Search

The strongly hydrogen bonded species (CH3)2SOH3O+formed in concentrated hydrochloric acid displays a new low energy feature in its sulfur K-edge X-ray absorption near edge structure (XANES) spectrum. Density Functional Theory-Transition Potential (DFT-TP) calculations reveal that the strong hydrogen bonding decreases the energy of the transition S(1s) → LUMO, which has antibonding σ*(S–O) character, with about 0.8 eV. Normal coordinate force field analyses of the vibrational spectra show that the SO stretching force constant decreases from 4.72 N cm−1in neat liquid dimethyl sulfoxide to 3.73 N cm−1for the hydrogen bonded (CH3)2SOH3O+species. The effects of sulfur coordination on the ambidentate dimethyl sulfoxide molecule were investigated for the trans-Pd((CH3)2SO)2Cl2, trans-Pd((CD3)2SO)2Cl2and cis-Pt((CH3)2SO)2Cl2complexes with square planar coordination of the chlorine and sulfur atoms. The XANES spectra again showed shifts toward low energy for the transition S(1 s) → LUMO, now with antibonding σ*(M–Cl, M–S) character, with a larger shift for M = Pt than Pd. DFT-TP calculations indicated that the differences between the XANES spectra of the geometrical cisand transisomers of the M((CH3)2SO)2Cl2complexes are expected to be too small to allow experimental distinction. The vibrational spectra of the palladium(II) and platinum(II) complexes were recorded and complete assignments of the fundamentals were achieved. Even though the M–S bond distances are quite similar the high covalency especially of the Pt–S bonds induces significant increases in the S–O stretching force constants, 6.79 and 7.18 N cm−1, respectively. [ABSTRACT FROM AUTHOR]

The infrared emission spectra of CO adsorbed on alumina-supported 1, 3, and 5 wt % Rh, Ir, and Pt metal-containing catalysts were studied at 423 and 473 K. While CO is adsorbed in dicarbonyl (dimer), linearly (on-top) bonded and bridged carbonyl forms on rhodium and platinum, the dimer form is dominant on iridium. The relative intensity of Rh−CO and Ir−CO linear bands decrease with increasing temperature compared to the intensity of the dicarbonyl bands; the corresponding bands on Pt behave the opposite way. Two dicarbonyl and two linear Pt−CO bands were identified in the infrared spectra of Pt/Al2O3 catalysts. The surface structure (kinked or planar Pt atoms), the dispersity of the metal, the temperature, and the quantity of adsorbed CO on the surfaces all have an effect on the fine structure of the Pt−CO stretching bands. The metal−carbon and CO stretching force constants were calculated for surface dicarbonyl, linearly bonded CO, and bridged carbonyl species. The metal−carbon stretching wavenumbers and force constants were predicted and compared between surface species and metal carbonyl complexes. The iridium−carbon bonds were found always stronger than the Rh−C and Pt−C ones in all surface species. The observed stretching wavenumbers and force constants seem to support the idea that CO and metal−carbon bonds are always stronger in metal carbonyl complexes than in adsorbed surface species. The distribution and mode of CO adsorption on surface metal sites can be effectively studied by means of infrared emission spectroscopy. [ABSTRACT FROM AUTHOR]