Synthesis and photoluminescent properties of series ternary lanthanide (Eu(III), Sm(III), Nd(III), Er(III), Yb(III)) complexes containing 4,4,4-trifluoro-1-(2-naphthyl)-1,3-butanedionate and carbazole-functionalized ligand

A series of new ternary lanthanide complexes Ln(TFNB)₃L (where Ln = Eu, Sm, Nd, Er, Yb, TFNB = 4,4,4-trifluoro-1-(2-naphthyl)-1,3-butanedionate, L = 1-(4-carbazolylphenyl)-2-pyridinyl benzimidazole) have been synthesised. The photoluminescence properties and TGA of them are described in detail. The trifluorinated ligand TFNB displays excellent antenna effect to sensitize the Ln(III) ions to emit characteristic spectra. The carbazole-containing ligand L is testified to be an outstanding synergistic ligand. The luminescence properties investigated and the quantum efficiency measured in dichloromethane solution of Eu(TFNB)₃L and Sm(TFNB)₃L show that the carbazole moiety is good at absorbing energy to sensitize the metal-centered emitting states and can make the complexes more rigid, provide efficient shielding of the Ln(III) core towards external quenching compared with the reference complexes of Eu(TFNB)₃(Pybm) and Sm(TFNB)₃(Pybm) (Pybm = 2-(2-pyridine)-benzimidazole) which have no carbazole unit. The quantum efficiency of Eu(TFNB)₃L in air-equilibrated CH₂Cl₂ solution is calculated to be 14.8% by using air-equilibrated aqueous [Ru(bpy)₃]²⁺·2Cl⁻ solution as reference sample (Φ_std = 2.8%).     

Aminopolycarboxylates of rare earths. 13. The apparent molal volumes of the lanthanide(III), cobalt(III) and chromium(III) ethylenediamine tetraacetate complexes

The apparent molal volumes of the complexes KLnedta (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Er and Yb), KCoedta and KCredta were determined from density measurements. The apparent molal volumes of the complexes KLnedta show a non-monotonous change with increasing atomic number; there is a significant increase in the values between Nd and Gd. To explain the observed trend, a structural change is postulated to take place gradually on progressing from Gd towards La. With increasing ionic size, there is an increase in the metal-ligand bond distances and in the mobility of the functional groups, resulting in a jump in the number of coordinated water molecules by one between Gd and Nd. There is a further increase in the hydration of the central ions, connected with the gradual de-coordination of a carboxylate group. As a result of the gradual structural change there is one free carboxylate group on average in Laedta^? and about four water molecules are coordinated in the inner sphere, while in the complexes of the elements heavier than Gd the ligand is hexadentate and only two water molecules are in the inner sphere. The apparent molal volumes of KCoedta and KCredta are practically equal and are higher than those of the lanthanide complexes; this has been explained by the stronger hydration and the more significant water-ordering effect of the Ln³⁺ ions coordinated in the complexes Lnedta^?.The postulated structural changes correlate with the trend of the protonation constant values, as well as with the results of ¹H NMR studies on the complexes Lnedta^?.     

Rare earth thiocyanate complexes with tripiperidinophosphine oxide: synthesis and characterization. Crystal structure of Pr(SCN)3(tpppO)3

