Ion solvation and hydrogen bonding in Eu 3+-doped mono-urethanesil hybrids carrying pendant short polyether chains

Abstract

Sol–gel derived Eu 3+-doped materials based on a poly(oxyethylene)/siloxane hybrid host incorporating two coordinating functionalities (polymer ether- and cross-link carbonyl-type oxygen atoms) have been investigated by mid-infrared and Raman spectroscopies with the goal of elucidating the cation/polymer and cation/cross-link interactions and hydrogen bonding. The organic/inorganic matrix of these ormosils is composed of a siliceous backbone bonded through urethane groups to methyl end-capped polyether chains with approximately seven oxyethylene repeat units. This framework, called mono-urethanesil, has been doped with europium triflate, Eu(CF 3SO 3) 3. Xerogels with salt composition n (where n is the molar ratio of OCH 2CH 2 moieties per Eu 3+ ion) ranging from ∞ to 5 have been analyzed. The results obtained indicate that in the mono-urethanesils with n≥60 the Eu 3+ ions coordinate solely to the urethane carbonyl oxygen atoms. The first evidences of the complexation of the polyether chains to the cations have been found at a salt concentration that corresponds to n=40, that is considerably lower than the saturation level the carbonyl groups has attained (in theory at n=7). At a higher salt content (n<40), both types of cation coordination are apparent.