Compounds RE Research Articles

Dirhenium Paddlewheel Compounds Supported by N,N‘-Dialkylbenzamidinates: Synthesis, Structures, and Photophysical Properties

Dirhenium(III,III) compounds Re2(DMBA)4Cl2 (1, DMBA=N,N'-dimethylbenzamidinate) and Re2(DEBA)4Cl2 (2, DEBA=N,N'-diethylbenzamidinate) were synthesized via molten reactions between Re2(OAc)4Cl2 and the corresponding amidine. Re2(DMBA)4(NO3)2 (3) was obtained through reacting Re2(DMBA)4Cl2 with AgNO3. Single crystal X-ray diffraction studies revealed that the Re-Re distances in compounds 1-3 are 2.212(1), 2.217(1), and 2.173(1) A, respectively, which are consistent with the presence of a Re-Re quadruple bond. Voltammetric studies revealed that compound 2 exhibits two quasireversible couples, an oxidation and a reduction, and an irreversible reduction, while compound 1 displays irreversible couples at similar potentials. The three complexes exhibit 1deltadelta* absorption as a shoulder at approximately 440 nm (epsilon approximately 1500 M(-1) cm(-1)). Upon excitation of solid samples or CH2Cl2 solutions of 2 with visible light, emission is observed at 824 nm (77 K) and 833 nm (298 K), respectively. The luminescence is assigned as arising from the 3deltadelta* excited state.

Segregation and interaction of rare earth and iron elements on grain boundaries in ZA27 alloys

The model of liquidphase of ZA27 cast alloy was set up in terms of the molecul ar dynamics simulation. The atomic structural models of the α phaseliquid int erf ace and the grain boundary of α phase with the coincidencesite lattice were c on structed by computer programming. The environmentsensitive embedding energy (E S E) of rare earth (or iron) atom in grain, on grain boundary and on α phaseliq uid interface was calculated by Recursion method. The bond order integrals (BOI) be tween Fe, RE atom and Al were also computed. The results show that RE and iron e lements are more stable on the α phaseliquid interface than in grain, which e xpl ains the fact of very small solid solubility of RE and iron elements in α phase , and the enrichment of RE and iron elements in the solid-liquid growth front whe n solidifying. This leads to the segregation of RE and iron atoms on the grain b oundaries and the formation of the complicated REcompounds.

Development of New Die-castable Mg-Zn-Al-Ca-RE Alloys for High Temperature Applications

New die-castable Mg–Zn–Al–Ca–RE alloys are developed and evaluated in order to determine their suitability for high temperature applications. The crystallization of an Al–Ca compound along the grain boundaries and Al–RE compounds both within the grains and along the grain boundaries helps to improve creep properties of the alloys. The creep resistance of diecast specimens of some of the investigated alloys is comparable to that of ADC12 aluminum alloy that is currently used for diecasting of automobile powertrain parts.

Luminescent property of Ce 3+ in RE–Al–B–O system

(La 1− x Ce x )Al 1.67+0.67 y (B 4O 10)O y is one of the compounds of RE–Al–B–O system (RE: rare-earth). There are no reports on luminescent property of activator-doped (La 1− x Ce x )Al 1.67+0.67 y (B 4O 10)O y . So we synthesized the solid solutions (La 1− x Ce x )Al 1.67+0.67 y (B 4O 10)O y , 0.01⩽ x⩽1.0 and characterized their emission properties.

EXAFS Study of the Structure of Desolvated Cluster Compounds of Re and Mo with Cyanide and Thiocyanate Ligands

This paper reports on EXAFS and XANES studies of structural changes in complex compounds (H3O)2Co3[Re6Se8(CN)6]2⋅14.5H2O, Cs2Co[Re6S8(CN)6]⋅2H2O, and Co(DMF)6[Mo6Br8(NCS)6] containing the octahedral cluster anions of rhenium [Re6X8(CN)6]4– (X = S, Se) or molybdenum [Mo6Br8(NCS)6]2–, induced by vacuum annealing at temperatures of up to 250°C. According to EXAFS and XANES data, the complex cluster anions do not undergo any pronounced changes during annealing. The parameters of the local environment of the cobalt cations have been determined. Structural models of the environment of the cations in various compounds after desolvation have been constructed. For Co(DMF)6[Mo6Br8(NCS)6], vacuum annealing at 250°C leads to a complete removal of DMF and formation of a new compound, Co[Mo6Br8(NCS)6], in which the cobalt atoms are coordinated by four sulfur atoms of the SCN groups.