The synthesis and characterization of rare-earth (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y) thiocyanate adducts with tripiperidinophosphine oxide (tpppO) with general formula (RE)(SCN)₃(tpppO)₃ are reported. Conductance measurements in acetonitrile indicate the non-electrolytic nature of the complexes. Infrared absorption spectra evidence that the SCN⁻ ion coordinates through the nitrogen atom (isothiocyanate form) and that tpppO coordinates through the phosphoryl oxygen. X-ray powder patterns suggest the existence of three different crystal forms: (1) La; (2) an isomorphous series including Ce, Nd and Pr; and (3) another isomorphous series, including Sm, Gd, Eu, Ho, Er, Tb, Lu and Y. The visible spectra of the Nd adduct and the calculated parameters β = 0.98, b^1/2 = 0.072 and δ = 1.06 indicate that the metal-ligand bonds are essentially electrostactic. The emission spectra of the Eu compound showed ⁵D₀ → ⁷F_J bands (J = 0, 1, 2), suggesting a C_3v symmetry for the coordination polyhedron. The lifetime of the ⁵D₀ state is 1.28 ms. The emission spectra of the Tb complex presented ⁵D₄ → ⁷F_J bands (J = 4, 5, 6) and the Dy complex showed the ⁴F_9/2 → ⁶H_13/2 band. The structure of the Pr complex showed that the coordination polyhedron is a trigonal antiprism, with the isothiocyanate anions in one base and three tpppO ligands in the other. Thermal analyses (TG-DTG) were carried out for the Ce, Nd and Gd adducts. Mass losses start between 250 and 334 °C. The final residues at 1300 °C are the corresponding phosphates.     

Lanthanide(III) complexes of amide derivatives of DOTA exhibit an unusual variation in stability across the lanthanide series

Luminescence excitation spectroscopy of the ⁷F₀→⁵D₀ transition of the Eu(III) complex of 1,4,7,10-tetrakis(carbamoylmethyl)-1,4,7,10-tetraazacyclododecane (TCMC, an amide derivative of DOTA) is used to measure the stability constant of the complex (K). A log K value of 10.6 is obtained for [Eu(TCMC)]³⁺ at 25 °C and an ionic strength of 0.1 M. Competition experiments with eleven other members of the lanthanide(III) series give stability constants for their complexes with TCMC. An unusual variation in stability is observed for complexes of [Ln(TCMC)]³⁺ across the lanthanide series with a pronounced optimum for the Sm(III) complex. This variation is quite different from that observed for other Ln(III) macrocyclic complexes, suggesting that the TCMC ligand is uniquely sensitive to Ln(III) ion radius.     

Formation and phosphodiesterolytic activity of lanthanide(III) N,N-bis(2-hydroxyethyl)glycine hydroxo complexes

Potentiometric titrations of N,N-bis(2-hydroxyethyl)glycine (bicine) in the presence of Ln(III) cations (Ln=La, Pr, Nd and Eu) in the pH range extended to ca. 9.5 reveal formation of two types of binuclear hydroxo complexes Ln₂(bic)₂(OH)₄ and Ln₂(bic)(OH)₄ ⁺ (bicH=bicine) in addition to previously reported mononuclear mono- and bis-complexes Ln(bic)²⁺ and Ln(bic)₂ ⁺, which predominate at pH below 8. ¹H NMR titrations of La(III)-bicine mixtures in D₂O show that the complex formation with bicine is slow in the NMR time scale and confirm formation of hydroxide rather than alkoxide complexes in basic solutions. Formation of a different type of hydroxide species under conditions of an excess of metal over ligand is confirmed by studying the absorption spectra of the Nd(III)-bicine system in the hypersensitive region. The binuclear hydroxide complexes are predominant species at pH above 9 and their stabilities increase in the order La < Pr ≈ Nd < Eu. They show fairly high catalytic activity in the hydrolysis of bis(4-nitrophenyl) phosphate (BNPP) at room temperature. Comparison of concentration and pH-dependences of the reaction rates with the species distribution diagrams shows that the catalytic hydrolysis of BNPP proceeds via a Michaelis-Menten type mechanism, which involves the Ln₂(bic)(OH)₄ ⁺ complex as the reactive species. The values of the catalytic rate constants and the Michaelis constants are in the range 0.002-0.004 s⁻¹ and 0.35-1.5 mM, respectively, for all lanthanides studied. The half-life for the hydrolysis of BNPP is reduced from 2000 years to ca. 10 min at 25 °C and pH 9.2 in the presence of 5 mM La(III) and 2.5 mM bicine.     

