Supramolecular lanthanide assemblies with cucurbit[6]uril: from synthesis and crystal structure to application

Abstract

Reactions between Ln(NO₃)₃ and cucurbit[6]uril in HNO₃ have been studied, aiming to create novel light-emitting systems. Aquanitrato complexes of lanthanides were obtained as supramolecular assemblies 1–10 with the organic macrocyclic cavitand cucurbit[6]uril. X-ray diffraction study demonstrated that these compounds have the following compositions: [{Ln(H₂O)₅(NO₃)}₂(C₃₆H₃₆N₂₄O₁₂)](NO₃)₄·HNO₃·nH₂O (Ln = Pr(1), Nd(2), Sm(3), Eu(4), Gd(5), Tb(6)) and 2[Ln(H₂O)₈](NO₃)₃·C₃₆H₃₆N₂₄O₁₂·2HNO₃·mH₂O (Ln = Dy(7), Ho(8), Er(9), Yb(10)). Compounds with different structures were shown to crystallize under the same synthesis conditions for the early and late lanthanides. The compounds were characterized by powder X-ray diffraction, thermogravimetric and elemental analyses, and IR spectroscopy. The magnetic property of compound 5 was also examined. The luminescent properties for compounds 1–10 were studied. The chromaticity coordinates (CIE) for compounds 1–10 were calculated. The color purity of compound 4 was found to be 96%, which is very close to that of the standard red light source. Compound 4 can be considered a potential red-emitting candidate for near-UV WLEDs. The color purity of compound 7 is very close to zero, so it is well suited for generation of white light, which further suggests its utility for W-LED applications. A cool white LED device was fabricated for the first time by combining the supramolecular coordination polymer 7 and a UV LED chip (365 nm) under a voltage of 3.0 V; the CIE, CCT and CP were (0.301, 0.325), 7228 K and 7%, respectively.