Size-Dependent Geometrical Structures of Platinum Oxide Cluster Cations Studied by Ion Mobility-Mass Spectrometry.

Structures of platinum oxide cluster cations (Pt n O m + ) were studied by ion mobility-mass spectrometry in combination with theoretical calculations. Structures of oxygen-equivalent Pt n O n + ( n = 3-7) clusters were discussed from the comparison between their collision cross sections (CCSs) obtained by mobility measurement and simulated CCSs of their structural candidates from structural optimization calculations. Assigned structures of Pt n O n + were found to be composed of Pt frameworks and bridging O atoms, which follows the previous theoretical prediction on the neutral clusters. The structures change from planar ( n = 3 and 4) to three-dimensional ( n = 5-7) with increasing cluster size by deforming platinum frameworks. Comparison with other group-10 metal oxide cluster cations (M n O n + ; M = Ni and Pd) showed that the Pt n O n + structures have a similar tendency to Pd n O n + rather than Ni n O n + .