II) And Lanthanide Research Articles

Complexes of cyclen side-bridged with a methylene-bis(phosphinate) group

A macrobicyclic cyclen-based ligand containing a geminal bis(phosphinate) N,N′-bridge was synthesized via a Mannich-type reaction. The other two macrocycle amine groups were modified with two acetate pendants, yielding ligand H4L. The cyclen-bis(phosphinate) intermediate, the ligand salt Na0.5(H5L)(H3.5L)Cl·20H2O and CuII complex Li2[Cu(L)]·4H2O were characterized by single-crystal X-ray diffraction. The ligand protonation constants and the stability constants of H4L complexes with Cu(II) and Zn(II) and lanthanide(III) ions were determined by potentiometry. The ligand protonation constants and the stability constants of H4L complexes with Cu(II) and Zn(II) ions are similar to those of H4dota. Conversely, the stabilities of its Ln(III) complexes are ~ 7–10 orders of magnitude lower than those of H4dota complexes due to steric restrictions of the methylene-bis(phosphinate) side bridge. Therefore, these findings indicate that the ligand H4L is suitable for the complexation of transition metal ions.

Water-Soluble Polynuclear Metallamacrocyclic Copper(II) and Lanthanide(III) Complexes Based on Amino Hydroxamic Acids

Data on the synthesis and structure of water-soluble polynuclear copper(II) and lanthanide(III) metallamacrocycles based on amino hydroxamic acids are presented. The structural features of the obtained 15-MC-5 metallacrown aqua complexes and their applicability as NMR contrast agents are considered. Additionally, the applicability as molecular precursors for the synthesis of nano-sized materials was demonstrated for Ce(III) compounds.

Coordination cluster nuclearity decreases with decreasing rare earth ionic radius in 1:1 Cr/Ln N-butyldiethanolamine compounds: a journey across the lanthanide series from Cr4(III)La4–Cr4(III)Tb4 via Cr3(III)Dy3 and Cr3(III)Ho3 to Cr2(III)Er2–Cr2(III)Lu2.

Reactions of the N-substituted diethanolamine ligand N-n-butyldiethanolamine with chromium(II) and lanthanide(III)/rare earth salts (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y) in the presence of coligands give access to three series of isostructural 1:1 3d(Cr(III))/4f(Ln(III)) coordination cluster compounds that can be designated in terms of octanuclear "square-in-square" (Ln = La-Tb), hexanuclear "triangle-in-triangle" (Ln = Dy, Ho, Y) and tetranuclear "butterfly" or defect dicubane core (Ln = Er-Lu) topologies as revealed by single-crystal X-ray crystallographic analysis. The bulk magnetic properties were also measured. The influences of the various components in the reaction system on the final topology and the role of the ionic radius are discussed.

Structural features of copper(II) and lanthanide(III) tartratogermanate(IV) complexes

Four heterometallic tartratogermanate complexes, namely [Cu2Ge2(Tart)3(H2O)10]n · 3nH2O and (H3O)[LnGe2(Tart)3(H2O)6] · nH2O (Ln3+ = Gd, n = 3.5; Tm, n = 3; Yb, n = 3), have been prepared via the reaction between germanium tetrachloride and D-tartaric acid (H4Tart) in aqueous acetic acid. All complexes contain {Ge2(Tart)3}n4n- polymer chains. The Cu2+ and Ln3+ atoms coordinate only Tart carbonyl oxygen atoms.

Heterometallic trinuclear 3d–4f–3d compounds based on a hexadentate Schiff base ligand

The new heterometallic trinuclear complexes [Ni2Ln(L)2(CH3COO)2(MeOH)2]NO3·4H2O (where Ln=Ce(III) 1, Pr(III) 2 and H2L=the Schiff base resulting from the condensation of 5-bromo-3-methoxysalicylaldehyde and 1,3-diaminopropane) were synthesized and characterized by elemental analysis, FTIR, TG/DSC, TG-FTIR, single crystal X-ray diffraction, magnetic, UV–Vis and luminescence studies. In the isostructural crystals of 1 and 2 the nickel(II) and lanthanide(III) ions are bridged by two Schiff base’s phenolato oxygens and additionally by the acetate ions. The clathrate type of crystal architecture in reported complexes, results in their quite high stability in air and nitrogen atmospheres at room temperature despite the relatively large amount of non-coordinated water. The temperature dependence (1.8–300K) of the magnetic susceptibility investigations and the field-dependent magnetization indicate crystal field effect, as well as, the presence of an antiferromagnetic interaction between spin carriers of NiII and LnIII pairs in the NiII–CeIII–NiII (1) and NiII–PrIII–NiII (2) compounds operating via oxygen atoms (JNiCe=−1.1(4)cm−1 (1) and JNiPr=−1.3(8)cm−1 (2)).

