posted on 2014-02-03, 00:00authored byMaría A. Palacios, Silvia Titos-Padilla, José Ruiz, Juan Manuel Herrera, Simon
J. A. Pope, Euan K. Brechin, Enrique Colacio
There
were new dinuclear ZnII–LnIII complexes
of general formulas [Zn(μ-L)(μ-OAc)Ln(NO3)2] (LnIII = Tb (1), Dy (2), Er (3), and Yb (4)), [Zn(μ-L)(μ-NO3)Er(NO3)2] (5), [Zn(H2O)(μ-L)Nd(NO3)3]·2CH3OH (6), [Zn(μ-L)(μ-9-An)Ln(NO3)2]·2CH3CN (LnIII =
Tb (7), Dy (8), Er (9), Yb(10)), [Zn(μ-L)(μ-9-An)Yb(9-An)(NO3)3]·3CH3CN (11), [Zn(μ-L)(μ-9-An)Nd(9-An)(NO3)3]·2CH3CN·3H2O
(12), and [Zn(μ-L)(μ-9-An)Nd(CH3OH)2(NO3)]ClO4·2CH3OH (13) prepared from the reaction of the compartmental
ligand N,N′,N″-trimethyl-N,N″-bis(2-hydroxy-3-methoxy-5-methylbenzyl)diethylenetriamine
(H2L), with ZnX2·nH2O (X = NO3– or OAc–) salts, Ln(NO3)3·nH2O, and, in some instances, 9-anthracenecarboxylate anion (9-An).
In all these complexes, the ZnII ions invariably occupy
the internal N3O2 site whereas the LnIII ions show preference for the O4 external site, giving
rise to a Zn(μ-diphenoxo)Ln bridging fragment. Depending on
the ZnII salt and solvent used in the reaction, a third
bridge can connect the ZnII and LnIII metal
ions, giving rise to triple-bridged diphenoxoacetate in complexes 1–4, diphenoxonitrate in complex 5, and diphenoxo(9-anthracenecarboxylate) in complexes 8–13. DyIII and ErIII complexes 2, 8 and 3, 5, respectively, exhibit field induced single molecule magnet
(SMM) behavior, with Ueff values ranging
from 11.7 (3) to 41(2) K. Additionally, the solid-state photophysical
properties of these complexes are presented showing that ligand L2‑ is able to sensitize TbIII- and DyIII-based luminescence in the visible region through an energy
transfer process (antenna effect). The efficiency of this process
is much lower when NIR emitters such as ErIII, NdIII, and YbIII are considered. When the luminophore 9-anthracene
carboxylate is incorporated into these complexes, the NIR luminescence
is enhanced which proves the efficiency of this bridging ligand to
act as antenna group. Complexes 2, 3, 5, and 8 can be considered as dual materials
as they combine SMM behavior and luminescent properties.