Silver thiolato complexes grafted on silica and dissolved in organic solution

Abstract

The formation of a covalent, stable, silver-thiolato bond was used to compare the coordination of the silver cation with mercaptopropylsilane molecules grafted on silica and dissolved in organic solvents. The characterization of the homemade ≡SiLH trap, performed by DRIFT, ²⁹Si- and ¹³C-CP-MAS-n.m.r., showed the presence of a ligand monolayer on the silica surface. This ligand was characterized by its free S—H function. The coordination of Ag⁺ ions was illustrated by the color change of the surface from white to yellow, the disappearance of the S—H vibration and the downfield shift of the carbon atoms located near the S atom. All these changes were also observed for the silver thiolates synthesized in homogeneous medium. Three molecular complexes were isolated as yellow solids and characterized using physicochemical techniques. Monomeric [HNEt₃][Ag(NO₃)L²] (1), tetrameric (AgL²)₄ (2) and trimeric (AgL³)₃ (3) species, each with a linearly coordinated silver cation, were proposed. L²H, (MeO)₃Si(CH₂)₃SH, and L³H, N(C₂H₄O)₃Si(CH₂)₃SH, are respectively trimethoxysilyl- and silatranyl- propanethiols. The silver salt and the steric hindrance of the ligand influenced the nuclearity of the molecular silver complexes. Optimization of the ≡SiLH trapping conditions with pH and time indicated that the best trapping of the Ag⁺ cation was performed for pH values 5–7 and 30 min in batch experiments. Safety discharged waters were obtained after percolation through an ≡SiLH filled column. The mercaptopropyl-modified silica gel was regenerated with a 1 M thiourea solution at pH 1.