Isostructural 3D Ln–Ag (Ln = Eu; Dy; Ho) coordination frameworks based on mixed nicotinate and oxalate ligands: Synthesis,crystal structures and luminescence

By control of mixed organic ligands with different geometries, three unusual 4d–4f heterometallic coordination polymers, [AgLn(nic)₂(ox)] · 2H₂O [Ln = Eu (1); Dy (2); Ho (3)] [nic = nicotinate; ox = oxalate] have been synthesized under hydrothermal reaction. Three structures represent 3D open heterometallic coordination frameworks that are constructed from rare zigzag lanthanide-ox-silver chains and nic linkers. Furthermore, the luminescent property of complex 1 was discussed.     

Structure and dielectric properties of Ln3NbO7 (Ln = Nd,Gd, Dy,Er, Yb and Y)

The structure and dielectric properties of Ln₃NbO₇ (Ln = Nd, Gd, Dy, Er, Yb and Y) ceramics are investigated. With decreasing ionic radius of Ln³⁺, the stable crystal structure of the compounds shifts from orthorhombic weberite to defect fluorite. It is experimentally observed that, with the exception of Gd₃NbO₇, the room temperature real part of the relative permittivity of Ln₃NbO₇ ceramics decreases from approximately 40 to 30 (at 1 MHz) with increasing ionic radius of Ln³⁺. The observed imaginary part of the relative permittivity is in order of 10⁻² to 10⁻¹ (room temperature and 1 MHz) and it is relatively stable up to 80 °C, where it increases with a rise in temperature. Interesting exceptions of these trends are Nd₃NbO₇ that crystallizes with a weberite-type structure and shows large positive temperature variation of the dielectric properties, and Gd₃NbO₇ that crystallized in a weberite related structure and displays frequency and temperature dependent dielectric relaxation behavior.     

Thermal Expansion of Ln6WO12 (Ln = Y,Ho, Er,Yb) and Ln2WO6 (Ln = Gd,Dy, Ho) – an In Situ Synchrotron X‐ray Diffraction Study

The thermal expansion (TE) behavior of cubic and rhombohedral Ln₆WO₁₂ (Ln = Y, Ho, Er, Yb) and monoclinic Ln₂WO₆ (Ln = Gd, Dy, Ho) was investigated by synchrotron X‐ray diffraction from room temperature to approximately 1500°C. The volumetric and lattice parameter expansions were measured for all compositions in both systems, and the respective expansion coefficients were derived and fitted over the observed temperature range with a second‐order polynomial. The relative TE evolution along the unit cell edges in each phase was described from a crystallographic perspective, with the reasons for TE dynamics explained in terms of the fundamental constituent units of the structure. Analysis of the TE ellipsoid of the monoclinic Ln₂WO₆ revealed a continuous change in both its shape and orientation, with the latter effect strongly manifested in the (010) plane. A noticeable reversal of the relative expansion rates between a, and b and c lattice parameters was attributed to the rotation of the ellipsoid cross section in this plane, bringing the larger of the two eigenvectors closer to a, while the smaller one to c. Investigating the structural dynamics of the constituent layers in Ln₂WO₆ suggested that the bridging role of the Ln polyhedron centered on the only general position in the unit cell may be the reason for the rotating TE ellipsoid.     

Novel complex ceramic oxides,Ln2TiO5 (Ln = La,Sm, Gd,Tb, Dy,Ho, Er,and Yb), for polyphase nuclear waste-forms

As part of a broader study of ceramic nuclear waste-forms, four different lanthanide titanates were fabricated; La_0.1Sm_0.1Gd_0.1Tb_0.1Dy_0.3Ho_0.1Er_0.2YbTiO₅, Sm_0.3Gd_0.3Dy_0.3Yb_1.1TiO₅, Sm_0.1Gd_0.4Dy_0.4Yb_1.1TiO₅, and Sm_0.2Gd_0.2Dy_0.2Yb_1.4TiO₅. The aim was to produce single-phase novel materials with cubic symmetry, capable of incorporating a wide variety of cations and with acceptable radiation tolerance. The chemistry flexibility and radiation tolerance are some of the major desirable properties for nuclear waste-form materials. By using multiple lanthanides the average lanthanide radius can be controlled and consequently the structure, along with properties such as radiation tolerance. The radiation tolerance was assessed using in situ 1 MeV krypton irradiation and transmission electron microscopy characterization. Those materials for which cubic symmetry was achieved displayed better radiation tolerance; a greater critical fluence of ions (F_c) was required for the crystalline to amorphous transition, and a lower temperature was required to maintain crystallinity (T_c) during irradiation.     

