Speciation of Ionic Uranyl-Containing Complexes in in Situ Formed Dicyanonitrosomethanide-Based Ionic Liquids.

A series of ionic uranyl-containing complexes, namely [C2mim]2[UO2(ccnm)4] (1), [C4mim]2[UO2(ccnm)4] (2), [N1111]2[UO2(ccnm)4][H2O]2 (3), and [P2444]2[UO2(dcnm)2(ccnm)2] (4) [(ccnm)- = carbamoylcyanonitrosomethanide; dcnm = dicyanonitrosomethanide; (C2mim)+ = 1-ethyl-3-methylimidazolium; (C4mim)+ = 1-butyl-3-methylimidazolium; (N1111)+ = tetramethylammonium; (P2444)+ = tributyl(ethyl)phosphonium)], were isolated from in situ formed dcnm-based ionic liquids and characterized systematically. It was found that the dcnm anions transformed into ccnm anions during the reactions. These anions coordinate with the uranyl cations in chelate or terminal monodentate coordination mode, affording negative divalent complex anions which can combine with different organic cations and form ionic uranyl-containing complexes. Plenty of C-H···O, N-H···O, C-H···N, N-H···N, and H···H weak interactions are formed in the crystal structures. The transformation of cyano to amide groups contributes to the crystallinity and leads to higher melting points as well as the luminescence quenching of these compounds.