Synthesis and Characterization of a Novel Quinoxaline-Substituted vic-Dioxime and Its Complexes Containing Bis(12-Diazacrown-4) Derivatives

A new quinoxaline-substituted vicinal dioxime ligand containing bis(12-diazacrown-4) units (H2L) was synthesized by the reaction of cyanogen di-N-oxide with compound 4. Mononuclear NiII and CuII complexes with a metal:ligand ratio of 1:2 for H2L and a trinuclear CuII complex were also synthesized. The mononuclear CuII species coordinated to two CuII ions through the deprotonated oximate oxygens to yield a trinuclear structure cis-bridged by the oximate groups, with 1,10-phenanthroline as an end-cap ligand. The mononuclear CoIII complex of H2L was isolated with pyridine and chlorine as axial ligands. In addition, a CoIII complex containing the BF2+ bridge macrocycle was synthesized using a precursor hydrogen-bridged CoIII complex via a template effect. The extraction abilities of 1, 3, and 11 were also evaluated in 1,2-dichloroethane by using several alkali (Li+, Na+, K+, and Cs+) and transition-metal picrates, such as Ag+, Pb2+, Cd2+, Cu2+, and Zn2+. Structures of the ligands and metal complexes were solved by elemental analyses, 1H and 13C NMR, FT-IR, UV–vis, and mass spectra.