2D Windmill-like Ln-Containing Organophosphonate-Based Polyoxomolybdates: Synthesis, Characterization, Fluorescence, and Magnetism

By integration of {Ln(H₂O)₆}³⁺ into organophosphonate-based polyoxometalates, three Ln-containing organophosphonate-functionalized polyoxomolybdates Na_1.5H_1.5[{Ln(H₂O)₆}₂{(Mo₃O₈)(O₃PC(C₃H₆NH₃)OPO₃)}₄]·(CH₃CO₂)·43H₂O (Ln = Eu (1), Tb (2), and Dy (3)) are successfully prepared and systematically characterized. The X-ray crystallography analyses display complexes 1-3 crystallize in the C2/c space group of the monoclinic system and compose several distinctive tetramer windmill-like compounds that further assemble into two-dimensional (2D) frameworks associated with the {Ln(H₂O)₆}³⁺ core. The fluorescence spectra of 1-3 show red, green, and chartreuse emissions, respectively, originating in the typical f-f transitions of Ln³⁺ ions. More interestingly, complex 3 shows the field-induced single-molecule magnet (SMM) properties, resulting from the fact that [(Mo₃O₈)₄{O₃PC(C₃H₆NH₃)OPO₃}₄]^8- offers excellent magnetic isolation for Dy³⁺ ions by the nearest Dy1···Dy2 distance of 11.207 Å. The study demonstrates that the incorporation of {Ln(H₂O)₆}³⁺ into organophosphonate-based polyoxomolybdates is an effective synthetic strategy in implementing late-model opto-magnetic materials.

Family of Nanoclusters, Ln33 (Ln = Sm/Eu) and Gd32, Exhibiting Magnetocaloric Effects and Fluorescence Sensing for MnO4. Inorg Chem 2022;61:8861-8869. [PMID: 35653200 DOI: 10.1021/acs.inorgchem.2c00898]

A family of nanoclusters, [Ln₃₃(EDTA)₁₂(OAc)₂(CO₃)₄(μ₃-OH)₃₆(μ₅-OH)₄(H₂O)₃₈]·OAc·xH₂O (x ≈ 50, Ln = Sm for 1; x ≈ 70, Ln = Eu for 2) and [Gd₃₂(EDTA)₁₂(OAc)₂(C₂O₄)(CO₃)₂(μ₃-OH)₃₆(μ₅-OH)₄(H₂O)₃₆]·x(H₂O) (x ≈ 70 for 3; H₄EDTA = ethylene diamine tetraacetic acid), was prepared through the assembly of repeating subunits under the action of an anion template. The analysis of the structures showed that compounds 1 and 2 containing 33 Ln³⁺ ions were isostructural, which were constructed by three kinds of subunits in the presence of CO₃^2- as an anion template, while compound 3 had a slightly different structure. Compound 3 containing 32 Gd³⁺ ions was formed by three types of subunits in the presence of CO₃^2- and C₂O₄^2- as a mixed anion template. The CO₃^2- anions came from the slow fixation of CO₂ in the air. Meanwhile, one kind of high-nuclearity lanthanide clusters showed high chemical stability. The quantum Monte Carlo (QMC) calculation suggested that weak antiferromagnetic interactions were dominant between Gd³⁺ ions in 3. Magnetocaloric studies showed that compound 3 had a large entropy change of 43.0 J kg^-1 K^-1 at 2 K and 7 T. Surprisingly, compound 2 showed excellent recognition and detection effects for permanganate in aqueous solvents based on the fluorescence quenching phenomenon.

