Matrix isolation infrared (IR) studies have been carried out on the vaporisation of the alkali-metal azides MN(3) (M = Na, K, Rb and Cs). The results show that under high vacuum conditions, molecular KN(3), RbN(3) and CsN(3) are present as stable high-temperature vapour species, together with variable amounts of nitrogen gas and the corresponding metal atoms. The characterisation of these molecular azides is supported by ab initio molecular orbital calculations and density functional theory (DFT) calculations, and for CsN(3) in particular, by the detection of the isotopomers CS((14)N(15)N(14)N) and Cs((15)N(14)N(14)N). The IR spectra are assigned to a "side-on" (C(2v)) structure by comparison with the spectral features predicted both by vibrational analysis and calculation. The most intense IR features for KN(3), RbN(3) and CsN(3) isolated in nitrogen matrices lie at 2005, 2004.4 and 2002.2cm(-1), respectively, and correspond to the N(3) asymmetric stretch. The N(3) bending mode in CsN(3) is identified at 629 cm(-1). An additional feature routinely observed in these experiments occurred at approximately 2323 cm(-1) and is assigned to molecular N(2), perturbed by the close proximity of an alkali-metal atom. The position of this band appeared to show very little cation dependence, but its intensity correlated with the extent of sample thermal decomposition.

A series of alkali metal azide-crown ether complexes, [Li([12]crown-4)(N3)], [Na([15]crown-5)(N3)], [Na([15]crown-5)(H2O)2]N3, [K([18]crown-6)(N3)(H2O)], [Rb([18]crown-6)(N3)(H2O)], [Cs([18]crown-6)(N3)]2, and [Cs([18]crown-6)(N3)(H2O)(MeOH)], has been synthesised. In most cases, single crystals were obtained, which allowed X-ray crystal structures to be derived. The structures obtained have been compared with molecular structures computed by density functional theory (DFT) calculations. This has allowed the effects of the crystal lattice on the structures to be investigated. Also, a study of the M-N(terminal) metal-azide bond length and charge densities on the metal (M) and terminal nitrogen centre (N(terminal)) in these complexes has allowed the nature of the metal-azide bond to be probed in each case. The bonding in these complexes is believed to be predominantly ionic or ion-dipole in character, with the differences in geometries reflecting the balance between maximising the coordination number of the metal centre and minimising ligand-ligand repulsions. The structures of the crown ether complexes determined in this work show the subtle interplay of such factors. The significant role of hydrogen bonding is also demonstrated, most clearly in the structures of the K and Rb dimers, but also in the chain structure of the hydrated Cs complex.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

The thermal decompositions of methyl azidoformate (N3COOMe), ethyl azidoformate (N3COOEt) and 2-azido-N,N-dimethylacetamide (N3CH2CONMe2) have been studied by matrix isolation infrared spectroscopy and real-time ultraviolet photoelectron spectroscopy. N-2 appears as an initial pyrolysis product in all systems, and the principal interest lies in the fate of the accompanying organic fragment. For methyl azidoformate, four accompanying products were observed: HNCO, H2CO, CH2NH and CO2, and these are believed to arise as a result of two competing decomposition routes of a four-membered cyclic intermediate. Ethyl azidoformate pyrolysis yields four corresponding products: HNCO, MeCHO, MeCHNH and CO2, together with the five-membered-ring compound 2-oxazolidone. In contrast, the initial pyrolysis of 2-azido-N,N-dimethyl acetamide, yields the novel imine intermediate Me2NCOCH=NH, which subsequently decomposes into dimethyl formamide (HCONMe2), CO, Me2NH and HCN. This intermediate was detected by matrix isolation IR spectroscopy, and its identity confirmed both by a molecular orbital calculation of its IR spectrum, and by the temperature dependence and distribution of products in the PES and IR studies. Mechanisms are proposed for the formation and decomposition of all the products observed in these three systems, based on the experimental evidence and the results of supporting molecular orbital calculations.

