Anionic Lanthanide Complexes Research Articles

Room-Temperature Ionic Liquid Cation Effects on the Structure and Stability of Anionic Lanthanide Complexes.

Room-temperature ionic liquids (RTILs) are a subset of molten salts that are liquids at room temperature and may offer an elegant, low-temperature route to predicting the properties of solvated metal complexes in their high-temperature analogues. This work studied the chemistry of chloride anion-containing RTILs to determine their similarity to inorganic molten chloride salts. The behaviors of complexes of Mn, Nd, and Eu were evaluated in a variety of chloride RTILs by absorption spectrophotometry and electrochemistry to elucidate trends in cation effects on the coordination geometry and redox properties of the solvated species. Spectrophotometric data indicated the metals are present as anionic complex (e.g., MnCl42- and NdCl63-) analogous to those observed in molten chloride salts. Strongly polarizing, charge-dense RTIL cations induced distortions to the symmetry of these complexes, resulting in lower oscillator strengths and red-shifted energies for the observed transitions. Cyclic voltammetry experiments were used to characterize the Eu(III/II) redox couple producing diffusion coefficients on the order of 10-8 cm2 s-1 and heterogeneous electron transfer rate constants ranging between 6 × 10-5 and 2 × 10-4 cm s-1. The E1/2 potentials for Eu(III/II) were also found to shift positively with increasing cation polarization power, stabilizing the Eu(II) oxidation state by removing electron density from the metal center over chloride bond networks. Both the optical spectrophotometry and electrochemistry results suggest that the polarization strength of an RTIL cation plays a major role in the geometry and stability of a metal complex.

Two Heterometallic Ionic Compounds with Isolated [3d] and [4f] Complex Units: Field‐Induced Single‐Ion Magnet (SIM) Behavior Observed from a Mononuclear Dysprosium(III) Complex

AbstractTwo new complexes, [Fe3(μ3‐O)(inicH)6(H2O)3][Gd(NO3)6]·(NO3)4·nH2O (1) and [Fe3(μ3‐O)(inicH)6(H2O)3][Dy(NO3)5 (H2O)]·(NO3)5·n(H2O) (2) with two isolated complex moieties, were generated when isonicotinic acid was treated with iron(III) nitrate and the corresponding lanthanide(III) nitrate in water. The structures were determined by single‐crystal X‐ray diffraction studies. In these compounds, the anionic lanthanide complexes are encapsulated by trinuclear [Fe3(μ3‐O)(inicH)6(H2O)3]7+ cationic cluster units, which is facilitated by hydrogen‐bonding interactions. Investigation of the magnetic properties reveals that 2 shows slow relaxation of magnetization at low magnetic field (Hdc = 1.0 kOe), with an energy barrier of 23 K originating from a single [Dy(NO3)5(H2O)]2– anion.

Anionic lanthanide complexes with 3-methyl-4-formyl-1-phenyl-5-pyrazolone

The coordination compounds Na[LnL4] · 2H2O and [NBu4][LnL4] (Ln = Nd, Sm, Eu, Tb; HL is 3-methyl-4-formyl-1-phenyl-5-pyrazolone) have been synthesized and studied by IR spectroscopy and thermogravimetry. According to X-ray diffraction data, the coordination polyhedra of lanthanides are shaped as square antiprisms and formed by the oxygen atoms of four deprotonated moieties of the enol form of 4-formyl-5-pyrazolone. In the complex Na[EuL4] · 2H2O, sodium cations are bonded to the two nitrogen atoms of pyrazole heterocycles, combining discrete complex anions into two interpenetrating three-dimensional frameworks. Polycrystalline samples of neodymium(III), samarium(III), and terbium(III) complexes manifest intense luminescence in the spectral regions that are typical for them.