Synthesis, Structure, and Magnetic Properties of a New Family of Tetra-nuclear {Mn2IIILn2}(Ln = Dy, Gd, Tb, Ho) Clusters With an Arch-Type Topology: Single-Molecule Magnetism Behavior in the Dysprosium and Terbium Analogues

Sequential reaction of Mn(II) and lanthanide(III) salts with a new multidentate ligand, 2,2'-(2-hydroxy-3-methoxy-5-methylbenzylazanediyl)diethanol (LH3), containing two flexible ethanolic arms, one phenolic oxygen, and a methoxy group afforded heterometallic tetranuclear complexes [Mn2Dy2(LH)4(μ-OAc)2](NO3)2·2CH3OH·3H2O (1), [Mn2Gd2(LH)4(μ-OAc)2](NO3)2·2CH3OH·3H2O (2), [Mn2Tb2(LH)4(μ-OAc)2](NO3)2·2H2O·2CH3OH·Et2O (3), and [Mn2Ho2(LH)4(μ-OAc)2]Cl2·5CH3OH (4). All of these dicationic complexes possess an arch-like structural topology containing a central Mn(III)-Ln-Ln-Mn(III) core. The two central lanthanide ions are connected via two phenolate oxygen atoms. The remaining ligand manifold assists in linking the central lanthanide ions with the peripheral Mn(III) ions. Four doubly deprotonated LH(2-) chelating ligands are involved in stabilizing the tetranuclear assembly. A magnetochemical analysis reveals that single-ion effects dominate the observed susceptibility data for all compounds, with comparably weak Ln···Ln and very weak Ln···Mn(III) couplings. The axial, approximately square-antiprismatic coordination environment of the Ln(3+) ions in 1-4 causes pronounced zero-field splitting for Tb(3+), Dy(3+), and Ho(3+). For 1 and 3, the onset of a slowing down of the magnetic relaxation was observed at temperatures below approximately 5 K (1) and 13 K (3) in frequency-dependent alternating current (AC) susceptibility measurements, yielding effective relaxation energy barriers of ΔE = 16.8 cm(-1) (1) and 33.8 cm(-1) (3).

Reaction of lanthanide(II) and lanthanide(III) phenylethynyl cuprates with acetyl chloride

Praseodymium and ytterbium phenylethynyl cuprates [(PhC≡C)3Cu]3Pr2(THF)6 and {[(PhC≡C)3Cu]·Yb(THF)2}2 react with acetyl chloride in tetrahydrofuran with elimination of phenylethynylcopper and formation of alkoxides [PhC≡C-CCl(CH3)O]nLn (n = 3, Ln = Pr; n = 2, Ln = Yb). Then praseodymium alkoxide forms ester [methyl (phenylethynyl)chloromethylethanoate] and praseodymium chloride, alkoxy derivative. Itterbium alkoxide is oxidized to unsymmetrical dialkoxyitterbium chloride PhC≡C-CH(CH3)-O-Yb(Cl)-O-CCl(CH3)C≡CPh·2THF.

Establishing the Binding Affinity of Organic Carboxylates to 15-Metallacrown-5 Complexes

The reaction of L-phenylalanine hydroxamic acid (H(2)L-pheHA) with copper(II) and lanthanide(III) salts yields 15-Metallacrown-5 structures of the general composition Ln(X)n[Cu(II)(L-pheHA)](5)((3-n)+) where X can represent a wide variety of anions. With five copper ions and one central lanthanide ion, the Ln[15-MC-5] complexes have multiple positions where these anionic guests may bind to the metallacrown host. In addition, these metallacrowns are amphiphilic, containing one face that is primarily hydrophobic (due to the five benzyl side chains which are oriented upon the same face of the molecule) and a face that is hydrophilic which has no impediment to solvent access. While it has been known that aromatic carboxylates bind preferentially to the hydrophobic face and short chain aliphatic carboxylates bind preferentially to the hydrophilic face, there have been no quantitative assessments of the stability of these host-guest complexes. Using Isothermal Calorimetry (ITC) we have determined the binding constants for several carboxylate anions to a variety of metallacrown complexes. The affinities of anions that coordinate to the lanthanide ion on the hydrophobic face are related to the hydrophobicities of the guests, with higher binding strength observed for the more hydrophobic carboxylates. Central metal such as La(III) or Nd(III) which are nine coordinate are able to accommodate two guests on the hydrophobic side; however, central metals such as Gd(III) or Dy(III) which are eight coordinate are limited to encapsulating one guest into the hydrophobic pocket. A second guest, bound to the hydrophilic face is often observed with these 8-coordinate lanthanides. The significantly weaker second binding constant between benzoate and Gd(III)[15-MC-5] supports the model that the second benzoate binds to the central metal through the hydrophilic side. Unlike the Gd(III)[15-MC-5], the higher binding constant of the second benzoate with La(III)[15-MC-5] is consistent with the crystallographic model which shows that the second guest binds to the hydrophobic side.

