Theoretical study of interaction of small clusters of IrPt with H-2

The study of the interaction of small clusters of IrPt with H-2 is reported here through ab initio multiconfiguration self-consistent field (MC-SCF) c alculations, plus extensive multireference configuration interaction (MR-CI ), in its variational and perturbative modes. These calculations provide a cluster model for the activation of hydrogen by IrPt bimetallic catalysts. First, we studied the IrPt dimer interaction with H-2. The five lowest stat es of the IrPt dimer are: (2)Sigma (+), (2)Delta (xy), (4)Pi (yz), (4)Sigma (+), and (4)Delta (xy). For the IrPt dimer interaction with H-2, we found that the IrPt dimer for both metal sides is able to capture the H-2 molecul e without any activation barriers, relaxing the H-H bond. The IrPt2 trimer interaction with H-2 was also studied. The ground and the lowest states of the IrPt2 trimer are a (4)A(1) electronic state and a B-4(2) electronic sta te, respectively. We found that for both metal sides, the IrPt2 cluster in its ground (4)A(1) and the low-lying B-4(2) electronic states can spontaneo usly capture and break the hydrogen molecule. Large H-H relaxation is obtai ned and no activation barriers were found. (C) 2000 John Wiley & Sons, Inc.