The obvious question is whether the stronger ethylene binding to the quasi-planar LM1 structure is sufficient to drive prismatic-to-quasi-planar isomerization of the cluster framework. It is not feasible to compute that barrier, however, there are several points that support the idea that ethylene-loaded Pt7 does adopt a quasi-planar structure. Fig. shows that the number of ethylene molecules that adsorb per Pt atom ranges from 0.53 for Pt4 to 0.56 for Pt7 to 0.45 for Pt11, suggesting that Pt7 exposes all Pt atoms to reactants, and only Pt11 retains its 3D structure when ethylene-saturated. The fact that ~4 ethylene molecules adsorb per Pt7 increases the tendency to isomerize to quasi-planar structures during ethylene exposure, as we have shown previously.