Bismuth(iii)-thiophenedicarboxylates as host frameworks for lanthanide ions: synthesis, structural characterization, and photoluminescent behavior.

Three bismuth-2,5-thiophenedicarboxylates (Bi-TDC) and two europium-2,5-thiophenedicarboxylates (Eu-TDC) were synthesized under ambient conditions. The structures were determined through single crystal X-ray diffraction, and three of the phases were further characterized by powder X-ray diffraction, Raman spectroscopy, and thermogravimetric analysis. Reactions of bismuth nitrate, 2,5-thiophenedicarboxylate, and pyridine in an acidic solution of acetic acid and ethanol yield Hpy[Bi(TDC)2(H2O)]·1.5H2O (1), whereas reactions in a water/ethanol mixture produce a minor phase, [Hpy]3[Bi2(TDC)4(HTDC)(H2O)]·xH2O (2) along with a major product, (Hpy)2[Bi(TDC)2(HTDC)]·0.36H2O (3). The structures of 1-3 are all built from anionic Bi-TDC chains that are further bridged through additional TDC linkages into interpenetrated 2D sheets. Addition of an aqueous lanthanide solution to the reaction mixtures that yielded 1 and 2-3 resulted in the formation of doped phases, Hpy[Bi1-xLnx(TDC)2(H2O)]·1.5H2O (Bi1-xLnx-1), where Ln = Nd, Sm, Eu, Tb, Dy, and Yb, and (Hpy)2[Bi0.99Eu0.01 (TDC)2(HTDC)]·0.36H2O (Bi0.99Eu0.01-3). Using europium nitrate rather than the bismuth precursor resulted in the formation of two homometallic europium based phases, [Eu(TDC)(NO3)(H2O)]n (4) and [Eu2(TDC)3(H2O)9]·5H2O (5), which adopt an extended 3D network and an interpenetrated 2D structure, respectively. Photophysical measurements were carried out for 1 and the lanthanide containing phases and quantum yield and lifetime values were determined for the visible light emitters. Herein, the structural chemistry, spectroscopic properties, and luminescence of the bismuth phases, their lanthanide doped analogs, and the europium compounds are presented.

A General Model of Sensitized Luminescence in Lanthanide-Based Coordination Polymers and Metal-Organic Framework Materials.

Luminescent lanthanides containing coordination polymers and metal-organic frameworks hold great potential in many applications due to their distinctive spectroscopic properties. While the ability to design coordination polymers for specific functions is often mentioned as a major benefit bestowed on these compounds, the lack of a meaningful understanding of the luminescence in lanthanide coordination polymers remains a significant challenge toward functional design. Currently, the study of these compounds is based on the antenna effect as derived from molecular systems, where organic antennae are used to facilitate lanthanide-centered luminescence. This molecular-based approach does not take into account the unique features of extended network solids, particularly the formation of band structure. While guidelines for the antenna effect are well established, they require modification before being applied to coordination polymers. A series of nine coordination polymers with varying topologies and organic linkers were studied to investigate the accuracy of the antenna effect in coordination polymer systems. By comparing a molecular-based approach to a band-based one, it was determined that the band structure that occurs in aggregated organic solids needs to be considered when evaluating the luminescence of lanthanide coordination polymers.

Rethinking Sensitized Luminescence in Lanthanide Coordination Polymers and MOFs: Band Sensitization and Water Enhanced Eu Luminescence in [Ln(C15H9O5)3(H2O)3]n (Ln = Eu, Tb).

A coordination polymer [Ln(C15H9O9)3(H2O)3]n (1-Ln = Eu(III), Tb(III)) assembled from benzophenonedicarboxylate was synthesized and characterized. The organic component is shown to sensitize lanthanide-based emission in both compounds, with quantum yields of 36% (Eu) and 6% (Tb). Luminescence of lanthanide coordination polymers is currently described from a molecular approach. This methodology fails to explain the luminescence of this system. It was found that the band structure of the organic component rather than the molecular triplet state was able to explain the observed luminescence. Deuterated (Ln(C15H9O9)3(D2O)3) and dehydrated (Ln(C15H9O9)3) analogues were also studied. When bound H2O was replaced by D2O, lifetime and emission increased as expected. Upon dehydration, lifetimes increased again, but emission of 1-Eu unexpectedly decreased. This reduction is reasoned through an unprecedented enhancement effect of the compound's luminescence by the OH/OD oscillators in the organic-to-Eu(III) energy transfer process.

Benzo[1,2-b:4,5-b']dithio-phene-4,8-dione.

The title mol-ecule, C(10)H(4)O(2)S(2), is situated on a crystallographic center of inversion. In the crystal, weak hydrogen bonding contributes to the packing of the mol-ecules.

Uranyl sensitization of samarium(III) luminescence in a two-dimensional coordination polymer.

