Photoluminescent layered lanthanide silicates

The hydrothermal synthesis and structural characterization of layered lanthanide silicates, K(3)[M(1-a)Ln(a)Si(3)O(8)(OH)(2)] (M = Y(3+), Tb(3+); Ln = Eu(3+), Er(3+), Tb(3+), and Gd(3+)), named AV-22 materials, are reported. The structure of these solids was elucidated by single-crystal (180 K) and powder X-ray diffraction and further characterized by chemical analysis, thermogravimetry, scanning electron microscopy, (29)Si MAS NMR, and photoluminescence spectroscopy. The Er-AV-22 material is a room-temperature infrared phosphor, while Tb- and Eu-AV-22 are visible emitters with output efficiencies comparable to standards used in commercial lamps. The structure of these materials allows the inclusion of a second (or even a third) type of Ln(3+) ion in the framework and, therefore, the fine-tuning of their photoluminescent properties. For the mixed Tb(3+)/Eu(3+) materials, evidence has been found of the inclusion of Eu(3+) ions in the interlayer space by replacing K+ ions, further allowing the activation of Tb(3+)-to-Eu(3+) energy transfer mechanisms. The occurrence probability of such mechanisms ranges from 0.62 (a = 0.05) to 1.20 ms(-1) (a = 0.1) with a high energy transfer efficiency (0.73 and 0.84, respectively).     

Novel microporous lanthanide silicates with tobermorite-like structure

The synthesis and structural characterization of microporous lanthanide silicates (Na(1.08)K(0.5)Ln(1.14)Si(3)O(8.5).1.78H(2)O, Ln = Eu, Tb, Sm, Ce) are reported. The structure of these solids is closely related with the structure of hydrated calcium silicate minerals known as tobermorites and was solved by powder X-ray diffraction ab initio (direct) methods and further characterized by chemical analysis, thermogravimetry, scanning electron microscopy, (23)Na and (29)Si MAS NMR and luminescence spectroscopy. These materials combine microporosity with interesting photoluminescence properties, and their structural flexibility allows fine-tuning of luminescence properties, by introducing a second type of lanthanide ion in the framework. Thus, they may find applications in new types of sensors.     

Network dimensionality and ligand flexibility in lanthanide terephthalate hydrates

Various lanthanide open framework materials incorporating the terephthalate (TP) entity were prepared using hydrothermal synthesis methods at a moderate temperature of 170 °C. The compounds Nd₂(TP)₃(H₂O)₄(1), Er₂(TP)₃(H₂O)₄(2), Yb₂(TP)₃(H₂O)₂(3), Yb₂(TP)₃(H₂O)₆(4), and Yb₂(TP)₃(H₂O)₈·2H₂O (5), were characterized by single crystal structural analysis and FT-IR spectroscopy. While compounds 1 and 2 have been reported before on the basis of powder X-ray diffraction, the structural characterization of any ytterbium terephthalate species is unprecedented. Compounds 1-5 crystallize in triclinic settings with space group P-1. The compounds are compared with their previously reported Er and Tb-counterparts and the reduction of the dimensionality of the resulting networks from 3D over 2D to 1D with increasing level of hydration is discussed. Compounds 1, 2, and 3 with the lowest water content assemble in three-dimensional network lattices. Compounds 4 and 5, however, form 2D layered systems and 1D rod like chains, respectively, which are held together by hydrogen bonds originating from coordinating H₂O. The crystal lattices of the 3D networks experience higher levels of tension as can be seen by increasing out-of-plane torsion with regard to the terephthalate carboxylate groups. Moreover, there seems to be a correlation between the level of strain on the aromatic ligands and the reduction of the number of carboxylate oxygen atoms that are part of the coordination polyhedra.     