Crystal Structures of Two Re(V) Complexes of 3,5-Dimethylpyrazole with Linear and Bent [OReOReO] 4+ Fragments

The crystal structures of two new dimer compounds of Re(V) containing an [OReOReO]4+ fragment have been studied. Re2O3Cl4(3,5-Me2pzH)4 (I): space group P21/n, Z = 4, a = 10.180(3), b = 18.132(3), c = 16.601(2) A, β = 94.60(2)°, V = 3054.4(1) A3, dcalc = 2.059 g/cm3, R1 = 0.0513, wR2 = 0.1493 for 4701 Ihkl > 2 σI of 4926 measured reflections; Re2O3Cl2(μ-3,5-Me2pz)2(3,5-Me2pzH)2⋅2[(3,5-Me2pzH2)Cl] (II): space group P21/n, Z = 4, a = 16.904(2), b = 14.573(1), c = 17.401(2) A, β = 107.23(1)°, V = 4094.2(7) A3, dcalc = 1.848 g/cm3, R1 = 0.025, wR2 = 0.0514 for 6102 Ihkl > 2 σI of 6315 measured reflections (Enraf-Nonius CAD-4 diffractometer, λMoKα, graphite monochromator). Compound I has a molecular structure, where molecules are dimers Re2O3Cl4(3,5-Me2pzH)4 with a bridging O atom. In II, the dominant motif is the ReOCl(3,5-Me2pzH) fragments bridged by the pyrazole molecules and the O atom.

X-ray diffraction structure of Re2(CO)8[(Z)-Ph2PCH=CHPPh2]. Proof for diphosphine ligation across the Re–Re bond

Treatment of either Re2(CO)8(μ-H)(μ-η1,η2-CH=CHBu) or Re2(CO)8(MeCN)2 with the unsaturated diphosphine ligand (Z)-Ph2PCH=CHPPh2 gives the known bridging phosphine compound Re2(CO)8[(Z)-Ph2PCH=CHPPh2]. The solid-state structure of Re2(CO)8[(Z)-Ph2PCH=CHPPh2] was established by X-ray diffraction analysis, which confirmed the attachment of the diphosphine ligand to each rhenium center. Re2(CO)8[(Z)-Ph2PCH=CHPPh2] crystallizes in the tetragonal space group P42bc, a = 18.054(2) A, c = 22.289(4) A, V = 7265(2) A3, Z = 8, and dcalc = 1.900. The two Re(CO)4 units that are tethered by the diphosphine ligand exhibit a staggered rotational geometry.

Two diphenylformamidinate compounds of the quadruply-bonded Re 26+ core

The compounds Re 2(DPhF) 3Cl 3 and Re 2(DPhF) 2Cl 4 have been prepared and structurally characterized (DPhF = anion of N, N-diphenylformamidine). The former has three bridging DPhF ligands, two equatorial Cl ligands and one axial Cl ligand. The Re–Re distances in two different crystallographic forms are 2.2318(8) Å and 2.2288(9) Å. The second compound has two trans DPhF ligands and the Re 2Cl 4 unit is planar with Re–Re = 2.177(1) Å, Re–Cl(av) = 2.319(5) Å, Re–N(av) = 2.06(1) Å and Cl–Re–Cl(av) = 106.0(1)°.

Structure and some properties of the previously unknown ytterbium silicate A-Yb2SiO5

Nonisothermal oxidation of ytterbium N-woehlerite (Yb4Si2O7N2), also known as the J-phase, has revealed a previously unknown and possibly unstable modification, Yb2SiO5. The phase is isostructural with the A type modification (RE)2SiO5 (RE=rare earth). A new crystallographic description is provided for the detected phase and thermal stability data are compared with such data available for analogous RE compounds. The results indicate that oxidation of RE oxynitrides may produce metastable phases of the type (RE)4Al2(1−x)Si2x·O9+x or phases that cannot be prepared by standard methods because their low-temperature stability range is so narrow.

