Series Of Ln Research Articles

Open-shell lanthanide(II+) or -(III+) complexes bearing σ-silyl and silylene ligands: synthesis, structure, and bonding analysis.

Complexes featuring lanthanide (Ln)–Si bonds represent a highly neglected research area. Herein, we report a series of open-shell LnII+ and LnIII+ complexes bearing σ-bonded silyl and base-stabilized N-heterocyclic silylene (NHSi) ligands. The reactions of the LnIII+ complexes Cp3Ln (Ln = Tm, Ho, Tb, Gd; Cp = cyclopentadienide) with the 18-crown-6 (18-cr-6)-stabilized 1,4-oligosilanyl dianion [(18-cr-6)KSi(SiMe3)2SiMe2SiMe2Si(SiMe3)2K(18-cr-6)] (1) selectively afford the corresponding metallacyclopentasilane salts [Cp2Ln({Si(SiMe3)2SiMe2}2)]−[K2(18-cr-6)2Cp]+ [Ln = Tm (2a), Ho (2b), Tb (2c), Gd (2d)]. Complexes 2a–2d represent the first examples of structurally characterized Tm, Ho, Tb, and Gd complexes featuring Ln–Si bonds. Strikingly, the analogous reaction of 1 with the lighter element analogue Cp3Ce affords the acyclic product [Cp3CeSi(SiMe3)2SiMe2SiMe2Si(SiMe3)2-Cp3Ce]2–2[K(18-cr-6)]+ (3) as the first example of a complex featuring a Ce–Si bond. In an alternative synthetic approach, the aryloxy-functionalized benzamidinato NHSi ligand Si(OC6H4-2-tBu){(NtBu)2CPh} (4a) and the alkoxy analogue Si(OtBu){(NtBu)2CPh} (4b) were reacted with Cp*2Sm(OEt2), affording, by OEt2 elimination, the corresponding silylene complexes, both featuring SmII+ centers: Cp*2Sm ← :Si(O–C6H4-2-tBu){(NtBu)2CPh} (6) and Cp*2Sm ← :Si(OtBu){(NtBu)2CPh} (5). Complexes 5 and 6 are the first four-coordinate silylene complexes of any f-block element to date. All complexes were fully characterized by spectroscopic means and by single-crystal X-ray diffraction analysis. In the series 2a–2d, a linear correlation was observed between the Ln–Si bond lengths and the covalent radii of the corresponding Ln metals. Moreover, in complexes 5 and 6, notably long Sm–Si bonds are observed, in accordance with a donor–acceptor interaction between Si and Sm [5, 3.4396(15) Å; 6, 3.3142(18) Å]. Density functional theory calculations were carried out for complexes 2a–2d, 5, and 6 to elucidate the bonding situation between the LnII+ or LnIII+ centers and Si. In particular, a decrease in the Mayer bond order (MBO) of the Ln–Si bond is observed in the series 2a–2d in moving from the lighter to the heavier lanthanides (Tm = 0.53, Ho = 0.62, Tb = 0.65, and Gd = 0.75), which might indicate decreasing covalency in the Ln–Si bond. In accordance with the long bond lengths observed experimentally in complexes 5 and 6, comparatively low MBOs were determined for both silylene complexes (5, 0.24; 6, 0.25) .

Lanthanide(III) complexation with an amide derived pyridinophane.

