Measuring Relative Energies of Ligand Binding Conformations on Nanocluster Surfaces with Temperature-Dependent FTIR Spectroscopy

We present a method to measure relative energies betweenbindingconformations of carboxylate ligands on InP magic-sized clusters in solution. Using Markov chain Monte Carlo global fitting analysison temperature-dependent vibrational spectra of cluster-bound ligands,we observe significantly different relative energies between variousbidentate and monodentate binding motifs. Relative to the monodentatemotif, the chelating conformation is 0.7 & PLUSMN; 0.3 kcal/mol morestable and the syn-syn bridgingconformation is 1.1 & PLUSMN; 0.5 kcal/mol more stable, but the syn-anti bridging conformation exhibitsno significant difference. Our results demonstrate that the relativeenergy between monodentate-bound carboxylates and unbound carboxylicacids is 4.52 & PLUSMN; 0.05 kcal/mol, or 1582 & PLUSMN; 19 cm(-1), nearly identical to the carboxylate asymmetric stretching frequency.We suggest that the ligand vibrational energy may play a key rolein ligand dissociation by compensating for energy differences betweenbound and dissociated ligand states. This approach gives importantexperimental insights into ligand binding and can inform future nanocrystalsurface engineering.