The effect of pressure on the magnetic susceptibility of alloys

A transition from the Kondo state to an intermediate-valence state takes place in the quasibinary alloys with cubic -type structure. The effect of pressure P up to 2 kbar on the magnetic susceptibility of this system was measured at 78, 150, and 295 K. The value of obtained is well above those observed for similar RE compounds with stable valences. This derivative tends to decrease with temperature, and to increase (but not monotonically) with the tin content x. The experimental data on were analysed in terms of the changes in the spin-fluctuation temperature .

Recent Studies of the Synthesis and Reactivity of Group 6 and 7 Transition Metal Compounds with Metal–Metal Bonds

Metal–metal bonded dinuclear compounds of Group 6 and 7 transition metals with several primary structural motifs and their reactivity toward halides and organic molecules are reviewed. The reactivities of dinuclear compounds of Cr, Mo, W, Mn, Tc, and Re are discussed in context with reaction types (ligand metathesis, oxidative addition), the types of ligands (carbon, sulfur or nitrogen containing), or the ligand substituted in the original starting material (carbonyl). Since the depth and breadth of the chemistry is extensive, the categories are fairly general and some overlap between ligand types and reaction types occurs. A brief history followed by recent studies of each of these transition metal centers provides a general overview of the reactivity of these metal–metal bonded systems.

Studies of the Insertion of an Organic Isothiocyanate into a Rhenium−Rhenium Single Bond and a New Mode of Metal-Promoted Coupling of Isothiocyanates

Five new compounds were obtained from the reaction of Re2(CO)9(MeCN) with EtO2CNCS in a hexane solution at reflux (68 °C). These were identified as Re(CO)4[s-trans-μ-C,S-EtO2CNCS]Re(CO)5 (2, 7% yield), Re(CO)4[μ-C,S,N-EtO2CNCS]Re(CO)4 (3, 40% yield), Re(CO)4[μ-C,N,S2-(EtO2C)2NCNCS2]Re(CO)4 (4, 17% yield), Re(CO)4[μ-C,N,S2-(EtO2C)2NCNCS2]Re(CO)3(NCMe) (5, 5% yield), and trace Re(CO)4[μ-C,N,S2-(EtO2C)(H)NCNCS2]Re(CO)4 (6). All five products have been characterized crystallographically. Compounds 2 and 3 can be described as dimetalated thioimidate complexes formed by the insertion of one EtO2CNCS molecule into the Re−Re bond of 1. Compounds 4 and 5 contain a (EtO2C)2NCNCS2 ligand that was formed by the insertion and rearrangement of two isothiocyanate molecules in the Re−Re bond of 1. Compound 6 is similar to 5 but contains a bridging (EtO2C)(H)NCNCS2 ligand instead. The reaction of Re(CO)4(PMe2Ph)Re(CO)4(NCMe) with EtO2CNCS yielded two isomeric products, trans-Re(CO)4(PMe2Ph)[μ-(EtO2C)NCN(CO2Et)CS2]Re(CO)4 (8) and cis-Re(CO)4(PMe2Ph)[μ-EtO2C)NCN(CO2Et)CS2]Re(CO)4 (9), plus a small amount of the dimetalated thioimidate compound Re2(CO)8(PPhMe2)(μ-EtO2CNCS) (10). Compounds 8 and 9 contain a bridging (EtO2C)N CN(CO2Et)CS2 ligand that was also formed by the coupling and rearrangement of two isothiocyanate molecules. This ligand is considered to be an intermediate en route to the (EtO2C)2NCNCS2 ligand as found in 4, since 8 and 9 can be transformed into the complex Re(CO)4[μ-C,N,S2-(EtO2C)2NCNCS2]Re(CO)3(PMe2Ph) (11), a phosphine derivative of 4. A small amount of the complex Re(CO)3(PPhMe2)(μ-S2CNCO2Et)Re(CO)3(PPhMe2) (12) was also formed from 8 and 9. Compound 12 contains a dithiocarbimato ligand in a novel tetradentate bridging coordination mode. A mechanism for the formation of the (EtO2C)2NCNCS2 ligand is presented and discussed.