Herein we report a detailed investigation of the solid state and solution structures of lanthanide(III) complexes with the 18-membered pyridinophane ligand containing acetamide pendant arms TPPTAM (TPPTAM = 2,2',2″-(3,7,11-triaza-1,5,9(2,6)-tripyridinacyclododecaphane-3,7,11-triyl)triacetamide). The ligand crystallizes in the form of a clathrated hydrate, where the clathrated water molecule establishes hydrogen-bonding interactions with the amide NH groups and two N atoms of the macrocycle. The X-ray structures of 13 different Ln(3+) complexes obtained as the nitrate salts (Ln(3+) = La(3+)-Yb(3+), except Pm(3+)) have been determined. Additionally, the X-ray structure of the La(3+) complex obtained as the triflate salt was also obtained. In all cases the ligand provides 9-fold coordination to the Ln(3+) ion, ten coordination being completed by an oxygen atom of a coordinated water molecule or a nitrate or triflate anion. The bond distances of the metal coordination environment show a quadratic change along the lanthanide series, as expected for isostructural series of Ln(3+) complexes. Luminescence lifetime measurements obtained from solutions of the Eu(3+) and Tb(3+) complexes in H2O and D2O point to the presence of a water molecule coordinated to the metal ion in aqueous solutions. The analysis of the Ln(3+)-induced paramagnetic shifts indicates that the complexes are ten-coordinated throughout the lanthanide series from Ce(3+) to Yb(3+), and that the solution structure is very similar to the structures observed in the solid state. The complexes of the light Ln(3+) ions are fluxional due to a fast Δ(λλλλλλ) ↔ Λ(δδδδδδ) interconversion that involves the inversion of the macrocyclic ligand and the rotation of the acetamide pendant arms. The complexes of the small Ln(3+) ions are considerably more rigid, the activation free energy determined from VT (1)H NMR for the Lu(3+) complex being ΔG(⧧)298 = 72.4 ± 5.1 kJ mol(-1).

Two series of Ln(iii)–Ag(i) heterometallic–organic frameworks constructed from isonicotinate and 2,2′-biphenyldicarboxylate: synthesis, structure and photoluminescence properties

Two new series of two-dimensional (2-D) lanthanide–silver heterometallic–organic frameworks with the formula [Ln2Ag(IN)2(BPDC)2(H2O)4]·(NO3)·2H2O (1-Ln) (Ln = Nd 1, Eu 2, Tb 3, and Dy 4) and [Ln2Ag(IN)2(BPDC)2(H2O)2]·(NO3)·2H2O (2-Ln) (Ln = Ho 5, Yb 6, HIN = isonicotinic acid, H2BPDC = 2,2′-biphenyldicarboxylic acid) have been hydrothermally synthesized and characterized by single crystal X-ray diffraction, elemental analysis, IR spectroscopy, thermogravimetric analysis (TGA) and powder X-ray diffraction (PXRD). In the structures of these six compounds, BPDC2− ligands link Ln3+ through their carboxylate groups, resulting in the formation of one-dimensional (1-D) {Ln(BPDC)}n infinite chains. These adjacent chains are further connected to each other via the coordination interaction between Ln3+ and carboxylate groups of IN− ligands, as well as the pillared Ag(IN)2 units, giving rise to 2-D layered structures. Although they have similar secondary building units (SBUs), the whole open frameworks of these two types of HMOFs that may be produced by the lanthanide contraction effect are quite different. Isostructural compounds 1–4 (1-Ln) crystallize in the monoclinic C2/c space group and possess a (6,3)-connected topology containing 1-D hexagonal microporous channels along the c axis, while isostructural compounds 5 and 6 (2-Ln) crystallize in the triclinic P space group and present a 2-D network of (4,4)-connected topology with 1-D rhombic channels along the b axis. Meanwhile, solid-state photoluminescence studies of compounds 1–3 and 6 were also conducted at room temperature and the luminescence intensity of 3 and 6 are found to be sensitive to small molecules.

Pentanuclear lanthanide pyramids based on thiacalix[4]arene ligand exhibiting slow magnetic relaxation.

A series of pentanuclear Ln(III) clusters, [Ln5(μ4-OH)(μ3-OH)4(L1)(acac)6] (H4L1 = p-tert-butylthiacalix[4]arene; acac = acetylacetonate; Ln = Dy, Ho, Er) and [Ln5(μ5-OH)(μ3-OH)4(L1)(L2)2(acac)2(CH3OH)2] (H3L2 = 5,11,17,23-tetrakis(1,1-dimethylethyl)-25,26,27-trihydroxy-28-methoxy thiacalix[4]arene; Ln = Dy, Ho, Er), have been synthesized based on the thiacalix[4]arene ligand. All of these complexes feature a square-based pyramid with four triangular Ln3 structural motifs. One μ4-OH group bridges four Ln(III) ions in the basal plane of , while the OH group in complexes adopts the μ5-coordination mode. Our results illuminate the coordination modes of the versatile thiacalix[4]arene ligands and their application to new cluster compounds. The structural and magnetic studies confirm that the molecular symmetries and coordination geometries for lanthanide metal cores have a significant effect on some parameters as single-molecule magnets. Among them, two Dy5 pyramids exhibit distinct slow magnetic relaxation.

