J. Mink

Mehrfachbindungen zwischen hauptgruppenelementen und übergangsmetallen: CXXVI. Heterocyclen-carbene als phosphananaloge liganden in metallkomplexen

Abstract Carbenes L derived from imidazole and triazole, as generated from the corresponding azolium precursor salts, smoothly react with simple metal carbonyls such as M(CO)6 (M  Cr, Mo, W), Fe(CO)5, and Ni(CO)4 to give the substitution products M(CO)5L, Fe(CO)4L, Ni(CO)3L, and Ni(CO)2L2, respectively, owing to the pronounced C-nucleophilicity of the free carbenes L. Dicarbenes L L form chelate complexes of type M(CO)4( L L ) upon treatment with M(CO)6 (M  Cr, Mo, W). The new bis(carbene)nickel (0) complex Ni(CO)2L2 and the first member of a metal complex M(CO)4( L L ) exhibiting a chelating dicarbene of the triazole series have been characterized by single-crystal X-ray diffraction. It is evident from the present study that heterocyclic mono- and (chelating) dicarbenes of the aza-type are congeners of phosphanes and diphosphanes, resp., with regard to their metal-coordination chemistry. Both in terms of ligand properties and metal complex synthesis, they closely resemble electron-rich phosphanes, e.g. trimethylphosphane.

A zeolite family with chiral and achiral structures built from the same building layer

Porosity and chirality are two of the most important properties for materials in the chemical and pharmaceutical industry. Inorganic microporous materials such as zeolites have been widely used in ion-exchange, selective sorption/separation and catalytic processes. The pore size and shape in zeolites play important roles for specific applications. Chiral inorganic microporous materials are particularly desirable with respect to their possible use in enantioselective sorption, separation and catalysis. At present, among the 179 zeolite framework types reported, only three exhibit chiral frameworks. Synthesizing enantiopure, porous tetrahedral framework structures represents a great challenge for chemists. Here, we report the silicogermanates SU-32 (polymorph A), SU-15 (polymorph B) (SU, Stockholm University) and a hypothetical polymorph C, all built by different stacking of a novel building layer. Whereas polymorphs B and C are achiral, each crystal of polymorph A exhibits only one hand and has an intrinsically chiral zeolite structure. SU-15 and SU-32 are thermally stable on calcination.

Density functional study of nitrogen oxides

Equilibrium geometries, bond dissociation energies, dipole moments, harmonic vibrational frequencies, and infrared intensities were calculated for a set of ten neutral nitrogen oxides (NO, NO2, NO3, N2O, sym N2O2, asym N2O3, sym N2O3, sym N2O4, asym N2O4, and N2O5) by applying one local and two gradient‐corrected nonlocal functionals in a Gaussian‐type‐orbital density functional method. Comparison with available experimental data shows that, except for the bond dissociation energies, the local functional gives very accurate molecular properties. Nonlocal functionals considerably improve the bond dissociation energies, but the results still overestimate the experimental values by about 10 kcal/mol on average. For the other properties, the results obtained with nonlocal functionals are not necessarily superior to those calculated with the local functional. The properties of two molecules (sym N2O3 and asym N2O4) are predicted for the first time and several reassignments are proposed in the vibrational spect...

FTIR and Raman studies on benzimidazole

Abstract The FTIR and laser Raman spectra of benzimidazole have been recorded. The observed frequencies were assigned to various modes of vibrations on the basis of normal coordinate calculations, assuming C s point group symmetry. The potential energy distribution associated with normal modes is also reported here. The assignment of fundamental vibrations agrees well with the calculated frequencies.

Vibrational spectroscopic studies of uranyl complexes in aqueous and non-aqueous solutions

Abstract Vibrational spectra have been obtained for aqueous solution of uranyl-perchlorates, -fluorides, -chlorides, -acetates and -sulphates over a range of solution composition with added anions. We have prepared [Bu n 4 N][UO 2 Cl 4 ], [Me 4 N][UO 2 Cl 4 ], [Pr n 4 N][[UO 2 (NO 3 ) 3 ], [Bu n 4 N][UO 2 (NO 3 ) 3 ], with the expectation that the large cation would give a better approximation to vibrational frequencies of the free anion and would allow measurements in non-coordinating solvents. As the perchlorate is not coordinated to [UO 2 ] 2+ in aqueous solution the expected structure is a solvated cation [UO 2 (OH 2 ) 5 ] 2+ with characteristic infrared 962.5, 253 and 160 cm −1 and Raman 874 and 198 cm −1 bands. The formation of weak, solvated [UO 2 X] + complexes (X=F, Cl) has been established with frequencies at 908, 827, 254, 380 cm −1 and 956, 871, 254 and 222 cm −1 for [UO 2 F] + and [UO 2 Cl] + , respectively. Bidentate NO 3 coordination has been established for solid and dissolved (in CH 2 Cl 2 ) [R 4 N][UO 2 (NO 3 ) 3 ] (R=Pr n , Bu n ). Aqueous solutions of UO 2 (NO 3 ) 2 and Cs[UO 2 (NO 3 ) 3 ] show no clear evidence that bidentate or monodentate nitrate is present. Both unidentate and bidentate linkage of acetate-uranyl were established for acetate complexes in aqueous solutions. For the uranyl sulphate system, monodentate sulphate coordination is the major mode at low SO 4 :U ratios, and even at a ratio of 3:1 there is very little free sulphate.