Solution studies of lanthanide (III) complexes based on 1,1,1,5,5,5-hexafluoro-2,4-pentanedione and 1,10-phenanthroline Part-I: Synthesis, H NMR, 4f-4f absorption and photoluminescence

Solution studies on the complexes of the type [Ln(hfaa)₃(phen)₂] (Ln = La, Pr and Nd) and [Ln(hfaa)₃phen] (Ln = Nd, Ho, Er and Yb; hfaa stands for the anion of 1,1,1,5,5,5-hexafluoro-2,4-pentanedione and phen stands for 1,10-phenanthroline) are presented. These complexes are synthesized in high yields by an in situ method in which hfaa, ammonium hydroxide, lanthanide chlorides and phen were allowed to react in 3:3:1:1 molar ratio in ethanol. In the case of neodymium both eight- and ten-coordinate complexes are isolated. The paramagnetic shifts of the methine protons of β-diketone have their sign opposed to those of paramagnetic shifts of phen protons and the shifts are dominated by dipolar interactions. The inter- and intramolecular shift ratios have been calculated and discussed. The 4f-4f absorption spectra of the complexes of Pr, Nd, Ho and Er are analyzed. The eight- and ten-coordinate neodymium complexes display distinctively different band shapes of the ⁴G_5/2,²G_7/2 ← ⁴I_9/2 hypersensitive transition. The efficient energy transfer from ligand to Pr(III) is reflected by strong red luminescence of this complex at room temperature.     

Coordination polymers of Ln(III): Synthesis, characterization, catalytic and antimicrobial aspects

Coordination polymers of HEAP-ED with La(III), Pr(III), Nd(III), Sm(III), Gd(III), Tb(III) and Dy(III) metal ions have been synthesized and characterized by elemental analyses, electronic spectra, magnetic susceptibilities, FTIR, NMR, scanning electronic microscopy (SEM) and thermogravimetric analyses. Catalytic activity of selected coordination polymers was examined for pharmaceutical important organic synthesis. Antimicrobial activity of isolated Ln(III) coordination polymers against Escherichia coli, Bacillus subtilis, Staphylococcus aureus (bacteria) and Saccharomyces cerevisiae (yeast) were measured. It was observed from the study that the Ln(III) coordination polymers acted as an efficient and effective catalysts and antimicrobial agents.     

Synthesis,density functional theory calculations and luminescence of lanthanide complexes with 2,6‐bis[(3‐methoxybenzylidene)hydrazinocarbonyl] pyridine Schiff base ligand

A pyridine‐diacylhydrazone Schiff base ligand, L = 2,6‐bis[(3‐methoxy benzylidene)hydrazinocarbonyl]pyridine was prepared and characterized by single crystal X‐ray diffraction. Lanthanide complexes, Ln–L, {[LnL(NO₃)₂]NO₃.xH₂O (Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy and Er)} were prepared and characterized by elemental analysis, molar conductance, thermal analysis (TGA/DTGA), mass spectrometry (MS), Fourier transform infra‐red (FT‐IR) and nuclear magnetic resonance (NMR) spectroscopy. Ln–L complexes are isostructural with four binding sites provided by two nitro groups along with four coordination sites for L. Density functional theory (DFT) calculations on L and its cationic [LnL(NO₃)₂]⁺ complexes were carried out at the B3LYP/6–31G(d) level of theory. The FT‐IR vibrational wavenumbers were computed and compared with the experimentally values. The luminescence investigations of L and Ln–L indicated that Tb–L and Eu–L complexes showed the characteristic luminescence of Tb(III) and Eu(III) ions. Ln–L complexes show higher antioxidant activity than the parent L ligand.     

