Thermally activated transformation of the adsorption configurations of a complex molecule on a Cu(1 1 1) surface

Temperature-dependent transformations of the adsorption configuration of a molecule containing 2,2′:6′,2″-terpyridine (terpy) end-groups on a flat Cu(1 1 1) surface are studied by a combination of scanning tunneling microscopy (STM) experiments and density functional theory (DFT) calculations. Several quite different adsorption configurations are detected for the terpy end-group, including flat physisorption, distorted chemisorption through N-Cu bonds, and H-dissociative chemisorption through N-Cu and C-Cu bonds. These illustrate and explore various bonding modes of molecules at surfaces, which also imply a greater richness of reaction pathways, both of which are of central importance in a wide variety of heterogeneous catalytic processes on metal catalysts. As deposited on the cold substrate (near 77 K), the molecules are preferably chemisorbed on the surface through N-Cu bonds. With increasing annealing temperature, the molecules are converted to a physisorption configuration at and above 300 K, and above 370 K a small fraction of molecules undergoes dehydrogenation and chemisorb on the surface through N-Cu and C-Cu bonds. The present study demonstrates that the combination of STM measurements and DFT calculations is very effective for probing the atomic details of molecular adsorption configurations on surfaces. © 2011 Elsevier B.V. All rights reserved.