Anion-directed assembly: Framework conversion in dimensionality and photoluminescence

Six novel Ni(II)-fluconazole complexes formulated as (C₁₃H₁₁N₆OF₂)₂Ni₂(NO₃)₂ (1), (C₁₃H₁₂N₆OF₂)₂Ni(NO₃)₂·H₂O (2), (C₁₃H₁₂N₆OF₂)Ni(SO₄)(DMF)₂(H₂O) (3), (C₁₃H₁₂N₆OF₂)₂Ni(H₂O)₂(SO₄)·4H₂O (4), (C₁₃H₁₂N₆OF₂)₂NiCl₂·2(CH₃OH) (5), (C₁₃H₁₂N₆OF₂)₄Ni₂ (MoO₄)₂·6H₂O (6) have been hydrothermally or solvothermally synthesized under similar conditions except different anions and solvents. They are structurally characterized by elemental analysis, IR, TG and single crystal X-ray diffraction. Complex 1 is a molecular binuclear nickel cluster. Complex 2 exhibits a one-dimensional (1D) chain linked by double-stranded fluconazole-bridge. Complex 3 shows a novel 1D chain linked by double-stranded fluconazole-bridge and double-stranded SO₄²⁻-bridge. Complex 4 shows a three-dimensional (3D) architecture and SO₄²⁻ anions occupy the cavity. Complex 5 exhibits a two-dimensional (2D) structure constructed by alternating left- and right-handed helices. Complex 6 exhibits a 3D architecture, in which the 2D layers are pillared by {MoO₄} tetrahedra. Complex 2 can be irreversibly converted to complex 1 in the presence of DMF (N,N′-dimethyllformamide). Complexes 1, 3 and 6 show antiferromagnetic interactions between the nickel (II) ions The photoluminescence properties of the six complexes indicated that the introduction of different anions can enhance or weaken the intra-ligand transitions of fluconazole.     

Near-infrared photoluminescence of lanthanide complexes containing the hemicyanine chromophore

The near-infrared luminescence properties of three (E)-N-hexadecyl-N′,N′-dimethylamino-stilbazolium tetrakis(1-phenyl-3-methyl-4-benzoyl-5-pyrazolonato) lanthanide(III) complexes are described. These three complexes, containing trivalent neodymium, erbium and ytterbium, respectively, show near-infrared luminescence in acetonitrile solution upon UV irradiation. Luminescence decay times have been measured. The complexes consist of a positively charged hemicyanine chromophore with a long alkyl chain and a tetrakis(pyrazolonato) lanthanide(III) anion. Because of the absence of an -hydrogen atom in the pyrazolonato ligands, and because of the saturation of the coordination sphere by four bidentate ligands, the luminescence properties are enhanced when compared to, e.g. quinolinate complexes.     

Synthesis, structures, and photoluminescence properties of novel lanthanide tetracyanoplatinates lacking Pt-Pt interactions

The synthesis of a series of lanthanide tetracyanoplatinates all incorporating 2,2′:6′,2″-terpyridine (terpy) have been carried out by reaction of Ln³⁺ nitrate salts with terpy and potassium tetracyanoplatinate. The incorporation of different Ln³⁺ cations results in the isolation of [Ln(DMF)₂(C₁₅H₁₁N₃)(H₂O)₂(NO₃)]Pt(CN)₄ (Ln=La-Nd, Sm-Yb) under otherwise identical reaction conditions. These compounds have been isolated as single crystals and X-ray diffraction has been used to investigate their structural features. All of the reported compounds are isostructural. Crystallographic data for the representative Eu³⁺ compound (EuPt) are (MoKα, λ=0.71073 Å): monoclinic, space group P2₁/c, a=10.1234(4) Å, b=18.7060(7) Å, c=17.1642(5) Å, β=97.249(3)°, V=3224.4(2), Z=4, R(F)=2.78% for 426 parameters with 7724 reflections with I>2σ(I). The structure consists of a zero-dimensional, ionic salt containing complex [Eu(DMF)₂(C₁₅H₁₁N₃)(H₂O)₂(NO₃)]²⁺ cations and anions. The complex cations contain the Eu³⁺ ions in a tri-capped trigonal prismatic coordination environment with one terdentate 2,2′:6′,2″-terpyridine molecule, one bidentate nitrate anion, two O-bound dimethylformamide molecules, and two coordinated water molecules. Photoluminescence data illustrate that EuPt displays intramolecular energy transfer from the coordinated terpy molecule to the Eu³⁺ cation. The uncoordinated tetracyanoplatinate anion also exhibits visible emission.     

