Fluorescence properties of heterotrinuclear Zn(ii)–M(ii) (M = Ca, Sr and Ba) bis(salamo)-type complexes

Abstract

A series of hetero-trinuclear Zn(II) complexes, [Zn₂Ca(L)(OAc)₂]·CHCl₃ (1), [Zn₂Sr(L)(OAc)₂] (2) and [Zn₂Ba(L)(OAc)₂] (3) with a bis(salamo)-type tetraoxime ligand H₄L were synthesized and characterized by elemental analyses, IR, UV-vis spectra etc. Spectral titrations and X-ray crystallography clearly show that the stoichiometry of the heterotrinuclear complexes are all 1 : 2: 1 (ligand/Zn(II)/M(II)). The different natures of the N₂O₂ and O₆ sites of the ligand H₄L lead to the site-selective introduction of two different kinds of metal(II) atoms. All the Zn(II) atoms are penta-coordinated with distorted square pyramidal geometries. The coordination numbers of Ca(II), Sr(II) and Ba(II) atoms in the O₆ environment are all 8, and they have slightly distorted square antiprism geometries. Furthermore, ion competitive experiments show that the coordinating capability in the central O₆ site is in the order of Ca(II) > Sr(II) > Ba(II).