Synthesis,crystal structure,magnetism, and absorption spectra of A2UX5 Type Halides (A = K,Rb; X = Cl,Br, I)

The ternary uranium(III) halides A₂UX₅ (A = K, Rb; X = Cl, Br, I) have been prepared from the binary components AX and UX₃ in sealed tantalum containers. According to their Guinier X-ray powder patterns, they all crystallize with the K₂PrCl₅/Y₂HfS₅ type of structure. Lattice constants for ambient temperature are reported. Single-crystal structure refinemens were undertaken for K₂UI₅ and Rb₂UCl₅. Magnetic susceptibility data were recorded with a SQUID magnetometer from liquid helium to room temperature. One-dimensional (intrachain) and three-dimensional antiferromagnetic ordering occur at low temperatures dependent upon the U³⁺? U³⁺ distance. Absorption spectra were recorded between 4 000 and 28 000 cm^?1. They show f—f transitions typical for U³⁺ and, depending on the halide, very strong f—d transitions above 14 000 to 15 000 cm^?1, respectively.     

Darstellung und Charakterisierung von Halogeno(diethyldithiocarbamato) (triethyl- und triphenylphosphin)palladium(II)-Komplexen

The Complexes [Pd(PEt ₃)₂ dtc]X (1) and Pd(PR ₃)Xdtc (2, 3) (dtc=S₂CNEt ₃;X=Cl, Br, I;R=Et, Ph) have been prepared. Conductivity, susceptibility, UV and IR measurements show that the cations [Pd(PEt ₃)₂ dtc]⁺ of1 and the complexes2, 3 have square-planar structure.

     

Mechanistic information on the reversible binding of NO to selected iron(II) chelates from activation parameters

Mechanistic insight on the reversible binding of NO to Fe(II) chelate complexes as potential catalysts for the removal of NO from effluent gas streams has been obtained from the temperature and pressure parameters for the "on" and "off" reactions determined using a combination of flash photolysis and stopped-flow techniques. These parameters are correlated with those for water exchange reactions on the corresponding Fe(II) and Fe(III) chelate complexes, from which mechanistic conclusions are drawn. Small and positive Delta V(++) values are found for NO binding to and release from all the selected complexes, consistent with a dissociative interchange (I(d)) mechanism. The only exception in the series of studied complexes is the binding of NO to [Fe(II)(nta)(H(2)O)(2)](-). The negative volume of activation observed for this reaction supports the operation of an I(a) ligand substitution mechanism. The apparent mechanistic differences can be accounted for in terms of the electronic and structural features of the studied complexes. The results indicate that the aminocarboxylate chelates affect the rate and overall equilibrium constants, as well as the nature of the substitution mechanism by which NO coordinates to the selected complexes. There is, however, no simple correlation between the rate and activation parameters and the selected donor groups or overall charge on the iron(II) complexes.     

Measurements and Utilization of Consistent Gibbs Energies of Transfer of Single Ions: Towards a Unified Redox Potential Scale for All Solvents

Utilizing the “ideal” ionic liquid salt bridge to measure Gibbs energies of transfer of silver ions between the solvents water, acetonitrile, propylene carbonate and dimethylformamide results in a consistent data set with a precision of 0.6 kJ mol⁻¹ over 87 measurements in 10 half-cells. This forms the basis for a coherent experimental thermodynamic framework of ion solvation chemistry. In addition, we define the solvent independent - and the values that account for the electronating potential of any redox system similar to the value of a medium that accounts for its protonating potential. This scale is thermodynamically well-defined enabling a straightforward comparison of the redox potentials (reducities) of all media with respect to the aqueous redox potential scale, hence unifying all conventional solvents′ redox potential scales. Thus, using the Gibbs energy of transfer of the silver ion published herein, one can convert and unify all hitherto published redox potentials measured, for example, against ferrocene, to the scale.     

Benzo[h]cinnolin

The synthesis of benzo[h]cinnolin ( 3 ) is reported. Its spectroscopic properties (uv, luminescence, pmr, ms) are similar to the other diazaphenanthrenes containing a diazine ring. The lowering of the basicity of 3 compared with a monoazaphenanthrene like other diaza-aromatic compounds appears to be due to an electrostatic field effect and not to an inductive effect.     

Synthesis and Reactivity of Stannyloligosilanes IV [1]: From Hydrido Substituted Stannasilanes Towards Stannasiloxanes

Summary.  Hydrido substituted stannasilanes of the type or (Z = H, Me, Ph; R, R′ = alkyl, Ph) are accessible by reaction of either alkali metal stannides (MSn(Z)R ₂; M = Li, Na) with halogen substituted silanes (; X = F, Cl) or chlorostannanes (R ₂SnCl₂, Ph₃SnCl) and fluorosilanes in the presence of magnesium. Stannasilanes with halogen substituents at the silicon as well as the tin atom are formed by treatment of the hydrido substituted stannasilanes with CHCl₃ or CCl₄. The hydrido substituted stannasilanes decompose in contact with air to distannanes and siloxanes or to the linear ( ^t Bu₂Sn(–O– ^t Bu₂Si–OH)₂) and cyclic ((– ^t Bu₂Sn–O– ⁱ Pr₂Si–O–)₂) stannasiloxanes. Received November 29, 2001. Accepted (revised) January 16, 2002     

Targeted ferromagnetic coupling in a trinuclear copperII complex: analysis of the St = 3/2 spin ground state

The trinuclear Cu(II) complex [(talen)Cu(II)(3)] (1) using the new triplesalen ligand H(6)talen has been synthesized and structurally characterized. The three Cu(II) ions are bridged in a m-phenylene linkage by the phloroglucinol backbone of the ligand. This m-phenylene bridging mode results in ferromagnetic couplings with an S(t) = (3)/(2) spin ground state, which has been analyzed by means of EPR spectroscopy and DFT calculations. The EPR spectrum exhibits an unprecedented pattern of 10 hyperfine lines due to the coupling of three Cu(II) ions (I = (3)/(2)). Resonances around g = 4 in both perpendicular and parallel mode EPR spectra demonstrate a zero-field splitting of D approximately 74 x 10(-4) cm(-1) arising from anisotropic/antisymmetric exchange interactions. The DFT calculations show an alteration in the sign of the spin densities of the central benzene ring corroborating the spin-polarization mechanism as origin for the ferromagnetic coupling.