Mössbauer effect study and magnetic properties of a ferromagnetic homologue of bromobis(diethyldithiocarbamato)iron(III)

Mossbauer spectroscopy and magnetic susceptibility properties of a crystal modification of the title complex, denoted Fe(dtc)₂Br, show that the iron atoms in this material become ferromagnetically ordered with T_c = 1.52 × 0.02 K. This result is consistent with a magnetic specific heat anomaly recently observed in similar material by Yoshikawa et al. Mössbauer effect hfs show that the lower Kramers doublet from the orbital singlet, spin quartet ground term is of composition |S = $\text{3}\text{2}$, M_S = ± $\text{1}\text{2}$).     

The rotational spectrum and molecular properties of a hydrogen-bonded dimer of phosphine and hydrogen fluoride

⁵⁷Fe Mössbauer spectra have been obtained for Fe(p-CH₃C₆H₄SO₃)₂ between 2.3 and 300 K in zero field, and at 2.3 and 4.2 K in longitudinal applied magnetic fields ranging from 1.1 to 5.6 T. The complex is a fast-relaxing paramagnet under all conditions studied and there is no evidence of antiferromagnetic exchange coupling. The FeO₆ chromophore is distorted by a trigonal elongation and the orbital ground state is the [($\text{2}\text{3}$)^{$\text{1}\text{2}$}|±2〉 ? ($\text{1}\text{3}$)^{$\text{1}\text{2}$}|?1〉] doublet. The temperature dependence of the quadrupole splitting has been analysed via a crystal-field model to provide estimates of the axial field splitting parameter Ds = -93 cm^-1, spin-orbit coupling constant λ = -70 cm^-1, and fine structure constant Dσ = -28 cm^-1. The magnetic properties of the complex are described by treating the ground state as a non-Kramers doublet with fictitious spin ? = $\text{1}\text{2}$. Five separate Mössbauer-Zeeman spectra can be fitted in this spin-hamiltonian approximation with identical values of the g- and A-tensor components, viz. g_⊥ = 1.0, g_u = 9.0; A_⊥ ≈ 2.0 mm s^-1. A_u = -1.79 mm s^-1. The trigonal z axis, the z axis of the electric field gradient tensor, and the easy axis of magnetisation are collinear, and the saturation value of the internal hyperfine field along this axis is +13.0 T.     

Microwave-optical double resonance in molecular ions. Co+

Microwave—optical double resonance signals have been detected in a mass-selected ion-beam spectrometer for ¹²C¹⁶O⁺. With the optical excitation of fluorescence from the R₁ ($\text{1}\text{2}$) line of the (0,0) band of the A²Π_{$\text{3}\text{2}$} ← X²∑ transition of 20350.6 cm^?1, the microwave resonances occurred at 118101.8 ± 0.2 MHz and at 117694 ± 2 MHz corresponding to the N= 1, J = $\text{3}\text{2}$ ← N = 0, J = $\text{1}\text{2}$ and the N = 1, J = $\text{1}\text{2}$ ← N = 0, J = $\text{1}\text{2}$ transitions.     

A novel case of magnetic relaxation in the 99Ru Mössbauer spectrum of Na3RuO4

The magnetic properties of Na₃RuO₄ have been studied using ⁹⁹Ru Mössbauer spectroscopy. Magnetic hyperfine splitting is seen at temperatures below 30°K. The value of the flux density at 4.2°K (58.58 T) is compatible with a saturation field at an $\text{S =}\text{3}\text{2}\text{Ru}{}^{\mathrm{V}}$ ion, and at intermediate temperatures approximately follows an $\text{S =}\text{3}\text{2}$ Brillouin function. The published interpretation of magnetic susceptibility data in terms of tetranuclear intracluster antiferromagnetism is shown to be incorrect, and it is concluded that Na₃RuO₄ shows antiferromagnetic three-dimensional long-range order with a Néel temperature of T_N = 30 ± 1°K. Between 25 and 30°K motional narrowing of the spectrum is seen, which is probably due to a slow spin-spin relaxation within the crystal-field levels of the ⁴A_2g ground state of the Ru^V ion. This is the first observation of relaxation effects in a ⁹⁹Ru spectrum.     

