De Anda, Elisa. Ligand substitutions of trinuclear rhodium (III) clusters. 2020.
Kinetic data regarding the exchange of bridging acetate groups from Rh3ClO4 with deuterated acetic acid was obtained through 1H-NMR analysis. The scheme depicted the replacement of terminal water molecules with deuterated acetic acid, as well as the exchange of the bridging acetate groups.
Kinetic experiments were conducted at four temperatures: 23 °C (in duplicate), 37 °C, 40 °C, and 45 °C. The duration of data collection ranged from 3 hours for the higher temperatures to 60 hours for the lower temperatures. The stacked 1H-NMR spectra from the 45 °C experiment was presented. Several signals are associated with the bridging groups due to the different substituted species of the cluster in solution, primarily resulting from the replacement of terminal waters with deuterated acetic acid.
The substitution of ligated waters leads to the presence of three species in solution: monosubstituted, disubstituted, and trisubstituted forms. Signals corresponding to the bridging acetate groups appear between 2.25 ppm and 2.35 ppm. Within this range, a notable decrease in signal intensity over time reflects the exchange of the bridging acetate groups, [Rh3(μ3-O)(μ-OOCCH3)6(H2O)3]+, with deuterated acetic acid, [Rh3(μ3-O)(μ-OOCCD3)6(H2O)3]+. Concurrently, an increase in the intensity of the signal at 2.04 ppm was observed, attributed to the formation of free acetate (-OOCCH3) ions in solution. Data concerning the exchange of the bridging acetates were quantified by integrating the signals corresponding to the starting material, Rh3+, within the 2.25 ppm to 2.35 ppm range.
Wachter, Nanette M., et al. NMR Spectroscopy in the Undergraduate Curriculum, 2021. 137-148.