Degree Of Character Research Articles

Synthesis of a Luminescent Arsolo[2,3-d:5,4-d′]bis(thiazole) Building Block and Comparison to Its Phosphole Analogue

The synthesis of 4-phenyl-4H-arsolo[2,3-d:5,4-d′]bis(thiazole) is reported, and its properties are compared to those of the previously prepared phosphole analogue. By comparison of their single-crystal structures, the harmonic oscillator model of heterocyclic electron delocalization (HOMHED) was used to directly compare the aromatic character of the two systems. The findings demonstrate that, although both compounds can be considered aromatic, the phosphole-containing compound had a greater degree of aromatic character than its arsole analogue. The arsole derivative exhibited excellent stability in ambient air with no formation of the arsole oxide observed upon storage. The absorption and photoluminescence spectra of the arsole derivate were subtly altered in comparison to the phosphole derivative, suggesting that changing pnictogenic atoms in such fused-ring systems to heavier analogues could be a viable way of tuning both the ambient stability and optoelectronic properties of such materials.

Modeling of 1-D Nanowires and analyzing their Hydrogen and Noble Gas Binding Ability

The theoretical calculation at the M05-2X/6-311+G(d,p) level reveals that the B–B bond length in [N4-B2-N4]2− system (1.506 Å) is slightly smaller than that of typical B=B bond in B2H2 (1.518 Å). These systems interact with each M+ (M = Li, Na, K) ion very strongly with a binding energy of 213.5 (Li), 195.2 (Na) and 180.3 (K) kcal/mol. Additionally, the relief of the Coulomb repulsion due to the presence of counter-ion, M+, the B–B bond contracts to 1.484–1.488 Å in [N4-B2-N4]M2. We have further extended our study to [N4-B2-N4-B2-N4]4− and [N4-B2-N4-B2-N4-B2-N4]6− systems. The B–B bond length is found to be 1.496 Å in the former case, whereas the same is found to be 1.493 Å and 1.508 Å, respectively, for the two B–B bonds present in the latter one. The M + counter-ions stabilize such negatively charged systems and thus, create a possibility to design a long 1-D nanowire. Their utilities as probable hydrogen and noble gas (Ng) binding templates are explored taking [N4-B2-N4-B2-N4]Li4 system as a reference. It is found that each Li center binds with three H2 molecules with an average binding energy of 2.1 kcal/mol, whereas each Ng (Ar–Rn) atom interacts with Li center having a binding energy of 1.8–2.1 kcal/mol. The H2 molecules interact with Li centers mainly through equal contribution from orbital and electrostatic interaction, whereas the orbital interaction is found to be major term (ca. 51–58%) in Ng-Li interaction followed by dispersion (ca. 24–27%) and electrostatic interaction (ca. 17–24%). The B-B bonds in [N4-B2-N4]2-, [N4-B2-N4-B2-N4]4- and [N4-B2-N4-B2-N4-B2-N4]6- possess some degree of triple bond character. These anionic systems can be stabilized by combining with an adequate number of M+ (M = Li, Na, K) ions. It opens up the possibility of designing a long 1-D nanowire. The Li centers of this nanowire can bind hydrogen molecules and noble gas atoms effectively.

Extended spin model in atomistic simulations of alloys

An extended atomistic spin model allowing for studies of the finite temperature magnetic properties of alloys is proposed. The model is obtained by extending the Heisenberg Hamiltonian via a parameterization from a first principles basis, interpolating from both the low temperature ferromagnetic and the high temperature paramagnetic reference states. This allows us to treat magnetic systems with varying degree of itinerant character within the model. Satisfactory agreement with both previous theoretical studies and experiments are obtained in terms of Curie temperatures and paramagnetic properties. The proposed model is not restricted to elements but is also applied to binary alloys, such as the technologically important material Permalloy, where significant differences in the finite magnetic properties of Fe and Ni magnetic moments are found. The proposed model strives to find the right compromise between accuracy and computational feasibility for accurate modeling, even for complex magnetic alloys and compounds.

