RE Cation Research Articles

Magnetic properties of Mn-substituted GdCo xMn 1−xO 3 and LaCo xMn 1−xO 3

Partial substitution of manganese by cobalt in rare-earth perovskites REMnO 3 leads to unusual magnetic phenomena because of the simultaneous presence of Mn 3+, Mn 4+, Co 2+ and Co 3+ species. The magnetic nature of the RE cation plays a fundamental role in the magnetic properties. We present herein two specific families: for RE=La the magnetic behavior of the |Co+Mn| network is observed, while for Gd its strong magnetic moment interacts with the transition metals, leading to a spin reversal state. Magnetic interactions are maximized at x=0.50, as if two regimes exist: for x<0.5 Co substitutes Mn in the REMnO 3 manganite, and for x>0.5 Mn substitutes Co in the RECoO 3 cobaltite.

Defect structure behaviour in metal halides

AbstractDefects in halide materials have been investigated using atomistic scale computer simulation. These defects are important in controlling a number of key materials properties. Rare‐earth halides (REX3 with X= F, Cl, Br, I) are currently being considered as scintillator hosts. Here we begin by investigating the fluorides (REF3). These materials undergo an experimentally observed structural change as a function of RE cation radius. We have reproduced this structural variation with an atomistic model. In order to optimise scintillator properties, the intrinsic defect mechanisms need to be assessed as such defects act as performance limiting trap sites. The predictions made are interpreted as a function of the host cation radius in order to reveal structural trends. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Growth and defect structure of CdF2 and nonstoichiometric Cd1−x R x F2+x phases (R = rare earth or in): 4. Ion transport in Cd0.9 R 0.1F2.1 crystals

Ion transport in the isoconcentration series of the Cd0.9R0.1F2.1 solid solutions (R = La-Lu or Y) is studied in the temperature range from 360 to 730 K. With a change of an RE cation along the series (from La to Lu and Y), the anionic conductivity increases from 6 × 10−6 to 6 × 10−5 S/cm at 500 K. The relation between the conductivity parameters and the structural characteristics of the Cd0.9R0.1F2.1 solid solutions is discussed. For a Cd0.9R0.1F2.1 crystal, the concentration and mobility of anionic carriers are equal to 2 × 1021 cm−3 and 2 × 10−7 cm2/(V s) at 500 K.

Catalytic Asymmetric Aldol Reactions in Aqueous Media

AbstractFor Abstract see ChemInform Abstract in Full Text.

Catalytic Asymmetric Aldol Reactions in Aqueous Media Using Chiral Bis‐pyridino‐18‐crown‐6—Rare Earth Metal Triflate Complexes.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Catalytic asymmetric aldol reactions in aqueous media using chiral bis-pyridino-18-crown-6-rare earth metal triflate complexes.

Catalytic asymmetric aldol reactions in aqueous media have been developed using Pr(OTf)(3) and chiral bis-pyridino-18-crown-6 1. In the asymmetric aldol reaction using rare earth metal triflates (RE(OTf)(3)) and 1, slight changes in the ionic diameters of the metal cations greatly affected the diastereo- and enantioselectivities of the products. The substituents (MeO, Br) at the 4-position of the pyridine rings of the crown ether did not significantly affect the selectivities in the asymmetric aldol reaction, although they affected the binding ability of the crown ether with RE cations and the catalytic activity of Pr(OTf)(3)-crown ether complexes. From X-ray structures of RE(NO(3))(3)-crown ether complexes, it was found that they had similar structures regardless of the RE cations and the crown ethers used. Accordingly, the binding ability of the crown ether with the RE cation and the catalytic activity of the complex are important for attaining high selectivity in the asymmetric aldol reaction. Various aromatic and alpha,beta-unsaturated aldehydes and silyl enol ethers derived from ketones and a thioester can be employed in the catalytic asymmetric aldol reactions using Pr(OTf)(3) and 1, to provide the aldol adducts in good to high yields and stereoselectivities. In the case using the silyl enol ether derived from the thioester, 2,6-di-tert-butylpyridine significantly improved the yields of the aldol adducts.

水系溶媒中での触媒的不斉アルドール反応

Catalytic asymmetric aldol reactions in aqueous media have been developed using Pr (OTf) 3 and chiral bis-pyridino-18-crown-6 1. In the asymmetric aldol reaction using rare earth metal triflates (RE (OTF) 3) and 1, slight changes in ionic diameters of the metal cations greatly affected the diastereo- and enantioselectivities of the products. It was found that the binding ability of the crown ether with the RE cation and the catalytic activity of the complex were important for achieving high selectivity in the asymmetric aldol reactions. In this reaction, water plays an essential role for the good yield and selectivities. Several aldehydes and silyl enol ethers derived from ketones and thioesters can be employed in the catalytic asymmetric aldol reactions using, Pr (OTf) 3 and 1 to provide the desired aldol adducts in good to high yields and stereoselectivities.

