Yb(C(4)H(4)O(4))(1.5)] undergoes a temperature-triggered single-crystal to single-crystal transformation. Thermal X-ray single-crystal studies showed a reversibly orchestrated rearrangement of the atoms generated by the breaking/formation of coordination bonds, in which the stoichiometry of the compound remains unchanged. The transformation occurs on heating the crystal at approximately 130 degrees C. This uncommon behavior was also studied by thermal methods, FTIR spectroscopy, and thermodiffractometry. Both polymorphs, alpha (room-temperature form) and beta (high-temperature form), are proven to be active heterogeneous catalysts; the higher catalytic activity of beta is owed to a decrease in the Yb coordination number. A mechanism based on spectroscopic evidence and involving formation of the active species Yb-O-OH is proposed for the sulfide oxidation.
A luminescent lanthanide metal-organic framework (MOF) based on Eu 3+ and Tb 3+ ions with 2-phenylsuccinate (EuTb-psa) was obtained solvothermally to explore its behavior as a temperature sensor in an unconventional temperature range through the study of the thermal evolution of the hypersensitive 4f-4f 5 D 0 → 7 F 2 transition and the luminescence lifetime. The efficiency of the luminescence process was evaluated through the europium intrinsic quantum yield (Q Eu ), and its variation as a function of temperature is also reported. The optical [a]
Reactions
in aqueous solution under hydrothermal conditions between
(±)-2,3-dimethylsuccinic acid and lanthanide chlorides lead to
two different isostructural types with chemical formulas [Ln2(C6H8O4)3(H2O)2] Ln(III) = Pr–Eu (except
Pm) (Type I, compounds 1–4) and [Ln2(C6H8O4)3] Ln(III) = Tb–Yb (except Tm) (Type II, compounds 5–9). The crystal structure has been solved
for the Pr (1)-, Sm (3)-, and Ho (7)-containing compounds by means of single-crystal XRD methods,
whereas powder XRD Rietveld refinement was used for the rest of the
MOFs. Compounds 1–4 crystallize in
the triclinic space group P1̅, whereas compounds 5–9 belong to the tetragonal space group P43212. Type I and II compounds are
3D frameworks consisting of chains of [LnO8(H2O)] or [LnO8] polyhedra, respectively, linked by
dimethylsuccinate anions, giving rise to I1O2 connectivity. All the compounds were characterized by X-ray diffraction,
variable-temperature Fourier transform infrared spectroscopy, and
thermal analysis. An exhaustive topological study was performed in
comparison with other related compounds. The photoluminescent (PL)
properties for compounds 3, 4, and 5 have been also explored, indicating that a metal-centered
luminescent process takes place.
Two new layered polymeric frameworks have been synthesized under different hydrothermal conditions and characterized by single-crystal X-ray diffraction, thermal analysis, and variable temperature-Fourier Transform Infrared Spectroscopy (VT-FTIR). The compound I, with formula [Er(2)(dms)(3)(H(2)O)(4)], has a triclinic cell with parameters a = 5.8506 A, b = 9.8019 A, c = 11.9747 A, alpha = 70.145 degrees , beta = 80.234 degrees , and gamma = 89.715 degrees , and the compound II, [Er(2)(dms)(3)(H(2)O)], is monoclinic and its cell parameters are a = 11.1794 A, b = 18.2208 A, c = 12.7944 A, beta = 112.4270 degrees , where dms = 2,2-dimethylsuccinate ligand. A theoretical study including energy calculations of the dms conformers was carried out at the Density Functional Theory (DFT-B3LYP) level of theory, using the 6-311G* basis set. Further calculations of the apparent formation energies of I and II crystalline structures were performed by means of the periodic density functional theory, using DF plane-waves. The analysis of the structural features, theoretical relative stabilities, and the influence of synthesis conditions are presented here. The heterogeneous catalytic activity of the new compounds is tested and reported.
Three new layered metal-organic frameworks (MOFs) based on 2-phenylsuccinic acid (H 2 psa) and lanthanide ions, with formula [Ln 2 (C 10 H 8 O 4 ) 3 (H 2 O)] (Ln= Eu, Sm and EuGd) have been synthesized under solvothermal conditions and fully characterized by singlecrystal X-ray diffraction, thermal and vibrational analysis. The compounds are isostructural featuring 2D frameworks that consist of infinite zig-zag chains composed by [LnO 8 ] and [LnO 8 (H 2 O)] edge-sharing polyhedra linked by psa ligands leading to layers further connected by weak π-π interactions in an edge orientation. Moreover, a topological study was carried out to obtain the simplified net for better comparison with structurally related compounds. The Eupsa crystals were exfoliated into nanolayers after miniaturization by addition of sodium acetate as capping agent in the reaction medium. Scanning electron microscopy was applied to characterize the miniaturized samples whereas the exfoliated hybrid nanosheets were studied by atomic force microscopy. The photoluminesce (PL) properties of the bulk compounds as well as the miniaturized and exfoliated materials were investigated and compared with other related ones. An exhaustive study of the Eu(III)-based MOFs was performed on the basis of the obtained PL parameters (excitation and emission spectra, k r , k nr , intrinsic quantum yields and lifetimes) to explore the underlying structure-property relationships.
Two new holmium-succinate frameworks have been synthesized by hydrolysis in situ of the succinylsalicylic acid under different hydrothermal conditions. Compound 1, [Ho(2)(C(4)H(4)O(4))(3)(H(2)O)(2)]·0.33(C(7)H(6)O(3)), P ̅i space group, has a novel structure composed by 1D-SBUs consisting of [HoO(9)] chains of polyhedra linked by the succinate ligands giving a 3D framework. Compound 2, [Ho(2)(C(4)H(4)O(4))(3)(H(2)O)(2)], also belonging to the P ̅i space group, has a denser structure. The role of the in-situ-generated salicylic acid on formation of both structures is studied by means of a synthesis design methodology. A topological study of the new holmium succinate compounds in comparison with the previously reported 3D holmium-succinate framework is performed here.
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