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.     

Novel gaseous polyatomic binary and ternary lanthanide oxides

A variety of novel gaseous polyatomic binary and ternary oxides were observed at ambient temperature arising from lanthanide (Ln) nitrate Schiff base complexes, simple salts and sesquioxides, in an FAB mass spectrometer. The new binary oxides (as singly positive ions) detected are Ln₂O₃, Ln₃O₃, Ln₃O₄, Ln₄O₄, Ln₄O₅, Ln₄O₆, Ln₅O₆, Ln₅O₇, Ln₅O₈, Ln₆O₈, Ln₆O₉, Ln₇O₁₀, Ln₈O₁₁, Ln₈O₁₂ and Ln₉O₁₃; the ternary gaseous oxides are CeEuO₂, CeEu₂O₃ and Ce₂EuO₄, LaYbO₂, La₂YbO₄ and LaYb₂O₄; NdHoO₃, Nd₂HoO₄, and NdHo₂O₄; YTmO₃; Y_xTm_3−xO₄, x=1−2; Y_xTm_4−xO₆, x=1−3; Y_xTm_5−xO₇, x=1−4; Y_xTm_6−xO₉, x=1−5. Some of these oxides show the lanthanide cations in unusual oxidation states. Gadolinium-gallium ternary oxides, GdGaO₂, GdGaO₃ and Gd₂GaO₄ were also detected. The FAB MS environment is significantly reducing, yielding a homologous series Eu_nO_n where Eu²⁺ is dominant (E°(Eu³⁺/Eu²⁺)=−0.35 V) and no gallium or indium oxides (E°(M³⁺/M°=−0.34 V (In), −0.53 V (Ga)) were formed. The stoichiometry of the polylanthanide ternary oxides formed is determined largely by the chemistry of the major metallic component. The gaseous polyatomic oxides are probably formed through a reductive condensation process involving primary species Ln⁺ and LnO⁺ formed when the rare earth compounds are struck by fast Xe atoms. The demonstrated possibility of double component oxide formation broadens the number and types of gaseous lanthanide oxides which are accessible.     

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.     

Synthesis, structure and spectroscopic properties of chloranilate-bridged 4f-4f dinuclear complexes: a comparative study of the emission properties with Cr-Ln complexes

New 4f-4f chloranilate-bridged dinuclear Ln^III complexes, [(HBpz₃)₂Ln(μ-C₆Cl₂O₄)Ln(HBpz₃)₂] (Ln(CA)Ln: Ln=Eu, Tb, Yb), were synthesized and characterized by the X-ray analysis. Their structure and spectroscopic properties were compared with those of dinuclear 3d-4f assembled molecular systems [(acac)₂Cr^III(μ-ox)Ln^III(HBpz₃)₂] (Cr(ox)Ln: acac⁻=acetylacetonate, ox²⁻=oxalate, HBpz₃ ⁻=hydrotris(pyrazol-1-yl)borate) and [(acac)₂Cr(μ-bpypz)Ln(hfac)₃] (Cr(bpypz)Ln: bpypz⁻=3,5-di(2-pyridyl)pyrazolate, hfac=hexafluoroacetylacetonate). The complex Yb(CA)Yb shows strong 4f-4f emission due to the ligand to metal energy transfer from the triplet state of the CA²⁻ to the excited 4f state of Yb^III. On the other hand, the observation of only the 4f-4f emission in the Cr(bpypz)Yb complex is in contrast to the simultaneous observation of the low temperature 3d-3d and 4f-4f emissions associated with the energy transfer from Cr^III to Yb^III in the Cr(ox)Yb complexes. This indicates that the energy transfer from Cr^III to Yb^III is faster in the Cr(bpypz)Yb as compared to that in the Cr(ox)Yb even at low temperatures leading to the stronger 4f-4f luminescence in the former complex. No observation of either Tb^IIIor Eu^III emission in the Tb(CA)Tb or Eu(CA)Eu complexes suggests the energy transfer or back-transfer from the Tb or Eu ions to the CA²⁻ moiety. Conversely, the Cr(bpypz)Eu and Cr(bpypz)Tb complexes show 3d-3d emissions as similarly to the corresponding Cr(ox)Eu and Cr(ox)Tb complexes; indicating the energy transfer from the Eu or Tb to the Cr^III moiety.     

