Synthesis, crystal structures and NIR luminescence properties of heterometallic 3d-4f complexes

Abstract

Three heterometallic 3d-Yb complexes [ZnYb<bold>L</bold>(NO₃)₂(OAc)] (<bold>1</bold>), [Zn₄Yb₂<bold>L</bold>₄(1,4-BDC)₂]·[Yb(NO₃)₅(H₂O)] (<bold>2</bold>) and [CuYb<bold>L</bold>(NO₃)₂(OAc)(CH₃OH)] (<bold>3</bold>) were synthesized from salen Schiff-base ligand <italic>N</italic>,<italic>N</italic>-bis(5-bromo-3-methoxysalicylidene)propylene-1,3-diamine (<bold>H₂L</bold>). The hexanuclear complex <bold>2</bold> was constructed from the binuclear complex <bold>1 </bold>and 1,4-benzenedicarboxylate (1,4-BDC). The crystal structure of <bold>2</bold> shows that two 1,4-BDC groups link two trinuclear Zn₂Yb units, resulting in the higer nuclearity complex. The study of luminescence properties of these complexes indicate that, in <bold>1</bold> and <bold>2</bold>, the Zn/L units can efficiently transfer energy to the lanthanide centers, resulting in the NIR emissions of Yb³⁺ ions. The NIR emission of <bold>2</bold> is stronger than that of <bold>1</bold>. In <bold>3</bold>, the 3d block metal ion (Cu²⁺) introduced into the complex can quench the NIR emission of Yb³⁺ ion, probably due to ligand→d or f→d energy transfer.