The crystal structures of α- and β-CdUO4

The structural parameters of α- and β-CdUO₄ crystals are determined by X-ray powder diffraction technique. α-CdUO₄ is rhombohedral and cell parameters are a = 6.233(3) Å and α = 36.12(5)°. β-CdUO₄ crystallizes in a C-centered orthorhombic cell with a = 7.023(4), b = 6.849(3), c = 3.514 (2) Å. The space groups are $\text{R}\text{3}\text{m}$ for α-CdUO₄ and Cmmm for β-CdUO₄. α-CdUO₄: 1U in (000), 1Cd in ($\text{1}\text{2}\text{1}\text{2}\text{1}\text{2}$), 2O(1) in ±(uuu), 2O(2) in ±(vvv); u = 0.113, v = 0.350, Z = 1. β-CdUO₄: 2U in ($\text{000;}\text{1}\text{2}\text{1}\text{2}\text{0}$), 2Cd in ($\text{1}\text{2}\text{0}\text{1}\text{2}\text{; 0}\text{1}\text{2}\text{,}\text{1}\text{2}$), 4O(1) in ($\text{0, ±y, 0;}\text{1}\text{2}\text{,}\text{1}\text{2}\text{±y, 0}$), 4O(2) in ($\text{±x, 0,}\text{1}\text{2}\text{;}\text{1}\text{2}\text{±x,}\text{1}\text{2}\text{,}\text{1}\text{2}$); x = 0.159, y = 0.278, Z = 2. β-CdUO₄ contains collinear uranyl UO²⁺₂ groups with a UO(1) distance of 1.91 Å, located either along or parallel to the c axis whereas the UO(1) bond length in α-CdUO₄ is 1.98 Å which is longer than the usual uranyl bond length.     

The importance of spin relaxation in the delayed fluorescence of molecular crystals

Deactivation rate constants of spin-orbital excited Br atoms in the reactions Br(²P_{$\text{1}\text{2}$}) + O₂ → Br(²P_{$\text{3}\text{2}$}) + O₂ (k₁), and Br(²P_{$\text{1}\text{2}$}) + NO → Br(²P_{$\text{3}\text{2}$}) + NO (k₄) have been measured with a photodissociative IBr laser on the electronic transition ²P_{$\text{1}\text{2}$}?²P_{$\text{3}\text{2}$} in the Br atom (λ = 2.7 μm). The values obtained are (6.4 ± 1.8) × 10^?14 cm³ s^?1 and (1.9 ± 0.6) × 10^?12 cm³ s^?1, respectively. Comparison with published data leads to the conclusion that, contrary to a widely accepted point of view, the high rate constants for the quenching of excited halogen atoms are due to resonant energy transfer processes and not to the paramagnetic nature of the quencher.     

Neutron powder diffraction and magnetic measurements on CsMnI3

Results of neutron powder diffraction and magnetic measurements on single crystals of CsMnI₃ are reported. Three-dimensional ordering takes place at T_c = 11.1(3) K. Above T_c very broad peaks occur in the neutron powder diffraction diagram, indicating one-dimensional correlations along the chain. Below T_c the Mn²⁺ ions are coupled antiferromagnetically along the chain. Interchain exchange leads to a 120° structure, slightly distorted due to anisotropy. One-third of the chains have their magnetic moment parallel to the c axis and the rest of the chains have magnetic moments making an angle of 50(2)° with the c axis. The magnetic moment as found from neutron diffraction extrapolated to 0 K is 3.7(1)μ_B, indicating a considerable zero-point spin reduction. The intrachain exchange $\text{J}\text{k}$ was found to be ?9.1(1)K, whereas the ratio of the inter- to intrachain interaction was determined as $\text{J′}\text{J}\text{= × 10}{}^{\mathrm{?3}}$. A spin flop occurs at H = 54 kOe on application of a magnetic field parallel to the c axis. When a field perpendicular to the c axis is applied a spin reorientation occurs at 1 kOe.     

