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The cobalt center in HCo(CO)4 exchanges with those in Co2(CO)g through a facile hydride ligand transfer reaction which has been studied by 59Co NMR line-shape analysis over the temperature range of 80 to 200 °C and total system pressures up to 370 atm in supercritical carbon dioxide. The lifetime of the cobalt center in HCo(CO)4 varies from 2 ms at 80 °C to 10 ns at 200 °C, exhibiting an activation energy of 15.3 ± 0.4 kcal/mol. The hydride ligand transfer process is highly specific for the HCo(CO)4 and Co2(CO)g complexes. Thus, neither Co4(CO)i2 nor MnCo(CO)g exhibit measurable chemical exchange line broadening in the 59Co NMR spectra within solutions where the resonances for HCo(CO)4 and Co2(CO)g coalesce. In addition, the full peak widths at half-height (W\¡i) for the hydride, dihydrogen, and water resonances vary by less than 3 Hz in the NMR spectra, while the line widths (IVi/2) for the HCo(CO)4 and Co2(CO)g resonances broaden by more than 15 000 Hz in the 59Co NMR spectra. A similar hydride ligand transfer reaction exchanges the hydride moieties in HCo(CO)4 and HMn(CO)s. This latter heterometallic hydride ligand transfer reaction has been investigated by *H NMR line-width analysis over the temperature range of 110 to 190 °C at two initial carbon monoxide concentrations, 1.39 and 4.13 M. The lifetime of the hydride moiety on the manganese center in the heterometallic hydride ligand transfer reaction between HCo(CO)4 and HMn(CO)s is independent of the carbon monoxide pressure and exhibits an activation energy of 19 ± 1 kcal/mol. The 55Mn NMR spectra indicate no measurable exchange (less than 30 transfers per second) between the manganese centers in HMn-(CO)5, MnCo(CO)g, and Mn2(CO)i0 under the same reaction conditions, where the hydride moieties in HMn(CO)5 and HCo(CO)4 are undergoing facile exchange (greater than 104 transfers per second) as evident in the *H NMR spectra. This lack of measurable exchange between the manganese centers in fíMn(CO)s, MnCo(CO)g, and Mn2-(CO)io is inconsistent with an oxidative addition reaction mechanism for the heterometallic hydride ligand transfer reaction. Alternatively, the kinetics of these hydride ligand transfer reactions are interpreted in terms of a hydrogen atom transfer reaction mechanism involving *Co(CO)4 and "Mn(CO)5 radicals. Thus, the degenerate hydrogen atom transfer reaction between HCo(CO)4 and *Co(CO)4 proceeds with activation parameters of AH* = 5.5 ± 0.6 kcal/mol and AS* = -16 ± 1 cal/(K-mol), while the endothermic hydrogen atom transfer from manganese in HMn(CO)5 to cobalt in "Co(CO)4 exhibits an activation enthalpy of 10 ± 1 kcal/mol. In addition, the kinetics for the ligand exchange reaction between the coordinated carbonyl groups in Co2(CO)g and free carbon monoxide has been studied in mesitylene solvent by 13C NMR line-shape analysis over the temperature range of 100 to 180 °C under 8.2 M of carbon monoxide.In this temperature range, the free carbon monoxide ligand exhibits a strongly temperature-dependent chemical shift in the presence of Co2(CO)g. T...

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The characterization of pore networks is extremely important in understanding transport and storage phenomena in unconventional gas and oil reservoir rocks. An ultrasmall-angle X-ray scattering (USAXS) measurement has been performed on Silurian black shales from the Baltic Basin, Poland, from a wide range of depths along a burial diagenetic sequence. This study provides insight into the nature of the pore structure, including the pore size distribution, total porosity, and fractal dimensions of the rocks. Samples were measured in both their air-dried state, equilibrated at ∼50% relative humidity, and prior to dehydration by drying at 200°C to make a comprehensive comparison of the pore structure changes induced by dehydration. Two trends were observed: porosity values decreased with depth as expected from the models of porosity evolution with burial and increased upon sample dehydration. The USAXS-measured porosity values show very good correspondence with the measurements by immersion porosity methods. The increase in porosity upon dehydration was found to be dominated by a volume increase in the pores of 100−1000 nm diameter; the pores were filled by capillary water and clay-bound water in the air-dry state and liberated during drying. The geometric irregularities of pore−shale rock interfaces have been quantified by fractal dimension. The removal of water from the sample also serves to increase the fractal dimension suggesting that the removal of water molecules increases the surface or mass irregularity. Implications to shale porosity measurement and shale gas models are discussed.