Coordination Polymers Based on Heterohexanuclear Rare Earth Complexes: Toward Independent Luminescence Brightness and Color Tuning

Reactions in solvothermal conditions between hexanuclear rare earth complexes and H₂bdc, where H₂bdc symbolizes terephthalic acid, lead to a family of monodimensional coordination polymers in which hexanuclear complexes act as metallic nodes. The hexanuclear cores can be either homometallic with general chemical formula [Ln₆O­(OH)₈(NO₃)₆]²⁺ (Ln = Pr–Lu plus Y) or heterometallic with general chemical formula [Ln_6<i>x</i>Ln′_{6–6<i>x</i>}O­(OH)₈(NO₃)₆]²⁺ (Ln and Ln′ = Pr–Lu plus Y). Whatever the hexanuclear entity is, the resulting coordination polymer is iso-structural to [Y₆O­(OH)₈(NO₃)₂(bdc)­(Hbdc)₂·2NO₃·H₂bdc]_∞, a coordination polymer that we have previously reported. The random distribution of the lanthanide ions over the six metallic sites of the hexanuclear entities is demonstrated by ⁸⁹Y solid state NMR, X-ray diffraction (XRD), and luminescent measurements. The luminescent and colorimetric properties of selected compounds that belong to this family have been studied. These studies demonstrate that some of these compounds exhibit very promising optical properties and that there are two ways of modulating the luminescent properties: (i) playing with the composition of the heterohexanuclear entities or (ii) playing with the relative ratio between two different hexanuclear entities. This enables the independent tuning of luminescence intensity and color

Characterization and Luminescence Properties of Lanthanide-Based Polynuclear Complexes Nanoaggregates

For the first time, hexanuclear complexes with general chemical formula [Ln₆O­(OH)₈­(NO₃)₆(H₂O)_<i>n</i>]²⁺ with <i>n</i> = 12 for Ln = Sm–Lu and Y and <i>n</i> = 14 for Ln = Pr and Nd were stabilized as nanoaggregates in ethylene glycol (EG). These unprecedented nanoaggregates were structurally characterized by ⁸⁹Y and ¹H NMR spectroscopy, UV–vis absorption and luminescence spectroscopies, electrospray ionization mass spectrometry, diffusion ordered spectroscopy, transmission electron microscopy, and dynamic light scattering. These nanoaggregates present a 200 nm mean solvodynamic diameter. In these nanoaggregates, hexanuclear complexes are isolated and solvated by EG molecules. The replacement of ethylene glycol by 2-hydroxybenzyl alcohol provides new nanoaggregates that present an antenna effect toward lanthanide ions. This results in a significant enhancement of the luminescence properties of the aggregates and demonstrates the suitability of the strategy for obtaining highly tunable luminescent solutions