Here we demonstrate that neat reactions of amphoteric azoles with more basic azoles give a family of finely tunable, nonstoichiometric liquids which are useful for N-donor coordination chemistry. Reacting 4,5-dicyanoimidazole (4,5-DCNIm) with 1-methylimidazole (1-mim) gives new compounds with composition-dependent speciation. Two crystalline compounds, a 1:1 protic salt, [H(1-mim)][4,5-DCNIm], and a 1:2 salt co-crystal, [H(1-mim)][4,5-DCNIm]⋅4,5-DCNIm, were isolated and structurally characterized, while differential scanning calorimetry revealed both suppression of crystallization and the presence of neutral and anionic species in the melt. Reactions of Cu(NO3 )2 ⋅2.5 H2 O, CuO, and ZnO with the neat 2:1 1-mim/4,5-DCNIm melt resulted in the isolation of entirely N-donor ligated complexes of the formula M(4,5-DCNIm)2 (1-mim)4 (M=Cu, Zn).

We investigated whether the relatively Lewis basic imidazole-2-thiones could be used to substitute water ligands bound to f-element cations and generate f-element soft donor complexes. Reactions of 1,3-diethylimidazole-2-thione (C 2 C 2 ImT) with Nd(NO 3 ) 3 •6H 2 O and UO 2 Cl 2 •3H 2 O led to the isolation of the anhydrous thione complexes Nd(NO 3 ) 3 (C 2 C 2 ImT) 3 and UO 2 Cl 2 (C 2 C 2 ImT) 2 , characterized by single crystal X-ray diffraction. Differences in the strength of metal−thione interactions have been examined by means of the crystal structure analysis and density functional theory (DFT) calculations. The C 2 C 2 ImT ligands were found to be affected by both coordination and noncovalent interactions, making it impossible to deconvolute the effects of one from the other. Calculated partial atomic charges indicated greater ligand-to-metal charge transfer in the [UO 2 ] 2+ complex, indicative of a stronger interaction. The reactivity of C 2 C 2 ImT demonstrates its usefulness in the preparation of f-element soft donor complexes from readily available hydrates that could be useful intermediates for promoting the coordination and studying the effects of soft donor anions.

Despite only being able to directly measure the solid state, single crystal X-ray diffraction is of use in understanding how the fully ionic environment of an ionic liquid (IL) affects complexation of rare earth element ions. Here we examine crystal structures of ionic lanthanide complexes as case studies in this context. The complexation of a dithiophosphate IL is compared to non-IL systems, where the crystal structure illustrates the formation of hydrophobic domains despite the presence of highly charged ions. The crystal structure of a lanthanum complex with 1,2-di(4-pyridyl)ethylene illustrates how a large, neutral ligand in a fully ionic system interrupts the ionic packing, leading to the inclusion of noncoordinating ligands in the outer coordination sphere. The crystal structure of a salt composed of discrete terbium and thorium complex ions illustrates how in two metal ions in a fully ionic environment need not be bridged directly with a ligand but can be linked entirely through noncovalent interactions. Because ILs are fully ionic systems, these effects can be interpreted in the context of rare earth element behavior in ILs.

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