Solventothermal syntheses, structures and photoluminescence of two-dimensional lanthanide coordination polymers with adipic acid

Four lanthanide coordination polymers formulated as [Ln₂(Ad)₃(H₂O)₄] · 0.25H₂O ( Ln = Tb (I), Pr (II), Ho (III), Dy (IV); H₂Ad = adipic acid), have been solventothermally synthesized from the self-assembly of the lanthanide ions (Ln³⁺) with the exible adipic dicarboxylate ligand. All of them were characterized by IR spectroscopy and single-crystal X-ray diffraction. Structural analyses revealed that these complexes had intricate two-dimensional interpenetrated metal-organic networks. In addition, the photoluminescent properties of complex I was discussed in detail, which shows strong green emission, corresponds to ⁵ D ₄ → ⁷ F ₅ transition of Tb³⁺ ions.     

Syntheses, structures, and photoluminescence of three-dimensional lanthanide coordination polymers with 2,5-pyridinedicarboxylic acid

Four new open-framework coordination polymers of lanthanide 2,5-pyridinedicarboxylates, with the formulas Pr2(pydc)₃(H₂O)₂ (1), Ln(pydc)(Hpydc) (Ln=Tb (2), Er (3), Eu (5)), and Gd(pydc)(nic)(H₂O) (4) (H₂pydc=2,5-pyridinedicarboxylic acid, Hnic=nicotinic acid), have been hydrothermally synthesized and four of them (except Eu (5)) have been structurally characterized. Complex 1 consists of two types of ligand-binding modes contributing to link the PrO₇N(H₂O) polyhedral chains to three-dimensional (3D) open-framework architecture. Complexes 2 and 3 are isostructural and feature unique 3D cage-like supramolecular frameworks remarkably different from that of 1, owing to the different ligand-bridging pattern. Complex 4, however, has the distinct 3D open-framework architecture due to the presence of unexpected nicotinate ligands, which may be derived from pydc ligands via in-situ decarboxylation under the hydrothermal condition.     

New lanthanide silicates based on anionic silicate chain, layer, and framework prepared under high-temperature and high-pressure conditions

Three new lanthanide silicates K(1.25)Gd(1.25)Si(2.5)O(7.5) (denoted as GdSiO-CJ7), Cs(3)TbSi(8)O(19)·2H(2)O (denoted as TbSiO-CJ8), and Cs(3)DySi(6)O(15) (denoted as DySiO-CJ9) were synthesized by using a high-temperature and high-pressure hydrothermal method. Their structures determined by single-crystal X-ray diffraction revealed anionic silicate chain, layer and framework, which are further connected with LnO(n) polyhedra to form novel lanthanide silicate frameworks. The structure of GdSiO-CJ7 consists of unbranched silicate chains [Si(5)O(15)](10-) extending along the b axis, which are linked together by edge-sharing linked GdO(6) and GdO(8) chains along the c axis to form a 3-D framework with two types of 10-ring channels along the [010] and [001] directions, respectively. The structure of TbSiO-CJ8 consists of double 4,8-net sheets [Si(8)O(19)](6-) built up from SiO(4) tetrahedra, which are linked together via TbO(6) octahedra to form a 3-D framework with 8-ring channels along the [100] and [010] directions. The structure of DySiO-CJ9 is based on a 3-D silicate framework [Si(6)O(15)](6-) with 6-rings, where DyO(6) octahedra are located between two adjacent 6-rings and connected with six Si atoms via O atoms. The photoluminescence photoluminescence properties of TbSiO-CJ8 and EuSiO-CJ8 were investigated.     