The Coordination of N,N‐Diethyl‐N′‐p‐tolylthiourea to Polynuclear Rhenium Carbonyl Complexes

AbstractThe reactions of Re2(CO)9(NCMe) and Re3(CO)10‐(CH3CN)2(μ‐H)3 with S=C(NEt2)N(H)(p‐tolyl) have yielded the new compounds Re2(CO)9[S=C(NEt2)N(H)(p‐tolyl)] (1) and Re3(CO)10(μ‐SC(NEt2)N(H)(p‐tolyl)](μ‐H)3 (2) in 89% and 98% yields, respectively. Compounds 1 and 2 were characterized by single‐crystal X‐ray diffraction analyses. Compound 1 contains an S‐coordinated S = C(NEt2)N(H)(p‐tolyl) ligand terminally coordinated in an equatorial coordination site on one of the rhenium atoms. Compound 2 contains the first example of an S‐coordinated bridging thiourea grouping. When solutions of 1 were heated to 97°C, it was transformed to the new compound {Re(CO)3[μ‐SC(N‐p‐tolyl)(NEt2)]}2 (3) plus Re2(CO)10. Compound 3 is a centro‐symmetrical dimer of the unit Re(CO)3[SC(N‐p‐tolyl)(NEt2)] in which the sulfur atom bridges the two rhenium atoms. The tolyl‐substituted nitrogen atoms are coordinated to the rhenium atoms to form two Re–S–C–N rings.

Mononuclear alkyl and acyl derivatives of rheniumpentacarbonyl: synthesis, characterization and properties

The extensive homologous series of acyl and n-alkyl compounds, [Re(COR)(CO) 5] and [Re(RXCO) 5] (R = CH 3 to n-C 18H 37), has been synthesized. The majority of the compounds are new and have been fully characterized by elemental analysis, IR, 1H and 13C NMR and mass spectrometry. The data for the series are discussed. Some properties of the compounds are described, including reactions of the alkyl compounds with PPh 3, which yield cis-[Re(R)(CO) 4(PPh 3)] and not cis-[Re(CORXCO) 4(PPh 3)] as might have been expected.

Standard enthalpies of formation of some carbides, silicides and germanides of cerium and praseodymium

The standard enthalpies of formation of some congruent-melting compounds in the binary systems ReX, where Re  Ce, Pr or La and X  C, Si or Ge have been determined by direct-synthesis calorimetry at 1473 ± 2 K. The following values of ΔH f o are reported: CeC 2, −25.4 ± 1.4 kJ (mol atom) −1; CeSi 2, −60.5 ± 2.0 kJ (mol atom) −1; CeSi, −71.1 ± 3.3 kJ (mol atom) −1; Ce 5Ge 3, −73.4 ± 2.3 kJ (mol atom) −1; CeGe 1.6, −75.6 ± 1.9 kJ (mol atom) −1; PrC 2, −29.4 ± 1.6 kJ (mol atom) −1; PrSi 2, −61.5 ± 1.7 kJ (mol atom) −1; PrSi, −78.1 ± 1.9 kJ (mol atom) −1; Pr 5Ge 3, −70.4 ± 2.3 kJ (mol atom) −1; PrGe 1.6, −81.7 ± 1.7 kJ (mol atom) −1; LaSi 2, −56.8 ± 2.5 kJ (mol atom) −1. The results are compared with earlier experimental data, with predicted values from Miedema's semiempirical model, and with available data obtained for Sn and Pb compounds by Borzone et al., by Palenzona and by Palenzona and Cirafici.

Magnetoresistance in magnetic and nonmagnetic rare earth compounds

The temperature dependence of the magnetoresistance Δρ/ρ of selected magnetic and nonmagnetic RE compounds in fields up to 10 T has been measured. The discussion of the positive magnetoresistance is based on Kohler's rule. It was found that deviations from Kohler's rule at low temperatures depend on the magnitude of the individual residual resistivity. Ferromagnetic compounds exhibit negative values and a minimum in the vicinity of the Curie temperature in accordance to a model calculation of Yamada and Takada. The positive Δρ/ρ contribution in the low temperature region, observed in all magnetic compounds, is due to the dominating classical magnetoresistance in this temperature range.

Magnetism in Incommensurate Layer Compounds (RES) x VS2 (Re=Rare Earths)

Abstract Magnetic properties are presented for incommensurate layer compounds (RES) x VS2. Antiferromagnetic transitions were observed in the compounds of RE=Ce and Gd at T N =5.6K and 4.8K, respectively. The magnetic ordering of the compound of (CeS)1.19VS2 is discussed in relation to the two dimensionality coming from layer structure of this material.

