Ready access to anhydrous anionic lanthanide acetates using imidazolium acetate ionic liquids as the reaction medium.

The access to lanthanide acetate coordination compounds is challenged by the tendency of lanthanides to coordinate water and the plethora of acetate coordination modes. We developed a straightforward, reproducible synthetic procedure by reaction of lanthanide chloride hydrates with defined ratios of the ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([C 2 mim][OAc]). This reaction pathway leads to two isostructural crystalline anhydrous coordination complexes, the polymeric [C 2 mim] n [{Ln 2 (OAc) 7 } n ] and the dimeric [C 2 mim] 2 [Ln 2 (OAc) 8 ], based on the ion size and the ratio of IL used. A reaction with an IL:Ln-salt ratio of 5:1 where Ln = Nd, Sm, and Gd led exclusively to the polymeric, whilst for the heaviest lanthanides (Dy-Lu) dimeric was observed. Reaction with Eu and Tb resulted in a mixture of both polymeric and dimeric forms. By increasing the amount of IL and/or the size of the cation, the reaction led to only the dimeric compound for all the lanthanide series. Crystallographic analyses of the resulting salts revealed three different types of metal-acetate coordination modes where η 2 μκ 2 is the most represented both structure types.