Structure and optical investigation of neodymium propylenediphosphonate NdH[O 3P(CH 2) 3PO 3

The rare earth propylenediphosphonate, REH[O 3P(CH 2) 3PO 3], (RE[diph]), RE=La–Lu, Y included, have been synthesized by hydothermal technique. The crystal structure is monoclinic with C2/m as space group. The RE cation is coordinated by eight oxygen atoms from the phosphonate groups. The absorption spectra of neodymium compound, Nd[diph], are recorded in the spectral domain from UV to far IR, 30 000 to 3900 cm −1, at various temperatures. In low temperature absorption spectra an unique local environment is found for the neodymium ion in agreement with the crystallographic data. The parametric simulation is performed on 67 experimental levels from 182 Kramer’s doublets of 4f 3 configuration of neodymium, using an approximate C 2v symmetry for the rare earth ion site in Nd[diph], with 14 free ion and 9 real crystal field parameters. A good r.m.s. standard deviation of 16.8 cm −1 is obtained.

New Lanthanide Selenophosphates. Influence of Flux Composition on the Distribution of [PSe(4)](3)(-)/[P(2)Se(6)](4)(-) Units and the Stabilization of the Low-Dimensional Compounds A(3)REP(2)Se(8), and A(2)(RE)P(2)Se(7) (A = Rb, Cs; RE = Ce, Gd).

The reaction of Ce or Gd with a molten mixture of A(2)Se/P(2)Se(5)/Se (A = Rb, Cs) produced the quaternary compounds Rb(3)CeP(2)Se(8) (I) and Cs(3)GdP(2)Se(8) (II), as well as Rb(2)CeP(2)Se(7) (III) and Rb(2)GdP(2)Se(7) (IV). The orange crystals of I, II and the red crystals of III, IV are air- and water-sensitive. Compounds I, II crystallize in the monoclinic space group P2(1)/c, and for I, a = 9.6013(2) Å, b = 18.0604(1) Å, c = 10.0931(1) Å, beta = 90.619(1) degrees, and Z = 4. Compounds III, IV crystallize in the monoclinic space group P2(1)/n, and for IV, a = 10.137(2) Å, b = 7.212(1) Å, c = 20.299(2) Å, beta = 98.23(1) degrees, and Z = 4. Compounds I, II have a 1-D structure with [(RE)P(2)Se(8)](n)()(3)(n)()(-) chains separated by A(+) cations. The RE(3+) lanthanide cation is in a bicapped trigonal prismatic coordination with four tridentate [PSe(4)](3)(-) ligands. Compounds III, IV possess a 2-D structure. Each layer consists of [RE(PSe(4))](x)() "chains" interstitched in two dimensions by hexadentate [P(2)Se(6)](4)(-) ligands. The trivalent RE cation is in a square antiprismatic coordination. The compounds were characterized with differential thermal analysis, far-IR, and solid-state UV/vis diffuse reflectance spectroscopy. Magnetic measurements indicate that the compounds obey the Curie law with &mgr;(eff) values close to those of the free RE(3+) ions.

Application of 23Na Nutation NMR to Characterize the Cation Effect in Ion-Exchanged NaY Zeolites

The two-dimensional sodium-23 nutation NMR was used to monitor the behavior of sodium ions in the partially alkali, alkali-earth or rare-earth ion exchanged NaY zeolites. The sodium-23 nutation spectra of the hydrated and rehydrated Y zeolites consist of two peaks at 1 and 2ωrf in F1 axis with chemical shifts of 0-10 ppm. For the degree of IA, IIA or RE cation exchange &lt;45%, only one peak at 1ωrf was found. For the degree of cation exchange &gt;45%, the second peak at 2ωrf might be observed. The correlation between the relative intensities and lineshapes of two peaks and the nature and distribution of cations in the supercages and sodalite cages with degree of exchange and heating treatment was studied.

An ionic model of the crystal chemistry in the superconducting copper oxides of stoichiometry (RE) 2CuO 4

The mixed rare earth systems La 2− x RE x CuO 4 (RE = NdY) have been investigated in an effort to understand the crystal chemistry and phase stability of the related K 2NiF 4 ( T)-, Nd 2CuO 4 ( T′)-, and hybrid T∗-type structures. The crystal chemistry of these (RE) 2CuO 4 phases is then discussed on the basis of a simple ionic model. A definitive correlation between the size of the RE cation and structure is found, and the stability limits of the T, T′, and T∗ phases are defined in terms of a perovskite-like tolerance factor ( t). The T structure is found to exist for 0.87 ≤ t ≤ 0.99, while the T′ structure occurs for 0.83 ≤ t ≤ 0.86. The smallest rare earths, or t ≤ 0.83, do not form stable (RE) 2CuO 4 compounds. The T∗ structure occurs in a very narrow region adjacent to the boundary of the T T′ stability field and is seen as resulting from a thermodynamic competition between the T and T′ structures, due to a tendency toward T T′ - site ordering. Metastable T∗ phases are observed for the larger rare earths Nd, Eu, and Gd, but the structure becomes quite stable for RE = Tb, Dy. Where both T′ and T∗ are of comparable thermodynamic stability, high oxygen activity is found to stabilize T∗, whereas low oxygen activity favors T′. The role of RE coordination preferences and the influence of the REO framework upon the structure and properties of these materials are discussed.

Thermal stabilities of selected rare earth oxyiodides

The thermal stabilities of lanthanum, neodymium, samarium and gadolinium oxyiodides were studied in a dynamic air atmosphere. Several intermediate phases with the general formulanREOI·RE2O3 (n=7,4,2 and 1) were observed during the decomposition scheme. The thermal stability decreases slightly with increasing atomic weight of the RE cation. Similar decreases with increasing atomic weight of the halide were observed in the lanthanum and in the gadolinium oxyhalide series. This decrease could be correlated to the changes in crystal structure.