Electronic Properties Of Group Research Articles

Theoretical insight into the regioselective formation of pyrazolo[1,4]-oxazepine and -oxazines

AuCl-, AuCl3-, or AuClPEt3-catalyzed formation mechanisms of pyrazolo[1,4]oxazepines and the NaH-promoted mechanism of pyrazolo[1,4]oxazines were investigated computationally. The structural properties of the reactants were studied in various solvents and with different functionals. The hybrid functionals B3LYP, M06, M06-2X, PBEPBE, and wB97X-D in density functional theory were used to determine and discuss the energetics of the compounds. The electronic properties of groups (R = H or R ≠ H) attached to the alkyne moiety played an essential role in the corresponding 7-endo-dig cyclization or 6-exo-dig cyclization in the presence of a gold catalyst. The regioselectivities of the products were investigated, and the natural bond orbitals of the reactants were determined. Furthermore, a gold-catalyzed alternative mechanism is suggested for synthesizing pyrazolo[1,4]oxazines using a terminal alkyne (R = H) moiety as substrate.

Computational analysis of the formation mechanisms of carbazoles.

Gold-, platinum-, and silver-catalyzed formation mechanisms of carbazole alkaloids were investigated computationally. The structural properties of the reactants were studied in various solvents and with different functionals. The hybrid functionals B3LYP and M06-2X in density functional theory were used to determine and discuss the energetics of the compounds. The electronic properties of groups attached to the terminal alkyne played an essential role in the formation of carbazoles. The stereo- and chemoselectivity of the mechanism were investigated and the natural bond orbitals of the reactants were determined. Furthermore, this theoretical study has suggested a gold-catalyzed alternative mechanism for the synthesis of 1,4-dihydrocyclopenta[b]indole derivative.

Role of Metals and Thiolate Ligands in the Structures and Electronic Properties of Group 5 Bimetallic-Thiolate Complexes.

Syntheses, structures, and electronic properties of group 5 metal-thiolate complexes that exhibit unusual coordination modes of thiolate ligands have been established. Room-temperature reaction of [Cp*VCl2]3 (Cp* = η5-C5Me5) with Na5[B(SCH2S)4] led to the formation of [Cp*VO{(SCH2)2S}] (1). The solid-state X-ray structure of 1 shows the formation of six-membered l,3,5-trithia-2-vanadacyclohexane that adopted a chair conformation. In a similar fashion, reactions of heavier group 5 precursors [Cp*MCl4] (M = Nb or Ta) with Na5[B(SCH2S)4] yielded bimetallic thiolate complexes [(Cp*M)2(μ-S){μ-C(H)S3-κ2S:κ2S',S″}{μ-SC(H)S-κ2C:κ2S‴,S''''}] (3a: M = Nb and 3b: M = Ta). One of the key features of molecules 3a and 3b is the presence of square-pyramidal carbon, which is quite unusual. The reactions also yielded bimetallic methanedithiolate complexes [(Cp*Nb)2(μ-S)(μ-SCH2S-κ2S,S')(μ,η2:η2-BH3S)] (2) and [(Cp*Ta)2(μ-O)(μ-SCH2S-κ2S,S')(μ-H){μ-S2C(H)SCH2S-κ2S″:κ2S‴,S''''}] (4). Complex 2 contains a methanedithiolate ligand that stabilizes the unsaturated niobaborane species. On the other hand, one ((mercaptomethyl)thio)methanedithiolate ligand {C2H4S3} is present in 4, which is coordinated to metal centers and exhibits the {μ-κ2S″:κ2S‴,S''''} bonding mode. Along with the formation of 3b and 4, the reaction of [Cp*TaCl4] with Na5[B(SCH2S)4] yielded [(Cp*Ta)2(μ-S){μ-(SBS)S(CH2S)2(BH2S)-κ2B:κ2S:κ4S',S″,S‴,S''''}] (5) containing a trithiaborate unit (BS3). Complex 5 consists of pentacoordinate boron that resides in a square-pyramidal environment. All the complexes have been characterized by multinuclear NMR, UV-vis spectroscopy, mass spectrometry, and single-crystal X-ray diffraction studies.

Density Functional Theory Study of Structural and Electronic Properties of Group V Transition Metal Carbides

The structural and electronic properties of group V transition metalcarbides: VC, NbC and TaC are studied using density functional theory with generalized gradient approximation for the exchange and correlation potential. Lattice constants, bulk moduli, elastic constants, energy band diagrams, density of states of the carbides are reported and their trends are discussed. From the band diagrams, the band separation, zone-centre d band splitting, non metal p and s band splitting, width of 2p band, and 4d band explains the insight of electronic structure of these compounds.

