Adsorption of O2 on Cobalt–(n)Pyrrole Molecules from First-Principles Calculations

概要

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In order to clarify the adsorption mechanism of the O2 molecule on Co–polypyrrole composite metallo-organic catalyst, we have investigated the interaction between the molecule and Co–(n)pyrrole model clusters ($n=4,6$) using the density functional theory. The stable adsorption site of the O2 molecule on Co–(4)pyrrole is found to be at the O–O center of mass located on top of the Co atom in side-on configuration, while for the case of Co–(6)pyrrole cluster, the O2 molecule is slightly deviated from the side-on configuration. The O–O bonds of the O2/Co–(4)pyrrole and the O2/Co–(6)pyrrole systems have elongated by 10.84 and 9.86%, respectively. The elongation mechanism of O2 on Co–(n)pyrrole is induced by the interaction between the cobalt d-orbitals and the O2 anti-bonding $\pi^{*}$ orbital, which results in a charge transfer from the cobalt atom toward the O2 molecule. This effect seems important in the adsorption of the O2 molecule on Co–(n)pyrrole. It is likely that the extra charge in the O2 molecule would fill its anti-bonding orbital and consequently weaken the O–O bond. In Co–(4)pyrrole, the elongation of the O2 bond is larger than that of Co–(6)pyrrole since a complete side-on configuration has more symmetric overlapping between the cobalt d-orbitals and the O2 anti-bonding orbital.
2009-09-15