Magnetic properties of the semiconducting lanthanide cuprates Ln2CuO4 and their interpretation: Evidence for a new series of planar copper antiferromagnets

The magnetic susceptibility of the semiconducting lanthanide cuprates Nd₂CuO₄, Pr₂CuO₄, Eu₂CuO₄, and Sm₂CuO₄ has been measured in the range 4–300 K. Below 300 K, the Cu²⁺ ions are ordered antiferromagnetically in the CuO₂ planes of these compounds, and the exchange interactions involving the Ln³⁺ ions are relatively weak. The suceptibility of the Ln³⁺ ions obeys the Curie-Weiss law at elevated temperatures, but deviations from this law occur at lower temperatures. An attempt is made to account for these deviations by fitting theoretical expressions for the susceptibility of isolated Ln³⁺ ions under the influence of a cubic crystal field to the experimental data. Excellent agreement is obtained for Nd³⁺ and Eu³⁺ over the entire temperature range and for Pr³⁺ and Sm³⁺ at elevated temperatures. Deviations at lower temperatures for the latter two ions may be due to structural changes, exchange interactions involving the Ln³⁺ ions, or possibly oxygen nonstoichiometry. The susceptibility parameters derived by fitting the theoretical expressions to the experimental data are also discussed. It is concluded that these compounds form an interesting new series of planar Cu²⁺-ion antiferromagnets.     

Synthesis and structure of the 1,1′-trimethylenebenzene- cyclopentadienyliron cation.

1,1′-Bis(3-phenylpropyl)ferrocene reacts with AlCl₃/Al inheptane to yield 1,1′trimethylenebenzenecyclopentadienyliron hexafluorophosphate (I). The structure of complex I was established by X-ray analysis.     

Factors affecting stability and equilibria of free radicals—VIII : 1-Cyano-2,2-diphenylhydrazyl

The oxidation of 3,3-diphenylcarbazonitrile (1-cyano-2,2-diphenylhydrazine) with lead dioxide or tetraacetate affords the stable violet free radical 1-cyano-2,2-diphenylhydrazyl whose ESR spectra in solution and solid state are reported and discussed.     

Anionic polymerization of methacrylonitrile—II.: Polymerization with 1,1-diphenyl-n-hexyllithium and sec-butyllithium as initiators

The anionic polymerization of methacrylonitrile has been investigated at ?75° in toluene with 1,1-diphenyl-n-hexyllithium and sec-butyllithium as initiators. With both initiators, initiation was fast and no unreacted initiator was left. The efficiency was much higher for 1,1-diphenyl-n-hexyllithium than for sec-butyllithium probably for steric reasons. With both initiators, a second order dependence on initiator was found. To check that this is not an artifact resulting from measurements in a medium starting to gel at a point which is difficult to detect precisely, kinetic measurements were also carried out with 2-polystyryl-l,l-diphenylethyllithium as an initiator. Second order kinetics were again obtained; the propagation rate constants, taking into account the efficiencies of initiators, were the same within experimental error for all three initiators. Viscosity measurements performed on a methacrylonitrile “capped” 2-polystyryl-l,l-diphenylethyllithium initiator showed the living polymethacrylonitrile chains to be associated.     

Kinetics and mechanism of the electrochemical reduction of 2,2′-bipyridine: Part III. Accurate kinetics and thermodynamics of the base catalyzed consecutive reactions

The isomerization reactions of the dihydrobipyridine Y, formed primarily from 2,2′ bipyridine by electrolysis at constant potential, were investigated in detail. The gross rate constants of the scheme Y→A agB agC were optimized from measured concentration vs. time curves at different temperatures with the hydroxyl ion concentration as a parameter. Between Y, A, B, C base catalyzed steps were found but also first-order parallel reactions independent of the pH. The reducible intermediate B is not a single substance but exists in two forms: B and BH⁺ that are connected by a fast equilibrium. A detailed reaction scheme was erected and the 9 individual rate constants and their dependence on the temperature as well as the equilibrium constants and the reaction enthalpies and entropies were determined.     

Direct observation of the splitting of the vibrationless level in a Jahn-Teller active state in deuterobenzenes of D2h symmetry

We have succeeded to record the splitting of the 00 band in the δ = 0.3 Rydberg series of benzene converning to the second ionization limit at 11.49 eV upon reducing the vibrational symmetry to D_2h. This measurement is the first direct observation of a splitting of a vibrationless level of a Jahn-Teller active state caused by a vibrational perturbation. This observation leads one inevitably to ascribe the second ionization process in benzene to a removal of an electron from the 3_e2g(σ) orbital.     

