Mixed anion-induced Salen-based Zn2Ln3 (Ln = Nd, Yb or Er) complexes with near-infrared (NIR) luminescent properties

A series of mixed anion-induced Zn2Ln3 complexes [Zn2(L)3Cl2(μ2-OH)(μ3-OH)2Ln3(N3)2] (Ln = La, 1; Ln = Nd, 2; Ln = Yb, 3; Ln = Er, 4 or Ln = Gd, 5) have been obtained by the self-assembly of the precursor [Zn(L)(MeCN)] (H2L = N,N′-bis(3-methoxy-salicylidene)cyclohexane-1,2-diamine) with LnCl3·6H2O (Ln = La, Nd, Yb, Er or Gd) and NaN3 in alcohol-containing solutions. In these reactions, transmetallation of the partial precursor leads to the coexistence of two Zn2 + ions and one Ln3 + ion in the inner cis-N2O2 core and the other two Ln3 + ions in the outer O2O2 moieties of three deprotonated ligands. Photophysical studies suggest that the characteristic near-infrared (NIR) luminescence of Nd3 + and Yb3 + ions is sensitized through both the excited singlet 1LC and triplet 3LC states of the depronated ligand (L)2 −, despite the luminescent quenching with three OH− oscillators arround the Ln3 + ions.