Yunshan Zhou

2-D lanthanide–organic complexes constructed from 6,7-dihydropyrido(2,3-d)pyridazine-5,8-dione: synthesis, characterization and photoluminescence for sensing small molecules

Four isostructural lanthanide–organic complexes [Ln(HPDH)(ox)(H2O)]n (Ln = Eu3+1, Tb3+2, Sm3+3, Gd3+4; H2PDH = 6,7-dihydropyrido(2,3-d)pyridazine-5,8-dione; H2ox = oxalic acid) have been synthesized successfully under hydrothermal conditions and characterized by means of elemental analysis, powder XRD, TG-DTA, IR and UV-vis spectroscopy. Complexes 1 and 2 were structurally characterized by single crystal X-ray diffraction analysis. All complexes are composed of 2-D layers, which further construct a 3-D supramolecular network. Each 2-D layer in complexes 1–4 is composed of 1-D Eu–ox infinite chains, which are further connected by biconnected HPDH− ligands. The photoluminescent properties of complexes 1–4 were studied in the solid state at room temperature. The singlet energy level (34722 cm−1) and the lowest triplet energy level (21786 cm−1) for the ligand H2PDH were calculated on the basis of its UV-vis absorbance edges (1 × 10−4 M in ethanol) and phosphorescence spectrum of complex 4 at 77 K, respectively. The complexes 1, 2, and 3 exhibit metal centered luminescence with characteristic red, green and pink emission, respectively. The energy transfer mechanism and photoluminescence properties were investigated. Complex 1, in which the energy transition from the triplet energy level (3ππ*) of ligand HPDH− to Eu3+ cation is more effective, has been selected as a representative to examine the potential for sensing small molecules by its luminescence properties in different emulsions. EtOH was found to be an excellent enhancing while DMF a highly quenching solvent in this study.

Two isomorphous 3-D lanthanide oxalatophosphonate frameworks based on glyphosate: syntheses, crystal structures, and luminescence properties

Two new 3-D isomorphous lanthanide(III) compounds [Eu2(H2L)2(C2O4)2]·2.51H2O (1) and [Tb2(H2L)2(C2O4)2]·2.46H2O (2, H3L = glyphosate), based on glyphosate and oxalate have been successfully synthesized under hydrothermal conditions, and structurally characterized. In the two compounds, tetra-connected glyphosate ligands are coordinated to Ln3+, resulting in the formation of 1-D {Ln2(H2L)2}n double chains along the c direction. Each of the chains is connected to its four neighbors via the O atoms of phosphates of H2L− ligands, resulting in a 3-D (4, 6)-connected framework with 43·58·63·7 topology, which possesses 1-D channels with oxalates and lattice water molecules as troglodytes. The oxalates are stabilized via chelating Ln3+ in the form of 1-D Ln-C2O42− zigzag chains along the c direction. To the best of our knowledge, compounds 1 and 2 represent the first single-crystal structures of lanthanide(III)-glyphosate compounds incorporating second ligands. The luminescent properties of compounds 1 and 2 have been investigated at room temperature. The energy gaps between the triplet excited state of oxalic acid and the lowest excited resonance levels of Eu3+ (5D0) and Tb3+ (5D4) are 7270 cm−1 and 4070 cm−1, respectively, indicating that oxalate is more suitable for the sensitization of Tb3+ luminescence than Eu3+ luminescence.

Synthesis, structures and photoluminescence of a series of 3D lanthanide–organic coordination polymers constructed from versatile 2,2′-bipyridine-3,3′-dicarboxylic acid 1,1′-dioxide and oxalic acid

A series of 3D coordination polymers {[Ln2(bdcd)(ox)2(H2O)3]·4H2O}n (Ln = Eu (1), Tb (2), Sm (3), Dy (4), and Gd (5)), which crystallize in the triclinic space group P with Z = 2, have been synthesized successfully based on the versatile ligands 2,2′-bipyridine-3,3′-dicarboxylic acid 1,1′-dioxide (H2bdcd) and oxalic acid (H2ox). The compounds were characterized by means of IR spectroscopy, elemental analysis, TG, and powder X-Ray diffraction, whereby compounds 1 and 2 were structurally characterized. All of the compounds are isomorphous and have a 3D open framework in which ox2− ligands bridge Ln3+ ions through their carboxylate groups resulting in the formation of a 1D Ln–ox infinite chain in the ac plane. The adjacent 1D Ln–ox infinite chains are then connected to each other through coordination interactions between Ln3+ ions and the carboxylate groups and N-oxide atoms of bdcd2− ligands resulting in a 3D (7,8)-connected open framework with a (38·49·54) (37·49·511·6) topology possessing 1D channels with lattice water molecules as residents. The photoluminescence properties of compounds 1, 2 and 4 were investigated in detail.

Photoluminescent 3D lanthanide-organic frameworks based on 2,5-dioxo-1,4-piperazinylbis(methylphosphonic) acid formed via in situ cyclodehydration of glyphosates.