Proteins in mesoporous silicates

Mesoporous silicates (MPS) have an ordered pore structure with dimensions comparable to many biological molecules. They have been extensively explored as supports for proteins and enzymes in biocatalytic applications. Since their initial discovery, novel syntheses methods have led to precise control over pore size and structure, particle size, chemical composition, and stability, thus allowing the adsorption of a wide variety of biological macromolecules, such as heme proteins, lipases, antibody fragments, and proteases, into their structures. This Review discusses the application of ordered, large-pore, functionalized mesoporous silicates to immobilize proteins for biocatalysis.     

Studies in colloidal silicates

Summary The electrical conductance of the mixture obtained by the progressive addition of a sodium silicate to a ferric chloride solution first decreases then increases and finally there is again a drop till the soda content of the silicate equals the chloride content of the ferric chloride solutions. This shows that the free hydrochloric acid already present in the ferric chloride from its hydrolysis is first used up in the reaction and it is followed by formation of a mixture of hydrous oxide and silicate of iron and silica. Subsequently a double silicate of iron and sodium comes out as a precipitate. Formation of ferric hydroxide and silica is favoured in dilute solutions, p_H curves show an inflection beyond the equivalent value of sodium silicate which indicates the generation of silica in the system.

---

Zusammenfassung Die elektrische Leitf?higkeit von Mischungen, die durch progressives Hinzufügen von Natriumsilikat zu einer Ferrichloridl?sung erhalten werden, steigt nach anf?nglicher Abnahme und sinkt, erneut, bis der Natriumgehalt gleich dem Ferrichloridgehalt der Bisensalzl?sung wird. Dies zeigt, da? die freie hydrochlorische S?ure, die durch Hydrolyse in der Ferrichloridl?sung schon vorhanden ist, zun?chst durch Reaktion aufgebraucht wird und da? dieser Reaktion die Bildung von Hydroxyd, Eisensilikat und Kiesels?ure folgt. Anschlie?end f?llt Doppelsilikat von Eisen und Natrium aus. Die Bildung von Ferrihydroxyd und Kiesels?ure wird in verdünnten L?sungen begünstigt. Die p_H-Kurven zeigen einen Umkehrpunkt oberhalb des ?quivalenzwertes von Natriumsilikat, was die Bildung von Kiesels?ure im System andeutet.

     

Analysis of silicates

Conclusions Using a new rapid method, K₂O, Na₂O, CaO, MgO, Al₂O₃, and Fe₂O₃ were determined in silicates according to a single procedure, from a single sample.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1648–1655, August, 1967.     

Synthesis,structure, and photoluminescence of a series of lanthanide coordination polymers constructed from nitrogen containing organic ligands

We have synthesized four coordination polymers with two different nitrogen containing organic ligands and different lanthanide metal ions, under hydrothermal condition. [{Ln₂(bpdc)₃(H₂O)₂}] _n (Ln = Dy (1), Sm (2)) (bpdc = 2,2-bipyridine-3,3-dicarboxylic acid) are isostructural, with 2-D supramolecular layer structure composed from 1-D chains. Like 1 and 2, [{Ln(pzda)₂(H₂O)₂} · 4H₂O] _n (Ln = Dy (3), Nd (4)) (pzda = pyrazine-2,6-dicarboxylic acid) are also isostructural with 1-D chain-like structures. The photoluminescence of 2 is studied.     

Studies in colloidal silicates

Summary The progressive addition of a silicate to a very dilute barium or strontium chloride solution shows a continuous increase of the electrical conductivity with a slight break, not necessarily at the equivalent point. If the concentration of the solutions are increased a break occurs earlier in the conductance curve. This has been explained by the hydrolysis of silicates of barium or strontium in the dilute solutions. The conclusion is further supported by the analytical observations carried on the precipitates obtained by progressive addition of sodium silicate to a barium or strontium chloride. It has been found here that the proportion of silica is high when the sodium silicate is dilute but it tends to theoretical values as the concentration of sodium silicate is increased.