Steady‐State Measurements of Vanadium Redox‐Flow Batteries to Study Particular Influences of Carbon Felt Properties

AbstractCarbon felts based on rayon and polyacrylonitrile (PAN) precursors constitute the most widespread porous electrode material for vanadium redox‐flow batteries. Since the raw materials exhibit rather poor wettability, it has become common practice to apply oxidative surface treatments prior to use in flow batteries. This study investigates the electrode‐specific effects of raw and thermally oxidized (PAN and rayon‐based) carbon felts on their electrochemical behavior at the negative and the positive electrode in all vanadium redox‐flow batteries. By means of steady‐state single cell measurements, it is verified that oxidative surface treatment has opposite effects on negative and positive redox couples and that the beneficial influence on the vanadium redox‐flow battery performance is mainly brought about by substantially improved charge‐transfer kinetics at the negative electrode. Similarly, the type of carbon precursor and the degree of graphitic character have a particular impact on the electrode behavior.

The Peculiar Role of the Au3 Unit in Aum Clusters: σ-Aromaticity of the Au5Zn+ Ion.

The stability of small Aum (m = 4-7) clusters is investigated by analyzing their energetic, geometric, vibrational, magnetic, and electron density properties. Gold clusters can be constructed from stable cyclic 3-center-2-electron (3c-2e) Au3+ units (3-rings) with σ-aromaticity. The stabilization requires a flow of negative charge from internal 3-rings with electron-deficient bonding to peripheral 3-ring units with stronger Au-Au bonds. The valence-isoelectronic clusters Au6 and Au5Zn+ have similar electronic properties: Au5Zn+ is a strongly σ-aromatic molecule. An understanding of the structure of Aum clusters is obtained by deriving a Clar's Rule equivalent for polycyclic gold clusters: The structure with the larger number of rings with dominant 3c-2e character and a smaller degree of 3c-3e character occupies the global minimum of the Aum potential energy surface.

Blue Light Photocatalytic Glycosylation without Electrophilic Additives.

Photocatalytic formation of glycosidic bonds employing stable and readily accessible O-glycosyl derivatives of 2,2,6,6-tetramethylpiperidin-1-ol is presented that employs an iridium-based photocatalyst and blue LEDs. The reaction proceeds at room temperature and in the absence of additives other than 4 Å molecular sieves. Stereoselectivities are modest but nevertheless dependent on the anomeric configuration of the donor, suggesting a substantial degree of concerted character.

A nilpotency criterion related to the minimal degree of a nonlinear irreducible character

Let [Formula: see text] be a finite nonabelian group, let [Formula: see text] be the minimal degree of a nonlinear irreducible character of [Formula: see text] and suppose that [Formula: see text] for some positive integer [Formula: see text]. Then [Formula: see text] is nilpotent.

Fitting heights of solvable groups with no nontrivial prime power character degrees

We construct solvable groups where the only degree of an irreducible character that is a prime power is $1$ and that have arbitrarily large Fitting heights. We will show that we can construct such groups that also have a Sylow tower. We also will show that we can construct such groups using only three primes.

Assessment of semi-empirical molecular orbital calculations for describing magnetic interactions

We report a thorough comparison between the spin-unrestricted semi-empirical molecular orbital (SE-UMO) and density functional theory (UDFT) calculations for a variety of π-conjugated diradical molecules which exhibit through-bond magnetic exchange interactions. The spin-unrestricted neglect of diatomic differential overlap (NDDO)-based methods (UPM6 and UrPM6) and self-consistent charge density functional tight-biding (UDFTB) are examined. The UCAM-B3LYP method is used as a representative of UDFT. We have found that NDDO-based and UDFTB methods give different performances with respect to the results of UCAM-B3LYP. The degree of diradical character in the target systems decreases in the order of UPM6>UrPM6≈UCAM-B3LYP>UDFTB. The conventional UPM6 and UDFTB calculations tend to overestimate and underestimate the diradical character, respectively, whereas UrPM6 is able to provide much the same results as UCAM-B3LYP. This is convincing evidence that UrPM6 will be useful for in silico screening of materials science at much lower computational cost.

