridges. The cation complexes 2 and 4 have a pentanuclear molecular structure in which four [Mn(salpn)(MeOH)](+) fragments are linked by the [Mn(CN)(5)NO](3-) or [Fe(CN)(5)(NO)](2-) moieties, respectively. The magnetic and photochromic properties of 1 and 3 have been studied. The thermal magnetic behaviour of the complexes indicates the presence of weak antiferromagnetic interactions between Mn3+ or Mn2+ mediated by diamagnetic [Fe(CN)(NO)-N-5](2-) bridges. Irradiation of 1 and 3 with light gives birth to the long-lived metastable states of nitroprusside