Exceptional Affinity of Nanostructured Organic–Inorganic Hybrid Materials towards Dioxygen: Confinement Effect of Copper Complexes

Abstract

We report the exceptional reactivity towards dioxygen of a nanostructured organic-inorganic hybrid material due to the confinement of copper cyclam within a silica matrix. The key step is the metalation reaction of the ligand, which can occur before or after xerogel formation through the sol-gel process. The incorporation of a Cu(II) center into the material after xerogel formation leads to a bridged Cu(I)/Cu(II) mixed-valence dinuclear species. This complex exhibits a very high affinity towards dioxygen, attributable to auto-organization of the active species in the solid. The remarkable properties of these copper complexes in the silica matrix demonstrate a high cooperative effect for O(2) adsorption; this is induced by close confinement of the two copper ions leading to end-on mu-eta(1):eta(1)-peroxodicopper(II) complexes. The anisotropic packing of the tetraazamacrocycle in a lamellar structure induces an exceptional reactivity of these copper complexes. We show for the first time that the organic-inorganic environment of copper complexes in a silica matrix fully model the protecting role of protein in metalloenzymes. For the first time an oxygenated dicopper(II) complex can be isolated in a stable form at room temperature, and the reduced Cu(2) (I,I) species can be regenerated after several adsorption-desorption cycles. These data also demonstrate that the coordination scheme and reactivity of the copper cyclams within the solid are quite different from that observed in solution.

Mesoporous Silica Functionalized by Cyclam–Metal Groups: Spectroscopic Studies and Numerical Modeling

“…magneto-optical switchers and bi-sensors [1][2][3], drug delivery controllers [4][5][6] or catalytic agents [7,8]. Thus, the considered materials are the subject of broad field of investigations [9][10][11][12] since the functionalities can be tuned by changing the nature of the functional groups such as nanoparticles [13], magnetic clusters [14], organic or organometallic molecules [15]. Besides, these materials can be prepared by incorporating several classes of organic chelates depending on the targeted property [16][17][18][19].…”

Reversible Coordination of Dioxygen by Tripodal Tetraamine Copper Complexes Incorporated in a Porous Silica Framework

“…Notably, the use of a polysilylated ligand, which has its hydrolyzable functions held apart from each other often leads to solids that are functionalized inside their framework and not in the pores. [44,66] Contrary to the macrocycles whose conformation is preserved from solution to the solid state, [35,46] the structure of TREN derivatives is obviously modified during each synthetic step, owing to their linear structure and geometric constraints resulting from the polycondensation reactions occurring during the sol-gel process. Thus, the tripodal topology of the ligand is not preserved in the sol-gel material.…”

“…[55] Thenceforth, a huge number of PMOs were prepared with rigid organic groups such as benzene, [56,57] biphenyl, [58,59] or ethylene, [60] but less is known about PMOs functionalized in their framework by linear [51,[61][62][63][64][65] or cyclic polyamine, [43][44][45]66] or other chelating agents. [67] The few complexation studies of PMOs functionalized by polyamines, such as cyclam, [35,44,45,66] or linear amines [61,62,65,68] reveal very promising results. However, to date the tripodal TREN amine has never been incorporated into the framework of hybrid silicas.…”

“…[36,37] Contrary to materials for which tetraazamacrocycles, such as cyclam, are tethered onto the silica surface by covalent grafting or by sol-gel synthesis, [32,[38][39][40][41][42] copolycondensation of tetraalkoxysilylated cyclams gave functionalized silica incorporating cyclic polyamines [43][44][45] into their framework, and these hybrid solids have shown different and sometimes unusual coordination properties compared to their analogues in solution. [35,46] In recent work, [35] we have shown that the incorporation of tetraazamacrocycles like cyclam in silica matrices by a sol-gel process gave materials able to complex copper(II) salts. After thermal activation, copper(II) to copper(I) reduction occurred, and coordination of dioxygen took place at room temperature with a good affinity and a high selectivity over dinitrogen and carbon monoxide.…”

“…Incorporation of such species into silica-based organic-inorganic hybrids is very attractive for various applications, such as gas binding, [32][33][34][35] because the complexes immobilized within the material are expected to be more stable than the analogous ones in solution by avoiding degradation of the active species. These materials can combine the properties of the rigid and porous inorganic framework with the intrinsic reactivity of the functional groups or complexes incorporated into the silica framework.…”