Three dimensional lanthanide-organic frameworks containing tetranuclear Ln (Ln = La,Nd) cluster secondary building blocks

The hydrothermal reactions of Ln₂O₃, o-phthalic acid (H₂L₁) and N,N’-Piperazine(bis-methylene phosphonic acid) hydrochloride (H₄L₂·HCl) yielded two three dimensional (3D) lanthanide-organic frameworks formulated as [Ln₄(L₁)₂(H₂L₂)₃(H₃L₂)₂]·18H₂O (Ln = La, 1; Nd, 2). Single-crystal X-ray diffraction revealed that they are isostructural. They feature 3D open framework structures containing rarely observed centrosymmetric tetranuclear lanthanide sub-building units (SBU). The photoluminescence property of 2 has been investigated, and it shows strong solid-emissions in the near-infrared region at room temperature.     

Syntheses,structures and properties of chiral Ln(III) coordination polymers based on (R)-4-(4-(1-carboxyethoxy)phenoxy)-3-fluorobenzoic acid

Two isomorphic chiral lanthanide coordination polymers (CCPs), namely, [Ln₂(cpfa)₃]_n {Ln = Yb Xu et al. (2011) and Lu Zheng et al. (2015) } {H₂cpfa = (R)-4-(4-(1-carboxyethoxy)phenoxy)-3-fluorobenzoic acid, have been synthesized under hydro(solvo)thermal conditions. Their structures have been determined by single-crystal X-ray diffraction analyses and further characterized by infrared spectra (IR), powder X-ray diffraction (PXRD), elemental analyses, thermogravimetric (TG) analyses and circular dichroism spectra (CD). Structure analysis reveals that CCPs 1 and 2 are isomorphic, crystallizing in Orthorhombic space group P2₁2₁2₁ and giving 3D rhombic framework. Further, CCP 1 show the strong NIR luminescence of Yb(III) ions, suggesting that [cpfa]^2 − is able to sensitize the luminescence of lanthanide ions efficiently. The two polymers also exhibit modest SHG efficiency indicating their potential application as optical materials. Thermogravimetric analyses show the remarkable thermal stabilities of the two lanthanide 3D frameworks up to 420 °C.     

Construction of isostructural Ln–Ag (Ln = Eu; Tb; Dy) nano-channel heterometallic coordination frameworks based on pyrazine-2-carboxylate and oxalate ligands

The self-assembly of pyrazine-2-carboxylate and oxalate with mixed-metal salts under hydrothermal conditions gave three isostructural 3D 4d-4f coordination polymers, LnAg(ox)(2-pzc)₂ · H₂O [Ln = Eu (1); Tb (2); Dy (3)] [ox = oxalate, 2-pzc = pyrazine-2-carboxylate]. All three structures exhibit same unusual 3D nanoporous heterometallic coordination frameworks constructed by zigzag lanthanide–oxalate chains and Ag(2-pzc)₂ units. Furthermore, the luminescent properties of complexes 1 and 2 are discussed.     

3D Ln–Ag (Ln = Nd; Eu) coordination polymers based on isonicotinate and oxalate ligands: Synthesis, crystal structures and luminescence

The self-assembly of isonicotinic acid with metal salts under hydrothermal conditions obtained two new 4d–4f coordination polymers, LnAg(OX)(IN)₂·H₂O (Ln = Nd (1); Eu (2), OX = oxalic acid, IN = isonicotinic acid). The 3D isostructural complexes 1 and 2 are constructed by the assembly of 2D layers, which are built by carboxylate groups of isonicotinic acid and oxalate ligands coordinating to metal centers, with 1D linear linkers completed by silver ions. Furthermore, the luminescent property of complex 2 was investigated.     

