Photoelectron spectroscopic investigation of perimidine derivatives

The Hel UPS spectra of acetamidine, perimidine, and four 2-substituted perimidine derivatives have been recorded and interpreted using ab initio and MNDO quantum-chemical calculations. A large interaction between the naphthalene and amidine fragment was concluded from the lowest ionization energy. The color-determining band of these compounds is strongly affected by the intramolecular charge-transfer transitions, which are of low energy because of the low ionization energy of the perimidine moiety.     

Generation, spectroscopy, and structure of cyanoformyl chloride and cyanoformyl bromide, XC(O)CN

Cyanoformyl chloride and cyanoformyl bromide, XC(O)CN (X = Cl and Br), have been investigated in the gas phase by UV photoelectron and mid-infrared spectroscopies. The ground-state geometries of the neutral molecules have been obtained from quantum-chemical calculations at the B3LYP and CCSD(T) levels using the aug-cc-pVTZ basis set. The individual spectroscopies provide a detailed investigation into the vibrational and electronic character of the molecules and are supported by quantum-chemical calculations. The results are compared to data for structurally and chemically related molecules.     

Carbon Microsphere-Supported Metallic Nickel Nanoparticles as Novel Heterogeneous Catalysts and Their Application for the Reduction of Nitrophenol

Nickel nanoparticles are gaining increasing attention in catalysis due to their versatile catalytic action. A novel, low-cost and facile method was developed in this work to synthesize carbon microsphere-supported metallic nickel nanoparticles (Ni-NP/C) for heterogeneous catalysis. The synthesis was based on carbonizing a polystyrene-based cation exchange resin loaded with nickel ions at temperatures between 500 and 1000 °C. The decomposition of the nickel-organic framework resulted in both Ni-NP and carbon microsphere formation. The phase composition, morphology and surface area of these Ni-NP/C microspheres were characterized by powder X-ray diffraction, Raman spectroscopy, scanning electron microscopy and BET analysis. Elemental nickel was found to be the only metal containing phase; fcc-Ni coexisted with hcp-Ni at carbonization temperatures between 500 and 700 °C, and fcc-Ni was the only metallic phase at 800–1000 °C. Graphitization and carbon nanotube formation were observed at high temperatures. The catalytic activity of Ni-NP/C was tested in the reduction of 4-nitrophenol to 4-aminophenol by sodium borohydride, and Ni-NP/C was proved to be an efficient catalyst in this reaction. The relatively easy and scalable synthetic method, as well as the easy separation and catalytic activity of Ni-NP/C, provide a viable alternative to existing nickel nanocatalysts in future applications.     

Gas-phase infrared and ab initio study of the unstable CF3CNO molecule and its stable furoxan ring dimer

The unstable trifluoroacetonitrile N-oxide molecule, CF3CNO, has been generated in high yield in the gas phase from CF3BrC=NOH and studied for the first time by gas-phase mid-infrared spectroscopy. Cold trapping of this molecule followed by slow warming forms the stable ring dimer, bis(trifluoromethyl)furoxan, also investigated by gas-phase infrared spectroscopy. The spectroscopy provides an investigation into the vibrational character of the two molecules, the assignments supported by calculations of the harmonic vibrational frequencies using in the case of CF3CNO both ab initio (CCSD(T)) and density functional theory (B3LYP) and B3LYP for the ring dimer. The ground-state structures of both molecules were investigated at the B3LYP level of theory, with CF3CNO further investigated using coupled-cluster. The CCSD(T) method suggests a slightly bent (C(s)) structure for CF3CNO, while the B3LYP method (with basis sets ranging from 6-311G(d) to cc-pVTZ) suggests a close-to-linear or linear CCNO chain. The CCN bending potential in CF3CNO was explored at the CCSD(T)(fc)/cc-pVTZ level, with the results suggesting that CF3CNO exhibits strong quasi-symmetric top behavior with a barrier to linearity of 174 cm(-1). Since both isomerization and dimerization are feasible loss processes for this unstable molecule, the relative stability of CF3CNO with respect to the known cyanate (CF3OCN), isocyanate (CF3NCO), and fulminate (CF3ONC) isomers and the mechanism of the dimerization process to the ring furoxan and other isomers were studied with density functional theory.     

Generation and Spectroscopic Identification of ClCNS,ClNCS and NCCNS

The photolysis of four chloro‐substituted thiadiazoles (3,4‐dichloro‐, 3‐chloro‐ and 3‐chloro‐4‐fluoro‐1,2,5‐thiadiazole; 3,5‐dichloro‐1,2,4‐thiadiazole) and 3,4‐dicyano‐1,2,5‐thiadiazole was investigated in inert solid‐argon matrices at cryogenic temperatures by means of UV irradiation at selected wavelengths of 254 and 280 nm. The photolysis products were identified by mid‐IR and UV spectroscopy. Evidence for the existence of three novel pseudohalides, namely, chloronitrile sulfide (ClCNS), chlorine isothiocyanate (ClNCS) and cyanogen N‐sulfide (NCCNS), was provided by direct spectroscopic methods supported by quantum chemical calculations. Ground‐state geometries, vibrational frequencies, IR intensities, and UV excitation energies of ClCNS, ClNCS and NCCNS were obtained from calculations using the B3LYP, CCSD(T) and SAC‐CI methods and the aug‐cc‐pV(T+d)Z basis set.     