Vibrational assignment of totally symmetric modes in phthalocyanine molecules

Abstract The vibrational assignment of totally symmetric modes in a series of D 4 h and C 4 v phthalocyanine (Pc) molecules was attempted using infrared, Raman, SERS, and vibrational calculations. The normal coordinate analysis for the in-plane vibrational modes of a metallated phthalocyanine molecule was carried out. Observed vibrational fundamentals for D 4 h and C 4 v were matched using correlation tables for descent in symmetry. Some new information was obtained from infrared, Raman and surface-enhanced Raman spectroscopy of Pc films in order to complete the existing set of vibrational frequencies for the series of compounds.

Cycloaddition of CO2 and epoxides catalyzed by imidazolium bromides under mild conditions: influence of the cation on catalyst activity

The synthesis and characterization of a library of imidazolium-based compounds of the type [R1R2R3im]Br (R1 = H, CH3, benzyl (Bz), 1-(2,3,4,5,6-pentafluoro)benzyl (BzF5); R2 = H, CH3, C2H5; R3 = n-butyl, n-octyl) are reported. All compounds were characterized by means of 1H and 13C NMR spectroscopy, elemental analysis and single crystal X-ray diffraction in the case of 1-BzF5-3-n-octylimidazolium bromide and examined as catalysts for the cycloaddition of carbon dioxide and propylene oxide (PO) to yield propylene carbonate (PC). The catalyst screening shows the influence of different substituents (steric and ion pairing effects) on the catalytic activity. It is shown that the most active catalyst, 1-BzF5-3-n-octylimidazolium bromide (10), gives very good conversions and carbonate yields at 70 °C and below 5 bar CO2 pressure, which is the lowest temperature for the synthesis of PC from PO and CO2 using metal-free catalysts. Catalyst 10 can be recycled and reused at least 10 times without loss of yield and activity.

Organonitrile ligated silver complexes with perfluorinated weakly coordinating anions and their catalytic application for coupling reactions

Homogeneous catalytic processes mediated by silver(I) complexes are relatively rare. This work describes the synthesis and characterization of acetonitrile ligated silver salts with three weakly coordinating anions [B(C6F5)4]−, [B{C6H3(CF3)2}4]− and [(C6F5)3B–C3H4N2–B(C6F5)3]−. The silver cation is coordinated either by four or by two acetonitrile ligands. All examined Ag(I) complexes show catalytic activity in coupling reactions of terminal alkynes with aldehydes and amines.

FTIR Spectroscopy of the Atmosphere. I. Principles and Methods

Abstract In recent years Fourier transform infrared (FTIR) spectroscopy has been the dominant technique used for measuring the infrared (IR) absorption and emission spectra of most materials, with substantial advantages in signal‐to‐noise ratio, resolution, speed, and detection limits. The major advantage of the FTIR technique over other spectroscopic methods is that practically all compounds show characteristic absorption/emission in the IR spectral region and based on this property they can thus be analyzed both quantitatively and qualitatively. The quest for highly sensitive detection methods for atmospheric trace gas samples, either in laboratory setup or in outdoor remote sensing, has been on agenda for several decades. The fast and intensive development of FTIR spectroscopic techniques has propelled the progress of trace gas analysis of the atmosphere. Since the early 1970s the number and scope of FTIR atmospheric measurements has increased steadily. In this review article we are making an attempt to summarize the results of the most significant contributions to the field of FTIR spectroscopy to trace gas analysis of the atmosphere. Beside the basic description of the extractive and open‐path measurement methods, the difficulties connected with collection of appropriate background reference spectra, the ways of qualitative analysis and quantitative evaluation of measured spectra, the problems of calibration, and the effects of spectral resolution on detection sensitivity are discussed. The techniques reviewed include in situ IR absorption measurements over open paths in the field, such as remote sensing using the sun, the sky, or natural hot objects as IR sources of radiation, and also IR emission measurements of hot trace gas sources e.g., stack emissions, exhaust gases of combustion sources, and other industrial effluents.

Intercalation study of clay minerals by Fourier transform infrared spectrometry

Abstract Intercalation complexes of two different Hungarian kaolinites with potassium acetate were investigated by IR and thermoanalytical methods. The intensities of hydrogen-bonded OH bands could be correlated with the decrease in the dehydroxylation temperature of the clay mineral. Based on the hydrogen bonding pattern conclusions can be drawn regarding the dehydroxylation mechanism of kaolinites.