Synthesis, Properties, and Structures of Low-Melting Tetraisocyanatocobaltate(II)-Based Ionic Liquids

A series of new ionic liquids of the formula Ax[Co-II(NCO)(4)] with the [CoII(NCO)(4)](2-) anion and nitrogen-based organic cations (A) were synthesized. The single-crystal structures of all of the compounds were determined by X-ray diffraction, and the presence of discrete ions was revealed for all cases. At room temperature, these compounds exhibit paramagnetic behavior owing to the presence of high-spin tetrahedrally coordinated CoII ions. The melting points or glass-transition temperatures are in the range for ionic liquids for some of the compounds with singly charged cations and above 100 degrees C for all compounds with doubly charged cations and the bis(triphenylphosphine) iminium ([PPN](+)) salt. Each compound was characterized by elemental analysis as well as NMR, IR, and UV/Vis spectroscopy. Measurements of the density, dynamic viscosity, conductivity, and surface tension of the low-melting substance [EMIm](2)[Co(NCO)(4)] ([EMIm](+) = 1-ethyl-3-methylimidazolium) show that they differ slightly to the corresponding values for the isothiocyanato complexes but are generally comparable.