Bifunctional Lanthanide-Based Coordination Polymers: Conversion of CO2 and Highly Selective Luminescence Sensing for Acetylacetone

A series of bifunctional Ln(III)-based coordination polymers (CPs) {Ln(L)(DMA)2(NO3)}n [Ln(III) = Eu (1), Gd (2), and Dy (3); organic ligand H2L = 2,2'-(1,3,5,7-tetrahydroxyoctahydro-4,8-ethanopyrrolo[3,4-f]isoindole-2,6(1H,3H)-diyl)diacetic acid)] have been successfully synthesized. CPs 1-3 are isostructural and constructed from the dimeric Ln2 unit in which two adjacent LnIII ions are bridged by two μ3-carboxyl oxygens, and the Ln2 dimeric unit is connected by two NO3- ions, four DMA molecules, and four completely protonated L2- ligands forming a 2D layer structure. The magnetic research reveals that CP 2 shows a significant cryogenic magnetocaloric effect (-ΔSm = 22.9 J kg-1 K-1; T = 2.0 K and ΔH = 7.0 T), whereas CP 3 exhibits slow magnetic relaxation property under Hdc = 0 Oe field. Additionally, the luminescence explorations revealed that CP 1 can act as a recyclable luminescent probe for pollutant acetylacetone among various small organic solvent molecules, and the corresponding detection limit is 10-7 mol/L. More importantly, CP 1 also exhibits good catalytic performance in the cycloaddition reaction of CO2 and epoxides or cyanamides under mild conditions. As far as we know, CP 1 represents the first bifunctional lanthanide homogeneous catalyst that can efficiently catalyze the reaction of cyanamides/epoxides with CO2 simultaneously.

Self-assembly of octanuclear Ln(III)-based clusters: their large magnetocaloric effects and highly efficient conversion of CO2

The design and construction of high-nuclear lanthanide clusters with fascinating topology and functional properties have been an active area of research, however, the development of an effective approach for obtaining high-nuclear lanthanide clusters with multifunctional properties is still extremely difficult. Up to now, a systematic approach for guiding the further expansion of Ln(III)-based clusters showing good functional properties is lacking. Herein, we design and synthesize a polydentate Schiff base ligand (HL), which reacts with β-diketonate salts Ln(acac)₃·2H₂O, and a series of Ln₈ clusters [Ln₈(acac)₆(L)₂(μ₃-O)₆(μ₂-C₂H₅O)₄(μ₂-Hacac)₂]·2CH₃CN (Ln(III) = Gd (1), Dy (2), and Ho (3); HL = pyridine-2-carboxylic acid (5-hydroxymethyl-furan-2-ylmethylene)-hydrazide, Hacac = acetylacetone) have been successfully synthesized. Single-crystal X-ray diffraction studies reveal that clusters 1-3 are isostructural and can be viewed as a Ln₈ core bridged by eighteen μ₂-O atoms, six μ₃-O atoms and two μ₄-O atoms. Magnetic studies show that cluster 1-Gd8 displays a large magnetocaloric effect with -ΔS_m = 46.14 J kg^-1 K^-1 (T = 2.0 K and ΔH = 7.0 T); cluster 2-Dy8 exhibits single-molecule magnet behavior under zero-field conditions. It is worth mentioning that the -ΔS_m of cluster 1-Gd8 is larger than that of most reported polynuclear Gd(III)-based clusters; the 2-Dy8 cluster is one of the rare polynuclear Ln_n SMMs (n ≥ 8) under zero dc field. Importantly, these Ln(III)-based clusters (1-3) can catalyze the cycloaddition of CO₂ with epoxides with high efficiency under mild conditions; and cluster 1-Gd8 as a catalyst could be reused at least three times without obvious loss of catalytic performance.

Molecular assemblies from linear-shaped Ln4 clusters to Ln8 clusters using different β-diketonates: disparate magnetocaloric effects and single-molecule magnet behaviours

A series of tetranuclear lanthanide-based clusters [Ln₄(dbm)₆(L)₂(CH₃OH)₄]·2CH₃OH (Ln(III) = Gd (1), Dy (2), and Ho (3); H₃L = 2-[(2-(hydroxyimino)propanehydrazide)methyl]-2,3-dihydroxybenzaldehyde, Hdbm = dibenzoylmethane) and octanuclear lanthanide-based clusters [Ln₈(HL)₁₀(CH₃O)₄(CH₃OH)₂]·6CH₃OH (Ln(III) = Gd (4), Dy (5)) were assembled using a polydentate Schiff-base ligand H₃L and two different β-diketone salts via a solvothermal method, and their structures and magnetic properties have been characterized. Interestingly, β-diketones play an important role in assembling and affecting the structures of Ln₄ to Ln₈ clusters. This is the first use of β-diketone to affect the structures of polynuclear Ln(III)-based clusters from linear-shaped Ln₄ clusters to Ln₈ clusters. Magnetic studies revealed that antiferromagnetic interactions exist in clusters 1-Gd4 and 4-Gd8. More importantly, clusters 1-Gd4 and 4-Gd8 display significant cryogenic magnetic refrigeration properties (-ΔS_m = 24.88 J kg^-1 K^-1 for 1-Gd4 and -ΔS_m = 32.52 J kg^-1 K^-1 for 4-Gd8); the results show that cluster 4-Gd8 exhibits a larger magnetocaloric effect than 1-Gd4. Cluster 2-Dy4 shows remarkable single-molecule magnet (SMM) behavior (ΔE/k_B = 67.5 K and τ₀ = 3.06 × 10^-7 s) under a zero dc field, and 5-Dy8 exhibits a field-induced SMM-like behavior (ΔE/k_B = 39.83 K and τ₀ = 2.12 × 10^-7 s) under a 5000 Oe dc field.

Lanthanide clusters of phenanthroline containing a pyridine-pyrazole based ligand: magnetism and cell imaging

In this contribution, we report the synthesis, characterization and luminescence-magnetic properties of Ln-clusters (Ln = Gd3+, Eu3+ and Tb3+) using a new pyridine-pyrazole functionalized ligand fitted with a chromophoric phenanthroline backbone. The unorthodox N-rich ligand forms isostructural trinuclear lanthanide complexes with a topology that closely resembles two interdigitating hairpins. The clusters crystallize in chiral space groups and also exhibit chirality for bulk samples, which were further confirmed using solid state CD spectra. Magnetic studies on the complexes reveal their interesting features while the Gd cluster shows a significant cryogenic magnetic cooling behaviour with a moderately high magnetic entropy change of -23.42 J kg-1 K-1 at 7 T and 2 K. On the other hand, Eu and Tb complexes exhibit interesting fluorescence properties. The compounds were subsequently used as fluorescent probes for the imaging of human breast adenocarcinoma (MCF7) cells. Live cell confocal microscopy images show that the complexes penetrate beyond the usual cytoplasm region and can be useful in imaging the nucleus region of MCF7 cells.