Hydrothermal reactions of lanthanide nitrates with glyphosate have resulted three new isostructural 3D lanthanide-organic frameworks, Ln(NO3)(H2L) [Ln = Eu (1), Tb (2), Gd (3); H4L = 2,5-dioxo-1,4-piperazinylbis(methylphosphonic) acid], with good yields, where H4L as a new ligand was formed via in situ cyclodehydration of original ligand glyphosates during the hydrothermal reaction. The compounds were thoroughly characterized by IR, UV-vis, elemental analysis, single-crystal X-ray diffraction analysis, powder X-ray diffraction analysis, and thermogravimetric/differential thermal analysis (TG-DTA). Three compounds display 3D 6,6-connected open frameworks with 4(13)·6(2) topology possessing 1D channels in which NO3(-) anions act as troglodytes by chelating Ln(3+) centers. The TG-DTA study of the compounds showed remarkable thermal stability up to 380 °C. Under room temperature UV-light irradiation, the Eu(3+) and Tb(3+) compounds showed the corresponding characteristic Ln(3+) intra 4f(n) emission peaks. The triplet energy level (21882 cm(-1)) of the ligand (H4L) was determined from the emission spectrum of its Gd(3+) compound at 77 K. The emission lifetimes (1.54 ms of (5)D0 for compound 1 and 1.98 ms of (5)D4 for compound 2) and absolute emission quantum yields (10.1% for compound 1 and 5.9% for compound 2) were also determined.

Synthesis, Structure, and Photoluminescence of Color-Tunable and White-Light-Emitting Lanthanide Metal–Organic Open Frameworks Composed of AlMo6(OH)6O183– Polyanion and Nicotinate

A series of isostructural compounds Na(HL)(CH3COO)Ln(Al(OH)6Mo6O18)(H2O)6·10H2O [L = nicotinate; Ln = Eu (1), Tb (2)] and Na(HL)(CH3COO)EumTbnLa1-m-n(AlMo6(OH)6O18)(H2O)6·10H2O (3-8, L = nicotinate), wherein Anderson-type polyanions AlMo6(OH)6O183- as basic inorganic building blocks are connected by Eu(CH3COO)(HL)(H2O)3]24+ and [Na2(H2O)8]2+ cations, resulting in formation of three-dimensional lanthanide metal-organic open frameworks, were synthesized successfully with AlCl3·6H2O, Na2MoO4·2H2O, nicotinic acid, and lanthanide nitrates as starting materials. The compounds were characterized by UV-vis, IR, elemental analysis, powder XRD, and TG-DTA measurements. The single-crystal structures of compounds 1 and 2 show that the two compounds display three-dimensional open frameworks with 1D channels along the b and c axes. Investigation of the energy transfer mechanism indicated that the organic nicotinate ligand can transfer energy efficiently to Tb3+ rather than Eu3+. The influence of the POM moiety on the fluorescence of the compounds is also studied. Compounds 1-8 exhibit tunable luminescence color, and emitting of white light was realized through adjusting the molar ratio of Eu:Tb:La within the compounds.

Polyoxometalate-based layered nano-tubular arrays: facile fabrication and superior performance for catalysis

Keggin-type polyoxoanion PW12O403−-containing one-dimensional nano-tubular arrays, with the structure polyethylenimine/polystyrenesulfonate/(poly(allylammonium)/polystyrenesulfonate)3(poly(allylammonium)/PW12O403−)8, were fabricated as a prototype using a layer-by-layer deposition technique in porous anodic aluminum oxide and polycarbonate templates with a pore diameter of 200 nm, and characterized by IR, UV-vis and SEM. The resulting nano-tubes have a uniform diameter of 180 ± 20 nm and a uniform wall thickness of 30 ± 5 nm. These arrays have shown superior performance in the UV light irradiated photo-degradation of Rhodamine B (selected as a representative dye) under mild conditions with respect to both the catalytic efficiency and operating convenience due to the confinement within the nano-tubes both in the latitudinal and radial direction. Remarkably, the catalytic activity of the nano-tubular arrays could be recovered by means of simple immersion in the polyoxoanion solution when the catalytic reactivity became reduced, which is vital in view of practical applications. The total organic carbon content changes and GC-MS measurements were conducted to identify the degradation products. The hydroxyl radical mechanism was found to be adopted by the photo-degradation reaction.

A new and efficient luminescence enhancement system of Eu-N-(3,5-dibromosalicylidene)-2-aminopyridine-1,10-phenanthroline and its application in the determination of trace amounts of europium.

A sensitive luminescence enhancement system has been developed for the determination of trace amounts of trivalent europium. The luminescence intensity of europium complex with N-(3,5-dibromosalicylidene)-2-aminopyridine (HL) was greatly enhanced after the addition of 1,10-phenanthroline (Phen) in acetonitrile solution. The excitation and emission wavelengths were 274 and 617 nm respectively. Under optimal conditions, the luminescence intensities varied linearly with Eu(3+) concentration in the range of 4.0 × 10(-6)∼2.4 × 10(-5) mol L(-1) with a detection limit of 4.3 × 10(-10) mol L(-1). This method was successfully applied to determine the trace amounts of Eu(3+) in a high purity Gd(2)O(3) matrix and in a mixed lanthanide sample. Energy transfer mechanism and luminescence enhancement of HL-Phen-Eu ternary system were studied. The results indicate that both HL and Phen are good sensitizers for the luminescence of Eu(3+) ions, as energy gap between the lowest triplet level of HL/Phen and the resonant level of Eu(3+) ((5)D(1)) exists around the optimal value (3000 ± 500 cm(-1)). The interference by some other lanthanide ions and common ions were also studied.