Synthesis and Up‐conversion Luminescence of Yb3+/Ln3+ (Ln = Er,Tm, Ho) Co‐Doped Strontium Cerate by Pechini Method

Novel up‐conversion (UC) luminescent nanopowders, Sr₂CeO₄:Yb³⁺,Ln³⁺ (Ln = Er, Tm, Ho) were prepared with Pechini method. The Sr₂CeO₄:Yb³⁺,Ln³⁺ (Ln = Er, Tm, Ho) nanopowders had an orthorhombic crystal structure, and showed olive‐like morphology with the length of about 260 nm and width of about 130 nm. Under 980 nm lazer excitation, the Sr₂CeO₄:Yb³⁺/Er³⁺, Sr₂CeO₄:Yb³⁺/Tm³⁺, and Sr₂CeO₄:Yb³⁺/Ho³⁺ nanophosphors exhibit strong green, blue, and green UC luminescence, respectively. The luminescence mechanisms for the doped lanthanide ions were thoroughly analyzed.     

In Situ Synchrotron X‐Ray Diffraction Study of the Cubic to Rhombohedral Phase Transformation in Ln6WO12 (Ln = Y,Ho, Er,Yb)

The fcc‐to‐rhombohedral phase transformation in Ln₆WO₁₂ (Ln = Y, Ho, Er, Yb) was investigated by in situ high‐temperature X‐ray diffraction. The transformation was determined to be an irreversible, first‐order, diffusional ordering process, which occurred over a temperature range starting at 1240°C. The transformation can be described as a shape change in the rhombohedral unit cell in the parent fcc phase, determined as elongation along the [111] axis and contraction in the (111) plane, resulting in an overall volume decrease on heating. A discontinuity in both volume per formula unit and rhombohedral angle α was observed across the transformation region for all four compositions. Trends in lattice parameters, ΔV and Δα at room and transformation temperatures were established according to Ln cation type and were found to closely mirror the cationic radii sequence of the corresponding rare earth elements.     

Crystal chemistry and ion-irradiation resistance of Ln2ZrO5 compounds with Ln = Sm,Eu, Gd,and Tb

The previously unattained fabrication of single phase Ln₂ZrO₅ (Ln = Sm, Eu, Gd, and Tb) compounds via relatively low sintering temperature (1400°C) is achieved in this study using a coprecipitation method. The crystal structures have been investigated by neutron, synchrotron X-ray powder diffraction, and electron diffraction techniques. While the general long-range structure may be well described by the defect-fluorite type structure with Fmm symmetry, electron diffraction has highlighted a complex underlying modulated structure that varies between each compound. These compounds have been tested for ion-irradiation response using in situ 1 MeV krypton ions and transmission electron microscopy characterization. None of the compounds undergo a crystalline to amorphous transition, even holding at 50 K. Both the underlying fluorite and modulated superstructures are little affected by the irradiation. However, some atomic rearrangements are observed in the postirradiated electron diffraction patterns for the Sm₂ZrO₅ specimen.     

Structure and photophysical properties of new trinuclear lanthanide complexes (Ln = Eu and Tb) with 1,10-phenanthroline

Examples of trinuclear lanthanide (Ln) complexes using bridging sulfato and hydroxo ligands for Ln = Eu and Tb are reported. Structural data demonstrate that three nine-coordinate Ln³⁺ ions are caged in a monomeric structure in [Ln₃(phen)₃(OH)(SO₄)₄(DMF)₃] · DMF · H₂O, with Ln?Ln distances slightly greater than 4 Å. The luminescence and excitation spectra have been recorded and interpreted.     