Characters of $p’$-degree and Thompson’s character degree theorem

A classical theorem of John Thompson on character degrees asserts that if the degree of every ordinary irreducible character of a finite group G is 1 or divisible by a prime p , then G has a normal p -complement. We obtain a significant improvement of this result by considering the average of p’ -degrees of irreducible characters. We also consider fields of character values and prove several improvements of earlier related results.

Determining the first-order character ofLa(Fe,Mn,Si)13

Definitive determination of first order character of the magnetocaloric magnetic transition remains elusive. Here we use a microcalorimetry technique in two modes of operation to determine the contributions to entropy change from latent heat and heat capacity separately in an engineered set of La(Fe, Mn, Si)13 samples. We compare the properties extracted by this method with those determined using magnetometry and propose a model independent parameter that would allow the degree of first order character to be defined across different families of materials. The microcalorimetry method is sufficiently sensitive to allow observation of an additional peak feature in the low field heat capacity associated with the presence of Mn in these samples. The feature is of magnetic origin but is insensitive to magnetic field, explicable in terms of inhomogeneous occupancy of Mn within the lattice resulting in antiferromagnetic ordered Mn clusters.

Crystal Engineering of Hand-Twisted Helical Crystals.

A strategy is outlined for the design of hand-twisted helical crystals. The starting point in the exercise is the one-dimensional (1D) plastic crystal, 1,4-dibromobenzene, which is then changed to a 1D elastic crystal, exemplified by 4-bromophenyl 4'-chlorobenzoate, by introduction of a molecular synthon -O-CO- in lieu of the supramolecular synthon Br···Br in the precursor. The 1D elastic crystals are next modified to two-dimensional (2D) elastic crystals, of the type 4-bromophenyl 4'-nitrobenzoate where the halogen bonding and C-H···O hydrogen bonding are well-matched. Finally, varying the interaction strengths in these 2D elastic crystals gives plastic crystals with two pairs of bendable faces but without slip planes. Typical examples are 4-chlorophenyl and 4-bromophenyl 4'-nitrobenzoate. This type of 2D plasticity represents a new type of bendable crystals in which plastic behavior is seen with a fair degree of isotropic character in the crystal packing. The presence of two sets of bendable faces, generally orthogonal to each other, allows for the possibility of hand-twisting of the crystals to give grossly helical morphologies. Accordingly, we propose the name hand-twisted helical crystals for these substances.

The processing accuracy of the gear

The paper presents analysis of processing quality of gears. A special attention was drawn to detecting and removing burns, the existence of which greatly reduced operating properties of gears. The study emphases the influence of schemes, processing modes and abrasive tools features on the physico-mechanical layer of teeth processed and phase changes, micro-cracks appearances, depth and degree of hardening, meaning and character of residual stresses distribution.

Reassessing spin-coupled (full generalized valence bond) descriptions of ozone using three-center bond indices

Domain-averaged Fermi hole analysis is carried out for the ground state of O3 at its equilibrium geometry using a complete-active-space self-consistent field CASSCF(18,14) wavefunction, based on a slightly expanded full-valence active space. This initial analysis is augmented with an examination of the corresponding localized natural orbitals (LNOs) and of the numerical values obtained with a new improved definition of three-center bond indices for correlated singlet systems. Much the same pattern of LNOs is observed when using instead a subsequent internally-contracted multiconfiguration-reference configuration interaction construction, which also provides very similar values for the three-center bond indices. This gives us confidence to use such bond indices, alongside relative energies and the electric dipole moment, to assess the relative merits of various combinations of spin-coupled (full generalized valence bond) components with ten active electrons: four π, four σ bonding and the two nonbonding σ electrons associated with the central O atom. These multi-component valence bond descriptions were generated either with or without subsequent orbital reoptimization. The description of the π system which emerges from all of our analysis conforms to a standard model of three-center four-electron π bonding that incorporates a nontrivial degree of (partial) diradical character. Whereas certain combinations of ten-electron spin-coupled components can faithfully reproduce such a picture, none of the individual rival components appears to have sufficient flexibility on its own.

