Accessing Lanthanide Tricyanomethanide Coordination Polymers Using Ionic Liquids

High Resolution Image Download MS PowerPoint Slide In contrast to alkaline, alkaline earth, and transition metals, tricyanomethanide complexes of f-elements are largely underexplored mainly due to synthetic challenges originating from the harder Lewis acidic character of the trivalent cations; only one crystal structure of an f-element-tricyanomethanide complex has ever been reported. Here, we report that by using the tricyanomethanide-based ionic liquids (ILs) 1-butyl-4-methylpyridinium tricyanomethanide ([C 4 mpyrid][TCM]) or 1-ethyl-3-methylimidazolium tricyanomethanide ([C 2 mim][TCM]), we have identified a way to begin building a library of 1D and 2D lanthanide/tricyanomethanide coordination polymers, although not yet in an optimized, controllable fashion. Saturation of NdX 3 ·6H 2 O (X = Cl – or [NO 3 ] − ) over 100 °C in [C 4 mpyrid][TCM] or [C 2 mim][TCM] followed by slow cooling allowed for the crystallization of [C 2 mim] n [Nd(NO 3 ) 2 (μ 3 -TCM)(μ 2 -TCM)(OH 2 )] n ( 1 ), [C 4 mpyrid] 2 n [Nd(μ 2 -Cl)Cl 2 (μ 2 -TCM)(TCM)(OH 2 )] n ( 2 ), [C 4 mpyrid] n [Nd(μ 2 -TCM) 2 (TCM) 2 (OH 2 ) 3 ] n ( 3 ), and [C 4 mpyrid] n [NdCl 2 (μ 2 -TCM) 2 (OH 2 ) 2 ] n ( 4 ) as anionic chains ( 2, 4 ) or layers ( 1, 3 ). Compound 3 could be isolated either by saturation and heating of Nd(NO 3 ) 3 ·6H 2 O or by reheating the reaction mixture leading to 2 . The use of [TCM] − -based ILs as solvent and sources of the coordinating ligand provides a method to promote f-element-[TCM] − complexation without the use of competing O-donor solvents or high temperatures, potentially opening a new route to structurally characterize [TCM] − complexes of the entire lanthanide series. Although these products were not synthesized in high yields, their isolation provides clues on how to modify and optimize the syntheses to obtain specific f-element-[TCM] − targets. This, in turn, should ultimately lead to dramatic diversification of the body of f-element-[TCM] − complexes available for study.