Antiprismatic crystal field and paramagnetic susceptibility of U4+ sulfates

On the basis of the simplified model of the U⁴⁺ ion in a distorted axial crystal field, the temperature dependence of the magnetic susceptibilities of three U⁴⁺ sulfates, U(SO₄)₂ · 4H₂O, U₆O₄(OH)₄(SO₄)₆, and U(OH)₂SO₄, within the temperature range 4.2–300°K has been investigated and interpreted. This model proved to be successful, and the only parameters fitted empirically were the values of the crystal field splitting. The antiprismatic coordination (D_4d) of the uranium ion in these compounds was confirmed and its electronic ground states were determined. The system of two singlets $\text{1}\text{2}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{| 3 > ±}\text{1}\text{2}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{| ? 3 >}$ originating from the doublet 1 ± 3 > is the ground state of the uranium ion in U(SO₄)₂ · 4H₂O. An analogous system of two singlets $\text{1}\text{2}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{| 2 > ±}\text{1}\text{2}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{| ? 2 >}$ is the ground state in U₆O₄(OH)₄(SO₄)₆. For U(OH)₂SO₄, the doublet | ± 2 > is the ground state above 21°K, whereas below this temperature it becomes split into the two singlets $\text{1}\text{2}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{| 2 > ±}\text{1}\text{2}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{| ? 2 >}$, probably because of a crystallographic distortion induced by the cooperative Jahn-Teller effect. Deviations from the D_4d symmetry of the uranium ion coordination occurring in these compounds are discussed.     

Experimental and theoretical investigations of the nuclear quadrupole resonance of 127I in orthoperiodic acid,H5IO6

Pure nuclear quadrupole resonance of ¹²⁷I in H₅IO₆ has been reported to occur at 44.976 MHz (m = ±$\text{3}\text{2}$?m = ±$\text{1}\text{2}$ transition) and 83.960 MHz (m = ±$\text{5}\text{2}$? m = ±$\text{3}\text{2}$ transition) at 296 K (ref. 1). Using an externally quenched frequency modulated super regenerative spectrometer Zeeman studies have been performed at 296 K on single crystals of H₅IO₆ growm from aqueous solution by observation of the ±$\text{sol3}\text{2}$?±$\text{1}\text{2}$ transition. The zero-splitting locus method has been employed for the determination of the EFG parameters. The data show that there are two physically inequivalent sites, having average asymmetry parameters, η, of 0.25, located in the unit cell. The maximum field gradient is found to lie along the short bond I-O(2) as suggested by Rama Rao and Weiss (ref. 1). The EFG parameters obtained by detailed molecular orbital calculations (CNDO/2 and INDO method) are compared with the experimental results.     

Quenching of the Ba + Cl2 chemiluminescence: Estimate of BaCl*2 radiative lifetime

The chemiluminescence produced by the Ba + Cl₂ reaction was recorded as a function of He and N₂ pressure. A modified Stern-Volmer treatment of competitive electronic quenching of BaCl^* and BaCl^*₂ emission yielded upper limits to the half pressures p_{$\text{1}\text{2}$}(He) ? 9.0 ± 3 mtorr and p_{$\text{1}\text{2}$} (N₂) ? 1.1 ± 0.2 mtorr for quenching of BaCl^*₂ by helium and nitrogen, respectively. A lower limit of the BaCl^*₂ radiative lifetime is placed at τ_R ? 100 μ.     

Structure cristalline et expansion thermique de l'iodure de nickel hexahydrate

The structure of NiI₂, 6 H₂O has been determined by X-ray diffraction techniques. The dimensions of the hexagonal unit cell are: a = 7.638 ± 0.005 Å and c = 4.876 ± 0.005 Å, with Z = 1. The space group is $\text{P}\text{3}\text{m1}$. The structure was deduced from Patterson and Fourier syntheses and refined by least-squares method to a final R value of 0.09. It is almost a layer structure, each layer is composed by n complex ions [Ni(H₂O)₆]²⁺ surrounded by 2 n ions I^?; this is in agreement with the good cleavage of crystals and with the marked anisotropy in the thermal expansion. But the structure may also be regarded as a derivation of NiAs structure, with only $\text{1}\text{8}$ of octahedral holes occupied. A structural classification of compounds MX₂, 6 H₂O is proposed.     

