First-Principles Calculations of Magnetism in Nanoscale Carbon Materials Confining Metal with <Emphasis Type="Italic">f</Emphasis> Valence Electrons

The f electrons in the unfilled shell of actinide and lanthanide display complex bonding behavior and the hybridized sp electrons in carbon could show spin polarization in finite nanostructures. Correspondingly, materials combining these two features exhibit abundant magnetic properties. In this paper, we outline our first-principles calculations on various nanoscale carbon materials confining U and Gd which are representative actinide and lanthanide, respectively. The complex interaction between f electrons and sp electrons make the induced magnetic property sensitive to metal specie and carbon confinement. Specially, (1) The magnetism could be suppressed by stronger adsorption with vacancy sites on graphene and adjusted by varying the valence state of some endohedral metallofullerenes (EMFs). (2) The magnetic coupling between metal and carbon structures could be promoted by large curvature when confinement site is carbon nanotubes and altered by the adatom defect on fullerene cages. (3) Untrivial magnetic property with large net spin and asymmetric spin distribution is obtained by confining U atom and Gd atom in one fullerene as a heteronuclear EMF. These results contribute to a systematic understanding of the magnetism in nanoscale carbon materials confining metal with f valence electrons.     

New framework nanostructures of carbon atoms in <Emphasis Type="Italic">sp</Emphasis><Superscript>2</Superscript> and <Emphasis Type="Italic">sp</Emphasis><Superscript>3</Superscript> hybridized states

A new family of framework nanostructures including carbon atoms in _sp ² and sp ³ hybridized states is reported. Structure optimization was fulfilled using MM+ molecular mechanics and Hückel semiempirical methods. The energy characteristics of the structures have been evaluated. Comparative analysis of the stability of the title nanostructures has been performed in relation to their geometry and relative contents of sp ²/sp ³ atoms.     

Phenylhydrazines. Structure and basicity

The main properties of phenylhydrazines are governed by the p-character of the unshared electron pair of the nitrogen of imino group changing in keeping with sp ³ → sp ²-regibridization of its atomic orbitals under the steric and electronic (-I effect of amino group) effect of substituents.     

New basicity/nucleophilicity scale on the basis of parameters of formation of axial <Emphasis Type="Italic">n</Emphasis>,ν-complexes derived from tetraphenylporphyrinatozinc(II) and base/nucleophile as ligand

The stability constants of complexes derived from tetraphenylporphyrinatozinc(II) and various ligands in chloroform at 25°C were proposed as nucleophilicity/basicity parameters of the latter, which reflect the effects of electronic and steric factors. Supernucleophilicity of heteroaromatic N-oxides in reactions with electrophiles was interpreted in terms of sp ²–sp ³ rehybridization of the N-oxide oxygen atom.     

Crystal structure of hydrobromides of pyridines and quinolines <Emphasis Type="Italic">N</Emphasis>-oxides

Structures of hydrobromides of quinoline, 4-methylquinoline, pyridine, and 4-methylpyridine N-oxides have been elucidated by means of X-ray diffraction analysis. In contrast to other salts, quinoline N-oxide hydrobromide crystallizes in the form of dimer with two water molecules. The oxygen atom of the organic molecule is coordinated with water protons, and its state is close to sp ²-hybridization. In the cases of other hydrobromides, the oxygen atom is strongly bound to the proton of НBr and exhibits sp ³-hybridization.     

Phonon Scattering by Externded Defects in Polycrystalline Graphene

Phonon scattering by static stress fields created by grain boundaries (GBs) in graphene was studied with the deformation potential method. This method provides exact analytical expressions for phonon mean free paths as a result of scattering by GBs with arbitrary geometries in the Born approximation. Two regimes, k^–1 and k^–3, of the mean free path behavior are discovered in the limit of small momenta. The first (dislocation) regime is realized for open configurations in polycrystalline graphene, while the second regime is realized for closed configurations and Stone-Wales defects in pure graphene. The mean free path does not depend on k for any GB in the short-wave limit (large k). Thermal conductivity in graphene with GBs was calculated using the Callaway model which considers both normal phonon processes and umklapp processes. The contribution from these defects to the thermal conductivity is shown to exceed substantially the contribution from point defects and vacancies in a wide range of temperatures.     

