Structure-based description of a step-by-step synthesis of heterodinuclear ZnIILnIII complexes and their luminescence properties

The stepwise course of the synthesis of ZnIILnIII complexes of a new compartmental heptadentate open amide crown ether ligand has been investigated through the determination of the intermediate and final products occurring in the process. In the first step, the ligand L is reacted with Ln(NO3)3·5H2O to give the electroneutral complex [LnIIIL(NO3)3] with the lanthanide ion being linked to the N3O2 coordination site of the ligand which are fairly stable and could be isolated. Addition of Zn(NO3)3·6H2O to the [LnIIIL(NO3)3] complexes yield the desired heterodinuclear [ZnIILnIIIL(NO3)5(H2O)] complexes. In all [ZnIILnIIIL(NO3)5(H2O)] complexes, the ZnII ions invariably occupy the N3O2 site whereas the LnIII ions show preference for the carbonyl O site. Additionally, the solid-state photophysical properties of these complexes show that the sensitized EuIII- and TbIII-based luminescence can be enhanced after ZnII ion is incorporated.