Coordination induced fluorescence enhancement and construction of a Zn3 constellation through hydrolysis of ligandimine arms

Abstract

The phenoxido and alkoxido bridged neutral Zn₃ complex [Zn₃(μ-H₂bemp)₂(μ₃-emp)₂] (1), with an angular Zn₃(μ-OPh)₂(μ-OEt)₂ core and capping nitrogen donors, was synthesized via simultaneous chelation-cum-bridging of the parent and hydrolysed ligands. Zinc(II) coordination triggered the solution phase imine (CN) bond hydrolysis of H₃bemp (2,6-bis-[(2-hydroxyethylimino)methyl]-4-methylphenol) and yielded the unexpected angular trinuclear Zn(II) complex 1, having structural similarity with the Zn₃ active site of P1 nuclease. H₃bemp also displays a zinc(II) selective chelation-enhanced fluorescence response from strong metal ion coordination. Complexation of zinc(II) with H₃bpmp (2,6-bis-[(3-hydroxypropylimino)methyl]-4-methylphenol), a close analogue of H₃bemp, instead provides only mononuclear [Zn(H₂bpmpH^N)₂](ClO₄)₂·2H₂O (2·2H₂O) (H^N is the proton attached to an imine nitrogen atom) of two zwitterionic ligands, generated through a kind of coordination driven acid–base reaction, without showing any aggregation reaction. As the sole metal–organic precursor, both the complexes under pyrolytic conditions give ZnO nano structures of two morphologies.