A fluorescent bis(benzoxazole) ligand: Toward binuclear Zn(II)–Zn(ii)assembly

Abstract

A bis(benzoxazole) ligand (HL) has been synthesized, and its reaction with Zn(OAc)₂ has led to fluorescent complexes via formation of binuclear Zn(II)–Zn(II) cores. The ligand-to-metal ratio of the complexes varies from 1 : 1 to 2 : 1, depending on the reaction conditions. A large binding constant K = 8.3 × 10²⁰ [M⁻³] has been determined for the reaction L + Zn²⁺→L₂:Zn₂²⁺. The result indicates that the bis(benzoxazole) ligand is a useful building block to construct a binuclear core. On the basis of X-ray analysis, the binuclear Zn(II)–Zn(II) distance in the complexes is determined to be ∼3.22 Å, which is quite comparable to that found in the enzymes (3.3 Å). Absorption and fluorescence study shows that a subtle chemical environmental change within the binuclear core can induce a large optical response.