Uranyl(VI) Complexes of Pyridine-Based Pentadentate Acyclic and Macrocyclic Ligands

The uranyl(VI) complexes of pyridine-based pentadentate ligands derived from 2,6-diacetylpyridine and semicarbazide (DAPSC) or benzoylhydrazide (DAPBH) are described, characterized on the basis of elemental analysis, electrical conductance, infrared and electronic spectra. The ligands form complexes of the type [(UO2)2(DAPSC)X4] and [(UO2)(DAPBH)X]X (where X = Cl). The template effect of uranyl(VI) has been studied in the cyclization of 2,6-diacetylpyridine with carbohydrazide and 2-phenylenediamine. The complexes obtained from 2,6-diacetylpyridine and 2-phenylenediamine represented as [(UO2Mac1)X2], where Mac1 is a macrocyclic hexadentate (M6) ligand and complexes obtained by the condensation of 2,6-diacetylpyridine and carbohydrazide has been formulated as [(UO2)2(Mac2)X4], where Mac2 is a heptadentate macrocyclic ligand. The formulation as macrocyclic ligand complexes is indicated by the absence of v(C=0) of 2,6-diacetylpyridine and formation of an azomethine linkage. The intense colour of these complexes also supports the formation of macrocyclic ligands.