Coordination-Driven Self-Assembled Zn-Ln Metallocycles Based on a Salicylamide Imine Ligand: Synthesis, Structure, and Selective Luminescence Enhancement Induced by OAc.

Five heterometallic Zn-Ln macrocycles based on a salicylamide imine multidentate unsymmetrical ligand HL [1-(2-hydroxy-3-methoxy-benzamido)-2-(2-hydroxy-3-methoxy-benzylideneamino)-ethane] have been prepared via a coordination-driven self-assembly strategy. Single-crystal X-ray diffraction analysis reveals that the five metallocycles are isomorphic with a formula of [ZnLnL(OH)(NO)(HO)]·3NO· nCHCN (ZnLn-1, where Ln = Pr, Nd, Eu, Tb, or Yb; for ZnPr-1, n = 4; for ZnNd-1, ZnEu-1, and ZnTb-1, n = 2; for ZnYb-1, n = 3), where six octadentate ligands L and two in situ-formed μ-OH ions bridged the alternating Zn-Ln-Zn subunits into a macrocycle. Along with the structural novelty, ZnNd-1 shows distinctive enhanced emission in the visible and near-infrared range upon addition of OAc. On the basis of ultraviolet-visible spectroscopy, H nuclear magnetic resonance, single-crystal X-ray diffraction, and high-resolution electrospray ionization mass spectrometry, we deduced that this emission enhancement could be attributed to the synergistic effect of TICT and the absent nonradiative transition of μ-OH induced distinctively by OAc bridging. Our results demonstrate that the Nd-containing heterometallic macrocycle can act as a host for anion exchanging and provide a nice example of heterometallic macrocycles with interesting properties and potential applications.