Host-sensitized luminescence properties in CaNb2O6:Ln(3+) (Ln(3+) = Eu(3+)/Tb(3+)/Dy(3+)/Sm(3+)) phosphors with abundant colors.

A series of Ln(3+) (Ln(3+) = Eu(3+)/Tb(3+)/Dy(3+)/Sm(3+)) ion doped CaNb2O6 (CNO) phosphors have been prepared via the conventional high-temperature solid-state reaction route. The X-ray diffraction (XRD) and structure refinement, diffuse reflection, photoluminescence (PL), and fluorescent decay curves were used to characterize the as-prepared samples. Under UV radiation, the CNO host present a broad emission band from about 355 to 605 nm centered around 460 nm originating from the NbO6 octahedral groups, which has spectral overlaps with the excitation of f-f transitions of Eu(3+)/Tb(3+)/Dy(3+)/Sm(3+) in CNO:Eu(3+)/Tb(3+)/Dy(3+)/Sm(3+) samples. They show both host emission and respective emission lines derived from the characteristic f-f transitions of activators, which present different emission colors owing to the energy transfer from the NbO6 group in the host to Eu(3+)/Tb(3+)/Dy(3+)/Sm(3+) with increasing activator concentrations. The decreases of decay lifetimes of host emissions in CNO:Eu(3+)/Tb(3+)/Dy(3+)/Sm(3+) demonstrate the energy transfer from the hosts to Eu(3+)/Tb(3+)/Dy(3+)/Sm(3+). The energy transfer mechanisms in CNO:Eu(3+)/Tb(3+)/Dy(3+) phosphors have been determined to be a resonant type via dipole-dipole mechanisms. For CNO:Sm(3+), the metal-metal charge transfer transition (MMCT) might contribute to the different variations of decay lifetimes and emission intensity from CNO:Eu(3+)/Tb(3+)/Dy(3+) samples. The best quantum efficiency is 71.2% for CNO:0.01/0.02Dy(3+). The PL properties of as-prepared materials indicate the promising application in UV-pumped white-emitting lighting diodes field.

Monomeric, dimeric and polymeric lanthanide(III) complexes of a hexaazamacrocyclic imine derived from 2,6-diformylpyridine and ethylenediamine

A series of mononuclear Ln(III) complexes of a hexaaza Schiff base has been obtained in a template condensation reaction of 2,6-diformylpyridine, ethylenediamine and the appropriate lanthanide nitrate salt. The X-ray crystal structures of the Ce(III), Pr(III), Eu(III) and Y(III) complexes, recrystallized from water or methanol, have been determined. The reaction of the obtained complexes with hydroxide anions results in formation of dinuclear hydroxo-bridged species. In particular, the reaction of sodium hydroxide with a mixture of the starting Eu(III) and Y(III) mononuclear complexes results in the formation of two homodinuclear hydroxo derivatives as well as a mixed Y(III)–Eu(III) hydroxo dimer, as indicated by NMR spectroscopy. The formation of dinuclear hydroxo species was confirmed by the X-ray crystal structure of the [Y2L2(μ-OH)2(H2O)2](NO3)4·4H2O complex. On the other hand, an attempt to crystallize a hydroxo derivative of the La(III) macrocyclic complex resulted in the fixation of atmospheric carbon dioxide and formation of a carbonate derivative. The X-ray crystal structure of this compound reveals a 1-D coordination polymer, where the macrocyclic [LaL]3+ units are linked by bridging carbonate anions.