Bis(undecatungstogermanate) lanthanates of potassium

The K₁₃[Ln(GeW₁₁O₃₉)₂]·nH₂O (Ln = Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Tm, Yb) have been prepared. Some properties of these compounds have been studied. The change of main bands in their IR spectra with reference to α-GeW₁₂O₄₀⁴⁻ is discussed. v_as (W---O_d) is shifted toward low wavenumber and v_as (W---O_b---W), δ(O---Ge---O) each appear as two distinct bands. X-ray powder diffraction shows that the molecular symmetry of K₁₃[Ln(GeW₁₁O₃₉)₂] is lower than that of α-K₈(GeW₁₁O₃₉). XPS determinations reveals that the Ln---O bond has coordination character and that the shifts of W_4f and O_ls are between K₁₃Ln (GeW₁₁O₃₉₂ and α-H₄(GeW₁₂O₄₀). Magnetic measurement confirms that the lanthanide elements are +3 valent in this complexes and the magnetic moments are very close to the values found by Van Vleck.     

New complexes of La(III), Ce(III), Pr(III), Nd(III), Sm(III), Eu(III) and Gd(III) ions with morin

New solid complex compounds of La(III), Ce(III), Pr(III), Nd(III), Sm(III), Eu(III) and Gd(III) ions with morin were synthesized. The molecular formula of the complexes is Ln(C₁₅H₉O₇)₃ · nH₂O, where Ln is the cation of lanthanide and n = 6 for La(III), Sm(III), Gd(III) or n = 8 for Ce(III), Pr(III), Nd(III) and Eu(III). Thermogravimetric studies and the values of dehydration enthalpy indicate that water occurring in the compounds is not present in the inner coordination sphere of the complex. The structure of the complexes was determined on the basis of UV-visible, IR, MS, ¹H NMR and ¹³C NMR analyses. It was found that in binding the lanthanide ions the following groups of morin take part: 3OH and 4CO in the case of complexes of La, Pr, Nd, Sm and Eu, or 5OH and 4CO in the case of complexes of Ce and Gd. The complexes are five- and six-membered chelate compounds.     

Complexes of lanthanoid salts with macrocyclic ligands. Part 25. Lanthanoid trifluoroacetate complexes with 12-crown-4, 15-crown-5, and 18-crown-6 ethers

The lanthanoid trifluoroacetates, Ln(TFA)₃, react with 12-crown-4, 15-crown-5, and 18-crown-6 ethers to give complexes with various metal:ligand ratios, 1:1, 3:2, and 2:1. The following complexes have been isolated and characterized: Ln(CF₃CO₂)₃· (C₈He₁₆O₄), Ln = La, Ce, Pr; [Ln(CF₃CO₂)₃]₃· (C₈H₁₆O₄)₂, Ln = Pr, Eu, Er; [Ln(CF₃CO₂)₃]₂· (C₈H₁₆O₄), Ln = Pr, Nd, Sm; [Ln(CF₃CO₂)₃]₂· (C₁₀H₂₀O₅), Ln = La---Eu; Ln(CF₃CO₂)₃·(C₁₂H₂₄O₆), Ln = La---Eu; [Ln(CF₃CO₂)₃]₂·(C₁₂H₂₄O₆), Ln = Y, Eu---Er, Yb. Thermogravimetric data show that the 2:1 complexes are usually thermally more stable. The 2:1 complexes with the 15-membered polyether undergo a slow hydrolysis in the presence of traces of water, which yields the hydroxo complex [Ln₂(CF₃CO₂)₃(OH)(C₁₀H₂₀O₅)₂] [Ln₂(CF₃CO₂)₈]. The vibrational spectra confirm the coordination of the coronands; the Δν_as(CCO) shifts are not large, which point to a moderate interaction between the polyethers and the metal ions. Magnetic susceptibilities and X-ray powder diagrams have been measured.High-resolution excitation and emission spectra have been analysed for the europium-containing compounds. The spectrum of Eu(CF₃CO₂)₃·3H₂O indicates the presence of a single species with low symmetry, in agreement with the crystal structure data for the isostructural Pr-salt. The anhydrous salt Eu(CF₃CO₂)₃ generates an emission spectrum with broad bands and probably contains several, closely related polymeric species. The spectrum of [Eu(CF₃CO₂)₃]₂(C₁₀H₂₀O₅) is consistent with the presence of two chemically different sites for Eu(III); the emission bands are broad. The double salt AgEu(CF₃CO₂)₄·3CH₃CN has also been investigated; the observed transitions point to the presence of a species with idealized D_2d symmetry. The emission spectrum of [Eu(CF₃CO₂)₃]₂(C₁₂H₂₄O₆) displays sharp bands and reveals the presence of two different sites for the metal ion with efficient energy transfers between them. One of the species may have a relatively high symmetry.In solution, all the complexes are non-electrolytes in acetonitrile and propylene carbonate and close to 1:1 electrolytes in methanol. Some dissociation occurs in acetonitrile for the 2:1 complexes with 18-crown-6 ether. On the other hand, ¹H NMR spectra of the lanthanum 1:1 complexes with 12- crown-4 and 18-crown-6 ethers indicate no dissociation of the complexed polyether. Log β₁ is greater than 6 for both complexes; it is equal to 4.4 for the samarium 1:1 complex with 18-crown-6 ether.     