Crystal structure, magnetism and 57Fe Mössbauer spectra of ternary RE 6Fe 11Al 3 and RE 6Fe 13Ge compounds

From room-temperature X-ray powder analysis, alloys with composition RE 6Fe 11Al 3 (RE = La, Ce, Pr, Nd, Sm, mischmetal) and RE 6Fe 13Ge (RE = Pr, Nd) were observed to crystallize with the tetragonal La 6Co 11Ga 3-type structure and the Nd 6Fe 13Si-type structure, respectively. The alloys were arc-melted, annealed in silica tubes at 600 to 800°C for up to 120 h and quenched. The compounds of RE = La, Pr, Nd and MM with aluminium order magnetically at 281–285 K, whereas the compounds with germanium order at 303 K for RE = Pr and 352 K for RE = Nd. All have a small net magnetization (2–13 J T -1 kg -1), which is ascribed to a ferrimagnetic spin structure of the iron sublattices (4d↓, 16k↑, 16l 1↓, 16l 2↑ or 4d↑, 16k↑, 16l 1↓, 16l 2↓). The compounds with Al, including RE = La, exhibit a sharp increase in magnetization in an applied field of 3–5 T at 6 K, and a similar effect is seen in the compounds with Ge, which is attributed to a ferrimagnetic → ferromagnetic transition of the iron sublattices. The rare-earth sublattices are antiferromagnetic and noncollinear. The average iron moment, deduced from the average 57Fe hyperfine field, is 1.5μ B for the Al compounds, and 2.0μ B for the Ge compounds. The largest iron moments (2.4μ B) are on 4d sites, while the smallest (1.2μ B) are on 16l 2 sites.

Flame photometric detection of some transition metals. II. Enhancement of selectivity

A flame photometric detector was used in single-channel and in differential dual-channel modes to characterize and control its selectivity for various transition elements against a hydrocarbon background. The experiments included gas-chromatographable compounds of Cr, Mn, Fe, Co, Ni, Ru, Re, and Os. Single-channel dispersive modes brought only modest gains in selectivity vis-a-vis the non-dispersive (no optical filter) mode. In dual-channel differential modes, however, metal–carbon selectivities could be improved by factors of one to two orders of magnitude. The highest still measurable selectivity ratios are now in excess of 107. The differential dual-channel operation of the detector also made it possible to increase the selectivity of one hetero-element vis-a-vis another; and to distinguish between two hetero-elements, by oppositely directed peaks, in a (spectrally suppressed) matrix of carbon compounds. Metal–metal selectivities could be improved by factors of one to three orders of magnitude over the best dispersive single-channel modes.

Schwingungsspektren und Normalkoordinatenanalyse der Acetatohalogenodimetallate M2(O2CCH3)4X2, M = Re, Tc; X = CI, Br/Vibrational Spectra and Normal Coordinate Analysis of Acetatohalogenodimetalates M2(O2CCH3)4X2, M = Re, Tc; X = Cl, Br

Abstract The orange-red Tc2(O2CCH3)4Br2 has been prepared for the first time by reaction of [Tc2Br8]2- with glacial acetic acid and acetic anhydride. The IR and Raman spectra have been recorded at 80 K and are compared with those of the analogous compounds Tc2(O2CCH3)4Cl2, Re2(O2CCH3)4Cl2 and Re2(O2CCH3)4Br2. The assignment according to the point group D4h is supported by normal coordinate analysis based on a general valence force field. The quadruple M - M bond is stabilized by the bridging acetato and destabilized by the axial halogeno ligands. The valence force constants fd(MM) are determined to 3,96-4,08 mdyn/Å. The interaction constants fdd(MM/MX), fdd(MM/MO) and fdα (MM/MMO) are about three times higher for the technetates as compared with the rhenates. The stronger interaction between oppo­site bonds in the equatorial ligand sphere is revealed by the stretching interaction constants fdd', which are about two times higher than fdd for M - O bonds at right angles. The strong coupling of the ring co-ordinates implies extensive mixing of the M - O valence and deformation modes. The electronic spectra of Tc2(O2CCH3)4X2, agree with those of the corresponding Re compounds.