In situ synthesis and structural characterization of a series of acylhydrazidate-extended Ln3+and Zn2+coordination polymers

By utilizing the in situ hydrothermal acylation of N2H4 with aromatic polycarboxylic acids, a series of new acylhydrazidate-extended two-dimensional (2-D) or three-dimensional (3-D) coordination polymers, [Ln(epdh)3(H2O)] (Ln3+ = Dy3+1, Eu3+2, Tb3+3, Gd3+4, Y3+5, Lu3+6; epdh = 5-ethylpyridine-2,3-dicarboxylhydrazidate), [Dy(ox)(pdh)(H2O)] (ox = oxalate, pdh = pyridine-2,3-dicarboxylhydrazidate) 7, [Zn2(mpth)(atez)2] (mpth = 4-methylphthalhydrazidate, atez = 5-aminotetrazolate) 8 and [Zn3(OH)2(Hpth)2(atrz)2] (pth = phthalhydrazidate, atrz = 3-amino-1,2,4-triazolate) 9 were isolated. X-ray single-crystal diffraction revealed that (i) the isomorphic compounds 1–6 posses 2-D layer structures with (4,4) topologies. Two types of epdh molecules act as the rod-like connectors; (ii) compound 7 also possesses a 2-D layer structure, but shows a (6,3) topology. The pdh molecules first link the Dy3+ ions into a dimer. The ox molecules further extend the dimers into this 2-D layer network; (iii) compound 8 has a 3-D network structure (symbol: (4·64·8)2(42·62·82)), which is constructed from the one-dimensional (1-D) Zn2(mpth)2+ chains by the atez molecules; (iv) the 2-D layer network of compound 9 also shows a (6,3) topology, but the geometrical form is different from that of compound 7. Only the atrz molecule serves as the linker in compound 9; (v) via the N–H⋯O and/or N–H⋯N interactions, compounds 1–6, 7 and 9 self-assemble into the different 3-D supramolecular networks. Photoluminescence analysis revealed that (i) compounds 2 and 3 exhibit the characteristic transitions of the Eu3+ or Tb3+ ion; (ii) compounds 1, 4, 5 and 6 emit green light, suggesting their behaviors are dominated by the epdh molecules; (iii) compound 8 emits violet light, whereas compound 9 does not emit light.

A Dissection Proof of Leibniz's Series for π/4

SummaryInspired by Lord Brouncker's discovery of his series for ln 2 by dissecting the region below the curve 1⁄x, Viggo Brun found a way to partition regions of the unit circle so that their areas correspond to terms of Leibniz's series for π⁄4. Brun's argument involved ad hoc methods which were difficult to find. We develop a method based on usual techniques in calculus that leads to Brun's result and that applies generally to other related series.

Structures and standard molar enthalpies of formation of a series of Ln(III)–Cu(II) heteronuclear compounds with pyrazine-2,3-dicarboxylic acid

Fifteen lanthanide–copper heteronuclear compounds, formulated as [CuLn2(pzdc)4(H2O)6]·xH2O (1–6(x=2), 8(x=3), 9–10(x=4)); [CuLn2(pzdc)4(H2O)4]·xH2O (7, 12–13, 15(x=4), 14(x=5), 11(x=8)) (Ln(III)=La(1); Ce(2); Pr(3); Nd(4); Sm(5); Eu(6); Gd(7); Tb(8); Dy(9); Ho(10); Er(11); Tm(12); Yb(13); Lu(14); Y(15); H2pzdc (C6H4N2O4)=pyrazine-2,3-dicarboxylic acid) have been hydrothermally synthesized. All compounds were characterized by element analysis, IR spectroscopy, single-crystal X-ray diffraction and thermal analysis. X-ray diffraction analyses confirm that all compounds are isostructural and feature a 3D brick-like framework structure with {4.62}2{42.62.82}{63}2{65.8}2 topology. Using 1molcm−3 HCl(aq) as calorimetric solvent, with an isoperibol solution–reaction calorimeter, the standard molar enthalpies of formation of all compounds were determined by a designed thermochemical cycle. In addition, solid state luminescence properties of compounds 5, 6, 8 and 9 were studied in the solid state.