The interaction of O-2 (O-18(2)) with [meso-triphenyl(4-pyridyl)porphyrinato]cobalt(II) [Co(MPyTPP)] has been investigated by means of IR spectroscopy under matrix-isolation conditions and by the action of dioxygen on thin sublimed layers. These studies have led to the characterisation of two dioxygen adducts: (1) a very unstable dioxygen adduct similar to that observed earlier for the closely related [meso-tetraphenylporphyrinato]cobalt(ii) Co(TPP), and (2) a new type of coordinated O-2 (O-18(2)) complex which is formed after warming Co(MPyTPP) either in pure oxygen matrices, or as sublimed layers in the presence of oxygen. The V(02) vibration in this second species is more than 100 cm(-1) lower than in the first, and the dioxygen adduct thus formed is thermally stable at 200 K. This adduct is identified as a six-coordinate dioxygen complex, with one coordination site occupied by the pyridyl group of an adjacent Co(MPyTPP) molecule. In the sublimed layers, the capacity for self-assembly of Co(MPyTPP) oligomers leads to the formation of microporous solids containing coordinatively unsaturated metal ions which have the ability to bind oxygen reversibly upon storage at ambient conditions.

. Ag + , Cu 2+ and Ag + - Cu 2 + binary mixtures with different Ag/Cu ratios were supported on mordenite with Si/Al ratio equal to 10 and reduced in the temperature range 323-673 K. Diffuse Reflectance UV-Visible spectra reveal appearance of Ag 8 clusters and small copper metal particles. Cu K-edge EXAFS show for Cu-rich non-reduced samples the presence of only oxygen shell; but for the Ag-rich sample, the presence of heavier backscatterer is also indicated producing a different EXAFS envelope. Silver EXAFS analysis suggests that, for the reduced samples, there are both Ag - O and Ag - Ag distances ( Ag - Ag and Ag - O coordination numbers of approx 2 and of 1.3 respectively for the Ag / Cu = 3:1 and 1:3 samples). Importantly, for the reduced sample, the EXAFS indicates that Ag appears to promote/stabilise Cu cluster formation whereas Cu appears to impede/destabilise Ag cluster formation.

The interaction of CO, NO and O2 gases with thin layers of meso-mono-4-pyridyl-tri-phenylporphyrinatoiron(II) (FeMPyTPP) obtained by sublimation onto low-temperature (T = 77 K) substrates has been investigated by means of IR and UV-visible spectroscopy. In contrast to the closely-related meso-tetraphenylporphyrinatoiron(II) (FeTPP), the formation of two types of axial complexes has been observed. In one of these the 5th coordination site is occupied by the pyridyl group of an adjacent molecule indicating the self-assembly of Fe(MPyTPP) in layers with formation of coordinatively linked oligomers. The degree of oligomerisation depends on the nature of the interacting gas. Due to the specificity of the supramolecular structure, the layers are fairly stable in ambient conditions and conserve their microporosity to bind reversibly with the aforementioned ligands.

The thermal decompositions of 2-azidoethanol and 2-azidoethyl acetate have been studied by matrix isolation infrared spectroscopy and real-time ultraviolet photoelectron spectroscopy. The products that were detected in a flow system at different temperatures (CH2NH, H2CO, N-2, CO, and HCN from N3CH2CH2OH and C2H4, CH2NH, HCN, CO2, and N-2 from N3CH2COOCH2CH3) allowed mechanisms for decomposition to be proposed. The experimental evidence obtained is consistent with 2-azidoethyl actetate decomposing via a concerted mechanism, similar to that found previously for azidoacetic acid, whereas the 2-azidoethanol decomposition is consistent with a stepwise decomposition mechanism as observed previously for azidoacetone.

The vaporization of ternary alkali metal oxo- and halo-complexes of transition metals has long been recognised as a potential factor in high temperature corrosion. This paper describes the characterization of a novel volatile species, molecular cesium manganate (VI), which is produced when samples of solid Cs2MnO4 or other related ternary Cs-Mn-O systems are heated in vacuo to temperatures in excess of 1000 K. The formation of a volatile Mn (VI) species from these systems is characterised by the production of an intense deep green-blue sublimate, and the vaporizing species is shown to be molecular Cs2MnO4 from a combination of molecular beam mass spectrometric and matrix isolation it spectroscopic studies. In particular, the ir spectrum of the molecule isolated in a nitrogen matrix shows prominent Mn-O modes at 854.5 and 815.0 cm(-1), and these results, together with supporting O-18 enrichment studies, indicate a D-2d structure for this species.