Hydrothermal investigation of the lanthanide (Ln=La, Ce, Pr, Nd, Sm) 2,6-pyridinedicarboxylate system

In this paper, two new dipicolinate complexes, Ln₂(dipic)₃(H₂O)₃ (1) with Ln=La, Ce, Pr, Nd, Sm and Ce₃(dipic)₅(H₂O)₂ (2), are described. Hydrothermal synthesis, crystal structure and thermal behaviour of both compounds are described, as well as the magnetic behaviour of the trinuclear complex (2). The structures consist of LaO₇N₂, LaO₇N (1) and CeO₇N, CeO₆N₃ (2) polyhedra linked to form three-dimensional networks. The magnetic study of 2 confirms that it corresponds to a Ce(III)-Ce(IV) molecular compound and that the magnetic interaction is certainly antiferromagnetic. According to the thermogravimetric analysis, thermal decomposition of compounds 1 starts at about 100-130 °C, when 2 is thermally stable up to 250 °C.     

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.     

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.     

Diene polymerizations with the lanthanide coordination catalysts. I. Piperylene polymerizations effected by the type of lanthanide

The present paper concerns studies into piperylene polymerizations with the catalytic systems LnHal₃· 3TBP-Al(i-C₄H₉)₃ (Ln=Ce, Pr, Nd, Gd, Tb, Dy; Hal=Cl, Br, I; TBP=tributylphosphate) occurring in various solvents. The activity and stereospecificity of these catalysts have been found to depend on the composition of the initial lanthanide component LnHal₃·3TBP and mostly on the lanthanide itself. With other conditions being equal, the highest polymerization rates are provided by the Nd catalyst, and the Gd catalyst favours the formation of polypiperylene with the maximum content of cis-1,4-units. The data obtained have proved the dependence of anti-sin isomerization of π-allyl active centres on the types of the lanthanide, halogen, hydrocarbon solvent and diene monomer used.     

Nature of the Ln-Co magnetic interactions in compounds [Ln2Co3(C5H4NPO3)6] · 4H2O with open-framework structures

The reactions of Ln(NO₃)₃ · xH₂O, CoSO₄ · 7H₂O or ZnSO₄ · 6H₂O and 2-pyridylphosphonic acid under hydrothermal conditions result in heterometallic phosphonate compounds with formula [Ln₂M₃(C₅H₄NPO₃)₆] · 4H₂O (Ln₂M₃; M = Co^II or Zn^II; Ln = La^III, Ce^III, Pr^III, Nd^III, Sm^III, Eu^III, Gd^III, Tb^III, Dy^III). These compounds are isostructural and crystallize in a chiral cubic space group I2₁3. Each structure contains the {LnO₉} polyhedra and {MN₂O₄} octahedra which are connected by edge-sharing to form an inorganic open-framework structure with a 3-connected 10-gon (10, 3) topology. The nature of Ln^III-Co^II magnetic interactions in Ln₂Co₃ is investigated by a comparison with their Ln^III-Zn^II analogues. It is found that the Ln^III-Co^II interaction is weak antiferromagnetic for Ln = Ce and ferromagnetic for Ln = Sm, Gd, Tb and Dy. In the cases of Ln = Pr, Nd and Eu, no significant magnetic interaction is observed.     

