Electrical conductance and ionic association of the bivalent transition metal tetrafluoroborates in acetonitrile solution

Visible absorption spectra of Co(BF₄)₂ and Ni(BF₄)² in acetonitrile (AN) indicate the existence of complex electrolytes solely of the type [M(AN)₆]²⁺·2BF ₄ ^– . Close agreement of the molar conductance curves for Mn(BF₄)₂, Co(BF₄)₂, Ni(BF₄)₂, Cu(BF₄)₂, and Zn(BF₄)₂ indicates that the same is true for the other tetrafluoroborates as well. Small specific differences in properties of the [M(AN)₆]²⁺ complex cations are reflected in the limiting molar conductances, while the first-step association constants to a good approximation are the same for the different metal cations. Penetration of the tetrafluoroborate anion in between the coordinated acetonitrile molecules is suggested as a possible explanation for the apparent independence of ionic association on the crystallographic radius of the cation.     

Solubility of Lanthanide Chlorides ( Ln Cl3) in Alkali Metal Chlorides ( M Cl): Thermodynamics and Electrical Conductivity of the M 3 Ln Cl6 Compounds

 Several compounds may exist in LnCl₃–MCl mixtures. Those corresponding to the M ₂ LnCl₅ and MLn ₂Cl₇ stoichiometries are formed in a few systems only, with diverse stability strongly dependent on both the corresponding lanthanide and alkali metal. On the other hand, M ₃ LnCl₆ that occur in most systems have a far larger stability range and melt congruently. These latter compounds were investigated in the present work by differential scanning calorimetry and electrical conductivity measurements. The thermodynamic and transport properties were correlated to structural features and related to the mechanism of compound formation.     

New distannanes containing the chiral 2-(4-isopropyl-2-oxazolinyl)-5-phenyl ligand

The N-coordinated tin hydrides containing the chiral 2-(4-isopropyl-2-oxazolinyl)-5-phenyl ligand in the presence of catalytic amounts of tetrakis(triphenylphosphine)palladium gave the corresponding distannanes in good yields. The distannanes have been fully characterized by means of the ¹H, ¹³C, ¹⁵N and ¹¹⁷Sn NMR measurements. The J(¹⁵N-^117/119Sn), J(¹¹⁷Sn-¹¹⁹Sn) couplings and single-crystal X-ray analysis of distannane 3 revealed a tendency towards penta-coordination at the tin center as a result of the Sn-N interaction.     

UV-induced generation of rare tautomers of 2-thiouracils: a matrix isolation study

Unimolecular photoisomerization reactions were studied for 2-thiouracil, 6-aza-2-thiothymine, 1-methyl-2-thiouracil, and 3-methyl-2-thiouracil isolated in low-temperature Ar matrixes. The IR spectra have revealed that before UV irradiation all the matrix-isolated compounds adopted exclusively the oxo-thione tautomeric form. Upon UV (lambda > 320 nm) irradiation of the matrixes, two oxo-thiol photoproducts were generated for monomeric 2-thiouracil as well as for monomeric 6-aza-2-thiothymine. Generation of these products corresponds to transfer of a proton from either the N(1)-H or N(3)-H group to the sulfur atom of the C(2)=S thiocarbonyl moiety. The first of the above reactions was photoreversible. As a consequence, after prolonged UV irradiation most of the material was transformed into the oxo-thiol-N(1)H form. The hydroxy-thiol tautomers of 2-thiouracil and 6-aza-2-thiothymine were also photogenerated as minor products. For 1-methyl-2-thiouracil and 3-methyl-2-thiouracil, thione --> thiol phototautomeric reactions yielded the oxo-thiol isomers of the compounds. Since these reactions were photoreversible, the final stages of the photoinduced processes corresponded, for both methylated 2-thiouracils, to photostationary states. All the products of the investigated photoreactions were identified by comparison of their IR spectra with the spectra calculated at the DFT(B3LYP)/6-311++G(2d,p) level.     

O‐Benzyl‐N‐tert‐butoxy­carbonyl‐N‐methyl‐l‐tyrosine

The crystal structure of the title compound, alternatively called 3‐[4‐(benzyl­oxy)­phenyl]‐2‐(N‐tert‐butoxy­car­bonyl‐N‐methyl­amino)­propi­onic acid, C₂₂H₂₇NO₅, has been studied in order to ex­amine the role of N‐methyl­ation as a determinant of peptide conformation. The conformation of the tert‐butoxy­carbonyl group is trans–trans. The side chain has a folded conformation and the two phenyl rings are effectively perpendicular to one another. The carboxyl­ate hydroxyl group and the urethane carbonyl group form a strong intermolecular O—H?O hydrogen bond.     

Some Equivalent Norms in Sobolev-Besov Spaces on Symmetric Riemannian Manifolds

In this paper we introduce local means on Riemannian symmetricmanifolds of the noncompact type corresponding to the Laplace-Beltramioperator, and investigate equivalent norms in the Sobolev andBesov spaces defined via these means.     

Current state of the investigation of superallowed Fermiβ decays

Nuclear Structure: Superallowed Fermiβ transitions; derivation of the effective vector (G′_v) and induced scalar (f _s) coupling constants from experimental data. At the present time, the crucial point in a systematic study of superallowed 0⁺-0⁺ β transitions is the evaluation of the isospin impurity correctionδ _c. In the literature,δ _c is decomposed into two parts,δ _c1 and δ_c2. Several estimates ofδ _c1 have been published, while only one is available forδ _c2. We analyze the compatibility of the different estimates ofδ _c1 with the most recent surveys of experimental data. The simplest evaluation ofδ _c1 reported some years ago by Damgaard is found to yield the most satisfactory ?t values; these provide reliable values of the effective vector coupling constantG _v [e.g.,G _v=(1.41242+0.00023)×10^?49 ergcm³]. These values are in excellent agreement with a recent valueG _v=(1.41248+0.00044)×10^?49 erg cm³ obtained by Wilkinson on the basis of a phenomenologic approach toδ _c. Conversely, the most recent and detailed parentageexpansion approaches toδ _c1 lead to?t values which increase with Z, showing pronounced slopes. This fact might be due to a relative overestimation ofδ _c1 for the lighter nuclei. Using the ?t values calculated withδ _c1 as reported by Damgaard, we evaluate the coupling constant for the induced scalar interaction following a procedure described in a previous paper. The mean of such values isf _s/f _v=(?0.17±0.80)×10^?3. In addition, we develop an alternative way of determining a limit forf _s/f _v using the phenomenological approach toδ _c suggested by Wilkinson. This new procedure yieldsf _s/f _v=(?0.16±0.87)×10^?3, a result which is in excellent agreement with that obtained using the former method; both values are consistent with a value of zero, supporting the conserved vector current theory. The better accuracy of the experimental data makes it possible to reduce by a factor of two the limit established in a previous work.