A general synthesis approach in action: preparation and characterization of polyoxomolybdenum(VI) organophosphonates through oxidative Mo–Mo bond cleavage in {MoV2O4}

Three new tetramolybdenum organophosphonate compounds, (NH4)7{FeIII[MoVI2O6CH3C(O)(PO3)2]2}·10H2O 1, (NH4)4[Na(H2O)6]{CrIII[MoVI2O6CH3C(O)(PO3)2H]2}·7.67H2O 2 and (NH4)8{MnII[MoVI2O6CH3C(O)(PO3)2]2}·9H2O 3 have been successfully synthesized by reacting metal-containing oxidants Fe2(C2O4)3, MnO4− and CrO42− with a simple aqueous solution containing {MoV2O4(H2O)6}2+, respectively, in the presence of (hydroxylethylidene) diphosphonic acid. These compounds are characterized by elemental analyses, spectroscopic methods (IR, UV-Vis, XPS), TG-DTA, single-crystal X-ray diffraction analyses (including bond valence sum calculations) and powder X-ray diffraction analysis. Single crystal X-ray diffraction analyses have revealed that Mo–Mo bonds of {MoV2O4(H2O)6}2+ are cleavaged in the oxidation reaction to form {MoVI2O6} motifs, which are concomitantly stabilized by organophosphate and linked by the resulted metal ions coming from the metal-containing oxidants and bring on the formation of compounds 1–3, whose anions have a general formula {M[MoVI2O6CH3C(O)(PO3)2]2}n−(M = FeIII1; CrIII2; MnII3). It is important that the successful synthesis and characterization of the three new compounds induces a simple yet general strategy which can be utilized for the preparation of polyoxomolybdenum(VI) organophosphonates through oxidative Mo–Mo bond cleavage with various metal-containing oxidants like FeIII, MnVII and CrVI in the presence of various organophosphonates.

Fabrication and notable optical nonlinearities of ultrathin composite films derived from water-soluble Keggin-type polyoxometalates and water-insoluble phthalocyanine

Composite films with the general formula (POM/CuTAPc)n derived from water-soluble Keggin-type polyoxometalates (POMs = H5PMo10V2O40, H4SiW12O40, H3PMo12O40 and H3PW12O40) and water-insoluble 4,9,16,23-copper tetraaminophthalocyanine (denoted CuTAPc) are successfully fabricated by a layer-by-layer self-assembly technique and systematically characterized. The structure of the polyoxometalate anions in the multilayers is kept intact; the deposition amounts of POM and CuTAPc remain constant in every adsorption cycle of the composite film assembly process. The nonlinear optical properties of the composite films were studied by a Z-scan technique at a wavelength of 532 nm and a pulse width of 7 ns. The results not only show that the composite films exhibit notable optical nonlinear self-defocusing behavior and a saturated absorption effect with the nonlinear optical absorption co-efficient β, refractive index n2, and third-order NLO susceptibility χ(3) of the films increasing with the increase in number of layers of the films, but also reveal importantly that the discrepancy of LUMO levels between CuTAPc and POMs is proportional to their third-order NLO response.

A new quaternary photoluminescence enhancement system of Eu-N-(o-vanillin)-1,8-diaminonaphthalene-1,10-phenanthroline-Zn and its application in determining trace amounts of europium and zinc.

A new sensitive quaternary photoluminescence enhancement system has been successfully developed to determine trace amounts of Eu(3+) and Zn(2+). The photoluminescence intensity of Eu - N-(o-vanilin)-1,8-diaminonaphthalene systems was greatly increased by the addition of specific concentrations of 1, 10-phenanthroline and Zn(2+). The excitation and emission wavelengths were 274 and 617 nm, respectively. Under optimal system conditions, the photoluminescence intensity showed a linear response toward Eu(3+) in the range of 5.0 × 10(-6)  ~ 2.0 × 10(-5)  M with a limit of detection (= 2.2 × 10(-9)  M) and the photoluminescence intensity of the system decreased linearly by increasing the Zn(2+) concentration in the range of 5.0 × 10(-8)  ~ 1.0 × 10(-6)  M with a limit of detection (= 8.8 × 10(-11)  M). This system was successfully applied for the determination of trace amounts of Eu(3+) in a high purity La2O3 matrix and in the synthetic rare earth oxide mixture, and of Zn(2+) in a high purity Mg(NO3)2 · 6H2O matrix and in synthetic coexisting ionic matrixes. The energy transfer mechanism, photoluminescence enhancement of the system and interference of other lanthanide ions and common coexisting ions were also studied in detail.