Structural and Photophysical Studies on Geometric (Er₂Yb₂/Yb₂Er₂) and Configurational (EuTb₃/Eu₃Tb) Isomers of Heterotetranuclear Lanthanide(III) Complexes

Heterotetranuclear geometrical (Er₂Yb₂/Yb₂Er₂) and configuational (EuTb₃/Eu₃Tb) isomeric lanthanide­(III) complexes have been synthesized and characterized by spectroscopy as well as X-ray crystallography. The geometric Er₂Yb₂/Yb₂Er₂ isomers exhibit dual emissions from both erbium­(III) and ytterbium­(III) ions. For the EuTb₃/Eu₃Tb configurational isomers, the Tb^III subunits transfer energy to the Eu^III centers in the EuTb₃ complex, whereas the Tb^III ion in the TbEu₃ complex serves mainly as a structural stabilizer

Hierarchical Assembly and Aggregation-Induced Enhanced Emission of a Pair of Isostructural Zn₁₄ Clusters

Information of solid-state and solution structures is crucial in the characterization of molecular clusters and in advancing the understanding of their diverse properties. [Et₃NH]₂[Zn₁₄(hmq)₈(OH)₄X₁₀] [X = Cl and Br; H₂hmq = 2-(hydroxymethyl)­quinolin-8-ol] consist of a peanut-shaped Zn₁₀O₁₂ core, in which the Zn atoms occupy the faces and corners of an octahedron and are protected by bonded halogen atoms and bulky organic ligands. Observation of the [Zn₁₄(hmq)₈(OH)₄X₁₀]^2– fragment in electrospray ionization mass spectrometry (ESI-MS) suggests that the cluster is stable in solution. ESI-MS analyses from dissolved crystals and mother liquors reveal that Zn­(hmq) self-assembles to Zn₅(hmq)₄Cl, then dimerizes through four [OH]⁻ bridges to Zn₁₀(hmq)₈(OH)₄Cl₂, and progressively captures four ZnCl₂ one-by-one to [Zn₁₄(hmq)₈(OH)₄Cl₁₀]^2–. Because the supramolecular interactions between the anion and cation in the solid suppress the rotation/vibration of the halogen atoms and confine the movable organic ligands on the rigid Zn–O core, both crystal phases exhibit intense photoluminescence, much stronger than that in solution. This is the first coordination cluster to exhibit “aggregation-induced enhanced emission”. In addition, preliminary tests indicate that these coordination clusters are promising for organic-light-emitting-diode applications