Construction of Cr(III)-Ln(III)-Salen (Ln = Nd, Yb, Er or Gd) hetero-binuclear complexes with high-purity near-infrared (NIR) luminescence

Abstract

Based on the treatments of the Salen-type Schiff-base ligand H2L (N,N’-bis(3-methoxy-salicylidene)cyclohexane-1,2-diamine) with CrCl2 and the subsequent Ln(OAc)3⋅6H2O (Ln = Nd, Yb, Er or Gd), series of hetero-binuclear Cr(III)-Ln(III)-Salen complexes [Cr(L)Cl(μ1-OAc)Ln(μ2-OAc)Cl(H2O)] (Ln = Nd, 1; Yb, 2; Er, 3 or Gd, 4) were obtained, respectively. Photo-physical property results show that in comparison to the Cr3+-characteristic (2E → 4A2 transition) high-purity NIR-luminescence for the complex [Cr(L)Cl(μ1-OAc)Gd(μ2-OAc)Cl(H2O)] (4), the complexes [Cr(L)Cl(μ1-OAc)Ln(μ2-OAc)Cl(H2O)] (Ln = Nd, 1; Yb, 2 or Er, 3), due to the effective intra-molecular Cr(III)-to-Ln(IIII) energy transfer, exhibit the corresponding Ln(III)-centered (Ln = Nd, Yb or Er) high-purity NIR-emissions, respectively.