Heterometallic carboxyphosphonates UO(2)(2+)/Ln(3+) have been prepared from the hydrothermal reaction of uranyl nitrate, lanthanide nitrate (Ln = Sm, Tb, Er, Yb), and phosphonoacetic acid (H(3)PPA). Compound 1, (UO(2))(2)(PPA)(HPPA)(2)Sm(H(2)O)·2H(2)O (1) adopts a two-dimensional structure in which the UO(2)(2+) metal ions bind exclusively to the phosphonate moiety, whereas the Ln(3+) ions are coordinated by both phosphonate and carboxylate functionalities. Luminescence studies of 1 show very bright visible and near-IR samarium(III)-centered emission upon direct excitation of the uranyl moiety. The Sm(3+) emissive state exhibits a double-exponential decay with lifetimes of 67.2 ± 6.5 and 9.0 ± 1.3 µs as measured at 594 nm, after excitation at both 365 and 420 nm. No emission is observed in the region typical of the uranyl cation, indicating that all energy is either transferred to the Sm(3+) center or lost to nonradiative processes. Herein we report the synthesis, crystal structure, and luminescent behavior of 1, as well as those of the isostructural terbium, erbium, and ytterbium analogues.

Para-derivatized pybox ligands as sensitizers in highly luminescent Ln(III) complexes.

New complexes of pyridine-bis(oxazoline) derivatized with -H, -OMe, and -Br at the para position of the pyridine ring with Eu(III) and Tb(III) have been isolated. These are highly luminescent in the solid state, regardless of the ligand-to-metal ratio. Several of the metal complexes were isolated and characterized by single crystal X-ray diffraction, showing the rich diversity of structures that can be obtained with this family of ligands. [Eu(PyboxOMe)(3)](NO(3))(3)·3CH(2)Cl(2), 1, crystallizes in the monoclinic space group P2(1)/n and has the cell parameters a = 14.3699(10) Å, b = 13.4059(9) Å, c = 25.8766(18) Å, ß = 95.367(1)°, and V = 4963.1(6) Å(3). The isostructural [Tb(PyboxOMe)(3)](NO(3))(3)·3CH(2)Cl(2), 2, crystallizes with the parameters a = 14.4845(16) Å, b = 13.2998(15) Å, c = 25.890(3) Å, ß = 94.918(2)°, and V = 4969.1(10) Å(3). 3, a 1:1 complex with the formula [Eu(PyboxBr)(NO(3))(3)(H(2)O)], crystallizes in the monoclinic P2(1)/c space group with a = 11.649(2) Å, b = 8.3914(17) Å, c = 20.320(4) Å, ß = 100.25(3)°, and V = 1954.5(7) Å(3). 4, a product of the reaction of PyboxBr with Tb(NO(3))(3), is [Tb(PyboxBr)(2)(η(2)-NO(3))(η(1)-NO(3)](2)[Tb(NO(3))(5)]·5H(2)O. It crystallizes in the monoclinic space group P2(1) with a = 15.612(3) Å, b = 14.330(3) Å, c = 16.271(3) Å, ß = 92.58(3)°, and V = 3636.5(13) Å(3). [Tb(Pybox)(3)](CF(3)SO(3))(3)·3CH(2)CN, 5, crystallizes in the triclinic space group P1̅ with a = 12.3478(2) Å, b = 15.0017(2) Å, c = 16.1476(4) Å, α = 100.252(1)°, ß = 100.943(1)°, γ = 113.049(1)°, and V = 2594.80(8) Å(3). Finally, compound 6, [Tb(Pybox)(2)(NO(3))(H(2)O)](NO(3))(2)·CH(3)OH, crystallizes in the triclinic P1̅ space group with a = 9.7791(2) Å, b = 10.1722(2) Å, c = 15.3368(3) Å, α = 83.753(1)°, ß = 78.307(1)°, γ = 85.630(1)°, and V = 1482.33(5) Å(3). In solution, the existence of 3:1, 2:1, and 1:1 species can be observed through absorption and luminescence speciation measurements as well as NMR spectroscopy. The stability constants in acetonitrile, as an average obtained from absorption and emission titrations, are log ß(11) = 5.4, log ß(12) = 8.8, and log ß(13) = 12.8 with Eu(III) and log ß(11) = 4.5, log ß(12) = 8.4, and log ß(13) = 11.7 for the Tb(III) species with PyboxOMe. Pybox displayed stability constants log ß(11) = 3.6, log ß(12) = 9.1, and log ß(13) = 12.0 with Eu(III) and log ß(11) = 3.7, log ß(12) = 9.3, and log ß(13) = 12.2 for the Tb(III) species. Finally, PyboxBr yielded log ß(11) = 7.1, log ß(12) = 12.2, and log ß(13) = 15.5 for the Eu(III) species and log ß(11) = 6.2, log ß(12) = 11.0, and log ß(13) = 15.4 with Tb(III). Photophysical characterization was performed in all cases on solutions with 3:1 ligand-to-metal ion stoichiometry and allowed determination of quantum yields and lifetimes of emission for PyboxOMe of 23.5 ± 1.6% and 1.54 ± 0.04 ms for Eu(III) and 21.4 ± 3.6% and 1.88 ± 0.04 ms for Tb(III). For Pybox these values were 25.6 ± 1.1% and 1.49 ± 0.04 ms for Eu(III) and 23.2 ± 2.1% and 0.44 ± 0.01 ms for Tb(III) and for PyboxBr they were 35.8 ± 1.6% and 1.46 ± 0.03 ms for Eu(III) and 23.3 ± 1.3% and a double lifetime of 0.79 ± 0.05/0.07 ± 0.01 ms for Tb(III). A linear relationship between the triplet level energies and the Hammett σ constants was found. Lifetime measurements in methanol as well as the NMR data in both methanol and acetonitrile indicate that all complexes are stable in the 3:1 stoichiometry in solution and that there is no solvent coordination to the metal ion.