Vapor pressure measurements of ferrocene,mono- and 1,1′-di-acetyl ferrocene

By using different techniques the vapor pressure of ferrocene, mono-acetyl ferrocene and 1,1′-di-acetyl ferrocene was measured. The following pressure—temperature equations were derived ferrocene log P(kPa)= 9.78 ± 0.14 ? (3805 ± 46)/T mono-acetyl ferrocene log P(kPa) = 14.83 ± 0.14 ? (5916 ± 48)/T 1,1′-di-acetyl ferrocene log P(kPa) = 8.82 ± 0.11 ? (4289 ± 44)/T By second- and third-law treatment of the vapor data the ΔH⁰_sub,298 = 74.0 ± 2.0 kJ mole^?1 for the sublimation process of ferrocene was calculated and compared with the literature data. For the sublimation enthalpy of mono- and 1,1′-di-acetyl ferrocene the values ΔH⁰_sub,298 = 115.6 ± 2.5 kJ mole^?1 and ΔH⁰_sub,298 = 91.9 ± 2.5 kJ mole^?1 were derived by second-law treatment. Thermal functions of these compounds were also estimated.     

Magnetic susceptibility and the spin-glass transition of Cd1−xMnxS and Zn1−xMnxS at low temperatures

Low-field magnetic susceptibility of the diluted magnetic semiconductors Cd_1?xMn_xS and Zn_1?xMn_xS was measured between 4.2 and 30 K for the Mn concentration range 0.25 < x < 0.40. When x > 0.25, both of these ternary systems show a spin-glass transition in the above temperature range, as evidenced by a somewhat rounded cusp in the susceptibility and by the presence of irreversible effects. Because these materials are insulators at low temperatures, and the interactions between the Mn ions are only antiferromagnetic, the observed spin-glass behavior is attributed to frustration inherent in the hcp lattices of these compounds. The phase diagrams for the boundary of the paramagnetic and the spin-glass phases are presented for the two alloy systems, and the difference between the two phase diagrams is discussed.     

Jahn-Teller distortion and electronic structure of the O− center in CaF2: an MS Xα study

The O^? center in CaF₂ is investigated by performing multiple scattering Xα calculations on the (OF₆)^7? cluster. In agreement with experiment, a strong Jahn-Teller distortion of tetragonal symmetry is predicted. Finally the ground state electronic structure of the cluster is discussed.     

Determination of hexafluoropropan-2,2-diol in its binary mixtures with water

A visual titration method for the determination of hexafluoropropan-2,2-diol (HFPD) in HFPD-water mixtures is suggested. The procedure involves the titration of the weakly acidic HFPD with sodium methoxide, using dimethylformamide or ethanol as solvent and thymol blue as indicator. The results are in good agreement with the ones obtained by potentiometric titration in water.     

The interaction of 1,1,3,3-tetrakis(trifluoromethyl)allene with sodium derivatives of iron and rhenium carbonyl compounds. Synthesis and structure of the σ- and π-complexes

1,1,3,3-Tetrakis(trifluoromethyl)allene reacts with π-C₅H₅Fe(CO)₂- and Re(CO)₅- to give σ-complexes. The iron σ-complex, when refluxed in decalin or exposed to UV radiation, is transformed to the π-allylidene analogue. Structures of the σ-complexes are determined from IR, Raman, ¹⁹F NMR and X-ray spectral data.     

Effect of hydrogen absorption-desorption cycle on the magnetic susceptibility of CeNi4Al

The effect of hydrogen on the magnetic susceptibility of CeNi₄Al has been investigated. It is observed that following a hydrogen absorption-desorption cycle, without exposing the sample to air, the magnetic susceptibility of CeNi₄AlH₀(I) increases over that of CeNi₄Al. If, after hydrogenation, the sample is kept in the air and then hydrogen removed, the increase in susceptibility of CeNi₄AlH₀(II) is even larger. Magnetic precipitation of Ni due to the presence of O₂ and H₂O is thought to be responsible for this behavior. An increase in susceptibility of CeNi₄AlH_3.7 over that of CeNi₄Al is also observed and attributed partly to the tendency of valence change of cerium from 4+ toward 3+.     

Preparation and electronic spectra of some alkyl- and aryl(2,2′-bipyridine)platinum(II) complexes

A series of alkyl- and aryl-(2,2′-bipyridine)-platinum (II) complexes has been prepared by displacement of the diene ligand in the corresponding cyclooctadiene complexes with 2,2′-bipyridine. Dimethyl(1,10-phenanthroline)platinum(II) was prepared in an analogous way. The electronic spectra of the complexes contain metal to ligand charge transfer bands whose energy is dependent on the nature of the substituents on platinum and on the solvent. It is suggested that π-bonding is important in the phenyl—platinum bond.     

