Fourier transform infrared, pump−probe polarization anisotropy, and twodimensional infrared spectroscopies were used to study the steady-state and time-dependent behavior of carbon dioxide dissolved in three different polymer systems. Gas reorientation dynamics in poly(methyl methacrylate), poly(methyl acrylate), and poly(dimethylsiloxane) were sensitive to the nature of chemical interactions between the gas and polymer, as well as whether the polymer was in a glassy or rubbery phase. The homogeneous dynamics experienced by the asymmetric stretching vibration were found to be fastest for rubbery polymers with weak, nonspecific gas−polymer interactions. Spectral diffusion was absent for the carbon dioxide vibrational mode in glassy poly(methyl methacrylate) but was activated for the chemically similar but rubbery poly(methyl acrylate). The vibrational dynamics are shown to have a direct correlation with the diffusivity of carbon dioxide through the polymer matrices.
Vibrational dynamics were measured by IR pump–probe spectroscopy and two-dimensional IR spectroscopy for triruthenium dodecacarbonyl and the undecacarbonyl hydride that forms when it is encapsulated in an alumina sol–gel glass. For comparison, a triruthenium undecacarbonyl hydride salt was also synthesized and studied in neat solution to identify the potential influence of the confined solvent environment on the dynamics experienced by carbon monoxide ligands. The vibrational lifetime was found to be significantly decreased for both hydride species relative to the dodecacarbonyl compound. Conversely, spectral diffusion of the CO vibrations was measured to be faster for the parent compound. The most significant dynamic changes occurred upon transformation from the starting compound to the hydride, while only minor differences were observed between the dynamics of the freely dissolved and sol–gel encapsulated hydrides. The results suggest that the structural change to the hydride has the largest impact on the dynamics and that its improved catalytic properties likely do not originate from confined solvent effects.
Triruthenium dodecacarbonyl exhibits increased catalytic activity toward hydrogenation reactions when encapsulated in alumina sol−gels. In this study, we demonstrate structural and electronic changes induced by the encapsulation process. Fourier transform infrared (FTIR) spectroscopy reveals that the carbonyl vibrational modes dramatically red shift during aging in the sol−gel glass. These shifts are attributed to the formation of the metal hydride: [HRu 3 (CO) 11 ] − . A comparison to the FTIR spectrum of synthesized [NEt 4 ]-[HRu 3 (CO) 11 ] confirms this assignment. XPS studies show that the Ru 3d 5/2 peak of [HRu 3 (CO) 11 ] − also shifts to lower binding energy, consistent with an increased electron density on the Ru nuclei compared to Ru 3 (CO) 12 and confirmed by density functional calculations. This study should open the door to further investigations into the hydride's role in the previously observed catalytic activity. To the best of our knowledge, this is the first study to identify the presence of [HRu 3 (CO) 11 ] − in the alumina sol−gel.
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