Transition metals infrared spectroscopy

The hydrogenation is catalysed by nickel and other transition metals. Vibrational spectroscopy (infrared, HREELS, INS) has been applied to determining the orientation and binding of benzene on the catalyst surface. We suimnarise INS studies of benzene, adsorbed benzene and model complexes. The intensities and frequencies of the vibrational modes are computed by the Wilson GF method. The benzene molecule... 

Studies to determine the nature of intermediate species have been made on a variety of transition metals, and especially on Pt, with emphasis on the Pt(lll) surface. Techniques such as TPD (temperature-programmed desorption), SIMS, NEXAFS (see Table VIII-1) and RAIRS (reflection absorption infrared spectroscopy) have been used, as well as all kinds of isotopic labeling (see Refs. 286 and 289). On Pt(III) the surface is covered with C2H3, ethylidyne, tightly bound to a three-fold hollow site, see Fig. XVIII-25, and Ref. 290. A current mechanism is that of the figure, in which ethylidyne acts as a kind of surface catalyst, allowing surface H atoms to add to a second, perhaps physically adsorbed layer of ethylene this is, in effect, a kind of Eley-Rideal mechanism. 

The duoroborate ion has traditionally been referred to as a noncoordinating anion. It has shown Httie tendency to form a coordinate—covalent bond with transition metals as do nitrates and sulfates. A few exceptional cases have been reported (13) in which a coordinated BF was detected by infrared or visible spectroscopy. 

Deprotonation of H2O2 yields OOH , and hydroperoxides of the alkali metals are known in solution. Liquid ammonia can also effect deprotonation and NH4OOH is a white solid, mp 25° infrared spectroscopy shows the presence of NH4+ and OOH ions in the solid phase but the melt appears to contain only the H-bonded species NH3 and H202. " Double deprotonation yields the peroxide ion 02 , and this is a standard route to transition metal peroxides. 

A. A. Davydov, Infrared spectroscopy of adsorbed species on the surfaces of transition metal oxides, Wiley, Chichester, 1990. 

Yeom and Frei [96] showed that irradiation at 266 nm of TS-1 loaded with CO and CH3OH gas at 173 K gave methyl formate as the main product. The photoreaction was monitored in situ by FT-IR spectroscopy and was attributed to reduction of CO at LMCT-excited framework Ti centers (see Sect. 3.2) under concurrent oxidation of methanol. Infrared product analysis based on experiments with isotopically labeled molecules revealed that carbon monoxide is incorporated into the ester as a carbonyl moiety. The authors proposed that CO is photoreduced by transient Ti + to HCO radical in the primary redox step. This finding opens up the possibility for synthetic chemistry of carbon monoxide in transition metal materials by photoactivation of framework metal centers. 

In addition to the simple chemical methods for following these processes, infrared spectroscopy may also be used. In Fig. 9 is shown the spectrum of silica dried at 200°C before and after reaction with Zr(allyl)4- The characteristic absorption bands of the transition metal-allyl group are clearly displayed, also a significant reduction in the number of hydroxyl groups (3740 cm-1) is also clearly evident. 

Varenne, A., Salmain, M., Brisson, C., and Jaouen, G. (1992) Transition metal carbonyl labeling of proteins. A novel approach to a solid-phase two-site immunoassay using Fourier transform infrared spectroscopy. Bioconjugate Chem. 3, 471-476. 

Thiazyl monomer is a radical with one unpaired electron. It exhibits an IR band at 1209 cm-1. The experimental dipole moment is 1.83 0.03 D in the opposite direction to that in NO (p = 0.16 D). Much less is known about selenazyl monomer, SeN, but it has been characterized by infrared spectroscopy.36 The structure of a transition-metal complex [OsTp(NSe)Cl2] (Tp=hydrotris(l-pyr-azolyl)borate) has been determined.39... 

