Uranyl Complexes of Alkyl-Bridged Ditopic Diaminotetraphenol Ligands and Their Use as Uranyl Ion Extractors

The
coordination chemistry of uranyl ions was studied using long n-alkyl chain (n = 5–8) bridged
by N,N,N′,N′-tetrakis­(2-hydroxy-3-methyl-5-tert-butylbenzyl)­diaminoalkanes (H4L1–H4L4) as ligands. All ligands formed 2:1 (U-to-L ratio) complexes with
uranyl ions, but in addition 1:1 complexes could be characterized
using ligands H4L2 and H4L3. The complexes were
characterized by elemental analysis, spectroscopy (IR and NMR), and
X-ray diffraction. The 2:1 complexes are of two types: [(UO2)2(H2Lm)­(NO3)2(solvent)2] (m = 1 and 2; solvent
= ethanol or propanol) or (cation)2[(UO2)2(H2Lm)­(NO3)2(anion)2]·xsolvent (m = 2 and 4; cation = triethylammonium, anion = nitrate or thiocyanate,
and solvent = dichloromethane and acetonitrile; x = 1 or 2). The 1:1 complexes have the formula [(UO2)2(H2Lm)2] (m = 2 and 3). In the solid state, 2:1 complexes are almost in a linear
conformation with the uranyl ion at both ends of the ligand. The 1:1
complexes are cyclic dinuclear molecules. Preliminary studies of the
ligands as uranyl ion extractors from water to dichloromethane were
also performed. A high extraction efficiency was observed with H4L3 for uranyl ions, and in the presence of CuII, NiII, CoII, and ZnII ions, a good
extraction selectivity for uranyl ions was found with H4L1.