S. Dobos

Spectroscopic and catalytic study on metal carbonyl clusters supported on Cab-O-Sil. I. Impregnation and decomposition of Fe3(CO)12

Impregnation of Fe3(CO)12 on Cab-O-Sil has been studied by ir spectroscopy, Mossbauer spectroscopy, and mass spectrometry. Isotope exchange between CO ligands of the impregnated sample and gas phase CO molecules was also investigated. On impregnation, two types of interaction can be distinguished: (i) interaction of the type FeCO…HOSi and CO…HOSi, shown by the shift to lower and higher ir frequencies for bridged and for terminal CO, respectively, and (ii) interaction between the metal framework and the support revealed in the oxidation of iron to form very small iron oxide particles. On impregnation a small amount of CO is evolved as a result of the interaction. CO exchange occurs faster with alumina-supported clusters than with silica-supported samples. On decomposition up to 370 K, the metal framework is retained and the cluster structure can be partly restored in a CO atmosphere. Above 420 K, Fe3(CO)12 is decomposed to form Fe2+ oxide on the surface. A possible mechanism for impregnation is discussed in terms of electron donation from the support oxygen to the iron d-bands as a result of which the metal-carbon bond strength is influenced. On decomposition the metallic iron interacts with the support OH groups causing oxidation and Fe2+ formation.

Infrared levels of monomeric uracil in cryogenic matrices

Abstract The infrared spectrum of monomeric uracil, trapped in Ar and N 2 cryogenic matrices, is presented and compared with the infrared and Raman spectra recorded for this same compound in associated forms, as observed in its pure solid state and in solution. The monomeric molecules are all in the 2,4-diketotautomeric form and are planar, as can be deduced indirectly from the absence of band multiplicity due to conformeric equilibrium. The assignment is based on comparison with previous works on uracil and with matrix isolation studies on other cis - and trans -imides and is supported by spectral comparison with N,N -dideuterouracil trapped in the same cryogenic matrices. With few exceptions, the assignment is consistent with that obtained by theoretical approaches. On passing from an Ar to an N 2 matrix, the bands due to νNH and γNH shift to lower and higher wavenumbers, respectively, as a result of a specific interaction between the NH groups and the N 2 molecules.

Interaction between FeRu bimetallic carbonyl clusters and oxide supports. II. Decomposition and thermal behaviour on hydrated alumina

Abstract As known, on hydrated alumina support the Ru3(CO)12 cluster quickly decomposes into monometallic subcarbonyls. By FT-IR spectroscopy combined with data handling procedures, the structure and thermal behaviour of the bimetallic systems of Fe2Ru(CO)12/ Al2O3 and H2FeRu3(CO)13 together with that of Ru3(CO)12 have been studied. At the end of an interaction with the hydrated alumina surface, iron ruthenium bimetallic clusters decompose into identical ruthenium anchored surface species RuA  RuIII(CO)2, RuBRuII(CO)2 and RuCRu0(CO)2, like pure ruthenium clusters, and no CO bonded to iron has been detected RuB and RuC are stable in a wide temperature range (300–500 K) and they can be interconverted by oxidation and reduction. RuA is less stable (300–400 K). These main molecule-like species, anchored onto uniform sites of the surface, are accompanied by mobile subcarbonyls and stable monocarbonylic species, which occupy a large variety of different sites.

Interaction between FeRu bimetallic carbonyl clusters and oxide supports. III: Mechanism of interaction and decomposition on hydrated alumina

Abstract Initial steps of the interaction of Ru 3 (CO) 12 , Fe 3 (CO) 12 , Fe 2 Ru(CO) 12 and H 2 FeRu 3 (CO) 13 clusters with hydrated alumina surfaces have been studied by FT-IR spectroscopy combined with data handling procedures. The first stage of the interaction is a pure physisorption. At the second stage the metal-metal bonds split producing a large variety of mobile subcarbonyls. In the case of Fe 3 (CO) 12 the subcarbonyls form molecular Fe(CO) 5 , while at the bimetallic clusters they form molecular Fe- (CO) 5 and Ru 3 (CO) 12 . Fe(CO) 5 loses CO ligands producing Fe 2+ and Fe 3+ anchored ions. Ru 3 (CO) 12 , through further intermediate subcarbonyls, slowly decomposes into incipient anchored species Ru O - (CO) 2 , Ru II (CO) 2 and Ru III (CO) 2 .

