Polyoxometalate-supported Y- and YbIII-hydroxo/oxo clusters from carbonate-assisted hydrolysis

Carbonate-assisted hydrolysis of Y or Yb(III) ions in the presence of the trivacant Wells-Dawson polyoxoanion, alpha-[P(2)W(15)O(56)](12-), produced two polyoxometalate-supported Y- or Yb(III)-hydroxo/oxo clusters, which have been characterized by single-crystal X-ray structure determination. The structure of the Y complex consists of a distorted Y(4)(OH)(4) cubane cluster encapsulated by two lacunary alpha-[P(2)W(15)O(56)](12-) units, while the Yb cluster features a hexametallic core centered around a mu(6)-oxo atom with each Yb(3)(III) triangular face capped by an oxo or a hydroxo group. Magnetization measurements of the ytterbium(III) derivative suggested that intermolecular dipolar exchange is present at low temperatures (below 15 K). Despite its absence in the structures themselves, control experiments show that carbonate not only functions in the hydrolysis, it also influences the structure of the complexes by complexation to yttrium and the f-block elements.     

Sonoluminescence of aqueous solutions of lanthanide salts

The influence of salts (TbCl₃, Tb(NO₃)₃, PrCl₃, EuCl₃, CeCl₃, and DyCl₃) on the spectrum and intensity of multi-bubble sonoluminescence (SL) of water was observed at a frequency of 20 kHz. Luminescence bands of the lanthanide ions were detected in the SL spectra of concentrated solutions of the Ce^III, Tb^III, and Dy^III chlorides (0.1—1 mol L^–1). No luminescence was observed for solutions of the other salts, and the shape of the spectra is due to the absorption of the water SL by the lanthanide ions. Possible mechanisms of the appearance of SL of lanthanides were considered. The first mechanism is the excitation of the lanthanide aqua ions in the solution bulk due to the absorption of the short-wave portion of glow of the excited water molecules and OH radicals emitted from the cavitation gas-vapor bubbles. The second mechanism involves the transfer of the lanthanide ions to the gas phase from the liquid layer adjacent to the cavitation bubble and their excitation in the bubble volume upon collisions with other hot or electron-excited particles.     

Crystal‐Structure Determination of Powdered Paramagnetic Lanthanide Complexes by Proton NMR Spectroscopy

Shifts for crystals : Solid‐state NMR spectroscopy can be used for structure determination of microcrystalline paramagnetic solids at natural isotopic abundance. The protocol makes use of paramagnetic effects, measured on suitably recorded ¹H NMR spectra, to define the conformation of a molecule in the lattice and the intermolecular packing in the solid phase. The method is illustrated with a family of lanthanide compounds (see picture).

     

New chiral lanthanide amide ate complexes for the catalysed synthesis of scalemic nitrogen-containing heterocycles

New chiral binaphthylamido yttrium and ytterbium ate complexes with lithium and potassium counterions have been synthesised and characterised. X-ray structures have been obtained for [Li(thf)4][Ln{(R)-C20H12(NC5H9)2}2] (Ln=Yb, Y) and [K(thf)5][Yb{(R)-C20H12(NCH2CMe3)2}2] as isostructural complexes. The efficiency of these complexes for the enantioselective intramolecular hydroamination was examined. [Li(thf)4][Yb{(R)-C20H12(NC5H9)2}2] afforded the highest enantiomeric excess (up to 87 %) for the synthesis of a spiropyrrolidine, while [Li(thf)4][Y{(R)-C20H12(NC5H9)2}2] proved to be slightly more active. The role of the counter cation in the active catalytic species was evidenced by the comparison between lithium and potassium ate complexes. The most active catalyst of this series, [Li(thf)4][Yb{(R)-C20H12(NCH2CMe3)2}2], was successfully used for the cyclisation of aminopentenes with internal double bonds.     

Sonoluminescence of aqueous solution of gadolinium chloride

A line of the Gd^III ion was detected at 311 nm in the multibubble sonoluminescence spectrum of a concentrated (1 mol L⁻¹) solution of gadolinium chloride. A comparison with the earlier studied sonoluminescence of the Ce^III and Tb^III ions shows that the Gd^III ion is excited in the volume and/or on the surface of cavitation bubbles upon collisions with “hot” particles. The efficiency of excitation of the lanthanide ions via this mechanism depends on the type of electron transition. For the same energy of the excited state, the efficiency of Gd^III excitation (f-f transition) exceeds by at least 50 times that of Ce^III excitation (f-d transition). Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1341–1344, June, 2005.     

Aqueous Geochemistry of Rare Earth Elements and Yttrium. XII: Potentiometric Stability Constant Determination of Bis-Tris Complexes with La, Nd, Eu, Gd, Yb, Dy, Er, Lu, and Y

Conditional stability constants of 2-[bis(2-hydroxyethyl)amino]-2(hydroxymethyl)-1,3-propanediol (BT) complexes of trivalent rare earth element (Ln) ions (La, Nd, Eu, Gd, Yb, Dy, Er, Lu) and Y were determined potentiometrically in aqueous NaCl solutions at 30°C and 0.1 M ionic strength. Least-squares fitting shows that, at <0.04 molal BT, the complex LnBT³⁺ is dominant, with LnBT₂ ³⁺ forming a secondary complex, where:

A new pyridine-2,6-bis(oxazoline) for efficient and flexible lanthanide-based catalysts of enantioselective reactions with 3-alkenoyl-2-oxazolidinones

