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

A series of new ionic liquids of the formula Ax[CoII(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 °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. New coordination compounds consisting of tetraisocyanatocobaltate(II) anions and nitrogen‐based organic cations are investigated. Some of these compounds show very low glass‐transition temperatures and are paramagnetic metal‐containing ionic liquids.