Benzyl Complexes of Lanthanide(II) and Lanthanide(III) Metals: Trends and Comparisons

A variety of benzyllanthanide complexes have been prepared by the metathesis reaction of benzylpotassium precursors with lanthanide halides. Syntheses and crystal structures for the following complexes are described: [2-Me2N-α-Me3Si-benzyl]2Eu(II)·(THF)2 (1-Eu), (2-Me2Nbenzyl) 3Ln(III) (2-Ln with Ln = Nd, Sm, Dy, Ho, Yb), (4-R-C6H4CH2)3Ln·(THF)3 (3-Y: Ln = Y, R = H; 3-La: Ln = La, R = tBu). Complexes of types 1 and 2 are thermally robust on account of a stabilization by a benzylic Me3Si substituent and/or intramolecular coordination of the Me2N substituent. Comparison of the crystal structures of these new series of lanthanide complexes shows several similarities and trends. In addition, comparisons with alkali metal and alkaline earth metal benzyl complexes are made.

Characterization of Metal Ions in Coordinating Solvent Mixtures by Means of Raman Spectroscopy

AbstractFor Abstract see ChemInform Abstract in Full Text.

Characterization of metal ions in coordinating solvent mixtures by means of Raman spectroscopy.

Titration Raman spectroscopy has been developed for studying the solvation structure of metal ions in solution. The method affords us the solvation number, and the value thus obtained in neat solvents is in good agreement with that determined by EXAFS. The method is then applied to solvent mixtures, and the individual solvation number for each solvent is extracted. In a solvent mixture of N,N-dimethylformamide (DMF) and N,N,N',N'-tetramethylurea (TMU), the metal ion prefers DMF to TMU, which is ascribed to the solvation steric effect. The same applies also for the solvent mixture of N,N-dimethylpropionamide (DMPA) and DMF. However, unlike TMU, DMPA changes its conformation from the planar cis to non-planar staggered upon solvation to the metal ion. The enthalpy for the conformational change of DMPA is positive in the bulk, while it is significantly negative in the coordination sphere of the manganese(II) ion. Here, we briefly describe the procedure of measurements and analyses for the titration Raman spectroscopy, and review the solvation structure of the alkaline earth, first transition metal(II) and lanthanide(III) ions in some solvent mixtures in view of solvation steric effect.

"Asymmetric" catalysis by lanthanide complexes.

Catalysis with lanthanide (Ln) complexes has been underestimated for long time, although Ln(III) complexes have great advantages as Lewis acid catalysts for "asymmetric" carbon-carbon bond-forming reactions. Lanthanide complexes are highly active in ligand-substitution reactions, especially with hard ligands. The association with substrates and dissociation of products are achieved fast enough for high catalyst efficiency. The asymmetric catalysis of organic reactions can be greatly advanced by the use of Ln complexes with chiral ligands such as binaphthol (binol). Ln(II) complexes are good reducing agents, which can be used in a wide variety of synthetically important reactions; when chiral ligands are used, many of these reactions are highly stereoselective. In the context of "green chemistry", the development of asymmetric Ln catalysts, and their recyclable use, is of increasing importance. This review gives an overview of the most recent developments in catalysis with lanthanide(II) and lanthanide(III) complexes.

Asymmetric catalysis in aqueous media: use of metal-chiral crown ethers as efficient chiral Lewis acid catalysts in asymmetric aldol reactions