Effects of heteroatoms on the electronic,sensor, and adsorption properties of graphene

The effects of doping heteroatoms on the structure, electronic and adsorption properties of graphene are investigated using density functional theory calculations. Six different doped graphenes (with Al, B, Si, N, P, and S) are considered, and to obtain the interaction and adsorption properties, three sulfur-containing molecules (H₂S, SO₂, and thiophene) were interacted with selected graphenes. The adsorption energies (E _ad) in the gas phase and solvents show the exothermic interaction for all complexes. The maximum E _ad values are observed for aluminum doped graphene (AG) and silicon doped graphene (SiG), and adsorption energies in the solvent are not so different from those in the gas phase. NBO calculations show that the AG and SiG complexes have the highest E ⁽²⁾ interaction energies and simple graphene (G) and nitrogen doped graphene (NG) have the least E ⁽²⁾ energies. Population analyses show that doping heteroatoms change the energy gap. This gap changes more during the interaction and these changes make these structures useful in sensor devices. All calculated data confirm better adsorption of SO₂ by graphenes versus H₂S and thiophene. Among all graphenes, AG and then SiG are the best adsorbents for these structures.     

Complexes of pyridine and quinoline N-oxides with boron trifluoride: the <Superscript>1</Superscript>H NMR study

The formation of complexes of pyridine and quinoline N-oxides with BF₃ was studied by ¹H NMR method. It was shown that the molecular complexes obtained are either individual isomers or a mixture of stereoisomers, whose structures are determined by both electronic and steric properties of substituents in a heterocycle. The type of hybridization (sp3 or sp2) of the O atom of the N-oxide group in the above adducts was assumed to be specified also by the above factors.     

The effect of particle shape on the structure and rheological properties of carbon-based particle suspensions

The structure and rheological properties of carbon-based particle suspensions, i.e., carbon black(CB), multi-wall carbon nanotube(MWNT), graphene and hollow carbon sphere(HCS) suspended in polydimethylsiloxane(PDMS), are investigated. In order to study the effect of particle shape on the structure and rheological properties of suspensions, the content of surface oxygen-containing functional groups of carbon-based particles is controlled to be similar. Original spherical-like CB(fractal filler), rod-like MWNT and sheet-like graphene form large agglomerates in PDMS, while spherical HCS particles disperse relatively well in PDMS. The dispersion state of carbon-based particles affects the critical concentration of forming a rheological percolation network. Under weak shear, negative normal stress differences(ΔN) are observed in CB, MWNT and graphene suspensions, while ΔN is nearly zero for HCS suspensions. It is concluded that the vorticity alignment of CB, MWNT and graphene agglomerates under shear results in the negative ΔN. However, no obvious structural change is observed in HCS suspension under weak shear, and accordingly, the ΔN is almost zero.     

Polarity and structure of eight-membered organosilicon compounds with planar fragments

For the first time is determined the polarity of eight-membered silocyns with planar fragments. By the methods of dipole moments and theoretical calculations (DFT B3LYP/6-31G*) of 1,3,2-dioxasilocyns is established that in these compounds occurs the conformational equilibrium of the forms bath-chair and distorted bath with the predominance of the first, in this case the bonds C(sp ³)-S and C(sp ³)-H of the exocyclic MeSCH₂ group are in the not eclipsed gauche orientation relative to each other.     

A novel oxido-vanadium(V) Schiff base complex: synthesis,spectral characterization,crystal structure,electrochemical evaluation,and biological activity

A new oxido-vanadium(V) complex, [VO(L)(PrOH)(OPr)] (L = [(3-methoxy-2oxidobenzylidene)benzohydrazidato], PrOH = propanol, OPr = propanolato) has been synthesized and characterized by means of elemental analysis, Fourier transform infrared (FTIR), proton nuclear magnetic resonance (¹HNMR), ultaviolet-visible (UV–Vis) spectroscopy, voltammetry and molar conductivity measurement. The structure of the complex has also determined using single crystal X-ray diffraction. The geometric structure around the V(V) ion has been found to be octahedral in which the positions around the central ion are occupied by ONO ligand donors, oxido groups, and oxygen atoms of coordinated propanol and propoxide group. Electrochemical behavior of this complex is also discussed in more details. In vitro antimicrobial effect of the title complex has investigated exhibiting significant activities against some Gram-positive (Staphylococcus aureus, Micrococcus luteus, Bacillus cereus, Eterococcus faecalis) and Gram-negative bacteria (Pseudomonas aeruginosa, Escherichia coli, Klebsiella sp, Pseudomonas sp) and fungus strain (Candida albicans).     

Effect of solvents on the morphology of NiCo<Subscript>2</Subscript>O<Subscript>4</Subscript>/graphene nanostructures for electrochemical pseudocapacitor application

