Heterovalent 2Eu(II)/4Eu(III) and Trivalent 5Eu(III) Clusters Assembled with a Macrocyclic Cyclen Derivative Ligand: Molecular Structures, Oxidation Stabilities, and Luminescence Properties

摘要

Two coordination complexes (Eu2Eu4III)-Eu-II(OH)(4)(bza)(4)L-2 (1) and Eu-5(III)(H2O)(OH)(4)(NO3)(3)(bza)(4)L (2) have been assembled with the tetrasubstituted cyclen ligand N,N,N,N-tetrakis(2-hydroxy-3-methoxy-5-methylbenzyl)-1,4,7,10-tetraazacyclododecane (H4L) and the auxiliary ligand benzoic acid (Hbza). Complex 2 is a pentanuclear Eu-III cluster whereas complex 1 is a huge heterovalent 2Eu(II)/4Eu(III) cluster in which two divalent europium ions are trapped within the macrocyclic cavities of the designed ligands L and are further isolated from the environment by peripheral phenyl rings and the tetrahedral 4Eu(III) cluster, which results in the enhanced oxidative stability of Eu2+. The luminescence of complex 1 was investigated and is discussed in comparison with the luminescence of ligand H4L and complex 2. Owing to the protection of Eu2+ by the macrocyclic ligands L, the heterovalent complex exhibits a strong broad emission band with a maximum at 533 nm as well as the characteristic sharp emissions of Eu3+. The broad emission is redshifted compared with that of ligand H4L and has been attributed to the Laporte-allowed 4f(6)5d(1)4f(7) transition of Eu2+.