Mono- and heterometallic europium (III) and terbium (III) complexes: Synthesis, crystal structures and luminescent properties

Ultra-low limit of luminescent detection of gossypol by terbium(III)-based metal-organic framework

The widespread use of gossypol-containing animal feed and cottonseed oil poses a great threat to water quality and livestock and human health, and there is an urgent need for a sensor for the rapid detection of trace amounts of gossypol in aqueous solutions and cottonseed oil. As a result, an unprecedented three-dimensional metal-organic framework sensor based on terbium(III) and a flexible ligand 4-(3,5-dicarboxyphenoxy)isophthalic acid (H₄L) was developed. Tb-MOF, {[Tb(H₂O)(HL)]·0.5MeCN·0.25 H₂O}_n, is highly stable in water and polar organic solvents and exhibits terbium-centered luminescence with 44% quantum yield. Suspensions of MOF in water and ethanol demonstrate a luminescence quenching response to cotton phytotoxicant gossypol with an unprecedented low detection limit of 0.76 nM and 1.89 nM, correspondingly, without interference from the components of cottonseed oil and blood plasma, making it suitable for the detection and determination of gossypol in real-life water and oil samples. Significantly, Tb-MOF is the first highly efficient sensor that uses water as a solvent to detect trace amounts of gossypol, and it can visualize and quantify gossypol in edible-grade cottonseed oil as well, which proves its great potential for practical application. In addition, Tb-MOF exhibited a detection limit for Fe³⁺ (0.23 μM) among the lowest reported for lanthanide-based MOFs in aqueous solutions so far.

Anion-directed assemblies of europium(III) coordination polymers based on 1H-benzimidazole-5,6-dicarboxylate: structures and luminescence properties

Two europium(III) coordination polymers (CPs), namely, poly[[diaquabis(μ₄-1H-benzimidazole-5,6-dicarboxylato-κ⁶N³:O⁵,O^5':O⁵,O⁶:O^6')(μ₂-oxalato-κ⁴O¹,O²:O^1',O^2')dieuropium(III)] dihydrate], {[Eu₂(C₉H₄N₂O₄)₂(C₂O₄)(H₂O)₂]·2H₂O}_n (1), and poly[(μ₃-1H-benzimidazol-3-ium-5,6-dicarboxylato-κ⁵O⁵:O^5',O⁶:O⁶,O^6')(μ₃-sulfato-κ³O:O':O'')europium(III)], [Eu(C₉H₅N₂O₄)(SO₄)]_n (2), have been synthesized via the hydrothermal method and structurally characterized. CP 1 shows a three-dimensional network, in which the oxalate ligand acts as a pillar, while CP 2 has a two-dimensional network based on a europium(III)-sulfate skeleton, further extended into a three-dimensional framework by hydrogen-bonding interactions. The structural diversity in the two compounds can be attributed to the different acidification abilities and geometries of the anionic ligands. The luminescence properties of 1 display the characteristic europium red emission with CIE chromaticity coordinates (2/3, 0.34). Interestingly, CP 2 shows the characteristic red emission with CIE chromaticity coordinates (0.60, 0.34) when excited at 280 nm and a near-white emission with CIE chromaticity coordinates (0.38, 0.29) when excited at 340 nm.

Electronic structure and spectral properties of terbium(III) nitrate complex with hexamethylphosphoramide

Spectral properties of terbium(III) nitrate complex with hexamethylphosphoramide have been studied by quantum-chemical methods within the density functional theory and methods of luminescent and X-ray photoelectron spectroscopy. Analysis of the luminescence excitation spectrum of the complex has indicated the absence of intramolecular transfer of electronic excitation energy from the ligand levels to the resonance levels of the rare earth central ion, so luminescence of the complex is associated with the electronic f-f-transitions of Tb³⁺ ion (transitions ⁵D₄→⁷F_J, J=3-6). According to quantum-chemical modeling of the excited singlet and triplet levels of the complex, the excitation energy transfer from the ligands onto the central ion does not occur because of the significant difference of energies of their excited states.