Fig. 2: STM overviews of reaction progression.

STM topographs of the same region of a sample imaged after active Fe-tpy site preparation (a), after subsequent exposure to CO and C₂H₄ (maximum temperature during dosing 11.1 K) (b), and after successive incremental sample annealing up to T = 30 K for t = 5 min (c). Free C₂H₄ (yellow triangle) is visible on the surface, along with changes to active sites labelled “CO prebond” (grey pentagon), after gas exposure (b). After subsequent annealing of the sample at T = 30 K for t = 5 min (c) three additional distinct changes to active tpy-Fe sites are visible and labelled: “CO bond” (black five point star), “C₂H₄ prebond” (light orange hexagon), and “C₂H₄ bond” (orange six point star). After the anneal, C₂H₄ molecules can form pseudo hydrogen bonds with the nitrogen lone pairs of the distal, outward pointing pyridyl of non-metalated tpy groups (c, yellow triangle). Images shown were acquired with a metal tip at V = 20 mV and I = 20pA (a–c).