The Missing Link in Ni(II)-Ln(III) System: Design and Synthesis of a Dinuclear [Ni2 ] and Three Pentanuclear [Ni3 Ln2 ] (Ln=La, Ce, Eu) Complexes of a Schiff Base Ligand

A new Schiff base ligand N-(2-hydroxyphenyl-3-methoxy-salicylideneamine)-5-nitrophenol (H2L) has been synthesized by the reaction of o-vanillin with 2-amino-4-nitrophenol. The ligand H2L has been employed to prepare homo- and heteronuclear metal complexes. For example, a dinuclear Ni(II) complex, [Ni2(L)2(H2O)3]⋅2DMF⋅3H2O (1) and a new family of three pentanuclear heterometallic [Ni3Ln2L6(H2O)4(DMF)2]⋅4DMF (Ln=La (2), Ce (3) and Eu (4) were prepared by the reaction of it with nickel nitrate hexahydrate and hydrated lanthanide nitrates. The solid state structures of ligand (H2L) and complexes 1–4 were determined by single crystal X-ray diffraction analyses. Single crystal X-ray diffraction and NMR data reveal that the ligand H2L exist as a keto-enamine form in the solid state. Structure of complex 1 indicates formation of a dinuclear Ni(II) complex. Complexes 2–4 are isostructural and exhibits a butterfly-like structure containing two Ln(III) ions and three Ni(II) ions. The Ni(II) and Ln(III) are bridged by phenoxo and aqua ligands resulting a pentanuclear chain with alternating Ni(II) and Ln(III) ions. Different coordination modes of ligand (H2L) have been explored. To the best of our knowledge, such pentanuclear complexes containing Ni−Ln and Schiff base ligand are hitherto unknown. The thermal stability and optical properties of all complexes are also investigated