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

Abstract

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 (13)C and (29)Si 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 [Cu(II)···Cu(II)] 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 ClO(4)(-)) 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.

One-pot pseudomorphic crystallization of mesoporous porous silica to hierarchical porous zeolites

“…Elemental chemical analysis showed that the C/N molar ratio of 16.3 in the as-made sample is much less than that of 19.0 in surfactant molecule, which indicated that TPA + molecules were ion-exchanged into pore channel, in line with results in literatures [26,[42][43][44]. The TG-DTG analysis also showed that surfactant molecules and TPA molecules coexisted in the particles (Fig.…”

Chelation Gradients for Investigation of Metal Ion Binding at Silica Surfaces

“…22,23,31,32,43,44 Mono (1:1) and bis (1:2) complexes have been noted, with monocomplexes favored at low surface coverage. 22,23,31,32,43,44 Formation of tris from bis complexes is not likely given that log K 3 = −1, 31,45 while log K 1 = ∼11 and log K 2 = ∼10.…”

“…45 Several coordination environments are possible as depicted in Scheme 2, including (a) Cu 2+ coordinated to two ethylenediamine ligands to form a bis (1:2) complex; 32 (b) Cu 2+ coordinated to one ethylenediamine ligand to form a mono (1:1) complex with the other two sites filled with oxygen, possibly from silanol or Si−O−Si groups; 32 (c) Cu 2+ coordinated to four oxygens from silanol or Si−O−Si groups present on the surface; 32 or (d) dinuclear copper. 44 Option c can be discounted as the control experiments (i.e., films and gradients prepared without diamine or triamine chelating groups) showed no copper ( Figure 3D). …”

P band intermediate state (PBIS) tailors photoluminescence emission at confined nanoscale interface

“…To further prove the core role of surface ligands packing for tuning the PL of metal NCs, functional organosilanes with targeted carbonyl and amino groups in 3-(triethoxysilyl)propylsuccinic anhydride and aminopropyl triethoxysilane, respectively, were covalently grafted on mesoporous silica (Fig. 4a, b) [28][29][30] . It should be mentioned that the functional group in the targeted organosilane contains electron-rich heteroatoms, such as oxygen (O) and nitrogen (N) with unpaired lone electrons, as with protective templates for the synthesis of metal NCs, such as unconjugated polymers containing carboxylate groups, proteins and amino acid molecules with nitrogen (N), oxygen (O), sulfur (S), phosphorus (P), and others.…”