Mono- and Mixed Metal Complexes of Eu3+, Gd3+, and Tb3+ with a Diketone, Bearing Pyrazole Moiety and CHF2-Group: Structure, Color Tuning, and Kinetics of Energy Transfer between Lanthanide Ions

Three novel lanthanide complexes with the ligand 4,4-difluoro-1-(1,5-dimethyl-1H-pyrazol-4-yl)butane-1,3-dione (HL), namely [LnL₃(H₂O)₂], Ln = Eu, Gd and Tb, were synthesized, and, according to single-crystal X-ray diffraction, are isostructural. The photoluminescent properties of these compounds, as well as of three series of mixed metal complexes [Eu_xTb_1-xL₃(H₂O)₂] (Eu_xTb_1-xL₃), [EuxGd_1-xL₃(H₂O)₂] (Eu_xGd_1-xL₃), and [Gd_xTb_1-xL₃(H₂O)₂] (Gd_xTb_1-xL₃), were studied. The Eu_xTb_1-xL₃ complexes exhibit the simultaneous emission of both Eu³⁺ and Tb³⁺ ions, and the luminescence color rapidly changes from green to red upon introducing even a small fraction of Eu³⁺. A detailed analysis of the luminescence decay made it possible to determine the observed radiative lifetimes of Tb³⁺ and Eu³⁺ and estimate the rate of excitation energy transfer between these ions. For this task, a simple approximation function was proposed. The values of the energy transfer rates determined independently from the luminescence decays of terbium(III) and europium(III) ions show a good correlation.

Luminescence thermometry based on one-dimensional benzoato-bridged coordination polymers containing lanthanide ions

Three 1D coordination polymers with benzoate bridges have been assembled in the presence of 18-crown-6-ether (18C6): 1∞[Tb(PhCOO)3(H2O)(EtOH)]·0.5(18C6) 1, 1∞[Eu(PhCOO)3(H2O)2]·0.5(18C6) 2, 1∞[Nd(PhCOO)3(H2O)2]·0.5(18C6) 3. Compounds 2 and 3 are isomorphous. The crown ether molecules co-crystallize with the resulting 1D coordination polymers and play an important role in the supramolecular architecture of the crystals. A molecular alloy was prepared in a similar way to compound 1 using TbCl3·6H2O and EuCl3·6H2O in a molar ratio of 95 : 5. The EuIII ions have statistically substituted the TbIII ions in the host lattice The luminescence thermometry performance of the Tb0.95Eu0.05 system was investigated using pulsed excitation into TbIII absorption at 352 nm. The maximum Sr value is 1.88% K-1 at 80 K which is slightly reduced at 1.60% K-1 at 313 K. Time-gated emission spectroscopy, employed here for the first time, allows us to reduce the spectral overlap of Tb and Eu emissions in the 610 to 625 nm range by 100% at 80 K, from 18 to 9%. Compound 1 as well as the molecular alloy, Tb0.95Eu0.05, show X-ray induced luminescence.

Sensitive magnetic-field-response magnetization dynamics in a one-dimensional dysprosium coordination polymer

A Dy(iii) coordination polymer shows significant single-molecule magnet behavior with a sensitive low-field response.

Single molecule magnets of cobalt and zinc homo- and heterometallic coordination polymers prepared by a one-step synthetic procedure

The synthesis of 1D cobalt and zinc monometallic and heterometallic coordination polymers (CPs) was carried out applying one-pot synthetic methods by using either supercritical carbon dioxide or ethanol as the solvent. A collection of four 1D CPs were thus obtained by the combination of a metal (or a mixture of metals) with the linker 1,4-bis(4-pyridylmethyl)benzene. The used metallic complexes were zinc and cobalt hexafluoroacetylacetonate, which can easily incorporate pyridine ligands in the coordination sphere of the metal centre. Independently of the used solvent, the precipitated phases involving Zn(ii), i.e., homometallic CP of Zn(ii) and bimetallic CP of Zn(ii)/Co(ii), were isostructural. Contrarily, homometallic CPs of Co(ii) were precipitated as an isostructural phase of Zn(ii) or with a different structure, depending on the used solvent. All the structures were resolved by XRD using synchrotron radiation. In addition, the magnetic properties of the new CPs involving Co(ii) were studied. Remarkably, at low temperatures with the application of an external field, they acted as field-induced single molecule magnets.

One-pot synthesis of heterometallic (Zn(ii)/Co(ii)) nodes directing CP magnetic behaviour to single molecule magnets.