Expedient Synthesis of 1,2-Thiaborines by Means of Sulfur Insertion into Boroles.

The propensity of boroles to undergo ring expansion reactions has been exploited as a route to generate 1,2-thiaborines, molecules that can be viewed as hybrid inorganic/organic analogues of benzene. Computational studies as well as structural data indicate that the species reported here have a high degree of aromatic character.

The Pt (II)⋅⋅⋅Cl Interactions: Nature and Strength

AbstractThe Pt (II)⋅⋅⋅Cl interactions between trans‐Pt (NH3)2X2/cis‐Pt (NH3)2X2 (X=OH, F, Cl, Br) and ClF were constructed and studied by Møller‐Plesset perturbation theory (MP2) method. The metal Pt (II)‐complex could act as the halogen bond acceptor, the Pt (II)⋅⋅⋅Cl interaction strength depends on the nature and the configuration of platinum (II) ligands: the metal halogen‐bonding interactions in trans‐Pt (OH)2(NH3)2⋅⋅⋅ClF/cis‐Pt (OH)2(NH3)2⋅⋅⋅ClF are obviously stronger than those in trans‐PtX2(NH3)2⋅⋅⋅ClF/cis‐PtX2(NH3)2⋅⋅⋅ClF (X=F, Cl, Br); the halogen bonds in cis‐complexes are somewhat stronger than those in respective trans‐complexes. This particular Pt (II)⋅⋅⋅Cl interactions is much stronger than hydrogen bond and has some degree of covalent character. For the Pt (II)⋅⋅⋅Cl interactions, the charge transfer between the related molecular orbitals of PtX2(NH3)2 and ClF are obvious, which is consistent with that the exchange energy contributes most to the total interaction energy. The stronger of the Pt (II)⋅⋅⋅Cl interactions, the more decreased electron density outside Pt (II) facing the chlorine atom, and the more increased electron density between Pt (II) and Cl, indicating that the polarization effect plays an important role in the formation of the Pt (II)⋅⋅⋅Cl interactions.

Features Pyramidal and Sensory Disorders in Multiple Sclerosis Patients Under Comorbidity

Reduced muscle strength is one of the most important factors in violation of life in multiple sclerosis (MS). Muscle spasticity – another significant common symptom in patients with MS, which is one of the main reasons for the deepening of disability. The objective: to determine the prevalence of pyramidal disorders (PD), and sensory disorders (SD) in patients with MS and to find out the characteristics of their curs in the aspect of comorbidity. Patients and methods. Neurological examination 216 MS patients with different forms of process was held a points assessment of the disturbed functional systems of the FS-1 – FS-7 (scale FS1 Functional System for J. Kurtzke, 1983), determined the level of disability (the EDSS), revealed the presence or absence PD and SD in the survey, to determine the degree of severity and character. Results. At 88,4% PC patients had PD. Changes in muscle tone were found in 73.2% of patients with MS. In 65.3% of MS patients the total sample were clinical signs of superficial and deep sensitivity changes. In addition to medication for relief of PD and SD in patients with MS were effectively used methods of acupuncture, which allowed more quickly and efficiently to reduce the severity of spasticity and pain. Conclusions. 1. The average prevalence of PD in our study of MS patients is 88.4%, and the average prevalence of the SD – 65.3%. 2. In the group with the presence of comorbid pathology PD significantly more often manifested tetraparesis and high spastic tone. 3. In the group with the presence of comorbid pathology SD significantly more often manifested dysesthesia, termogiperestesia, palleanestesia.

