Intracrystalline and Electronic Structures of Copper(II) Complexes Stabilized in Two-Dimensional Aluminosilicate

Abstract

X-ray absorption spectroscopic studies at the Cu K-edge have been performed for [Cu(en) 2 ] 2+ , [Cu(cyclam)] 2+ , and their intercalated forms of two-dimensional layer silicate to examine how the structural and electronic modifications influence the stabilization of copper complexes in the charged interlayer space. According to the EXAFS analysis, copper complex ions in the layer silicate are stabilized at the center of the siloxane ring, and negatively charged layers are likely to act as axial counteranions. It is spectroscopically confirmed that the covalent bonding character between copper and ligand is enhanced by the intercalation into the silicate layers, depending upon the kind of ligands. There is a good linear relationship between the shoulder peak position of Cu K-edge XANES spectra and d-d transition band position of UV-visible spectra, which means that the former reflects the ligand-to-metal charge transfer effect.

Polarized XANES and EXAFS spectroscopic investigation into copper(II) complexes on vermiculite

“…Two different ligand effects can alter the covalent bond strength between the Cu-equatorial ligands, and thus cause a shift in peak B. The first is a change in equatorial ligands, which changes the covalent character of the equatorial bond based on electronegativity difference between Cu and the ligand (Shadle et al, 1982;Choy et al, 1997). For example, exchanging a water molecule with a structural hydroxide from a clay-mineral edge would increase the covalent character of the equatorial bond, and thus shift peak B to a lower energy.…”

“…Furthermore, the use of polarized XANES analysis on oriented samples provides additional information on the orientation of the ligand environment. Thus, XANES analysis can be used to investigate molecular orbital configurations, angular dependence, and degree of covalent bond character of Cu complexes (Kau et al, 1987;Choy et al, 1994;Choy et al, 1997;DeBeer et al, 2000;Choy et al, 2002).…”

Elucidating the Ultrafast Dynamics of Photoinduced Charge Separation in Metalloporphyrin-Fullerene Dyads Across the Electromagnetic Spectrum

“…[61][62][63][64][65][66][67] In this relaxed state, the core hole is stabilized through additional screening due to partial charge transfer from the ligand orbital L to the half-filled metal orbital 3dx 2 -y 2 , a process generally known as shakedown. This transition denoted 1s  4p+shakedown is a sensitive fingerprint for any modification in the covalency of the metal-ligand bond.…”

“…This transition denoted 1s  4p+shakedown is a sensitive fingerprint for any modification in the covalency of the metal-ligand bond. [61][62][63][64][65][66][67] Specifically, when a molecular complex experiences a decrease in bond covalency, e.g. when the spatial overlap between the d and L energy levels diminishes, the charge transfer from the ligand to the metal occurs less efficiently, hence the shakedown process becomes less probable and the energy separation between M 1 and S decreases.…”

“…when the spatial overlap between the d and L energy levels diminishes, the charge transfer from the ligand to the metal occurs less efficiently, hence the shakedown process becomes less probable and the energy separation between M 1 and S decreases. [64][65][66][67][68] Consequently, a relative shift of S to higher photon energy directly reflects a decrease in bond covalency. Figure 3b (blue trace) shows the difference spectrum between the static X-ray absorption coefficients of Cu II P-C 60 and Cu II P acquired under the same experimental conditions.…”