---

Zusammenfassung Die progressive Zugabe von Silikat zu einer sehr verdünnten Barium-oder Strontiumchloridl?sung ergibt einen stetigen Anstieg der elektrischen Leitf?higkeit mit einem schwachen Knick, der nicht notwendig mit dem ?quivalentpunkt zusammenf?llt. Mit steigender Konzentration der L?sungen findet der Knick bei kleineren Zugabewerten statt. Dies wird durch Hydrolyse der Silikate in den verdünnten L?sungen erkl?rbar. Eine solche Folgerung wird durch die Analyse der F?llungen gestützt: der Anteil an Kiesels?ure ist hoch, wenn das Natriumsilikat verdünnt ist, aber er tendiert zu den theoretischen Werten mit wachsenden Konzentrationen an Natriumsilikat.

     

A rare earth-DOTA-binding antibody: probe properties and binding affinity across the lanthanide series

An antibody that binds rare earth complexes selectively could be used as a docking station for a set of probe molecules, of particular interest for medical imaging and therapy. The rare earths are rich in probe properties, such as the paramagnetism of Gd, the luminescence of Tb and Eu, and the nuclear properties of Lu and Y. We find that antibody 2D12.5, initially developed to bind analogues of Y-DOTA (1,4,7,10-tetraazacyclododecane-N,N',N' ',N' '-tetraacetic acid) for radiotherapy, binds not only Y-DOTA analogues but also analogous DOTA complexes of all of the lanthanides. Surprisingly, chelates of some metals such as Gd3+ bind more tightly than the original Y3+ complex. When the shape of the complex is perturbed by either increasing or decreasing the radius of the lanthanide ion, the thermodynamic stability of the protein-ligand complex changes in a regular fashion. The behavior of DeltaDeltaG as a function of ionic radius fits a parabola, as might be expected for a system that behaves in a thermodynamically elastic way. The broad specificity and high affinity of this antibody for all rare earth-DOTA complexes make it particularly interesting for applications that take advantage of the unique characteristics of lanthanides. For example, UV excitation of the Tb-DOTA-2D12.5 complex leads to energy transfer from aromatic side chains of the antibody to bound Tb-DOTA, enhancing green terbium luminescence >104 relative to unbound Tb-DOTA.     

Homochiral porous lanthanide phosphonates with 1D triple-strand helical chains: synthesis, photoluminescence, and adsorption properties

Four homochiral porous lanthanide phosphonates, [Ln(H2L)3].2H2O, (H3L = (S)-HO3PCH2-NHC4H7-CO2H, Ln = Tb (1), Dy (2), Eu (3), Gd (4)), have been synthesized under hydrothermal conditions. These compounds are isostructural, and they possess a 3D supramolecular framework built up from 1D triple-strand helical chains. Each of the helical chain consists of phosphonate groups bridging adjacent Ln(III) ions. The helical chains are stacked through hydrogen bonds to form 1D tubular channels along the c axis. Moreover, helical water chains are located in the 1D channels, and after removal of these water chains, the compounds exhibit selective adsorption capacities for N2, H2O, and CH3OH molecules. Compounds 1 and 3 show strong green and red fluorescent emissions, respectively, in the solid state at room temperature. Crystal data for 1: TbP3O17N3C18H37, tetragonal (No.76), space group P4(1), a = 12.4643(3) Angstrom, b = 12.4643(3) Angstrom, c = 18.7577(5) Angstrom, V = 2914.17(13) Angstrom(3), and Z = 4. For 2: DyP3O17N3C18H37, a = 12.4486(3) Angstrom, b = 12.4486(3) Angstrom, c = 18.7626(5) Angstrom, V = 2907.60(13) Angstrom(3), and Z = 4. For 3, EuP3O17N3C18H37, a = 12.4799(3) Angstrom, b = 12.4799(3) Angstrom, c = 18.8239(5) Angstrom, V = 2931.78(13) Angstrom(3), and Z = 4. For 4: GdP3O17N3C18H37, a = 12.4877(18) Angstrom, b = 12.4877(18) Angstrom, c = 18.824(4) Angstrom, V = 2935.5(8) Angstrom(3), and Z = 4.