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.