Toward the synthesis of thiadiazole-based therapeutic agents: synthesis,spectroscopic study,X-ray analysis,and cross-coupling reactions of the key intermediate 3,5-diiodo-1,2,4-thiadiazole

Research on Chemical Intermediates - The 1,2,4-thiadiazole moiety is an important component of several biologically active compounds, and varying substituents on this aromatic ring is one of the...     

Generation and spectroscopic identification of selenofulminic acid and its methyl and cyano derivatives (XCNSe, X=H, CH3, NC)

Evidence for the existence of nitrile selenides, potential 1,3-dipolarophiles in cycloaddition reactions, has been provided by direct spectroscopic methods. The parent nitrile selenide, selenofulminic acid (HCNSe), and its methyl and cyano derivatives have been photolytically generated in an inert solid argon matrix from 1,2,5-selenadiazoles by 280, 254, and 313 nm UV irradiation, respectively, and studied by ultraviolet spectroscopy and mid-infrared spectroscopy. Ground-state geometries have been obtained from quantum-chemical calculations at the CCSD(T)/aug-cc-pVTZ level. Nitrile selenides are predicted to be linear with a relatively weak N-Se bond.     

Quantum-chemical study of the structure and stability of pseudohalogens: OCN-NCO and its isomers

The equilibrium geometries, stability, and isomerisation of pseudohalogen isomers, C(2)N(2)O(2), have been investigated by DFT calculations at the B3LYP level and by ab initio calculations at the CCSD(T) level of theory using the 6-311+G(2d) and cc-pVTZ basis sets, as well as at the CBS-QB3 level. Minimum energy structures and their interconnecting transition states, as well as transition states for bond dissociations have been calculated, and possible isomerisation and decomposition pathways are suggested. Calculations have predicted that four isomers, OCNNCO, ONCCNO, ONCOCN, and ONCNCO are kinetically stable toward unimolecular isomerisation or dissociation at room temperature with the lowest kinetic energy barrier of 209, 232, 159, and 95 kJ mol(-1), respectively (CCSD(T)//B3LYP), and other isomers, like NCONCO, CNONCO, and CNOCNO are unstable. Calculations have also predicted that valence formulations like NCOOCN, CNOOCN, and CNOONC do not represent existing molecules. The gas-phase generation of OCNNCO has been attempted by thermolysing Me(3)SiON(Me(3)SiO)CC(OSiMe(3))NOSiMe(3), synthesised by a novel method from oxalyl chloride and N,O-bis(trimethylsilyl)hydroxylamine; the thermolysis, however, have not produced OCNNCO, but trimethylsilylisocyanate and hexamethyldisiloxane.     

Evidence of quasi-intramolecular redox reactions during thermal decomposition of ammonium hydroxodisulfitoferriate(III), (NH4)2[Fe(OH)(SO3)2]·H2O

Synthesis of ammonium hydroxodisulfitoferriate(III), (diammonium catena-{bis(μ ²-sulfito-κO,κO)-μ ²-hydroxo-κ²O}ferrate(III) monohydrate) (NH₄)₂[Fe(OH)(SO₃)₂]·H₂O (compound 1) and its thermal behavior is reported. The compound is stable in air. Its thermal decomposition proceeds without the expected quasi-intramolecular oxidation of sulfite ion with ferric ions. The disproportionation reaction of the ammonium sulfite, formed from the evolved NH₃, SO₂ and H₂O in the main decomposition stage of 1, results in the formation of ammonium sulfate and ammonium sulfide. The ammonium sulfide is unstable at the decomposition temperature of 1 (150 °C) and transforms into NH₃ and H₂S which immediately forms elementary sulfur by reaction with SO₂. The formation and decomposition of other intermediate compounds like (NH₄)₂S_nO_x (n = 2, x = 3 and n = 3, x = 6) results in the same decomposition products (S, SO₂ and NH₃). Two basic iron sulfates, formed in different ratios during synthesizing experiments performed under N₂ or in the presence of air, have been detected as solid intermediates which contain ammonium ions. The final decomposition product was proved to be α-Fe₂O₃ (mineral name hematite).

     

Structure of thionyl imides — the new isomer

Equilibrium geometries of the molecules XNSO (where X = Li, Na, HBe, HMg, H₂B or H₂Al) were calculated using the second-order Møller-Plesset perturbation theory. The four-membered planar cyclic form, previously postulated for a number of other pseudohalides, is predicted to be the dominant isomer in the vapour phase. Potential energy curves for the migration of the substituent between the end atoms of the NSO group were also calculated and the relative stabilities of the new structures are compared to the ‘conventional’ open chain isomers.