Nuclear magnetic resonance study of NbBex compounds

Nuclear magnetic resonance techniques have been employed to study powder samples of the compounds NbBe₂, NbBe₃, Nb₂Be₁₇ and NbBe₁₂. Nuclear quadrupole coupling constants and Knight shifts were determined for the Nb sites in these compounds. The ${}^{93}\text{Nb NMR}$ from NbBe₂ is a single unsplit line with zero quadrupole coupling constant and a Knight shift of 0.70 ± 0.03%. The ⁹³Nb NMR from a NbBe₃ sample shows the presence of three resonance lines having values of $\text{e}{}^2\text{qQ}\text{h}\text{= 0, 24.2 ± 0.2, 30.1 ± 0.3}\text{MHz}$ and corresponding Knight shifts of 0.69 ± 0.03, 0.72 ± 0.03, 0.53 ± 0.03%. One of these lines was identified as a NbBe₂ impurity. The ${}^{93}\text{Nb NMR}$ of Nb₂Be₁₇ exhibits a quadrupole coupling, $\text{e}{}^2\text{qQ}\text{h}\text{= 5.93 ± 0.15}\text{MHz}$, and a Knight shift, K_axiat = 0.014% and K_isotropic = 0.34 ± 0.02%. The ${}^{93}\text{Nb}$ resonance from NbBe₁₂ was split by a quadrupole interaction of $\text{e}{}^2\text{qQ}\text{h}\text{= 21.7 ± 0.3}\text{MHz}$ and a Knight shift of 0.55% ± 0.02%. The beryllium NMR was examined, yielding little information, since no measurable quadrupole interaction or Knight shift were present.     

Étude quantitative d'équilibres chimiques en solution dans les sels fondus par spectrophotométrie d'absorption: Application au neptunium

The following reactions: NpO₂⁺+4 HCl ? Np⁴⁺ + 2 H₂O + $\text{1}\text{2}$ Cl₂ + 3Cl^- NpO₂⁺+$\text{1}\text{2}$ Cl₂ ? NpO₂²⁺ +Cl^- 2HCl+O^2- ? H₂O +Cl^- have been examined quantitatively. The reactions were studied in fused LiCl-KCl sparged with gas mixtures of definite compositions. The concentrations of the diffrent neptunium species were measured by absorption spectrophotometry. The values of respective equilibrium constants are: K = (9.3±0.4)· 10^-6 atm(^{-$\text{1}\text{2}$}); K₁ = (2.3±0.1)·10^-2 atm(^{-$\text{1}\text{2}$}); k = 10^3.8 1 mol^-1 atm^-1 The standard potential of the system NpO₂²⁺ / NpO₂⁺ was determinedto be E⁰ = 0.220 V (vs.standard chlorine electrode).     

High resolution photoelectron studies: Electric field gradient splittings of Cd and Sn 4d energy levels in organometallic compounds

High resolution photoelectron spectra of Me₂Cd (Me = CH₃) in the gas phase, and organotin compounds in the solid state show that the 4d⁹ final state produced in the photoelectron experiment splits in the presence of ligand fields. Only the C₂⁰ crystal field term (the term that transforms like the electric field gradient) contributes to the splitting. The 4d_{$\text{3}\text{2}$} splitting in Me₂Cd and trans-Me₂Sn(BzBz)₂ (BzBz = anion of dibenzoylmethane) are 0.21 ± 0.01 eV and 0.35 ± 0.1 eV respectively. The observed 4d_{$\text{5}\text{2}$} linewidth for Ph₄Sn (Ph = C₆H₅) of 0.67 eV indicates that very narrow linewidths can be obtained on molecular nonconducting solids. The constant spin-orbit splitting values, combined with nuclear field gradients from Mössbauer and NQR measurements, strongly indicate that a previously proposed explanation for the increase in apparent spin-orbit coupling in Cd metal is untenable.     