A new method for production of glass-Ln2Ti2O7 pyrochlore (Ln = Gd,Tb, Er,Yb)

Glass-Ln₂Ti₂O₇ pyrochlore (Ln = Gd, Tb, Er, Yb) was fabricated by sintering the pelletized mixture of glass precursor and Ln-Ti composite at 1200 °C. The phase pure pyrochlore was in-situ crystallized in the amorphous glass matrix. The Ln-Ti composite was prepared by a simple soft chemistry route in an aqueous solution to ensure the homogeneity of the product. Thermal analysis, Fourier transform infrared spectroscopy, X-ray diffraction, Raman spectroscopy, and scanning electron microscopy techniques were employed to investigate the glass-Ln₂Ti₂O₇ pyrochlore structure formation. The cell parameters for the pyrochlore structures by Le Bail fitting are in good agreement with the published data. The presence of the melting glass matrix facilitates the pyrochlore formation, with particle sizes in the range of 1–3 μm. This new aqueous synthetic method provides a simple pathway to produce glass-Ln₂Ti₂O₇ pyrochlore without using organic solvent and/or milling procedures, making it an attractive potential method for scale-up production.     

Synthesis and characterization of decanuclear Ln(III) cluster of mixed calix[8]arene-phosphonate ligands (Ln = Pr,Nd)

Two novel decanuclear Ln(III) compounds (Ln = Pr for 1, Nd for 2) have been solvothermally obtained by using p-tert-butylcalix[8]arene (H₈TBC8A) and phenylphosphonate (PhPO₃H₂) as ligands. Single crystal X-ray diffraction studies reveal that both compounds are stacked by dumbbell-like Ln₁₀ clusters, which are capped by two TBC8A^8 − supports and linked by four complementary PhPO₃^2 − ligands as well as other bridging anions. In addition, the self-assembly behavior of both compounds is interesting: the cationic Ln₁₀ cluster layers are separated by the layers of H₆TBC8A^2 − ligands. Moreover, the luminescent and magnetic properties of both compounds were examined.     

Syntheses,structures and photocatalytic properties of three copper(II) coordination polymers

Three coordination polymers [Cu₂(obtz)₂(tdc)₂]_n (1), {[Cu(obtz)₂(H₂O)₂][Cu₂(obtz)₂(sip)₂]5.5H₂O}_n (2) and [Cu(obtz)(nip)]_n(3) were synthesized by the hydrothermal reaction (obtz = 1.2-bis(1,2,4-triazol-1-ylmethyl)benzene, tdc = 2.5-thiophenedicarboxylate, sip = 5-sulfoisophthalate, nip = 5-nitroisophthalate). 1 shows a ladder-like one-dimensional chain with two side arms. 2 is comprised of two distinct and crystallographically independent polymeric motifs. The first motif in 2 is the ladder-like one-dimensional anionic chain with two side arms. The second motif in 2 is the cationic chain. 3 exhibits the intriguing 2-fold interpenetrated network based on the undulated 2D (4.4) network. 1, 2 and 3 are good photocatalysts for the degradation of methyl orange (MO) under UV irradiation.     

Near-infrared luminescent properties of Ln:LaGdZr2O7 (Ln = Nd,Yb) transparent ceramics for solid-state laser applications

Via a facile solid reactive method, transparent Ln_0.1La_0.9GdZr₂O₇ (Ln = Nd, Yb) ceramics were successfully fabricated for the first time. The highest in-line transmittances of Nd:LaGdZr₂O₇ and Yb:LaGdZr₂O₇ ceramics reached 68% and 69%, respectively, at 1100 nm. The microstructure and crystal structure of Ln_0.1La_0.9GdZr₂O₇ transparent ceramics were fully investigated, indicating that the solid reactive technique is a good method of industrially fabricating Ln_0.1La_0.9GdZr₂O₇ transparent ceramics. The PL spectra demonstrated that Ln_0.1La_0.9GdZr₂O₇ ceramics can effectively be excited at 808 nm and 976 nm, which correlates with the widely applied output wavelengths of AlGaAs and InGaAs laser diodes. The luminescence decay curves were also studied, showing that the average fluorescence lifetimes of Nd_0.1La_0.9GdZr₂O₇ and Yb_0.1La_0.9GdZr₂O₇ transparent ceramics was 355 μs and 663 μs, respectively. Combined with its high temperature resistance and good mechanical strength, Ln_0.1La_0.9GdZr₂O₇ (Ln = Nd, Yb) transparent ceramics can have potential applications in Nd/Yb solid-state laser construction.     