Four 2D Ln–Cd heterometal–organic coordination polymers based on tetranuclear Ln–Cd oxo-cluster with highly selective luminescent sensing of organic molecules and metal cations

Two series of 2D-layered Ln–Cd heterometal–organic complexes based on tetranuclear [Ln2Cd2] oxo-clusters with selective luminescent sensing have been synthesized.

Thermal behaviour of light lanthanide(III) complexes with 2,3-pyridinedicarboxylic acid

AbstractThe lanthanide(III) complexes with 2,3-pyridinedicarboxylate ligand (PDC) were obtained as crystalline compounds from the water solutions. These compounds form the series of Ln

Study of One Step Synthesis of Rare Earth Zeolite (Ln–ZSM-5) and Application for Low Temperature CO Catalytic Oxidation

A series of rare earth zeolites Ln–ZSM-5 (Ln = La, Ce, Pr, Nd) were synthesized directly via a one-step hydrothermal method. The obtained zeolites were used as support and applied in low-temperature CO oxidation. The influence of various factors such as rare earth types, rare earth contents, particle sizes of molecular sieve, and silica alumina ratios, etc., on the catalytic activity of CO oxidation were investigated in detail. The results showed that low silica small size Ce–ZSM-5 (1 % Ce content) had the highest activity. The results also showed that Ce–ZSM-5 zeolite prepared by one-step direct synthesis was more suitable as catalytic support than ZSM-5 or Ce/ZSM-5 zeolite, prepared by impregnation of ZSM-5 with Ce.

Simulating the synthesis and thermodynamic characteristics of the desolvation of lanthanide borohydride tris-Tetrahydrofuranates

Lanthanide borohydride tris-tetrahydrofuranates (Ln(BH4) · 3THF, where THF is tetrahydrofuran and Ln is La, Nd, Sm, Gd, Er, Yb, and Lu) is synthesized via the exchange reaction of lanthanide(III) chloride and sodium borohydride in THF. It is found that synthesis proceeds according to a stepwise mechanism and the product of the reaction (lanthanide borohydride) initiates the process. The two-step character of the desolvation of Ln(BH4)3 · 3THF under steady-state conditions in the temperature range of 300 to 400 K is determined through X-ray phase and chemical analyses, tensiometry, and gas volumetry. It is established that one mole and then two moles of THF are removed from the initial sample at the first and second steps, respectively. Equations for barograms are obtained and the thermodynamic characteristics of desolvation of Ln(BH4)3 · 3THF under study are calculated. Gibbs energy values of the stages of process are determined semi-empirically. The law of its change for the entire series of Ln(BH4)3 · 3THF is determined with the emergence of the tetrad effect.

Syntheses, structures and luminescence of a series of 4d–4f heterometallic coordination polymers constructed by 4,4′-oxybis(benzoicacid)

A series of Ln(III)-Ag(I) 4d–4f heterometallic coordination polymers [LnAg(oba) 2 (H 2 O)] n (Ln = Dy 1 , Ho 2 , Er 3 ) have been synthesized under hydrothermal reactions of 4,4′-oxybis(benzoicacid) (H 2 oba) with Ln(NO 3 ) 3 · 6H 2 O and AgNO 3 at 180 °C. All complexes are isostructural with 3D networks expanded from 1D zigzag chains and 2D layers. In addition, the luminescent property of compound 1 was investigated in the solid-state at room temperature. The coordination mode of H 2 oba ligand. • A series of Ln(III)-Ag(I) 4d-4f heterometallic polymers have been synthesized. • They are the first 4d-4f heterometallic polymers built by 4,4’- oxybis (benzoicacid). • The luminescent property of polymer 1 was investigated in the solid-state.

Fast UV-Vis photorefractive response of Zr and Mg codoped LiNbO_3:Mo

A series of LN:Mo,Zr and LN:Mo,Mg crystals with different doping concentrations were grown and their holographic properties were investigated from UV to the visible range. Each crystal allows for holographic storage from UV to the visible as LN:Mo. When the concentration of MgO is enhanced to 6.5 mol%, the response time can be dramatically shortened to 0.22 s, 0.33 s, 0.37 s and 1.2 s for 351, 488, 532, and 671 nm laser, respectively. The results show that LN:Mo,Mg is a promising candidate for all-color holographic volume storage with fast response.

