Dioxouranium(VI) Schiff base complexes as ligands towards Cu(II) and NI(II) ions

Two mononuclear UO2(VI) complexes of the general formula [(HL)UO2(OH2)(2)] . 0.5H(2)O, where L is a pentadentate N2O3 asymmetric Schiff base ligand, were synthesized and used as ligands for further coordination of either Cu(II) or Ni(II) ions. The UO2(VI) ion occupies the outer O2O sites of the ligands, thus leaving the inner N2O2 sites of the ligands vacant for further coordination. Different types of products were obtained according to the type of the counter anion of the transition metal cations and using LiOH as a deprotonating agent. Metal acetates always yield heterotrinuclear complexes of the type [(ML)(2)UO2(OH2)], M = Cu(II) or Ni(II), in the presence or absence of LiOH. In these complexes, two transition metal cations are coordinated to the inner N2O2 sites of two parent molecules, losing one of their uranyl cations and the remaining one shifts its coordination to the outer O-O sites of these molecules. On the other hand, metal perchlorates yield different products depending on the presence or absence of LiOH. In the presence of LiOH the following complexes were obtained: [{UO2L1(OH2)(2)}2M] . 4.5H(2)O, M = Cu(II) or Ni(II), and [(CuL2)(2)UO2(OH2)] . 4H(2)O. In the former case a transition metal cation was linked to the rear of two parent uranyl molecules, through their N2N2 coordinating sites. In the absence of LiOH, either a cationic complex ion is formed, similar to those obtained in the case of metal acetates but without deprotonating the inner imine groups, or transmetallation occurs where a transition metal cation replaces the uranyl ion, [(NiHL1)(2)UO2(OH2)](ClO4)(2) and [(HLM)-M-2], respectively. These latter products thus differ according to the type of ligand in the parent uranyl compound. The structures of the complexes were elucidated by elemental analyses, IR, UV VIS, and H-1 NMR spectroscopy, magnetic moments, and conductivity measurements.