4-Bromo-N,N,N,N-tetra-ethyl-pyridine-2,6-dicarboxamide.

The title compound, C(15)H(22)BrN(3)O(2), consists of a pyridine ring with a bromine atom in the para position and two diethyl-amide groups in the ortho positions of the ring. Despite the positions of the three substituents on the pyridine ring, the mol-ecule does not exhibit either local or crystallographic twofold symmetry as the two diethyl-amido units exhibit significantly different N(py)-C-C-N(am) torsion angles of 46.3 (4) and 62.7 (4)° (py is pyridine and am is amine). Inter-molecular C-H⋯O inter-actions support the packing.

Exploring lanthanide luminescence in metal-organic frameworks: synthesis, structure, and guest-sensitized luminescence of a mixed europium/terbium-adipate framework and a terbium-adipate framework.

Two lanthanide-organic frameworks were synthesized via hydrothermal methods. Compound 1 ([(Eu,Tb)(C6H8O4)3(H2O)2].(C10H8N2), orthorhombic, Pbcn, a = 21.925(2) A, b = 7.6493(7) A, c = 19.6691(15) A, alpha = beta = gamma = 90 degrees, Z = 4) takes advantage of the similar ionic radii of the lanthanide elements to induce a mixed-lanthanide composition. Compound 2 ([Tb2(C6H8O4)3(H2O)2].(C10H8N2), orthorhombic, Pbcn, a = 21.866(3) A, b = 7.6101(10) A, c = 19.646(3) A, alpha = beta = gamma = 90 degrees, Z = 8) is the terbium-only analogue of compound 1. Solid-state measurements of their luminescence behavior demonstrate that the neutral guest molecule (4,4'-dipyridyl) residing in the extraframework channels is successful in sensitizing lanthanide ion emission. In compound 1, columinescence occurs, and both lanthanide ions show emission. Additionally, quantum yield and lifetime measurements support the premise that the Tb3+ center is also acting to sensitize the Eu3+, effectively enhancing Eu3+ emission.

An unusually high thermal stability within a novel lanthanide 1,3,5-cyclohexanetricarboxylate framework: synthesis, structure, and thermal data.

A novel three-dimensional lanthanide-organic framework has been synthesized; this material has an exceptionally high thermal stability (600 degrees C) and an unusually low coordination number for a lanthanide ion (CN = 6).

Templated metal-organic frameworks: synthesis, structures, thermal properties and solid-state transformation of two novel calcium-adipate frameworks.

Two novel calcium-adipate framework materials have been synthesized hydrothermally. GWMOF-7 ([Ca(C6H8O4)(H2O)2]*(C10H8N2)) and GWMOF-8 ([Ca(C6H8O4)(H2O)2]*(C12H12N2)) both formed three-dimensional structures and were characterized with single-crystal X-ray diffraction, powder X-ray diffraction, IR spectroscopy and elemental analysis. Thermal properties were also studied with thermogravimetric analysis, and show that these structures undergo a solid-state transformation into a denser three-dimensional framework.

Toward templated metal-organic frameworks: synthesis, structures, thermal properties, and luminescence of three novel lanthanide-adipate frameworks.

Three novel praseodymium-adipate frameworks were synthesized hydrothermally. GWMOF-3 ([Pr(2)(adipic acid)(3)(H(2)O)(4)].adipic acid.4H(2)O) and GWMOF-6 ([Pr(2)(adipic acid)(3)(H(2)O)(2)].4,4'-dipyridyl) formed three-dimensional structures, whereas GWMOF-4 ([Pr(2)(adipic acid)(3)(H(2)O)(2)].H(2)O) produced a more dense, two-dimensional topology. Single-crystal X-ray and powder diffraction, IR spectroscopy, fluorescence spectroscopy, thermogravimetric analysis, and elemental analysis were employed to characterize all samples. GWMOF-6 represents an innovative step forward in metal-organic framework synthesis where a neutral molecular species not used in the construction of the framework is utilized as a structure-directing agent, or template. Furthermore, this template molecule (4,4'-dipyridyl) is shown to sensitize the fluorescence of lanthanide metal centers in a europium analogue of GWMOF-6.