Polarization-dependent X-ray absorption spectroscopic study of [Cu(cyclam)]2+-intercalated saponite

The [Cu(cyclam)](2+) (copper-1,4,8,11-tetraazacyclotetradecane)-saponite complex has been obtained by an ion exchange reaction, and a thin film for the [Cu(cyclam)](2+)-saponite complex has been prepared by spin-coating onto glass slides. The orientation and the structural change of the guest complex ion in the interlayer space of saponite have been investigated using X-ray diffraction (XRD) and polarization-dependent X-ray absorption spectroscopy (XAS). The interlayer thickness of 3.75 Angstrom from XRD analysis suggests that the copper complex ions are intercalated as a monolayer with the square planes of (Cu-N-4) parallel to the silicate layers. Angle-resolved Cu K-edge XAS from 10 to 80degrees for the incident beam shows the well-resolved peak intensity variation of the xy (in-plane) and z (out-of-plane) components. From the polarized Cu K-edge X-ray near-edge spectroscopic (XANES) analysis, all the peaks can be assigned to the in-plane and out-of-plane components. The change of the bonding character also can be explained by the amount of LMCT (ligand-to-metal charge transfer). The Cu-N bonds in the [Cu(cyclam)](2+) complex within the interlayer space of saponite show more covalent character compared to those of [Cu(cyclam)j(ClO4)(2) but less covalent character compared to those of [Cu(cyclam)]-montmorillonite and [Cu(cyclam)]-hectorite, which is attributed to the amount of LMCT due to the difference in the magnitude of the layer charge of these clays as well as the difference in the origin of the layer charge of the silicate.