NIR luminescence and catalysis of multifarious salen type ytterbium complexes modulated by anions

Abstract

A series of five N,N′-bis(2-hydroxy-3-methoxybenzylidene)-1,3-propanediamine (H₂L) ytterbium complexes, namely, [Yb(H₂L)₂(CH₃OH)](ClO₄)₃ (1), [Yb(H₂L)(NO₃)₃]₂·CH₂Cl₂ (2), [Yb(H₂L)₂(NO₃)]₂(PF₆)₄·4H₂O·2CH₂Cl₂ (3), [Yb(H₂L)(OAc)₂]₂(PF₆)₂·4CH₂Cl₂ (4) and [Yb₃L′₃(OH)₂Cl(H₂O)₅]Cl₃·4H₂O (5) (HL′ = 2-hydroxy-3-methoxybenzaldehyde), have been synthesized by reactions of H₂L with multifarious Yb(III) salts. X-ray diffraction analysis reveals that complex 1 shows a unique mononuclear structure constructed from two chelating H₂L ligands in crossover mode. Complex 2 exhibits a dinuclear structure bridged by two H₂L ligands. Complexes 3 and 4 possess two novel dinuclear structures linked by NO₃⁻ and OAc⁻ anions, respectively. Complex 5 displays a trinuclear structure supported by three L′ and two OH⁻ anions. Noticeable, complex 3 can be transformed from 2 by introducing (NH₄)(PF₆). The PF₆⁻ counterion plays an essential role in steering the structural transformation. The anions dominate the final structures of 1–5. All complexes 1–5 exhibit NIR luminescence, which can be rationalized on the basis of different structural effects. Preliminary catalytic studies reveal that all complexes 1–5 are able to catalyze effectively a typical Henry reaction with good yields.