Four Salamo-type 3d–4f hetero-bimetallic [ZnIILnIII] complexes: syntheses, crystal structures, and luminescent and magnetic properties

Abstract

Four hetero-bimetallic [Zn^IILn^III] complexes with the general formula [Zn(L)(OAc)Ln(NO₃)₂] (Ln = Sm, Eu, Tb and Dy) were synthesized by the Salamo-type ligand H₂L (6,6′-diethoxy-2,2′-[1,2-ethylenedioxybis(nitrilomethylidyne)]diphenol) with Zn(OAc)₂·2H₂O and Ln(NO₃)₃·6H₂O (Ln = Sm, Eu, Tb and Dy), respectively. X-ray crystal diffraction analyses revealed that all the Zn(II) atoms were penta-coordinated, adopting distorted square pyramidal geometries, and the Ln(III) atoms were nona-coordinated, forming distorted tricapped trigonal prism geometries. In addition, three-dimensional supramolecular structures were assembled through intermolecular hydrogen-bond interactions. In the [Zn^IILn^III] complexes, only [Zn(L)(OAc)Sm(NO₃)₂] showed obvious orange-red light emission under UV light due to the characteristic f–f transitions of Sm³⁺ ions, which meant that the ligand H₂L could transfer energy from its excited state to the lowest excited state of the Sm³⁺ ion effectively. A decrease in the χ_MT value illustrated weak antiferromagnetic interaction exciting in the [Zn(L)(OAc)Tb(NO₃)₂] and [Zn(L)(OAc)Dy(NO₃)₂] complexes.