Spin-resolved NOCV analysis of the zeolite framework influence on the interaction of NO with Cu(i/ii) sites in zeolites

In the present work the function of a zeolite framework in modifying the properties of copper sites has been studied. The [Al(OH)4CuNO]0/+ systems were studied by applying the analysis of the electron density flows – contributions to deformation density between two interacting fragments. The systems were divided in the following partition scheme: the first fragment, [Al(OH)4]− (tagged T1), and the second one, [CuNO]+/2+. The analysis allowed us to elucidate the function of the zeolite fragment in modification of the cation properties towards activating the NO molecule. For both [(T1)CuNO]0/+ systems several channels showing the role of the zeolite framework have been identified. The geometry of the adducts influences either the efficiency of the channels or spin polarization. The two most important channels, zeolites–cations, influence the flow of electrons between the copper site and the antibonding NO orbitals. One channel favors the π-backdonation in the plane perpendicular to the Cu–N–O plane while the other contribution influences the π-backdonation in the C–N–O plane. The first one is found only in the system with copper(I) and it is essential for facilitating the π-backdonation and activating the NO molecule. The second channel is spin sensitive for both copper(I) and copper(II) sites. In the case of the system with copper(I) the second channel favors the π-backdonation while in the system containing copper(II) the direction of these flows is opposite for α and β electrons.