Synthesis, Magnetism, and Thermostability of a Series of Two‐Dimensional Lanthanide–Nickel Heterometallic Coordination Polymers

AbstractA series of Ln–Ni heterometallic coordination polymers, {[Ln2Ni(MIDA)4(H2O)6](H2O)4} (Ln = La (1), Ce (2), Pr (3), and Nd (4); H2MIDA = N‐methyl‐iminodiacetic acid), were obtained under hydrothermal conditions. Single crystal X‐ray diffraction revealed that they feature two‐dimensional isomorphic frameworks, which could be viewed as the construction by one‐dimensional {Ln}n chain connecting by bridges of [Ni(MIDA)2]2. The magnetic measurements reveal that compounds 2–4 exhibit antiferromagnetic properties. TGA results indicate compounds 1 and 4 have good thermostability with the critical temperature of 375 °C.

Modulating water-exchange rates of lanthanide(iii)-containing polyaminopolycarboxylate-type complexes using polyethylene glycol

We have synthesized a series of Ln(III)-containing polyethylene glycol conjugates and studied the structural and electronic properties of these complexes. These studies demonstrate that polyethylene glycol can be used to fine-tune water-exchange rates of Ln(III)-containing polyaminopolycarboxylate-type complexes; this control is desirable in developing Ln(III)-containing contrast agents for magnetic resonance imaging.

Syntheses and crystal structures of the novel oxide chloride oxoborates Ln4O4Cl[BO3] (Ln = Eu–Tm)

AbstractThe here reported compounds of the isotypic series Ln

New tris-3,4-HOPO lanthanide complexes as potential imaging probes: complex stability and magnetic properties

There is a growing interest in the development of new medical diagnostic tools with higher sensibility and less damage for the patient body, namely on imaging reporters for the management of diseases and optimization of treatment strategies. This article examines the properties of a new class of lanthanide complexes with a tripodal tris-3-hydroxy-4-pyridinone (tris-3,4-HOPO) ligand - NTP(PrHP)(3). Among the studies herein performed, major relevance is given to the thermodynamic stability of the complexes with a series of Ln(3+) ions (Ln = La, Pr, Gd, Er, Lu) and to the magnetic relaxation properties of the Gd(3+) complex. This hexadentate ligand enables the formation of (1 : 1) Ln(3+) complexes with high thermodynamic stability following the usual trend, while the Gd-chelates show improved relaxivity (higher hydration number), as compared with the commercially available Gd-based contrast agents (CAs); transmetallation of the Gd(3+)-L complex with Zn(2+) proved to be thermodynamically and kinetically disfavored. Therefore, NTP(PrHP)(3) emerges as part of a recently proposed new generation of CAs with prospective imaging sensibility gains.

Syntheses, structures and near-infrared luminescent properties of a series of Ln(III) coordination polymers

Abstract Using aromatic carboxylic acids as main ligands, four Ln(III) coordination polymers, [Er(CH3C6H4COO)2(Ac)(H2O)]n (1), [Yb(β-C10H7COO)2(Ac)(H2O)]n (2), [Nd(C9H7O2)3]n (3) and [Ho(C9H7O2)3]n (4) (CH3C6H4COO = p-toluylate, Ac = acetate, β-C10H7COO = β-naphthoyloxy, C9H7O2 = cinnamate), were synthesized by hydrothermal method and their structures were studied by single-crystal X-ray diffraction. Polymers 1 and 2 possess 2D layer structures, and polymers 3 and 4 possess 1D chain structures. At room temperature in the solid state, the IR, UV–Vis–NIR spectra and the emission spectra in the visible and near-infrared (NIR) regions of the four polymers were determined. In the NIR region, polymers 1–4 show characteristic emission bands of the corresponding Ln(III) ions which exhibit shift, splitting or broadness in comparison with their theoretical emission bands. This can be confirmed by their UV–Vis–NIR spectra and discussed emphatically.