The study of silver-zeolite samples by a combination of EXAFS and Diffuse Reflectance UV-Visible spectroscopy has been utilised to discover the effect of the structural type and Si/Al ratio of zeolite matrix as well as influence of reduction temperature on the size, structure and oxidation of silver species stabilised inside zeolite voids. The preparation of silver-zeolite samples at high temperature using mordenite with medium Bronsted acid strength or at low temperature using mordenite with high acid strength leads to fast oxidation of reduced silver species. After reduction at medium temperatures silver clusters interpreted as Ag(8)(0) and Ag(8)(delta+) are formed in mordenites with intermediate Bronsted acid strength. The reduction of silver samples at high temperature utilising mordenite with a very small concentration of weak Bronsted acid sites leads to the formation of amorphous Ag particles. Deformation of the eight-atom clusters is more prominent in the erionite cavities, where space is more severely restricted than in mordenite channels. It is proposed that the charged Ag(8)(delta+) clusters are more deformed than neutral Ag(8)(0) clusters.

The ultraviolet photoelectron spectrum of F2O was recorded with a higher resolution than previously published. New vibrational structure was observed in the second and third bands. Near state-of-the-art molecular orbital calculations were performed on the (X) over tilde (1)A(1) state of F2O and the (X) over tilde B-2(1), B-2(2), (2)A(1), and (2)A(2) state of F2O+, and their potential energy functions were computed. Spectral simulations based on Franck-Condon factor calculations including the Duchinsky effect were carried out within the harmonic oscillator model and also with the inclusion of anharmonicity, in order to assist spectral assignment. Based on the computed ionization energies obtained with the coupled cluster and multireference configuration interaction methods with basis sets of up to quintuple zeta quality, the order of the low-lying cationic states of F2O+ has been firmly established. However, the detailed assignment of the overlapping second and third photoelectron bands was only achieved with the aid of spectral simulation. The iterative Franck-Condon analysis (IFCA) procedure was carried out for the first band {F2O+ ((X) over tilde B-2(1))<--F2O ((X) over tilde (1)A(1))} in the photoelectron spectrum. With the geometrical parameters of F2O ((X) over tilde (1)A(1)) being fixed at the available experimental values, geometrical parameters of the (X) over tilde B-2(1) state of F2O+ were derived. Based on anharmonic Franck-Condon factor calculations, the recommended IFCA geometrical parameters for the ground state of F2O+ are R(FO) = 1.323 +/-0.002 Angstrom and angle FOF=107.3 +/-0.2 degrees. (C) 2001 American Institute of Physics.

Irradiation using a low pressure mercury lamp (λ=ca. 250 nm) of argon matrices containing ca. 1% (Me2Si)6 and ca. 20% ethylene oxide (C2H4O) or nitrous oxide (N2O) for a period of ca. 20 h leads to the formation of the cyclic compound (Me2SiO)6. This has a 12-membered ring with alternating Si and O atoms. It is identified by comparison of its infrared spectrum with a spectrum of an authentic sample. The reaction appears to proceed by stepwise insertion of O atoms into SiSi bonds.

Ultraviolet photoelectron spectra of UBr4 and ThBr4 have been recorded in the gas-phase and interpreted using relativistic density functional calculations. For ThBr4, eight bands were observed which are interpreted as ionization from the five Br 4p symmetry orbitals of a Br4 unit in Td symmetry, with three of the bands [the (4t2)−1, (1t1)−1, and (3t2)−1 ionizations] each being split into two by spin–orbit interaction. The observed splittings are rationalized in terms of the Th 6p and Br 4p contributions to the orbitals and by comparison with the known ultraviolet photoelectron spectra of ThF4 and ThCl4. The first vertical ionization energy (VIE) of ThBr4 was measured as (10.92±0.03) eV. UBr4 shows a very similar photoelectron spectrum with an extra band at (9.65±0.02) eV VIE. This is associated with a (5t2)−1 (U 5f,6d) ionization. Supporting matrix isolation infrared experiments were also carried out under very similar vaporization conditions to those used in the photoelectron spectroscopy experiments to check the composition of the vapor beams used. In these experiments, the T2 stretching modes of ThBr4 and UBr4 have been measured as 230±2 and 239±2 cm−1, respectively. Both the photoelectron and infrared matrix isolation spectra are consistent with an effective tetrahedral geometry for UBr4 and ThBr4.