Electron spin resonance spectra of α-sulfonyl iminoxy radicals

Syn- andanti-α-sulfonyl iminoxy radicals have been generatedin situ by lead tetra-acetate oxidation of α-oximino sulfones. The ESR spectra of the geometrical isomers have been assigned and the¹⁴N and¹H hyperfine splitting constants are discussed in terms of the proposed structures.     

Cumulative author index: Vol. 126(1977)–150(1978)

The synthesis of μ-[phenyl(dicyclohexylphosphonio)ethenidyl]-μ-(diphenylphosphido)hexacarbonyldiiron, Fe₂(CO)₆[CC(PCy₂H)Ph](PPh₂) via nucleophilic attack by dicyclohexylphosphine at the β-carbon atom of the σπ-acetylide in Fe₂(CO)₆(CCPh)(PPh₂) is described. This complex, which contains a one-carbon 3-electron bridging ligand has been characterised by microanalysis, infrared, mass, Mössbauer and ³¹P NMR spectroscopy and by a single crystal X-ray structure determination. Crystals are monoclinic, space group P2₁/c with a 10.932(3), b 8.983(2), c 38.644(6) Å, β 94.48(2)°. With four molecules per unit cell and a formula weight of 764.4, the calculated density of 1.342 g cm^?3 agrees with the measured value of 1.34 g cm^?3. The structure was solved by heavy atom methods and refined by least squares techniques with iron and phosphorus atoms having anisotropic thermal parameters, to R and R_w values of 0.068 and 0.075 respectively. In the binuclear molecule an ironiron bond of length 2.550(2) Å is bridged by a diphenylphosphido group and the carbon atom of an unusual dipolar ligand Cy₂(H)P⁺C(Ph)C^?. In the bridging one-carbon-3-electron ligand the coordinated carbon atom is trigonal and the atoms P(1), C(8), C(31), C(7) are virtually coplanar. Structural parameters are compared with those of other complexes containing bridging one-carbon, 3-electron and two-carbon, 3-electron ligands. Nucleophilic attack by phosphorus and nitrogen nucleophiles on σπ-acetylides appears to be a general route to these ligands.     

Pyrolysis—gas chromatographic determination of run numbers in methyl methacrylate--styrene copolymers using the boundary effect

By considering the effect of neighbouring monomer units in depropagating polymer chain radicals on the formation of degradation products, a new boundary effect theory was developed in order to elucidate the sequence distributions in vinyl-type copolymers using the corresponding monomer yields. This theory was applied succesfully to the calculation of the sequence distributions in methyl methacrylate—styrene copolymers in terms of the run numbers. The significance of newly introduced parameters (monomer formation probability constants) is also discussed.     

Three-coordinate mercury in (2,2′-bipyridyl)methylmercury(II) nitrate and related complexes

Methylmercury(II) forms complexes [MeHgL]⁺ [NO₃]^? (L = bidentate ligand) having three-coordinate mercury; an X-ray crystal structure analysis shows that the complex with 2,2′-bipyridyl has a planar CHgN₂ group with unsymmetrically chelated 2,2′-bipyridyl.     

Heats of mixing of 2,2-dimethoxypropane and diethoxymethane with some 1-alkenes

The excess enthalpies of 2,2-dimethoxypropane + 1-hexene, + 1-heptene and + 1-octene, and of diethoxymethane + 1-hexene + 1-octene have been measured at 298.15 K. The values of H^E for all the systems are positive and increase with increasing chain length of the alkene. The results are analysed in term of the quasi-lattice theory of mixtures using the zeroth approximation.     

The densities and molar volumes of molten lead(II) dodecanoate/dodecanoic acid mixtures over their complete composition range: Evidence for non-ideal behaviour

Data are presented for the densities and molar volumes of the molten system lead(II) dodecanoate/dodecanoic acid over its complete composition range. For equimolar mixtures, plots of molar volume against temperature show curvature at high temperatures, suggesting deviations from ideal behaviour. Support for this comes from a plot of molar volume at constant temperature against acid mole fraction. Densities and molar volumes are reported for lead (II) carboxylate/carboxylic acid (0.5 mole fraction) and for pure carboxylic acid for the even chain acids C₁₀ to C₁₈. The molar volumes at constant temperature in these cases are linear functions of chain length, although the volume occupied per methylene group in equimolar mixtures is suggested to be slightly smaller than with pure soap or pure acid. An explanation for non-ideal behaviour becoming more marked at higher temperature is given in terms of acid monomer-dimer equilibria.