Babai, Arash (2006) Rare Earth Complexes in Ionic Liquids - Structures, Electrochemical and Optical Properties. PhD thesis, Universität zu Köln.
The thesis presented here deals with solvent-solute interactions of rare-earth ions in bis(trifluoromethanesulfonyl)amide ([Tf2N)- and trifluoromethanesulfonate ([OTf])-based ionic liquids (IL). In order to elucidate the process of solvatation, rare earth iodides, triflates and bis(trifluoromethanesulfonyl)amides are synthesized as precursors and reacted with [Tf2N]- and [OTf]-based ionic liquids, containing substituted pyrrolidinium or imidazolium heterocycles as cations. Interaction of NdI3 with the room temperature ionic liquid (RTIL) 1-butyl-1-methylpyrrolidinium [Tf2N] ([bmpyr][Tf2N]) leads to the formation of the sparingly soluble compound [bmpyr]4[NdI6][Tf2N], the anion of the RTIL being incorporated in the structure in a non-coordinating fashion. By displacing the butyl chain in [bmpyr]+ by a methyl group, the compound [mppyr]3[NdI6], a [Tf2N]-free compound is obtained. The solvatation of the other trivalent iodides of the rare-earth elements leads to similar compounds with the composition [bmpyr]4[LnI6][Tf2N] (Ln = La, Pr, Sm, Dy, Er) in which the metals are coordinated octahedrally by iodine atoms. A structural change is observed between Pr and Nd, which is manifested in the arrangement of the [LnI6]-ocahedra with respect to each other. The coordination mode of the [Tf2N]-anion was determined by reaction of Ln(Tf2N)3 with [bmpyr][Tf2N]. X-Ray structure determinations reveal that [bmpyr]2[Ln(Tf2N)5] is formed for the larger lanthanides (La-Tb), whereas the smaller ones (Dy-Lu) are coordinated by four ligands in [bmpyr][Ln(Tf2N)4]. The RTIL 1-butyl-1-methylimidazolium [Tf2N] ([bmim][Tf2N]) reacts with Eu(Tf2N)3 to give a lanthanide-based RTIL [bmim][Eu(Tf2N)5] (glass-transition point: -50°C). Ligand exchange examinations reveal that [OTf]-anions are able to displace [Tf2N]-ligands. For example the compound [bmpyr]4[Yb(OTf)6][Tf2N] can be crystallized from Yb(Tf2N)3 and [bmpyr][OTf]. Simple halides of the salt-like divalent rare-earth dissolve in [Tf2N]-based ILs under complete ligand exchange as can be shown by the formation of [mppyr]2[Yb(Tf2N)4] from YbI2 and [mppyr][Tf2N]. In addition, [mppyr]2[AE(Tf2N)4] (AE = Ca, Sr) and [mppyr][Ba(Tf2N)3] were synthesized as model compounds for the larger divalent lanthanides (Eu, Sm).
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