Complexes of lanthanoid salts with macrocyclic ligands. Part 32. Synthesis and characterization of the complexes between lanthanoid nitrates and a tetraoxadiaza macrocycle

Lanthanoid nitrates react with 1,7,10,16-tetraoxa- 4,13-diaza-N,N′-dimethylcyclooctadecane, Me₂(2,2), to give complexes with two different metal:ligand ratios, 1:1 (Ln = La, Ce, Tb) and 4:3 (Ln = Pr, Nd, Sm, Eu, Gd, Th, Dy, Ho). The complexes were isolated from anhydrous solutions in acetonitrile and characterized by elemental analysis, X-ray diffraction, magnetic susceptibility measurements and vibrational analysis.The La and Ce 1:1 complexes are non-ionic and probably 12-coordinated, with the metal ion bound to the six donor atoms of the ligand and to three bidentate nitrate ions. The 4:3 complexes are ionic; they contain three bis(nitrato) complex cations [Ln(NO₃)₂·Me₂(2,2)]⁺ and one hexakis(nitrato) anion [Ln(NO₃)₆]³⁻. Spectroscopic data, including luminescence spectra, point to the 1:1 Tb-complex as being a 4:3 complex with an additional outer-sphere coordinated molecule of ligand.In solution, the 1:1 complexes remain essentially non-ionic, although some dissociation cannot be ruled out, whereas the 4:3 complexes behave as 2:1 (of even 3:1) electrolytes.     

Ultramicroporous channel lanthanide coordination polymers of 2,5-pyrazinedicarboxylate

Five lanthanide coordination polymers with composition {[Ln(pzdc)_1.5(H₂O)₃] · 0.5H₂O}_∞, (Ln = Pr, 1; Nd, 2; Sm, 3; Eu, 4; Gd, 5; pzdc = 2,5-pyrazinedicarboxylate), have been synthesized by reacting Ln(NO₃)₃ · 6H₂O with 2,5-pyrazinedicarboxylic acid under hydrothermal condition in the absence of additional base and characterized by elemental analysis, IR spectra and TG analysis, as well as single-crystal X-ray diffraction. They crystallize isostructurally in the triclinic space group P-1 and the cell parameters agree with the ionic radii of the Ln(III) ions. Each trivalent rare earth ion is nine coordinate in an N₂O₇ environment. The ligand 2,5-pyrazinedicarboxylate adopts three coordination modes, through which the lanthanide ions are linked together to form an infinite three dimensional structure. A 1D channel exists along the (1 0 0) direction which accommodates uncoordinated water by hydrogen bonds. Heating of 4 at 120 °C evacuated the uncoordinated water while retaining its single crystallinity with only minor change in cell parameters (crystal 6, [Eu(pzdc)_1.5(H₂O)₃]_∞). This hydrophilic ultramicroporous channel is selective to accommodate water only among common solvents, which has some potential interest for solvent separation.     

Synthesis and characterization of new lanthanide complexes with hexadentate hydrazonic ligands

In this paper, we report the synthesis and the characterization of a novel series of lanthanide (III) complexes with two potentially hexadentate ligands.The ligands contain a rigid phenanthroline moiety and two flexible hydrazonic arms with different donor atom sets (NNN′N′OO and NNN′N′N″N″, respectively for H₂L¹ (2,9-diformylphenanthroline)bis(benzoyl)hydrazone and H₂L² (2,9-diformylphenanthroline)bis(2-pyridyl)hydrazone).Both nitrate and acetate complexes of H₂L¹ with La, Eu, Gd, and Tb were prepared and fully characterized, and the X-ray crystal structure of the complex [Eu(HL¹)(CH₃ COO)₂] · 5H₂O is presented.The stability constants of the equilibria Ln³⁺ + H₂L¹ = [Ln(H₂L¹)]³⁺ and Ln³⁺ + (L¹)²⁻ = [Ln(L₁)]⁺ (Ln = La(III), Eu(III), Gd(III), and Tb(III)) are determined by UV spectrophotometric titrations in DMSO at t = 25 °C. The nitrate complexes of H₂L² with La, Eu, Gd and Tb were also synthesized, and the X-ray crystal structures of [La(H₂L²)(NO₃)₂(H₂O)](NO₃), [Eu(H₂L²)(NO₃)₂](NO₃) and [Tb(H₂ L²)(NO₃)₂](NO₃) are discussed.     