Assembly of two ferrous coordination polymers with triazole derivative: Syntheses,structures and magnetic properties

The reactions of Fe(II) salts with 1,4-bis(1,2,4-triazole-1-ylmethyl-benzene) (btx) give two new Fe(II) coordination polymers {[Fe(btx)₃](ClO₄)₂}_n (1) and {[Fe(btx)(SO₄)(H₂O)₂]}_n (2), which have been characterized by element analysis, PXRD, single-crystal X-ray diffraction and magnetic susceptibility. 1 shows infinite plait-like chain structure, while 2 exhibits as 2D grid. Magnetic studies indicate that the Fe(II) ions in the two coordination polymers retain in high-spin ground state upon cooling from 300 to 2 K, showing antiferromagnetic interactions.     

PNBE-supported metallopolymer-type hybrid materials through grafting of Ln3-benzimidazole-arrayed (Ln = Nd,Yb or Er) complex monomers with efficient NIR luminescence

Through the ring-opening metathesis polymerization (ROMP) of norbornene (NBE) with each of the obtained allyl-containing complex monomers {[Ln₃(L)₄Cl₄(MeOH)₂]·Cl} (Ln = La, 1; Nd, 2; Yb, 3; Er, 4 or Gd, 5; HL = 4-allyl-2-(1H-benzo[d]imidazol-2-yl)-6-methoxyphenol), a series of metallopolymers Poly({[Ln₃(L)₄Cl₄(MeOH)₂]·Cl}-co-NBE) were obtained, respectively. Especially for Poly(NBE-co-2) and Poly(NBE-co-3), covalently-bonded grafting endows significantly improved physical properties including efficient NIR luminescence (Φ_Nd^L = 0.58% and Φ_Yb^L = 0.88%) in solid state.     

Facile one-pot synthesis of porous Ln2Ti2O7 (Ln = Nd,Gd, Er) with photocatalytic degradation performance for methyl orange

Porous nanocrystalline Ln₂Ti₂O₇ (Ln = Nd, Gd, Er) was prepared by a facile self-propagating combustion method using metal nitrates (Ln(NO₃)₃ (Ln = Nd, Gd, Er), TiO(NO₃)₂) and glycine. The photocatalytic activity of Ln₂Ti₂O₇ (Ln = Nd, Gd, Er) was evaluated by the photocatalytic degradation of methyl orange (MO). The results showed that the photocatalytic activity of Ln₂Ti₂O₇ (Ln = Gd, Er) with cubic pyrochlore structure was higher than that of Nd₂Ti₂O₇ with monoclinic perovskite structure and Gd₂Ti₂O₇ showed the best photocatalytic activity. The different photocatalytic activities observed for Ln₂Ti₂O₇ (Ln = Nd, Gd, Er) could be related to its different crystal structures and Ln 4f shells.     

Gas sensing and electrochemical properties of rare earthferrite,LnFeO 3 (Ln = Nd,Sm)

In this paper, nanostructured perovskite-type LnFeO₃ (Ln = Nd, Sm) oxides were synthesized by thermal treatment method (TTM). Characterization analysis conducted by X-ray diffraction (XRD), scanning electron microscopy (SEM) and micro-Raman spectroscopy, have confirmed the perovskite structure of the synthesized nanomaterials. To study the effects of Nd and Sm lanthanides substitution at the A-site on the chemical sensing performance, conductometric and electrochemical sensors based on the synthesized LnFeO₃ samples were fabricated. LnFeO₃-based conductometric and electrochemical sensors were tested for acetone and dopamine sensing, respectively. The data revealed that Nd and Sm in the A-position lead to a significant influence in the gas sensing and electrochemical properties of perovskite LnFeO₃ samples. In particular, it has been demonstrated the good gas sensing characteristics of SmFeO₃ for acetone gas (Response = R/R₀ = 8.3–20 ppm acetone at 200 °C), whereas NdFeO₃ displayed better performance as electrode for the electrochemical detection of dopamine reaching a low detection limit (LOD) of 270 nM at S/N = 3. The electrical and electrochemical characteristics of the perovskite LnFeO₃ samples were discussed in detail with respect to their chemical composition and microstructure.