Metal-chiral crown ether complexes have been developed as efficient chiral Lewis acid catalysts for asymmetric aldol reactions of silyl enol ethers with aldehydes in aqueous media. While many excellent catalytic asymmetric reactions have been developed recently, most of them have to be carried out under strictly anhydrous conditions in organic solvents. This is probably due to the instability of many catalysts and/or intermediates in the presence of even a small amount of water. To address this issue, we searched for metal-crown ether complexes on the basis of our "multi-coordination" hypothesis, and found that lead(II) and lanthanide(III) catalysts worked well as chiral Lewis acids in aqueous media. To the best of our knowledge, these are the first examples of chiral crown-based Lewis acids that can be successfully used in catalytic asymmetric reactions. The catalysts have been characterized by X-ray diffraction, and their unique structures as chiral catalysts have been revealed. Use of water as a solvent is essential in these asymmetric catalysis, and the role of water on these reactions to explain the high reactivity and selectivity has been suggested. Another important point is that kinetic studies have shown the possibility that these types of crown ether complexes would be suitable as chiral catalysts employed in aqueous media. In addition, although the catalytic asymmetric aldol reactions are one of the most powerful carbon-carbon bond-forming methodologies and several successful examples have been reported, the use of aprotic anhydrous solvents and low reaction temperatures (-78 °C) has been needed in almost all successful cases. On the other hand, the present reactions proceeded smoothly at -10-0 °C in water-alcohol solutions while retaining high levels of diastereo- and enantioselectivities.

Syntheses, structures and magnetic behaviors of di- and trinuclear pivalate complexes containing both cobalt(II) and lanthanide(III) ions.

The syntheses and X-ray structures of the di- and trinuclear pivalates [C9H7NH][CoTb(Piv)3(C9H7N)(NO3)3]·0.5H2O, [CoLn(Piv)5(C9H7N)(H2O)]·0.5C9H7N (Ln = Gd, Dy), and [Co2Gd(Piv)6(C9H7N)2(NO3)] (Piv = O2CCMe3) are reported. The four complexes all exhibit weak ferromagnetic interactions between their corresponding heterometallic ions.

Complexes of lead(II) and lanthanide(III) ions with two novel 26-membered-imine and -amine macrocycles derived from 2,6-bis(2-formylphenoxymethyl)pyridine

acrocyclic Schiff-base lanthanide(III) complexes, [LnL 1] [X] 3 (X = NO 3, Ln = La, Ce, Pr, Ce, Pr, Nd, Sm, Eu, Gd Tb, Ho, Er, Tm, Yb or Lu: X = ClO 4, Ln = La, Ce, Pr, Nd, Sm, Eu, Tb, Dy or Er) and the complex [PbL 1] [ClO 4] 2 have been prepared by cyclocondensation of 2,6-bis(2-formylphenoxymethyl)pyridine and 1,5-bis(2-aminophenoxyl)-3-oxapentane in the presence of the appropriate metal salt as a template agent. The Schiff-base macrocycle L 1 is also formed in the absence of the metal ion. Treatment of L 1 with NaBH 4 in methanol gave the di-amine macrocycle L 2. The reactions of lanthanide(III) ions with L 2 were also investigated.

Synthesis, characterisation and reactions of 1,3-bis(trimethylsilyl)-1-aza-allyl-lanthanide complexes; X-ray structures of [Sm(LL′) 2I(thf)], [Yb(LL′) 2] and [RNC(Bu t)CH(R)] 2 (thf = tetrahydrofuran, LL′ = η3-N(R)C(Bu t)CHR, RSiMe 3)

Several lantahanide(II) and lanthanide(III) complexes of formula [Ln(LL′) 2X(thf) n ](LL′ = η 3-N(R)C(Bu 1)CHR, R  SiMe 3; X  Cl, n = 1 and Ln  Ce 1 and Nd 2; or X = I, n = 1 and Ln = Sm 3; or X = I, n = 0 and Ln = Yb 4), [Sm(LL′) 2(thf)] 5 and [Yb(LL′) 2] 6 have been synthesized by the reaction of the appropriate lanthanide(II) or lanthanide(III) halide with two equivalents of 1,3-bis(trimethylsilyl)-1-aza-allyl-potassium [K(LL′)] n . Oxidation of 6 with Ag(OTf) afforded [Yb(LL′) 2(OTf)] 7 (Tf = SO 2CF 3). The reaction of 6 with half an equivalent of I 2 yielded as the main oxidative product 4 but also led to ligand coupling, forming [RN=C(Bu 1)CH(R)] 2 8, which was also prepared by the reaction of [K(LL′)] n with I 2. Treatment of 6 with two equivalents of PhCN yielded the previously known β-diketiminate [Yb(L′L″) 2][L′L″=N(R)C(Ph)C(H)C(Bu 1)NR]. Complexes 1–8 were identified by C, H and N elemental analysis, multinuclear ( 1H, 13C, 29Si{ 1H}, 17Yb or 19F) NMR and mass spectra, of which 3, 6 and 8 were additionally characterised by single crystal X-ray diffraction.