Lanthanide nitrate complexes of 4-N-(2′-Hydroxy-1 ′-naphthylidene)-aminoantipyrine

Lanthanide nitrates form with 4-N-(2′-hydroxy-l′- naphthylidene)aminoantipyrine (HNAAP) complexes of the type [Ln(HNAAP)₂(NO₃)₃] (where Ln = La, Pr, Nd, Sm, Gd, Tb, Dy, Ho and Y). The IR spectra of these complexes show that HNAAP acts as a bidentate neutral ligand and nitrate group is coordinated monodentately. The electronic spectra of the Nd complex show reasonable covalency in the metal-ligand bond. The magnetic moments of these complexes are in better agreement with the Van Vleck values. All these complexes are thermally stable up to200 °C.     

Electrochemical and Thermodynamic Properties of Ln(III) (Ln?=?Eu,Sm, Dy,Nd) in 1-Butyl-3-Methylimidazolium Bromide Ionic Liquid

The electrochemical behavior and thermodynamic properties of Ln(III) (Ln = Eu, Sm, Dy, Nd) were studied in 1-butyl-3-methylimidazolium bromide ionic liquid (BmimBr) at a glassy carbon (GC) electrode in the range of 293–338 K. The electrode reaction of Eu(III) was found to be quasi-reversible by the cyclic voltammetry, the reactions of the other three lanthanide ions were regarded as irreversible systems. An increase of the current intensity was obtained with the temperature increase. At 293 K, the cathodic peak potentials of −0.893 V (Eu(III)), −0.596 V (Sm(III)), −0.637 V (Dy(III)) and −0.641 V (Nd(III)) were found, respectively, to be assigned to the reduction of Ln(III) to Ln(II). The diffusion coefficients (D _o), the transfer coefficients (α) of Ln(III) (Ln = Eu, Sm, Dy, Nd) and the charge transfer rate constants (k _s) of Eu(III) were estimated. The apparent standard potential (E ⁰*) and the thermodynamic properties of the reduction of Eu(III) to Eu(II) were also investigated.     

Titanium dioxide nanomaterial doped with trivalent lanthanide ions of Tb, Eu and Sm: Preparation, characterization and potential applications

Mesoporous Ln(III)-TiO₂ (Ln = Tb, Eu, Sm) nanomaterials composites have been successfully synthesized by using sol-gel technique.XRD pattern, FT-IR, Raman spectra, and SEM were used to characterize the Ln(III)-TiO₂ nanomaterials. The prepared lanthanide doped TiO₂ nanomaterials have anatase phase and exhibit Ti-O-Ln bond. The absorption spectra of all prepared samples reflect the increasing photoresponse of doped samples to visible light over pure TiO₂. Surface area is remarkably increased due to lanthanide ion-doping.Two newly prepared Ln(III)-TiO₂ (Ln = Eu, Sm) luminescent nanomaterials exhibit enhanced pure red or orange light emission due to energy transfer from host TiO₂ to guest Eu(III) or Sm(III), respectively.In addition, the commercially available textile dye Remazol Red RB-133 degradation was used as a probe reaction to determine the efficiency of the Ln(III)-TiO₂ photocatalysts. The Ln(III) doping brought about remarkable improvement in the photoactivity over pure TiO₂.     

Synthesis, characterization and preliminary cytotoxicity evaluation of five lanthanide(III)-plumbagin complexes