A.A. Davydov and C.H. Rochester, Infrared Spectroscopy of Adsorbed Species on the Surface of Transition Metal Oxides, Wiley, New York, 1990. 

Fourier-transform infrared (FTIR) spectroscopy Spectroscopy based on excitation of vibrational modes of chemical bonds in a molecule. The energy of the infrared radiation absorbed is expressed in inverse centimeters (cm ), which represents a frequency unit. For transition-metal complexes, the ligands -C N and -C=0 have characteristic absorption bands at unusually high frequencies, so that they are easily distinguished from other bonds. The position of these bonds depends on the distribution of electron density between the metal and the ligand an increase of charge density at the metal results in a shift of the bands to lower frequencies. 

High pressure infrared (HP IR) spectroscopy has now been used for over 30 years for the study of homogeneous transition metal catalysed processes. The technique is particularly useful for reactions involving carbon monoxide, for which transition metal carbonyl complexes are key intermediates in the catalytic mechanisms. Such complexes have one or more strong r(CO) absorptions, the frequencies and relative intensities of which provide information about the geometry and electronic character of the metal center. As well as probing the metal species, HP IR spectroscopy can also be used to monitor the depletion and formation of organic reactants and products if they have appropriate IR absorptions. 

Infrared diode laser spectroscopy, 46 119, 148 Infrared emission, transition,-metal ions, 35 334-335... 

Raman spectra of adsorbed species, when obtainable, are of great importance because of the very different intensity distributions among the observable modes (e.g., the skeletal breathing frequency of benzene) compared with those observed by infrared spectroscopy and because Raman spectra of species on oxide-supported metals have a much wider metal oxide-transparent wavenumber range than infrared spectra. Such unenhanced spectra remain extremely weak for species on single-crystal surfaces, but renewed efforts should be made with finely divided catalysts, possibly involving pulsed-laser operation to minimize adsorbate decomposition. Renewed efforts should be made to obtain SER and normal Raman spectra characterizing adsorption on surfaces of the transition metals such as Ni, Pd, or Pt, by use of controlled particle sizes or UV excitation, respectively. 

Ward (, 6) determined the acidity of several transition metal X and Y zeolites by infrared spectroscopy but could find no simple relationship between the proton acid concentration and physical parameters of metal ions or catalytic activity for o-xylene isomerization. 

Through a co-assembling route, mesostructured lamellar molybdenum sulfides are formed hydrothermally at about 85 °C using cationic surfactant molecules as the templates. The reaction temperature and the pH value of the reaction system are important factors that affect the formation of the mesostructured compounds. The amount of the template and that of the S source are less critical in the synthesis of the compounds. For the three as-synthesized mesostructured materials, the interlayer distance increases linearly with the chain length of the surfactant. Infrared and X-ray photoelectron spectroscopy reveals that the individual inorganic layers for the three compounds are essentially the same both in composition and in structure. The formal oxidation state of the molybdenum in the materials is +4 whereas there exist S2 anions and a small amount of (S-S)2 ligands in the mesostructures. The successful synthesis of MoS-L materials indicates that mesostructured compounds can be extended to transition metal sulfides which may exhibit physico-chemical properties more diverse than non-transition metal sulfides because of the ease of the valence variation for a transition metal. 

Infrared data have been tabulated for benzotriazole and a wide range of its transition metal complexes or adducts (172). Far infrared spectra have been recorded for copper(II) benzotriazole adducts and bands at 270-320 cm-1 have been assigned to Cu-N vibrations (172). Infrared absorptions at approximately 825, 800, and 775 cm-1 in the spectra of cobalt(III)/4,5-disubstituted triazolate complexes have been attributed to triazolate ring vibrations (109). Infrared data have been reported and assignments made for palladium and platinum thiatriazoline-5-thionate complexes (37) and for the parent thione (127). Vibrational spectroscopy has been employed in an attempt to determine coordination sites for a range of 8-azapurine complexes (108). 

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