Thermodynamic and Structural Aspects on Solvation Steric Effect in Nonaqueous Solution

Abstract Formation thermodynamics and structure of halogeno and pseudo-halogeno complexes of transition metal(II) and lanthanide(III) ions have been studied in N,N-dimethylacetamide (DMA) and hexamethylphosphoric triamide (HMPA), and compared with those in N,N-dimethylformamide (DMF). Significant differences in the formation thermodynamics and structure among solvents has been explained in terms of a solvation steric effect. A structural survey by EXAFS demonstrates that solvent coordination number of a solvate metal ion is kept unchanged (weak solvation steric effect) or reduced (strong solvation steric effect) when the metal ion is transferred to DMA or HMPA, respectively, from DMF. DMA usually exhibits a weak solvation steric effect. It elucidates that a weak solvation steric effect of DMA is ascribable mainly to a distortion of the M–O–C–N dihedral angle. The solvent effect operates for a complex with a coordination number larger than four in DMF, but it does not for a complex of four-coordination. Lanthanide(III) ions exhibit a specific solvation steric effect, and an outer-sphere bromo complex in DMF changes to an inner-sphere complex in DMA. Besides, the solvent coordination number varies with solvent composition in DMF–DMA mixtures, and the variation manner strongly depends on the metal ion or the ionic radius. HMPA shows a strong solvation steric effect, and halogeno complexation is significantly enhanced in HMPA relative to that in DMF, although HMPA has a stronger electron-pair donating ability. The coordination number is four or five, and the M–O(HMPA) bondlength is significantly shortened.

Formation and dissociation kinetics of triaza-crown-alkanoic acid complexes of transition metal(II) and lanthanide (III)

The formation and dissociation rates of some transition metal(II) and lanthanide(III) complexes of the 1,7,13-triaza-4,10,16-trioxacyclooctadecane N′, N″, N‴-triacetic acid ( 1) and 1,7,13-triaza-4,10,16-trioxacyclooctadecane- N′, N″, N‴- trimethylacetic acid ( 2) have been measured by the use of stopped-flow and conventional spectrophotometry. Experimental observations were made at 25.0 ± 0.1°C and at an ionic strength of 0.10 M KCl. The complexation of Zn 2+ and Cu 2+ ions with 1 and 2 proceeds through the formation of an intermediate complex (MH 3L +∗) in which the metal ion is incompletely coordinated. This may then lead to a final product in the rate-determining step. Between pH 4.68 and 5.55, the diprotonated (H 2L −) form is revealed to be a kinetically active species despite its low concentration. The stability constants ( log K MH 3 L +∗ ) and specific base-catalyzed rate constants ( k OH) of intermediate complexes have been determined from the kinetic data. The dissociation reactions of 1 and 2 complexes of Co 2+, Ni 2+, Zn 2+, Ce 3+, Eu 3+ and Yb 3+ were investigated with Cu 2+ ions as a scavenger in acetate buffer. All complexes exhibit acid-independent and acid-catalyzed contributions. The buffer and Cu 2+ concentration dependence on the dissociation rate has also been investigated. The metal and ligand effects on the dissociation rate of some transition metal(II) and lanthanide(III) complexes are discussed in terms of the ionic radius of the metal ions, the side-pendant arms and the rigidity of the ligands.

Complexes of lead(II) and lanthanide(III) ions with a macrocyclic ligand containing a furan head unit. Crystal structure of a methanol inclusion compound of a novel macrocycle

Abstract A Schiff-base polyoxaazamacrocycle derived from 2, 5-diformylfuran and 1, 5-bis(2-aminophenoxy)-3-oxapentane was obtained by a template procedure as mononuclear lanthanide(III) and lead(II) complexes. In the absence of the metal salt the macrocycle was not formed. The complexes were characterized by elemental analysis, molar conductivity, mass spectrometry and IR, 1 H NMR and 13 C NMR spectroscopy. The reduction of the Pb II complex with sodium borohydride yielded a novel polyoxaazamacrocycle containing a furan head and aromatic lateral units; the X-ray crystal structure of its methanol inclusion compound is reported.

Spectrophotometric determination of the stability constant of the Eu(III)—murexide complex

The values of the stability constants of the Ca(II) and lanthanide(III) complexes of murexide reported in the literature were determined without proper correction for binding of buffer ions to the metal ion. The constants are best determined without a buffer present. Accurate values of conditional stability constants for the Eu(III)—murexide complex (relative standard deviation better than 3%), of the differential molar absorptivity of the Eu(III)—murexide complex with respect to murexide at 480 nm (relative standard deviation better than 0.5%) and of the molar absorptivity of murexide at 520 and at 506 nm (precision better than 0.4%) at pH 5.0 and 6.5 at 15, 25 and 35° are reported. The accuracy and precision of the concentration of metal ion solution determined by using these conditional stability constants are discussed.