Plumbagin (5-hydroxy-2-methyl-1,4-naphthoquinone, H-PLN) was isolated from Plumbago zeylanica, the anticancer traditional Chinese medicine (TCM). Five new lanthanide(III) complexes of deprotonated plumbagin: [Y(PLN)₃(H₂O)₂] (1), [La(PLN)₃(H₂O)₂] (2), [Sm(PLN)₃(H₂O)₂]⋅H₂O (3), [Gd(PLN)₃(H₂O)₂] (4), and [Dy(PLN)₃(H₂O)₂] (5) were synthesized by the reaction of plumbagin with the corresponding lanthanide salts, in amounts equal to ligand/metal molar ratio of 3:1. The PLN-lanthanide(III) complexes were characterized by different physicochemical methods: elemental analyses, UV-visible, IR and ¹H NMR and ESI-MS (electrospray ionization mass spectrum) as well as TGA (thermogravimetric analysis). The plumbagin and its lanthanide(III) complexes 1-5, were tested for their in vitro cytotoxicity against BEL7404 (liver cancer) cell lines by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. The five PLN-lanthanide (III) complexes 1-5 effectively inhibited BEL7404 cell lines growth with IC₅₀ values of 11.0 ± 3.5, 5.1 ± 1.3, 6.1 ± 1.1, 6.4 ± 1.3, and 9.8 ± 1.5 μM, respectively, and exhibited a significantly enhanced cytotoxicity compared to plumbagin and the corresponding lanthanide salts, suggesting a synergistic effect upon plumbagin coordination to the Ln(III) ion. The lanthanide complexes under investigation also exerted dose- and time-dependent cytotoxic activity. [La(PLN)₃(H₂O)₂] (2) and plumbagin interact with calf thymus DNA (ct-DNA) mainly via intercalation mode, but for [La(PLN)₃(H₂O)₂] (2), the electrostatic interaction should not be excluded; the binding affinity of [La(PLN)₃(H₂O)₂] (2) to DNA is stronger than that of free plumbagin, which may correlate with the enhanced cytotoxicity of the PLN-lanthanide(III) complexes.     

Remarkable chiral and luminescent properties of novel Yb(III) and Eu(III) complexes containing BINAPO ligand

Lanthanide complexes are of great importance for their prospective applications in wide range of science and technology. Chiral lanthanide complexes can constitute stereo-discriminating probes in biological media, owing to the luminescent properties of the rare-earth ions. Sensitized emission with narrow bandwidth, having fast radiation rate and high emission quantum efficiency are the main perspective for synthesizing the complexes. Attention has been given on remarkable chirality with high dissymmetry factors (g = Δε_ext/ε_max) of the complexes. For this purpose, beta-diketonato ligands with chiral BINAPO (1,1′-binapthyl phosphine oxide) ligand were chosen to achieve the goal. The complexes [Ln(TFN)₃(S-BINAPO)](TFN = 4,4,4-trifluoro-1(2-napthyl)-1,3-butanedione), [Ln(HFT)₃(S-BINAPO)] (HFT = 4,4,5,5,6,6,6-heptafluoro-1-(2-thienyl)-1,3-hexanedione) and [Ln(HFA)₃(S-BINAPO)](hfa = hexafluoroacetylacetonate) (where Ln = Yb, Eu) were synthesized. The complex, [Eu(TFN)₃(S-BINAPO)] gives strong red emission at 615 nm with narrow emission band (<10 nm) when excited by 465 nm light with quantum efficiency 86%. The dissymmetry factors (g = Δε_ext/ε_max) corresponding to the ⁷F₁ → ⁵D₀ transition at 590 nm is 0.091 for [Eu(TFN)₃(S-BINAPO)] and for [Yb(hfa)₃(S-BINAPO)](hfa = hexafluoroacetylacetonate) corresponding to the ²F_7/2 → ²F_5/2 transitions is 0.12, are among the largest values for both Eu and Yb complexes to date, respectively. The Eu complexes, [Eu(HFT)₃(S-BINAPO)] and [Eu(TFN)₃(S-BINAPO)] are found to be spontaneously emissive, showing bright red emission, when placed in sunlight or even in the laboratory when light is switched on.     

