Temperature-dependent self-assembly of near-infrared (NIR) luminescent Zn2Ln and Zn2Ln3 (Ln = Nd, Yb or Er) complexes from the flexible Salen-type Schiff-base ligand

Through the self-assembly of the precursor [Zn(L)(MeCN)] (H2L, = N,N'-bis(3-methoxy-salicylidene) cyclohexane-1,2-diamine) with LnCl(3)center dot 6H(2)O (La = La, Nd, Yb, Er or Gd) and NaN3 in alcohol-containing solutions, two series of mixed anions-induced Zn(2)Ln-arrayed complexes [Zn-2(L)(2)(MeOH)ClLn(N-3)]center dot Cl (Ln = La, 1; Ln = Nd, 2; La = Yb, 3; La = Er, 4 or La = Gd, 5) and Zn(2)Ln(3)-arrayed complexes [Zn-2(L)(3)Cl-2(mu(2)-OH)(mu(3)-OH)(2)Ln(3)(N-3)(2)] (La = La, 6; La = Nd, 7; La = Yb, 8; La = Er, 9 or La = Gd, 10) are obtained at room temperature or under reflux, respectively. In contrast to Zn(2)Ln-arrayed complexes with the two Zn2+ ions in the inner cis-N2O2 cores and one Ln(3+) ion in the outer O2O2 moieties, the demetalation of partial precursors leads to the selective exchange of Zn2+ centers for the Ln(3+) ions for the formation of novel heterometallic Zn(2)Ln(3)-arrayed complexes with the Ln(3+) ions in both the inner cis-N2O2 core and the outer O2O2 moieties of the ligands. The result of their photophysical properties shows that the characteristic near-infrared (NIR) luminescence of Nd3+ or Yb3+ ion has been sensitized from the excited state (both (LC)-L-1 and (LC)-L-3) of the ligand H2L, while relatively lower quantum yields for Zn(2)Ln(3)-arrayed complexes than those for Zn(2)Ln-arrayed complexes, correspondingly, should be due to the luminescent quenching with the involvement of OH- oscillators around the Ln(3+) ions. (C) 2014 Elsevier B.V. All rights reserved.