Diethyl and diisopropyl phosphite complexes of lanthanide(III) chlorides

Lanthanide chlorides form adducts of the type [Ln(L)_nCl₃] (where Ln = La, Pr, Nd, Sm, Eu, when n = 6; and Ln = Gd, Tb, Dy or Yb when n = 5; and L = (EtO)₂P(O)H or (PrⁱO)₂P(O)H upon interacting with the diethyl and diisopropyl phosphites in dry ethyl and isopropyl alcohol, respectively. Complexes were recrystallised from ethanol or isopropanol and washed with n-hexane. On the basis of elemental analysis, infrared, ¹H NMR and ³¹P NMR spectral studies, it is concluded that these phosphites coordinate to the lanthanide metal atom through the oxygen atom which has the greatest affinity for lanthanides in these adducts.     

Synthesis of homodinuclear macrocyclic complexes of lanthanides and phenolic schiff bases

Successful syntheses of the first examples of homodinuclear macrocyclic lanthanide complexes are reported. The complexes were obtained as compounds of the 2:2 Schiff base formed by condensing 2,6-diformyl-p-cresol and triethylenetetramine (L₇) by a template procedure using lanthanide nitrates and perchlorates. When reactant methanolic solutions were concentrated the complexes were deposited as yellow or orange microcrystalline precipitates, Ln₂L₇(NO₃)₄sigma; nH₂O or Ln₂L₇(NO₃)_{4tau; x}(OH)_x, x = 1 or 2, whereas solutions diluted three times deposited complexes as flaky off-white crystalline precipitates of light lanthanides. The orange Ln₂L₇(NO₃)₂(OH)₂ complexes can be converted in quantitative yield to the off-white flaky form of Ln₂L₇(NO₃)₄sigma; nH₂O by refluxing them in methanolic solution containing triethylenetetramine and a three-fold excess of Ln(NO₃)₃. The complexes were characterized by elemental analysis, fast atom bombardment mass spectrometry, UV-Vis and infrared spectroscopy and thermogravimetry. Interesting and mostly new polyatomic oxo clusters, e.g. Ln₂O₃⁺, Ln₃O₄⁺, Ln₄O₆⁺, Ln₅O₇⁺, were dominant in the mass spectra but are treated in detail elsewhere.     

Heterobinuclear Zn‐Ln (Ln = La,Nd, Eu,Gd, Tb,Er and Yb) complexes based on asymmetric Schiff‐base ligand: synthesis,characterization and photophysical properties

With a novel asymmetric Schiff‐base zinc complex ZnL (H₂L = N‐(3‐methoxysalicylidene)‐N′‐(5‐bromo‐3‐methoxysalicylidene)phenylene‐1,2‐diamine), obtained from phenylene‐1,2‐diamine, 3‐methoxysalicylaldehyde and 5‐bromo‐3‐methoxysalicylaldehyde, as the precursor, a series of heterobinuclear Zn‐Ln complexes [ZnLnL(NO₃)₃(CH₃CN)] (Ln = La, 1; Ln = Nd, 2; Ln = Eu, 3; Ln = Gd, 4; Ln = Tb, 5; Ln = Er, 6; Ln = Yb, 7) were synthesized by the further reaction with Ln(NO₃)₃·6H₂O, and characterized by Fourier transform‐infrared, fast atom bombardment mass spectroscopy and elemental analysis. Photophysical studies of these complexes show that the strong and characteristic near‐infrared luminescence of Nd³⁺, Yb³⁺and Er³⁺ with emissive lifetimes in the microsecond range has been sensitized from the excited state of the asymmetric Schiff‐base ligand due to effective intramolecular energy transfer; the other complexes do not show characteristic emission due to the energy gap between the chromophore and lanthanide ions. Copyright © 2012 John Wiley & Sons, Ltd.     

Polynuclear complexes of 3d and 4f transition metals. Synthesis and structure of lanthanide(III) adducts with copper and nickel Schiff's base complexes as ligands

The synthesis and characterization of trinuclear complexes containing both 3d and 4f metal ions is presented: Ln(NO₃)₃[Cu(salpn)]₂ (Ln = Eu, Dy) and Ln(NO₃)₃ [Ni(salpn)(pn)]₂ ·2H₂O (Ln = La-Lu). The crystal and molecular structure of Ce(NO₃)_3^? [Cu(salpn)]₂·CH₃NO₂ has been determined by single-crystal X-ray diffraction. The complex forms orthorhombic crystals, space group Fdd2 (ITC No 43), a = 19.479(2), b = 26.980(2), c = 30.698(2) Å, Z = 16. The structure was solved by Patterson and Fourier techniques and refined by least squares to a final conventional R_F = 0.045 (R_w= 0.052). The Ce(III) ion is 10-coordinate, with an irregular coordination polyhedron. This polyhedron may be best described as a trigonal bipyramidal arrangement of five bidentate ligands, two axial nitrates, one equatorial nitrate and two equatorial [Cu- (salpn)] ligands. The average CeO bond length is 2.53(10) Å. The two Cu(II) ions form distorted octahedral CuN₂O₄ and square-based pyramidal CuN₂O₃ chromophores, respectively. A molecule of nitromethane links pairs of complex molecules, related by a twofold axis, into dimers. Cell parameters could also be determined for Sm(NO₃)₃[Cu- (salpn)]₂: a = 10.309(2), b = 14.768(2), c = 10.998(1) Å. The nickel complexes form an isomorphous series and their structure is discussed on the basis of spectroscopic data and of comparison with the copper complexes.     

