Accessing Lanthanide Tricyanomethanide Coordination Polymers Using Ionic Liquids

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 NdX3 center dot 6H(2)O (X = Cl- or [NO3](-)) over 100 degrees 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(NO3)(2)(mu(3)-TCM)(mu(2)-TCM)(OH2)](n) (1), [C(4)mpyrid](2n)[Nd(mu(2)-Cl)Cl-2(mu(2)-TCM)(TCM)(OH2)](n) (2), [C(4)mpyrid](n)[Nd(mu(2)-TCM)(2)(TCM)(2)(OH2)(3)](n) (3), and [C(4)mpyrid](n)[NdCl2(mu(2)-TCM)(2)(OH2)(2)](n) (4) as anionic chains (2, 4) or layers (1, 3). Compound 3 could be isolated either by saturation and heating of Nd(NO3)(3)center dot 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.