The large internal surface areas and outstanding electrical and mechanical properties of graphene have prompted to blend graphene with NiCo₂O₄ to fabricate nanostructured NiCo₂O₄/graphene composites for supercapacitor applications. The use of graphene as blending with NiCo₂O₄ enhances the specific capacitance and rate capability and improves the cyclic performance when compared to the pristine NiCo₂O₄ material. Here, we synthesized two different nanostructured morphologies of NiCo₂O₄ on graphene sheets by solvothermal method. It has been suggested that the morphologies of oxides are greatly influenced by dielectric constant, thermal conductivity, and viscosity of solvents employed during the synthesis. In order to test this concept, we have synthesized nanostructured NiCo₂O₄ on graphene sheets by facile solvothermal method using N-methyl pyrrolidone and N,N-dimethylformamide solvents with water. We find that mixture of N-methyl pyrrolidone and water solvent favored the formation of nanonet-like NiCo₂O₄/graphene (NiCoO-net) whereas mixture of N,N-dimethylformamide and water solvent produced microsphere-like NiCo₂O₄/graphene (NiCoO-sphere). Electrochemical pseudocapacitance behavior of the two NiCo₂O₄/graphene electrode materials was studied by cyclic voltammetry, chronopotentiometry, and electrochemical impedance spectroscopy techniques. The supercapacitance measurements on NiCoO-net and NiCoO-sphere electrodes showed specific capacitance values of 1060 and 855 F g^?1, respectively, at the current density of 1.5 A g^?1. The capacitance retention of NiCoO-net electrode is 93 % while that of NiCoO-sphere electrode is 77 % after long-term 5000 charge-discharge cycles at high current density of 10 A g^?1.     

Adsorption-Induced Deformation of Adsorbents

Adsorption-induced deformation of AR-V and AUK carbon adsorbents and NaX zeolite has been studied upon adsorption of n-С₅Н₁₂, n-С₆Н₁₈, n-С₇Н₁₆, and CO₂ at temperatures of 193?423 K. It has been shown that adsorption-induced deformation is positive upon the physical adsorption of gases and vapors on the surface of a nonporous (macroporous) solid when the excess adsorption is positive. When calculating the adsorption-induced deformation in the region of the capillary-condensation filling of mesopores, the additional pressure in capillaries, which is negative (contraction of an adsorbent), must be taken into account in the case of wetting a solid surface with a liquid adsorbate. The compressibility of AUK microporous carbon adsorbent as a porous solid is almost independent of the temperature and the properties of an adsorbate, and, for adsorption of n-C₅H₁₀ and n-C₇H₁₆ hydrocarbons and CO₂, it is γ_а = (5.6 ± 0.6) × 10^?6 bar^?1. The compressibility of AUK adsorbent appears to be 87% higher than that of nonporous graphite.     

Thermal and redox dual responsive poly(<Emphasis Type="SmallCaps">L</Emphasis>-glutamate) with oligo(ethylene glycol) side-chains

A series of poly(L-glutamate)s grafted with oligo(ethylene glycol) (OEG) side-chains through the thioether linkages (PALG _n -g-EG _x , x = 2, 3 and 4) were prepared by ring-opening polymerization (ROP) of γ-allyl-L-glutamate N-carboxyanhydride (ALG-NCA) and thiol-ene photoaddition. The chemical structures and physical properties were characterized by ¹H-NMR, Fourier transform infrared (FTIR), circular dichroism (CD), etc. The PALG _n -g-EG _x samples with x = 3 and 4 displayed lower critical solution temperature (LCST) in water due to the presence of OEG units. The clouding point (CP) of polypeptides can be finely tuned by changing the side chain structures, molecular weights and sample concentrations. In addition, the thioether linkages in the side chains offer additional redox-responsive properties. The influence of both OEG units and thioether linkages on the LCST behavior was systematically investigated. This work provides an efficient way to prepare multi-stimuli responsive materials with highly tunable properties.     

Synthesis,structures, and magnetic properties of crystals of dinuclear copper(II) and cobalt(II) complexes with 3-(3,5-dimethylpyrazol-1-yl)-6-R-1,2,4,5-tetrazines

Dinuclear complexes of Cu^II with 3-(3,5-dimethylpyrazol-1-yl)-6-(2-hydroxyethylami-no)-1,2,4,5-tetrazine (1) and CoII with 3-(3,5-dimethylpyrazol-1-yl)-6-(piperidin-1-yl)-1,2,4,5- tetrazine (2) were synthesized and structurally characterized, and the magnetic (SQUID) and resonance (EPR) properties of van der Waals crystals based on these complexes were studied. Unusual behavior of the effective magnetic moment μ_eff(T) is observed at T < 60 K. A nonmonotonic increase in μeff(?) for 1 (s~6 %) and a 20% reduction of μeff(?) for 2 have a common origin and are due to the influence of spin-orbital coupling on the character of the splitting between the t2g and eg levels of the central ion. Distortions of the coordination site “switch on” a positive (1) or negative (2) contribution of the orbital magnetic moment near 6 K. Irreversible temperature behavior of μeff(T) in the heating and cooling regimes in the vicinity of 60 K suggests that the character of structural distortions and the magnetic properties are related to ligand geometry. This factor plays a significant role in crystal engineering of magnetoactive structures with polynitrogen ligands.     

