Isotopic Ligand Exchange in the High-Nuclearity Platinum Clusters (Pt24(CO)30)n and (Pt26(CO)32)n (n-0 to -6) in Dichloromethane: Substitution Kinetics, Carbonyl Dipole Coupling, and Comparisons with Pt(111) Electrodes

The effect of substituting 12CO by 13CO on the infrared spectra of (Pt24(CO)30)n and (Pt26(CO)32)n (n = 0 to -6) in dichloromethane has been studied in order to explore the nature of the ligand substitution kinetics and dynamic dipole-dipole coupling for these high-nuclearity clusters in relation to metal surfaces. The chargeable nature of the platinum clusters, as scrutinized by FTIR spectroelectrochemical tactics, offers interesting comparisons with the potential-dependent dipole coupling observed for mixed 13CO/12CO adlayers at the Pt(111)-dichloromethane interface, also reported here. Unlike the electrochemical surface, CO ligand exchange on (Pt24(CO)30)(2-) and (Pt26(CO)32) (2-) is slow and non-random, incomplete 12CO/13CO substitution occurring even on long (> several hours) timescales. Substantial deviations from first-order substitution kinetics are also observed, especially for (Pt24(CO)30)(2-) where only 65% of the CO ligands are observed to undergo exchange. (Author)