The Electronic Structures of Small Nin (n=2-4) Clusters and Their Interactions with Ethylene and Triplet Oxygen: A Theoretical Study

Density functional theory (DFT) calculations of small nickel clusters and their interacting systems are carried out using the BLYP and B97-2 methods, after DFT calibration. All bare nickel clusters in this study have high multiplicities and are paramagnetic. Our results for the interactions between ethylene and oxygen with Ni-n (n = 2-4) clusters at different adsorption modes show that for ethylene, pi-orientation is preferred, and that oxygen adsorption in a bridge mode is stronger than on-top coordination. Vibrational frequency analysis reveals that the vibrational modes of ethylene pi-coordinated to nickel clusters converge toward the corresponding value for surfacebound ethylene, as the cluster size increases from two to four, showing that finite clusters can be used as localized models for ligand adsorption on nickel surfaces. We also calculate DFT global reactivity descriptors, chemical potential and hardness, and use these to predict the relative stability and reactivity of each bare cluster.