A Convenient Solvothermal Synthesis of Group 6 PNP Pincer Tricarbonyl Complexes

The solvothermal synthesis of a series of zerovalent Cr, Mo, and W complexes of the type [M(PNP)(CO)3] featuring PNP pincer ligands based on 2,6-diaminopyridine is described. We demonstrate that the solvothermal synthesis technique presented provides a powerful, simple, and practical synthetic method resulting in high isolated yields in a short time. In particular, Cr and W complexes are not readily accessible via conventional methods. Moreover, this study allows a direct comparison of steric and electronic properties of group 6 metal PNP pincer tricarbonyl complexes.

Investigation of structural stability and electronic properties of group III nitrides: a first principles study

The high-pressure structural phase transition, electronic, superconducting and elastic properties of group III nitrides (ScN, YN and LaN) are investigated by first principles calculation with the density functional theory. The calculated lattice parameters are in good agreement with the experimental and other theoretical values. Electronic structure reveals that these materials are semiconductors with an indirect band gap of 1.4, 0.87 and 0.65 eV for ScN, YN and LaN, respectively. The obtained cubic NaCl structure is energetically the most stable structure at ambient pressure. A pressure-induced structural phase transition from NaCl to CsCl structure is predicted. The structural phase transition of ScN, YN and LaN occurs at a pressure of 158, 132 and 26.5 GPa, respectively. On further increase in the pressure, semiconductor-to-metallic transition and superconductivity is observed in these nitrides. The estimated T c values as a function of pressure for ScN, YN and LaN are 31.79, 15.50 and 12.84 K, respectively.

Electronic properties of group III‐A nitride sheets by molecular simulation

AbstractWe have performed first principles total energy calculations to investigate the structural and reactivity parameters of novel N12X12H12 (X=B, Al, Ga, In, Tl) nitrides, in their coronene‐like (C24H12) structure to simulate these sheets. The exchange and correlations potential energies are treated in the Generalized Gradient Approximation (GGA), and the Local Density Approximation (LDA) within the parameterization of Perdew‐Wang and Perdew‐Burke‐Ernzerhof (PWC, PBE) and the double Numeric plus polarization (DNP) atomic base. The chemical potential, hardness and electrophilicity index, as well as bond length are reported. The bond length of the structures is similar to the bulk. The gap between the HOMO and LUMO decreases from BN (5.18 eV) to TlN (1.76 eV). At the same time, the polarity increases except for TlN. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Investigation of optical phonons and electronic properties of group III‐V nitride multi quantum wells by using far infrared magnetoplasmon spectroscopy

AbstractIn this work, the behavior of optical phonons and magnetoplasmon‐ modes in the doped group III‐V Nitride semiconductor multi quantum wells are investigated in the presence of high magnetic fields parallel to the surface of the layers and perpendicular to the propagation direction by using p‐ and s‐polarized infrared magnetoplasmon reflectivity and employing an effective medium approach. Also, the modified random‐element isodisplacement model is employed to obtain the vibrational modes of GaNAs and AlGaN ternary alloy with zinc‐blend and wurzite structure. The effective carrier mass, the free carrier concentration and the mobility parameters can be quantified upon model analysis of the infrared p‐polarized magnetoplasma reflectivity and the infrared Voigt dielectric function. Theoretical results are compared and discussed with the existing far infrared and Raman scattering data. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The Nitro Valence Vibrations and Ultraviolet Spectra of cis- and trans-β-Nitrostyrenes

Abstract The infrared spectra of NO2 symmetric and asymmetric stretching vibrations and ultraviolet spectra for a series of cis- and trans-β-nitrostyrene derivatives are examined and correlated with the stereochemical configuration of the structure, the planarity of the conjugated system, and the electronic properties of groups on the carbon bearing the nitro group. From these correlations, the cis-, and trans-isomers of β-nitrostyrene derivatives have been readily distinguished from each other.

The Structure of Polyisoprenes. III. Ultraviolet Absorption Spectra

Abstract The quartz ultraviolet absorption spectra of highly purified polyisoprenes correspond closely to those of simple ethylenes having the same degree of alkyl substitution at the double bond. This is also true of geranylamine hydrochloride, which shows no obvious characteristic that can be identified with the structural anomaly revealed by x-ray crystal analysis. The extent to which spectral variations are a measure of the electronic properties of groups and molecules of this type is therefore discussed—with the conclusion that for formally saturated substituents the correlation is still obscure. Evidence is presented to show that inductive influence is slight, and that interpretations hitherto advanced on the basis of hyperconjugation are unsound.