Coordination of metalloligand [NiL] (H₂ = salen type N₂O₂ Schiff base ligand) to the f-block elements: structural elucidation and spectrophotometric investigation

Abstract

To investigate the coordinative interaction of a bidentate metalloligand [NiL] with f-block metal ions, two di-phenoxo bridged Ni-nf (n = 4 and 5) complexes [(NiL) ₂Ce(NO₃)₃] (1) and [(NiL)UO₂(NO₃) ₂] (2) have been synthesized and characterized (H₂L = N,N′-bis(α-methylsalicylidene)-1,3-propanediamine, a N₂O₂ donor Schiff base ligand). Single crystal structural characterizations revealed that [NiL] formed 2:1 adduct with a lanthanide Ce(NO₃)₃ whereas with the actinyl UO₂ (NO₃) ₂, 1:1 adduct was obtained. In complex 1 the central Ce(III) ion is connected to two terminal [NiL] metalloligands through μ_1,1-diphenoxido bridges to form a trinuclear coordination cluster with three chelating nitrato coligands (CeO₁₀ tetradecahedron). Whereas in complex 2 one [NiL] is chelated to the U^VIO₂²⁺ ion along with two chelating nitrato coligands to form a dinuclear core (UO₈ hexagonal bipyramid). Moreover, to examine the formation of these complexes in solution, we performed UV–Vis spectrophotometric titrations of [NiL] with the respective metal ions which revealed the formation of bimetallic 1:1 and 2:1 complexes for both Ce(III) and UO₂²⁺ ions. However, we got only 1:1 and 2:1 adducts for UO₂²⁺ and Ce³⁺ respectively on crystallization even of varying the stoichiometry of the reactants probably due to the differences in solubility of the adducts formed.