Mononuclear–Dinuclear Equilibrium of Grafted Copper Complexes Confined in the Nanochannels of MCM‐41 Silica

Following the structural concept of copper‐containing proteins in which dinuclear copper centers are connected by hydroxide bridging ligands, a bidentate copper(II) complex has been incorporated into nano‐confined MCM‐41 silica by a multistep sequential grafting technique. Characterization by a combination of EPR spectroscopy, X‐ray photoelectron spectroscopy (XPS), UV/Vis spectroscopy, IR spectroscopy , and solid‐state 13C and 29Si cross‐polarization magic‐angle spinning (CP‐MAS) NMR suggests that dinuclear Cu complexes are bridged by hydroxide and other counterions (chloride or perchlorate ions), similar to the situation for EPR‐undetectable [CuII⋅⋅⋅CuII] dimer analogues in biological systems. More importantly, a dynamic mononuclear–dinuclear equilibrium between different coordination modes of copper is observed, which strongly depends on the nature of the counterions (Cl−or ClO4−) in the copper precursor and the pore size of the silica matrix (the so‐called confinement effect). A proton‐transfer mechanism within the hydrogen‐bonding network is suggested to explain the dynamic nature of the dinuclear copper complex supported on the MCM‐41 silica.