Gadolinium(III) and europium(III) l-glutamates: Synthesis and characterization

Two lanthanide(III) complexes with l-glutamate ligands [{Ln₂(l-Glu)₂(H₂O)₈} · 4(ClO₄) · 2.5H₂O]_n (Ln = Gd (1), Eu (2)) have been prepared and characterized by single-crystal X-ray diffraction. The compounds are isomorphous with infinite cationic 2D layers stacked together by secondary bonds. The building blocks are slightly different non-centrosymmetric dinuclear units placed in alternating layers, the resulting structures thus containing four non-equivalent Ln metal sites. The dinuclear units contain a fourfold bridge, two in the η¹:η¹:μ₂ and two in the η²:η¹:μ₂ modes, from two α- and two γ-carboxylates of four different l-Glu residues, respectively.     

A series of pyrazolone lanthanide (III) complexes: Synthesis, crystal structures and fluorescence

A series of pyrazolone lanthanide complexes: Ln(PMPP)₃ · 2H₂O · C₂H₅OH (Ln = Nd (1), Sm (2), Gd (3), Dy (4); PMPP = 1-phenyl-3-methyl-4-propionyl-5-pyrazolone) have been synthesized by the hydrothermal method with the starting ligand PMPP-SAH (1-phenyl-3-methyl-4-(salicylidene hydrazone)-propionyl-5-pyrazolone) changed into PMPP during the formation process of complexes. All the complexes were structurally characterized by X-ray crystallography. The fluorescence of these four complexes 1-4 in solid state and DMF solution was investigated via F-4500 spectrophotometer and all of them indicate a fluorescent behavior at room temperature.     

The mononuclear and dinuclear dimethoxyethane adducts of lanthanide trichlorides [LnCl3(DME)2]n, n=1 or 2, fundamental starting materials in lanthanide chemistry: preparation and structures

Some new dimethoxyethane (DME) adducts of lanthanide trichlorides of formula [LnCl₃(DME)₂]_n, n=1 or 2; (n=2, Ln=La, Ce, Pr, Nd; n=1, Ln=Eu, Tb, Ho, Tm, Lu) have been prepared by treating Ln₂O₃, or LnCl₃ · nH₂O, or Ln₂(CO₃)₃, in DME as medium, with thionyl chloride at room temperature, eventually in the presence of water in the case of Ln₂O₃ and Ln₂(CO₃)₃. The complexes from lanthanum to praseodymium included are chloro-bridged dimers. In the case of neodymium, the new results complement the literature data, showing that both the mononuclear and dinuclear species exist: neodymium can therefore be regarded as the turning element from dinuclear to mononuclear structures along the series. Only mononuclear complexes were isolated in the Eu-Lu sequence. The lanthanide contraction has been evaluated on the basis of the Ln-O and Ln-Cl bond distances on the isotypical series of the mononuclear complexes LnCl₃(DME)₂ covering a range of 12 atomic numbers.     

Syntheses, structures and photophysical properties of a series of Zn-Ln coordination polymers (Ln = Nd, Pr, Sm, Eu, Tb, Dy)

Six novel heterometallic Zn-Ln coordination polymers {[ZnLnCl(pydc)₂(H₂O)₆]·3H₂O}_n (Ln = Nd 1, Pr 2, Sm 3, Eu 4, Tb 5, Dy 6; pydc = pyridine-2,5-dicarboxylate) were synthesized by the hydrothermal method, and their structures were measured by the single-crystal X-ray diffraction. The IR and UV-Vis-NIR absorption spectra, and the luminescence spectra in the visible and near-infrared (NIR) regions of the six complexes were determined at room temperature. They possess the same crystal structure, and the Zn(II) and Ln(III) ions in each complex are bridged into 1D infinite chain by pyridine-2,5-dicarboxylates. Meanwhile, there are numerous hydrogen bonds which result in the 3D hydrogen bonding network in the crystal. In the visible and NIR regions, the emission spectra of the complexes show the characteristic bands of the corresponding Ln(III) ions, which are mainly attributed to the sensitization from the d-L-moiety to f-L-moiety after forming the Zn-Ln complexes. In this paper, we first report the Zn-Sm complex which can exhibit the emission bands of Sm(III) in the NIR region, and discuss the sensitization from the d-L-moiety to f-L-moiety on the basis of the different characteristics of levels for different Ln(III) ions.