Hydrogen-bonding Interactions between Apigenin and Ethanol/Water: A Theoretical Study.

In this work, hydrogen-bonding interactions between apigenin and water/ethanol were investigated from a theoretical perspective using quantum chemical calculations. Two conformations of apigenin molecule were considered in this work. The following results were found. (1) For apigenin monomer, the molecular structure is non-planar, and all of the hydrogen and oxygen atoms can be hydrogen-bonding sites. (2) Eight and seven optimized geometries are obtained for apigenin (I)–H2O/CH3CH2OH and apigenin (II)–H2O/CH3CH2OH complexes, respectively. In apigenin, excluding the aromatic hydrogen atoms in the phenyl substituent, all other hydrogen atoms and the oxygen atoms form hydrogen-bonds with H2O and CH3CH2OH. (3) In apigenin–H2O/CH3CH2OH complexes, the electron density and the E(2) in the related localized anti-bonding orbital are increased upon hydrogen-bond formation. These are the cause of the elongation and red-shift of the X−H bond. The sum of the charge change transfers from the hydrogen-bond acceptor to donor. The stronger interaction makes the charge change more intense than in the less stable structures. (4) Most of the hydrogen-bonds in the complexes are electrostatic in nature. However, the C4−O5···H, C9−O4···H and C13−O2···H hydrogen-bonds have some degree of covalent character. Furthermore, the hydroxyl groups of the apigenin molecule are the preferred hydrogen-bonding sites.

Binuclear trivalent and tetravalent uranium halides and cyanides supported by cyclooctatetraene ligands

AbstractAlthough the first organoactinide chloride Cp3UCl (Cp=η5-C5H5) was synthesized more than 50 years ago, binuclear uranium halides remain very rare in organoactinide chemistry. Herein, a series of binuclear trivalent and tetravalent uranium halides and cyanides with cyclooctatetraene ligands, (COT)2U2Xn(COT=η8-C8H8; X=F, Cl, CN;n=2, 4), have been systematically studied using scalar-relativistic density functional theory (DFT). The structures with bridging halide or cyanide ligands were predicted to be the most stable complexes of (COT)2U2Xn, and all the complexes show weak antiferromagnetic interactions between the uranium centers. However, for each species, there is no significant uranium-uranium bonding interaction. The bonding between the metal and the ligands shows some degree of covalent character, especially between the metal and terminal halide or cyanide ligands. The U-5f and 6d orbitals are predominantly involved in the metal-ligand bonding. All the (COT)2U2Xnspecies were predicted to be more stable compared to the mononuclear half-sandwich complexes at room temperature in the gas phase such that (COT)2U2X4might be accessible through the known (COT)2U complex. The tetravalent derivatives (COT)2U2X4are more energetically favorable than the trivalent (COT)2U2X2analogs, which may be attributed to the greater number of strong metal-ligand bonds in the former complexes.

Magnetic relaxation dynamics driven by the first-order character of magnetocaloric La(Fe,Mn,Si)13.

Here, we study the temporal evolution of the magnetic field-driven paramagnetic to ferromagnetic transition in the La(Fe,Mn,Si)13 material family. Three compositions are chosen that show varying strengths of the first-order character of the transition, as determined by the relative magnitude of their magnetic hysteresis and temperature separation between the zero-field transition temperature Tc and the temperature Tcrit, where the transition becomes continuous. Systematic variations in the fixed field, isothermal rate of relaxation are observed as a function of temperature and as a function of the degree of first-order character. The relaxation rate is reduced in more weakly first-order compositions and is also reduced as the temperature is increased towards Tcrit At temperatures above Tcrit, the metastability of the transition vanishes along with its associated temporal dynamics.This article is part of the themed issue 'Taking the temperature of phase transitions in cool materials'.