The structure of silver clusters stabilised in erionite has been studied by EXAFS, and the results support an interpretation given previously that the absorption peaks at 322 and 293 urn in the optical spectra of the sample belong to the cluster species Ag 8 0 and Ag 8 δ+ . Five possible geometries were considered for an Ag8 cluster, and for each one, the expected Ag EXAFS was calculated and compared with the experimental data. The observed coordination numbers indicate an absence of bulk silver metal, and the best fit was obtained for a polyhedron with D2d symmetry, which corresponds closely with the results of minimum energy structure calculations. The derived Ag—O distances discount the formation of silver oxides, but are consistent with a weak interaction between the silver clusters and the oxygen atoms of the surrounding channel. The results therefore indicate that erionite promotes the formation of 8-atom silver clusters in the channels of the crystalline framework.

2-Azidoacetone (N3CH2COCH3) has been synthesized and characterized by a variety of spectroscopic techniques, and the thermal decomposition of this molecule at temperatures in the region 300-1150 K has been studied by matrix isolation infrared spectroscopy and real-time ultraviolet photoelectron spectroscopy. The results show the effectively simultaneous production of six prominent decomposition products: CH2NH, CH2CO, HCN, CO, N-2, and CH3CHO, and several reaction pathways are proposed to account for their formation. Results of ab initio molecular orbital calculations indicate that the primary reaction intermediate is the imine HNCHCOCH3, with the nitrene NCH2COCH3 being a transition state. No experimental evidence was found for the presence of the imine HNCHCOCH3, but mechanistic considerations, and the existence of several weak unassigned IR bands point to the presence of a further decomposition product, which may be CH2NCH3.

High temperature salt molecules have been known for many years, and are known to play a significant role in several high temperature transport and corrosion processes. Accurate thermodynamic modelling of such systems requires knowledge of molecular vibration frequencies, and the initial aim of this paper is to consider the errors in selected thermodynamic parameters arising from uncertainties in low frequency vibrations. This is followed by a presentation of results from recent experiments designed to locate metal-oxygen modes in a variety of high temperature oxo-anion salt molecules. In particular, matrix isolation far ir studies on alkali metal nitrates show characteristic M-O stretches at ca. 225 and 189 cm(-1) (M=K), 179 and 144 cm(-1) (M=Rb), 164 and 130 cm(-1) (M=Cs). Force constant parameters are evaluated, and the possibility of transferability to other salt molecules is discussed.

H-2-doped argon matrices containing CsF were examined using FTIR with 1 cm(-1) spectral resolution. Several distinct trapping sites were identified with one, two, and three hydrogen molecules perturbed by CsF. CsF(H-2) gives a band at 4022 cm(-1) while the features of CsF(H-2)(x), x > 1, are displaced to higher wavenumbers. It is clear from the similarity of the spectra of H-2 and HD that the rotation of H-2 is quenched in the presence of CsF, Analogous spectra are observed using KF with the 1:1 adduct absorbing at 4016 cm(-1) The spectrum of H-2 in argon matrices doped with NaCl shows three absorptions that exhibit fine structure even under highly dilute conditions, Analogous features are exhibited by HD, indicating that the several bands are probably not due to rotation of the hydrogen. The three bands are assigned to conformers of NaCl:H-2 which are differentiated by an interaction between the sodium ion and H-2 that is modulated by the matrix.

2-Azidoacetic acid (N3CH2CO2H) has been synthesized and characterized by a variety of spectroscopic techniques, and the thermal decomposition of this molecule studied by matrix isolation infrared spectroscopy and real-time ultraviolet photoelectron spectroscopy. The results are consistent with the vapor phase thermal decomposition following a pathway involving concerted ejection of molecular Nz and the simultaneous formation of CO2 and methanimine (CH2NH). No evidence was found for the presence of intermediates such as the nitrene NCH2CO2H or the imine HNCHCO2H. At higher temperatures, CH2NH further decomposes to give HCN and H-2.