A new pyridine-2,6-bis(oxazoline) (4) has been easily synthesised from the reaction of (1S,2S)-2-amino-1-phenylpropane-1,3-diol (1) and dimethyl pyridine-2,6-dicarboximidate (2), followed by TIPS (TIPS=triisopropylsilyl) protection of the 4'-CH2OH group. The catalysts derived from 4 and eight lanthanide(III) triflates have been tested over three reactions involving 3-acryloyl- and 3-crotonoyloxazolidinones (5 a,b): the Diels-Alder (DA) reaction with cyclopentadiene, the 1,3-dipolar cycloaddition with diphenyl nitrone and the Mukaiyama-Michael reaction with 2-trimethylsilyloxyfuran. Several reactions exhibit very good enantioselectivity (ee>90 %), and the opposite enantiomers can be easily obtained simply by changing the cation. This specific feature of the ligand can be appreciated in the DA reaction of 5 a, since the catalyst [Sc(III)4] gives the adduct (2'S)-9 a with 99 % ee, whereas the catalyst [Y(III)4] gives the opposite enantiomer with 95 % ee. A rationale of the enantioselectivity is proposed on the basis of the NMR spectra of La-based complexes involving 4 and 5 as ligands.     

A Gd3+-based magnetic resonance imaging contrast agent sensitive to beta-galactosidase activity utilizing a receptor-induced magnetization enhancement (RIME) phenomenon

Magnetic resonance imaging (MRI) permits noninvasive three-dimensional imaging of opaque organisms. Gadolinium (Gd(3+)) complexes have become important imaging tools as MRI contrast agents for MRI studies, though most of them are nonspecific and report solely on anatomy. Recently, MRI contrast agents have been reported whose ability to relax water protons is triggered or greatly enhanced by recognition of a particular biomolecule. This new class of MRI contrast agents could open up the possibility of reporting on the physiological state or metabolic activity deep within living specimens. One possible strategy for this purpose is to utilize the increase in the longitudinal water proton r(1) relaxivity that occurs upon slowing the molecular rotation of a small paramagnetic complex, a phenomenon which is known as receptor-induced magnetization enhancement (RIME), by either binding to a macromolecule or polymerization of the agent itself. Here we describe the design and synthesis of a novel beta-galactosidase-activated MRI contrast agent, the Gd(3+) complex [Gd-5], by using the RIME approach. beta-Galactosidase is commonly used as a marker gene to monitor gene expression. This newly synthesized compound exhibited a 57% increase in the r(1) relaxivity in phosphate-buffered saline (PBS) with 4.5% w/v human serum albumin (HSA) in the presence of beta-galactosidase. Detailed investigations revealed that RIME is the dominant factor in this increase of the observed r(1) relaxivity, based on analysis of Gd(3+) complexes [Gd-5] and [Gd-8], which is generated from [Gd-5] by the activity of beta-galactosidase, and spectroscopic analysis of their corresponding Tb(3+) complexes, [Tb-5] and [Tb-8].     

Pentanuclear heterobimetallic 3d-4f complexes of Ln<Subscript>2</Subscript>M<Subscript>3</Subscript>-type — structure and magnetism

From a series of pentanuclear, heterobimetallic complexes of the general composition [{Ln(H₂O)_n}₂{Ni(dto)₂}₃] · xH₂O, four complexes (Ln = Gd(III) with n = 4; Ln = Dy(III), Ho(III), or Er(III), with n = 5; x = 9–12; dto = 1,2-dithiooxalate) were studied due to their large magnetic moments (up to 14.65 B.M.). The magnetic properties of these complete series were measured at room temperature and the temperature dependent magnetic properties of the complexes Gd₂Ni₃, Dy₂Ni₃, Ho₂Ni₃, and Er₂Ni₃ were studied at room temperature down to 1.8 K. Whereas the intramolecular metal-metal distances were rather long (Ni1-Ni2: 11.0–11.5 Å; Ln-Ni: 6.0–6.3 Å), relatively short intermolecular metal-metal distances (Ni1-Ni2′: 3.5 Å; Er-Er′: 6.0 Å) were found in the crystal lattice, giving rise to weak intermolecular metal-metal interactions. These weak spin interactions were also supported by the EPR spectrum of a powdered sample of the diamagnetically undiluted Gd₂Ni₃ complex.     

Structure, magnetism and theory of a family of nonanuclear Cu(II)5Ln(III)4-triethanolamine clusters displaying single-molecule magnet behaviour

Synthesis, crystal structures and magnetic studies are reported for four new heterometallic Cu(II)-Ln(III) clusters. The reaction of Cu(NO(3))(2)·3H(2)O with triethanolamine (teaH(3)), pivalic acid, triethylamine and Ln(NO(3))(3)·6H(2)O (Ln=Gd, Tb, Dy and Ho) results in the formation of four isostructural nonanuclear complexes of general formula [Cu(II)(5)Ln(III)(4)O(2)(teaH)(4){O(2)CC(CH(3))(3)}(2)(NO(3))(4)(OMe)(4)]·2MeOH·2Et(2)O [Ln=Gd (1), Tb (2), Dy (3) and Ho (4)]. The metal core of each cluster is made up of four face- and vertex-sharing tetrahedral units. Solid-state DC magnetic susceptibility studies reveal competing anti- and ferromagnetic interactions within each cluster leading to large-spin ground states for 1-4. Solid-state AC magnetic susceptibility studies show frequency-dependent out-of-phase (χ'(M)) signals for 2-4 below 4 K, suggestive of single-molecule magnet behaviour. Ab initio calculations on one of the anisotropic examples (3) provided a rare set of J values for Dy-Cu and Cu-Cu exchange interactions (Dy-Dy zero), some ferro- and some antiferromagnetic in character, that explain its magnetic behaviour.