ADSORPTIONS OF CH4 AND C2H4 ON MOP-28 BASEDCLUSTERS: A COMBINED QM AND QM/MM STUDY

摘要

The adsorption properties of CH4 and C2H4 on MOP-28 based clusters have beeninvestigated by quantum mechanics (QM) and QM/MM approaches. The quantumclusters of the reaction center termed "paddlewheel" and "paddlewheel-ligand" arestudied at the B3LYP/6-31G(d, p) level of theory. The environmental framework of theMOP-28 is included via a QM/MM model, where the QM has been represented by usingthe B3LYP while the MM is well represented by a well-calibrated universal force field,UFF. Thiophene as a ligand was found to polarize the paddlewheel. From the populationcharge analysis, thiophenes induced the electron transfer in the "paddlewheel" from its Catoms to 0 atoms, and passing over to Cu atoms. Their adsorption energies in both QMand QM/MM approaches are in the order of CH4 (-1 kcal/mol) < C2H4 (-6 kcaUmol). Thevan der Waals contribution due to the environmental framework of the MOP-28 for allcomplexes can be accounted for up to, at most, 20% of their interactions. The combinedinteractions of the p-bond of the alkene molecule with Cu and backbonding of the metalto alkene have been nicely demonstrated by the natural bond orbital (NBO) analysis.