Luminescent silicon clusters have been synthesized by the chemical vapor deposition of Si2H6 into the α-cages of H32Na24Y zeolite. The synthetic process was monitored by FTIR, TGA-MS, and 29Si and 1H solid-state NMR spectroscopies. In the initial step at 100 °C, Si2H6 reacts with the Brønsted acid sites to produce anchored ZO−Si2H5. Si2H6 is also chemisorbed at Na+ cation sites to give Si2H6/NaHY and is possibly physically trapped within the α-cage by the anchored disilyl groups. Multiple quantum 1H NMR spin counting shows that each α-cage contains 38 H atoms. This is equivalent to 14 Si atoms present as a combination of disilyl and disilane. Subsequent thermal treatment of the entrapped disilane precursors leads, via H2 and SiH4 elimination, to the formation of Si clusters. The formation of Si clusters is complete at 550 °C. These clusters are capped by up to 5 H atoms (determined by 1H NMR spin counting) and attached to the zeolite framework through SiO x linkages (determined by Si K-edge XANES). The average size of the resulting silicon clusters is 12 ± 2 Si atoms (determined by XPS and Si K-edge XANES). The encapsulated Si clusters are air-stable and exhibit a room-temperature photoluminescence in the green-yellow region with a peak energy at ∼2.2 eV. The HOMO−LUMO energy gap in the Si cluster is estimated to be 2.2 eV, from a comparison of the band edges of the Si clusters and bulk Si (c-Si) (determined by synchrotron photoabsorption (Si K-edge XANES) and photoemission spectroscopies). The close correspondence of the HOMO−LUMO energy gap and the photoluminescence peak energy confirms the origin of luminescence from the Si cluster as a predominantly electron−hole radiative recombination process.

High-resolution variable-energy photoelectron spectra of Os(CO)5 and Os(CO)4PMe3 are reported. Using variable-energy synchrotron radiation, both the metal 5p → 5d resonance and the Cooper minimum effect are observed on the osmium 5d orbitals, and they have been successfully used to assign the osmium 5d-based bands. The Xα-SW calculation for Os(CO)5 is used to assign the valence level molecular orbitals. Experimental branching ratios of Os(CO)5 agree well with the theoretical results from both Xα-SW and Gelius methods. The electronic structure of Os(CO)5 from the present study is shown to be similar to that of Fe(CO)5, both of which have a trigonal-bipyramidal structure. The binding energies of the Os 5p core level have been determined, which are shown to be important in the observation of 5p → 5d resonances. Both vibrational and ligand field splittings are shown to be important in the line broadening in the high-resolution Os 4f core level spectra. The chemical shifts of valence and core levels for Os(CO)5 and of Os(CO)4PMe3 are compared.

Can. J. Chem. 58,694 (1980). N,, binding energies for 36 pyridines substituted at the 2-, 3-, and 4-positions have been determined by X-ray photoelectron spectroscopy. The differences in BE relative to pyridine are analysed in terms of existing theoretical approaches (electrostatic, ground potential, and relaxation potential models) and compared with ABEc,, values calculated for analogous monosubstituted benzenes. One finds good correlations of &BENls with solution determined o-substituent values although some substituent values deviate from the correlation probably due to solution effects which are not present in the gas phase. Correlations between ABENIS and 14W nmr chemical shifts are poor, particularly for electron withdrawing substituents. The relationship between BEN,, and gas phase basicity values (AGO) is good, and it appears as if the BENls is more sensitive to the substituent than AGO. MIND013 calculations on the methoxypyridines and their conjugate acids employing full geometry optimizations are presented and analysed in order to determine the effect of geometric relaxation on the gas phase basicity. R. S. BROWN et A. TSE. Can. J. Chem. 58,694(1980). On a determine les energies de liaison N,, de 36 pyridines substituees en positions 2 , 3 et 4 par la spectroscopie photoelectronique de rayons-X. On a analyse la difference des EL relatives a la pyridine en fonction d'approches theoriques existantes (modeles electrostatique. de potentiel de I'etat fondamental et de potentiel de relaxation) et on les a comparees aux valeurs de AELc18 calculees pour les benzenes monosubstitues analogues. On trouve de bonnes correlations entre les &ELN,, et les valeurs o des substituants determinees en solution bien que certaines valeurs de substituants devient de la correlation probablement par suite des effets de solution qui ne sont pas presents dans la phase gazeuse. Les correlations entre les AELN,, et les deplacements chimiques en rmn I4N ne sont pas bonnes, particulierement dans le cas des substituants electroattracteurs. La relation entre les ELNIa et les valeurs de basicitt de la phase gazeuse (AGO) sont bonnes et il semble que les ELN18sont plus sensibles aux substituants qu'aAGO. On presente des calculs MINDO/3 sur les methoxypyridines et leurs acides conjugues en utilisant une optimisation maximale de la geometrie et on les analyse dans le but de determiner l'effet de la relaxation geometrique sur la basicite de la phase gazeuse.[Traduit par le journal]

Density functional theory calculations were carried out on the transition metal phosphorus monoxide complexes (CO) 12 PO] -, and [Ru 5 (CO) 15 PO] -. The results indicate that π-bonding dominates the interaction of PO with transition metal clusters and that electrostatic effects, as well as orbital interactions, have a significant influence on the PO bond strength and can lead to IR frequencies above that of free PO.