Change in the hybridization of the N→O group oxygen atom upon complex formation of pyridine and quinoline <Emphasis Type="Italic">N</Emphasis>-oxides with v-acceptors

It was shown on the basis of X-ray structural and NMR data that the (sp ²→sp ³) rehybridization of the oxygen atom of the N→O group can take place in reactions of heteroaromatic N-oxides with Lewis and Bronsted-Lowry acids. The hybridization type depends on the ligand and acceptor natures, composition of a complex, and spatial stresses arising during the complex formation.     

Study on the Mixed ZnO Clusters and Ring-Like ZnO Ions

The pure Zn_m (m?=?2–10), mixed Zn_mO_m (m?=?1–10), Zn_mO_10??m (m?=?1–9) clusters and the univalent and divalent ring-like Zn_mO_m (m?=?2–10) cluster ions are systematically investigated by using Amsterdam density functional (ADF) program with Triple-zeta with two polarization functions basis set in conjunction with self-consistent field. Our calculated results show that the Zn₄ and Zn₇ clusters are the magic clusters. The structures of the Zn_mO_m (m?=?1–10) clusters evolve from two-dimension to three-dimension after m?=?8. For the Zn_mO_10??m (m?=?1–9) clusters, the Zn-rich structures evolve gradually from three-dimension to plane with an increase in the O ratios. The Zn₅O₅ cluster with equal ratio has a two dimensional structure. In the O-rich clusters, the O dimers can be easily detached from them. The O and Zn atoms partly adopt sp² and sp hybridization, respectively, in the ring-like Zn_mO_m (m?=?2–10) clusters and their ions. Gain and loss charge would affect the degree of hybridization and change their geometries. Their structural changes can be explained by valence bond theory.     

Adsorption properties of γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> as measured by gas chromatography

The adsorption properties of γ-Al₂O₃ were studied using gas chromatography. Isotherms of adsorption of n-alkanes (C₆–C₉), hex-1-ene, benzene, and isobutanol were measured within 70–100°C. The isosteric heats of adsorption and contributions to them from dispersion (Δq _dis) and specific (Δq _sp) interactions were determined for hex-1-ene, benzene, and isobutanol. Under the conditions covered, hex-1-ene molecules are adsorbed mainly on account of dispersion interactions. For the adsorption of benzene, Δq _dis is nearly twice as large as Δq _sp, while for the adsorption of isobutanol, Δq _sp is nearly twice as large as Δq _dis. At 100°C, isobutyl alcohol is chemisorbed.     

Formation of solvate structures by the <Emphasis Type="Italic">ortho</Emphasis>-, <Emphasis Type="Italic">meta</Emphasis>-, and <Emphasis Type="Italic">para</Emphasis>-isomers of hydroxybenzoic acid in supercritical fluid

The solvate structures formed by the ortho-, meta-, and para-isomers of hydroxybenzoic acid (o-HBA, m-HBA, and p-HBA) with a polar co-solvent (methanol at a concentration of 0.030 and 0.035 mole fractions) in supercritical carbon dioxide at a constant density of 0.7 g/cm³ and temperatures of 318 and 328 K have been studied by the classic molecular dynamics. It has been determined that a stable hydrogen-bonded complex with the co-solvent forms via the hydrogen of the carboxyl group for all isomers. The probability of this complex existence is high at all temperatures and concentrations. In the o-HBA molecule, the other functional groups are engaged in the intramolecular hydrogen bond, but not involved in interactions with methanol. It has been found that m-HBA and p-HBA can be involved in hydrogen bonds with methanol via hydroxyl hydrogen and oxygen atoms; they are characterized by the presence of one more co-solvent molecule (rarely, two molecules) in their solvation shell and intermittent formations/breakages of hydrogen bonds via other functional groups. These bonds are far less stable, and their formation is sensitive to change of temperature and co-solvent concentration. It has been concluded that the degree of selective solvation of m-HBA and p-HBA by co-solvent molecules is approximately the same, but the rate of structural rearrangements in the nearest environment of m-HBA is higher than that of p-HBA.     

Ion-solvent and ion-ion interactions of phosphomolybdic acid in aqueous solution of catechol at 298.15, 308.15, and 318.15 K

Apparent molar volume (V _Ø) and viscosity B-coefficients were measured for phosphomolybdicacid in aqueous solution of catechol from solution density (ρ) and viscosity (η) at 298.15, 308.15, and 318.15 K at various solute concentrations. The experimental density data were evaluated by Masson equation and the derived data were interpreted in terms of ion-solvent and ion-ion interactions. The viscosity data have been analyzed using Jones-Dole equation and the derived parameters, B and A, have been interpreted in terms of ion-solvent and ion-ion interactions respectively. The structure-making or breaking capacity of the solute under investigation has been discussed in terms of sign of (δ ² V _Ø ^o /δT ²) _P . The activation parameters of viscous flow were determined and discussed by application of transition state theory.