2-cyano Δ3 piperidines vi1 : a general method for the stereoselective synthesis of cis and trans 2,6-dialkylpiperidine alkaloids

The cis 2,6-dialkylpiperidine alkaloid (±) dihydro-pinidine $\text{7b}$ and the trans alkaloid (±) solenopsin A $\text{5a}$ were synthesized from a common α-aminonitrile synthon $\text{1}$. The key step in this synthesis was the stereoselective reductive decyanation of the 1-benzyl-2cyano-2′, 6-dialkylpiperidines $\text{3a}$ and $\text{3b}$.     

The enthalpies of formation of bis-(benzene)molybdenum and of bis-(toluene)tungsten

Microcalorimetric measurements at 520–523 K of the heats of thermal decomposition and of iodination of bis-(benzene)molybdenum and of bis-(toluene)tungsten have led to the values (kJ mol^?): ΔH^o_f[Mo(η-C₆H₆)₂, c] = (235.3 ± 8) and ΔH^o_f[W(η⁶-C₇H₈)₂, c] = (242.2 ± 8) for the standard enthalpies of formation at 25°C. The corresponding ΔH^o_f(g) values, using available and estimated enthalpies of sublimation, are (329.9 ± 11) and 352.2 ± 11) respectively, from which the metalligand mean bond-dissociation enthalpies, $\text{D}$(Mo—benzene) = (247.0 ± 6) and $\text{D}$(W—toluene) = (304.0 ± 6) kJ mol^?1, are derived.     

Transition metal iodates. IV. Crystallographic,magnetic and nonlinear optic survey of the copper iodates

Three anhydrous polymorphs of cupric iodate, two hydrates, and the basic iodate salesite have been investigated. α-Cu(IO₃)₂ is monoclinic, space group P2₁, with a = 5.551 ± 0.008, b = 5.101 ± 0.004, c = 9.226 ± 0.010 Å and β = 95°4′ ± 11′, with two formulas in the unit cell. Below Θ_N = 8.5 K, α-Cu(IO₃)₂ is antiferromagnetic and also pyroelectric. β-Cu(IO₃)₂ is triclinic, space group $\text{P}\text{1}$, with a = 11.230 ± 0.006, b = 11.368 ± 0.009, c = 10.630 ± 0.009 Å, α = 99°18.3′ ± 0.3′, β = 107°0.4′ ± 0.2′ and γ = 114°23.8′ ± 0.2′ and eight formulas per unit cell: the crystal is paramagnetic to 1.4K. γ-Cu(IO₃)₂ is monoclinic, space group $\text{P2}{}_1\text{m}$, with a = 4.977 ± 0.004, b = 6.350 ± 0.004, c = 8.160 ± 0.004 Å and β = 92°20′ ± 4′, with two formulas per unit cell; γ-Cu(IO₃)₂ becomes antiferromagnetic below Θ_N = 5 K. Cu(IO₃)₂·2H₂O is monoclinic, space group $\text{P2}{}_1\text{c}$, with a = 6.725 ± 0.005, b = 4.770 ± 0.007, c = 11.131 ± 0.013 Å and β = 103°1′ ± 4′, with two formulas per unit cell; Cu(IO₃)₂·2H₂O is paramagnetic to 1.4 K. $\text{Cu(IO}{}_3\text{)}{}_2\text{·}\text{2}\text{3}\text{H}{}_2\text{O}$ (mineral bellingerite) is triclinic, space group $\text{P}\text{1}$, with a = 7.197 ± 0.005, b = 7.824 ± 0.004, c = 7.904 ± 0.004 Å, α = 105°2′ ± 2′, β = 97°7′ ± 2′ and γ = 92°54′ ± 2′ with three formulas per unit cell; this crystal is paramagnetic to 1.4 K, with a moderate antiferromagnetic Cu-Cu interaction. Cu(OH)IO₃ (mineral salesite) is orthorhombic, with a = 10.772 ± 0.004, b = 6.702 ± 0.002 and c = 4.769 ± 0.002 Å and four formulas per unit cell. The magnetic susceptibility indicates the possibility of antiferromagnetic ordering at 162 K; strong antiferromagnetic interactions give Θ_p = ?340 K. The only copper iodate studied that generates second harmonics is α-Cu(IO₃)₂. Indexed powder patterns are given for all six compounds.