Reactivity of CO on Ni4 cluster- effect of spin multiplicity and H doping-A DFT investigation

Abstract

We investigated the reactivity of carbon monoxide on tetrahedral Ni4 clusters at different spin multiplicity applying density functional theory calculations considering pure and hybrid functional. The stability of the clusters increases with the increasing spin multiplicity and doping hydrogen in Ni4 cluster. The adsorption or binding energy of CO on Ni4 cluster is thermodynamically feasible process at normal condition whereas dissociation is not feasible. Ab initio molecular orbital analysis shows the orbital overlaps are observed at bridging site, three fold sites, and tetra coordinated centre and formation of δ-bond in the cluster. In NBO analysis, CO binds strongly to the Ni4 cluster not only by two NiC bond (spd hybrid), but also donor-acceptor delocalization interactions, for example, σ type BD(CO) → BD*(NiC) and BD(NiC) → BD*(NiC/CO), two π-type BD(CO) → LP*(Ni) and several diffuse RY*(C) ← LP(Ni) and π*(CO) ← LP(Ni) interactions. Singlet Ni4 cluster shows highest activation energy barrier, 3 eV. H-doped Ni4 cluster decreases dissociation barrier and favors CH bond formation.