Anionic lanthanide complexes with 3-methyl-1-phenyl-4-formylpyrazole-5-one and hydroxonium as counter ion

A series of [H3O]+[LnL4]−·nH2O complexes (n=1–3, Ln=Nd, (1), Sm (2), Eu (3), Tb (4); HL=3-methyl-1-phenyl-4-formylpyrazole-5-one) were synthesized and characterized. The structures of the SmIII and EuIII complexes were investigated by X-ray diffraction. The isostructutal crystalls 2 and 3 consist the tetrakis [LnL4]− anions which are linked by H-bonding with the hydroxonium counter-ion and water molecules. The lanthanide ion is situated in the center of distorted tetragonal antiprism formed by eight oxygen atoms of 4-formyl-5-hydroxypyrazolonate anions. The TbIII and SmIII complexes show strong luminescence in solid state, whereas the EuIII and NdIII complexes show low luminescence activity.

Anionic lanthanide complexes supported by a pyrrole-based tetradentate Schiff base ligand: Synthesis, structures and catalytic activity toward the polymerization of ε-caprolactone

The synthesis of the anionic organolanthanide complexes supported by H2bppda (H2bppda=N,N′-bis(2-pyrrylmethylidene)-1,2-phenylenediamine) ligand via different synthetic strategies is reported. Treatment of 1:4 mixture of LnCl3(THF)3 and LiN(SiMe3)2 with 2 equivalents of H2bppda in THF gave complexes of the formula [Li(THF)4][Ln(bppda)2]·THF (Ln=Nd (1·THF), Sm (2·THF), Gd (3·THF), Dy (4·THF), Er (5·THF)) and [Li(THF)5][Yb(bppda)2] (6). Reaction of Nd(BH4)3(THF)3 with 2 equivalents of Na2bppda in THF generated [Na(THF)6][Nd(bppda)2] (7) in good yield. Treatment of 1·THF with 1 equivalent of CoCp2 in THF led to the isolation of [CoCp2][Nd(bppda)2] (8). All of the complexes have been characterized by single crystal X-ray diffraction and elemental analyses. Complexes 1·THF–5·THF are isomorphous and isostructural, and the geometry of the octa-coordinated Ln3+ ion in [Ln(bppda)2]− unit in these complexes is well described as either distorted dodecahedron or distorted bicapped trigonal prism. Lanthanide contraction was observed in 1·THF–5·THF and 6. The structures of complexes 1·THF, 7 and 8 are different from each other due to the variation of the cationic ions. The ring-opening polymerization reaction of ε-caprolactone initiated by 1·THF was conducted; it showed good activity.

Anionic Lanthanide Complexes Bearing a Bis(phenoxy)‐Functionalized N‐Heterocyclic Carbene Ligand: Syntheses and Molecular Structures

AbstractA series of anionic lanthanide complexes supported by bis(phenoxy)‐functionalized N‐heterocyclic carbene (NHC) ligand L, where L = 1,3‐bis[O‐4,6‐di‐tBu‐C6H2‐2‐CH2][C{N(CHCH)N}], were synthesized by the amine‐elimination reaction. The in situ reaction of LH3Cl with Li(thf)Ln(NiPr2)4 and nBuLi in a 2:1:2 molar ratio in thf afforded the discrete ion‐pair complexes [L2Ln][Li(dme)3] (Ln = Sm 1, Er 2, Yb 3) upon crystallization from dme/toluene (10 mL:15 mL). The reaction of LH3Cl with Li(thf)Sm(NiPr2)4 and nBuLi in a 2:1:2 molar ratio proceeded in thf, followed by crystallization from thf/toluene (2 mL:15 mL), to yield an “ate” complex [(thf)Li(μ‐L)SmL] (4). The analogous “ate” complex with sodium metal [(Et2O)Na(μ‐L)SmL] (5) was also prepared by the in situ treatment of LH3Cl with Sm[N(SiMe3)2]3 and NaN(SiMe3)2 in a 2:1:3 molar ratio. Single‐crystal X‐ray structural analyses of 1–5 revealed that complexes 1–3 have ion‐pair structure consisting of an anion [L2Ln]– and a cation [Li(dme)3]+, in which the coordination geometries about each lanthanide metal ion can be best described as a distorted octahedron, while the samarium ion and the alkali metal ion in complexes 4 and 5 are connected together by two phenoxide oxygen bridges, and each alkali metal ion is bound to anadditional oxygen atom of one thf (for 4) and one Et2O (for 5).(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Synthesis and characterization of anionic lanthanide complexes {[ o-(Me 3SiN) 2C 6H 4]Ln(MeC 5H 4) 2}{Li(DME) 3} (Ln = Yb, Sm, Nd) and their catalytic activity for the polymerization of methyl methacrylate