Lanthanide-containing and bridged polyoxometalate chains: Syntheses,crystal structures and magnetic properties

Two lanthanide-decorated polyoxometalates K[Ln₂(α-SiW₁₁O₃₉)(H₂O)₁₁] (Ln = La, Ce) have been successfully synthesized and characterized with single-crystal X-ray diffraction, IR spectroscopy and thermogravimetric analysis. The two compounds have analogy structures, which consist of one-dimensional chains based on [α-SiW₁₁O₃₉]⁸⁻ building blocks. The chains are further connected to a two-dimensional layer by potassium ions. The magnetic studies of compound 1 demonstrate a ferromagnetic interaction in 1.     

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.     

Syntheses, spectroscopic characterization and X-ray structural studies of lanthanide complexes with adamantyl substituted 4-acylpyrazol-5-one

Synthesis and spectroscopic characterization of new lanthanide complexes [Ln(Q_AD)₃(EtOH)(H₂O)], (Ln = Tb, Eu; HQ_AD = 1-phenyl-3-methyl-4-adamantylcarbonyl-pyrazol-5-one), [H₃O][Tb(Q_AD)₄], [Ln(Q_AD)₃(N-N)] (Ln = Tb, Eu; N-N = 1,10-phenanthroline (Phen), 2,2′-bipyridyl (Bipy), 4,4′-dimethyl-2,2′-bipyridyl (4,4′-Me₂Bipy)) are reported. The crystal structures of the proligand HQ_AD and of complexes [H₃O][Tb(Q_AD)₄] and [Tb(Q_AD)₃(4,4′-Me₂Bipy)] have been determined. In both complexes the lanthanide ions are in a square antiprismatic environment, the H₃O⁺ cation in the former acid complex being stabilized by H-bonding. Luminescence studies have been performed on selected derivatives.     

Monazite transformation into Ce- and La-containing oxalates by Aspergillus niger

Monazite is a naturally occurring lanthanide (Ln) phosphate mineral [Ln _x(PO₄) _y] and is the main industrial source of the rare earth elements (REE), cerium and lanthanum. Endeavours to ensure the security of supply of elements critical to modern technologies view bioprocessing as a promising alternative or adjunct to new methods of element recovery. However, relatively little is known about microbial interactions with REE. Fungi are important geoactive agents in the terrestrial environment and well known for properties of mineral transformations, particularly phosphate solubilization. Accordingly, this research examined the capability of a ubiquitous geoactive soil fungus, Aspergillus niger, to affect the mobility of REE in monazite and identify possible mechanisms for biorecovery. It was found that A. niger could grow in the presence of monazite and mediated the formation of secondary Ce and La-containing biominerals with distinct morphologies including thin sheets, orthorhombic tablets, acicular needles, and rosette aggregates which were identified as cerium oxalate decahydrate (Ce₂(C₂O₄)₃·10H₂O) and lanthanum oxalate decahydrate (La₂(C₂O₄)₃·10H₂O). In order to identify a means for biorecovery of REE via oxalate precipitation the bioleaching and bioprecipitation potential of biomass-free spent culture supernatants was investigated. Although such indirect bioleaching of REE was low from the monazite with maximal lanthanide release reaching >40 mg L⁻¹, leached REE were efficiently precipitated as Ce and La oxalates of high purity, and did not contain Nd, Pr and Ba, present in the original monazite. Geochemical modelling of the speciation of oxalates and phosphates in the reaction system confirmed that pure Ln oxalates can be formed under a wide range of chemical conditions. These findings provide fundamental knowledge about the interactions with and biotransformation of REE present in a natural mineral resource and indicate the potential of oxalate bioprecipitation as a means for efficient biorecovery of REE from solution.