A new phenolato-bridged dinuclear manganese(II) complex as a turn-on fluorosensor for Zn2+ ions via Mn2+ ion replacement

Abstract

A new synthesized and structurally characterized phenolato bridged di-nuclear manganese(II) complex, formulated as [Mn2L(OAc)2(DMF)2]PF6 (1) (where HL = 4-methyl-2,6-bis-[(2-morpholin-4-yl-ethylimino)-methyl]-phenol and OAc = acetate anion), can act as a turn-on Zn2+ sensing probe through the in situ formation of the corresponding dinuclear Zn(II) complex, [Zn2L(OAc)2]PF6 (2) via direct Mn2+ ion replacement in MeOH/DMF (1/14) medium. The selective and specific fluorescent change due to addition of Zn2+ ions to a solution of 1 enables the detection of Zn2+ ions in dimethylformamide (DMF). The fluorescent dinuclear zinc(II) complex 2 has also been produced through the direct reaction between Zn2+ ions and HL. Both complexes 1 and 2 have been characterized by using physico-chemical and spectroscopic tools, and finally by single crystal X-ray crystallography for a detailed structural determination. The crystallographic investigation indicates that the Mn(II) and Zn(II) ions in the complexes exhibit a distorted octahedral and distorted trigonal bipyramidal coordination geometry, respectively. Interestingly, complex 1 showed very weak fluorescence in solution and no emission in the solid state, whereas complex 2 gave a strong bluish-green coloured fluorescence in both solution and in the solid state, which may be due to the distinct packing of complex 2 compared to 1, as well as to intermolecular hydrogen bonding and CH---π, CH---N and CH---O interactions in the crystal packing, likely playing crucial roles for the fluorescence behavior.