Rhenium tricarbonyl as a common intermediate in the CO+H2 reaction over H3Re3(CO)12/Al2O3 and NH4ReO4/Al2O3 samples

Abstract A comprehensive mechanism is provided for surface transformations in the H 3 Re 3 (CO) 12 /Al 2 O 3 and NH 4 ReO 4 /Al 2 O 3 induced by treatment in vacuo , hydrogen and CO + H 2 mixtures. Both inorganic and organometallic precursors are partly transformed to the same, rather stable Re 4+ species during pretreatment. Regardless of the nature of the starting materials, a common intermediate species, Re(CO) 3 (OAl)(HOAl) 2 , is shown to be formed under the reaction conditions employed, provided that the Re 0 or Re 4+ species produced possess ultra-high dispersion.

Infrared spectra and structure of bridging carbonyls in Fe2Ru(CO)12 and Fe3(CO)12

IR spectra of crystal, solution and pseudo-gas phases (argon and nitrogen matrices) of Fe2Ru(CO)12 and of crystal and solution phases of Fe3(CO)12 were recorded. By quantitative data-handling procedures, structures and bond angles for bridging carbonyls were estimated. Fe2Ru(CO)12 in crystal has a bridging structure analogous to that of Fe3(CO)12, with two bridged carbonyls and C2v or pseudo-C2v symmetry. In solution, both samples contain the same carbonyl bridged structure of C2v symmetry,just as in pseudo- gas phase; the latter, however, contains other bridged molecules of unknown structures, too.

Infrared spectra and structure of [(η-C5H5)Fe(CO)2]2 adsorbed on oxide surfaces

Abstract The surface reaction of [(η-C 5 H 5 )Fe(CO) 2 ] 2 adsorbed on hydrated silica and alumina has been studied by FTIR spectroscopy. Hydrogen bonding of one or both bridging carbonyls of the molecule with the surface hydroxo groups, protonation on metalmetal bonds, and forming adducts with Lewis acidic sites of the surface have been taken into consideration, and a series of surface species was detected suggesting a co-existence of most above surface reactions. Cyclopentadienyl group has stabilised FeFe frame, cleavage of metalmetal bond in a small rate was only detected.

Stabilization effect of oxide supports on the decomposition of iron-ruthenium carbonyl clusters

Ru3(CO)12, Fe2Ru(CO)12 and H2FeRu3(CO)13 deposited on Cab-O-Sil and A12O3 have been investigated. Infrared and Mossbauer spectroscopy revealed a strong interaction between a molecular cluster and alumina which leads to the disintegration of the cluster framework up to monoruthenium subcarbonyl species and iron oxide. Temperature-programmed decomposition showed carbon retained in alumina-supported catalyst whereas with Cab-O-Sil the ligands from the adsorbed cluster could be recovered. After temperature-programmed decomposition in hydrogen and vacuum, CO adsorption resulted in four IR bands at about 2138, 2075, 2020 and 20432050 cm−1. From these data the formation of highly dispersed bimetallic particles on alumina is discussed.

Infrared dichroism and molecular conformation of crystalline tetramethyldisiloxanediol

Abstract Vibrational spectra of tetramethyldisiloxanediol (TMDD) have been studied in solution and also in the solid state. Polarized IR spectra of oriented crystalline films have been recorded in the frequency range 4000–200 cm −1 . The structure of the molecules in solution has been found to be of C 2v symmetry. On the basis of the IR dichroitic data obtained for the oriented crystalline films, the molecules should have no symmetry in crystals ( C 1 site symmetry) and the structure of OC 2 SiOSiC 2 O skeletal fragment may be described with an angle of torsion of about 70° around the (Si)O-Si bond.

FT-IR study of stable surface species derived from [(η-C5H5)Fe(CO)2]2

Abstract The thermal behaviour of [(η-C 5 H 5 )Fe(CO) 2 ] 2 adsorbed on partly dchydroxylated alumina and silica surfaces has been followed by FT-IR spectroscopy in the temperature range of 303–723 K. The main products of surface reactions were the vcry stable tetrameric [(η-C 5 H 5 )Fe(μ-CO)] 4 and the less stable monomeric (η-C 5 H 5 )Fe(CO) 2 (-O-) species. On alumina traces of 1:1 and 1:2 adducts of [(η-C 5 H 5 )Fe(CO) 2 ] 2 with surface Lewis acidic sites, while on silica traces of the 1:2 hydrogen bonded complex and oxidized monomeric cation [(η-C 5 H 5 )Fe(CO) 3 ] + were also detected.