The syntheses and structures of a series of new lanthanide complexes supported by a chelating diamide ligand N, N′-bis(trimethylsilyl)- o-phenylenediamine are described. Anhydrous LnCl 3 reacts with Li 2[ o-(Me 3SiN) 2C 6H 4], followed by treatment of NaC 5H 4Me in 1:1:2 molar ratio to afford the corresponding anionic complexes: {[ o-(Me 3SiN) 2C 6H 4]Ln(MeC 5H 4) 2}{Li(DME) 3} [Ln = Yb ( 1), Sm ( 2), Nd( 3)] in high yield. These complexes were characterized by elemental analysis, IR and 1H NMR. The molecular structures of 1 and 2 were further determined by X-ray diffraction techniques to be an ion-pair complex composed by an anion [ o-(Me 3SiN) 2C 6H 4]Ln(MeC 5H 4) 2] and a cation [Li(DME) 3]. Complexes 1– 3 showed high catalytic activity for the polymerization of methyl methacrylate (MMA) at r.t., giving the syndiotactic-rich polymers with relatively narrow molecular weight distributions ( M w/ M n = 1.64–1.82).

Crystal structures of anionic lanthanide complexes as constituents of ionic liquids

Crystal structures of anionic lanthanide complexes as constituents of ionic liquids

Mechanisms of metal ion transfer into room-temperature ionic liquids: the role of anion exchange.

The structure and stoichiometry of the lanthanide(III) (Ln) complexes with the ligand 2-thenoyltrifluoroacetone (Htta) formed in a biphasic aqueous room-temperature ionic liquid system have been studied by complementary physicochemical methods. Equilibrium thermodynamics, optical absorption and luminescence spectroscopies, high-energy X-ray scattering, EXAFS, and molecular dynamics simulations all support the formation of anionic Nd(tta)4(-) or Eu(tta)4(-) complexes with no water coordinated to the metal center in 1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide (C4mim+Tf2N(-)), rather than the hydrated, neutral complexes, M(tta)(3)(H2O)n)(n = 2 or 3), that form in nonpolar molecular solvents, such as xylene or chloroform. The presence of anionic lanthanide complexes in C4mim+Tf2N(-) is made possible by the exchange of the ionic liquid anions into the aqueous phase for the lanthanide complex. The resulting complexes in the ionic liquid phase should be thought of as weak C4mim+Ln(tta)4(-) ion pairs which exert little influence on the structure of the ionic liquid phase.

Synthesis and single-crystal x-ray diffraction examination of a structurally homologous series of tetracoordinate heteroleptic anionic lanthanide complexes: Ln[N[Si(CH3)2CH2CH2Si(CH3)2]]3(mu-Cl)Li(L)3 (Ln = Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb; (L)3 =(THF)3, (Et2O)3, (THF)2(Et2O)

Anhydrous lanthanide(III) chlorides (Ln = Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb) react with 3 equiv of lithium 2,2,5,5-tetramethyl-2,5-disila-1-azacyclopentanide, Li[N[Si(CH3)2CH2Ch2Si(CH3)2]], in THF or Et(2)O to afford the monomeric four-coordinate heteroleptic ate complexes Ln[N[Si(CH3)2CH2CH2Si(CH3)2]]3(mu-Cl)Li(THF/Et2O)3 (Ln = Sm (1), Eu (2), Gd (3), Tb (4), Dy (5), Ho (6), Er (7), Tm (8), Yb (9)), whose solid-state structures were determined by the single-crystal X-ray diffraction technique. All complexes additionally were characterized by melting point determination, elemental analyses, and mass spectrometry.

Fermi contact and dipolar nuclear magnetic resonance shifts in paramagnetic ion-paired systems. Anionic lanthanide complexes

Fermi contact and dipolar nuclear magnetic resonance shifts in paramagnetic ion-paired systems. Anionic lanthanide complexes