Voltammetric and titrimetric study of acid-base properties of some μ-oxo dimeric iron(III) complexes inDMF

Summary The acid-base properties of the -oxo bridged dimeric iron complexes [FeL]₂O with the ligands based on S-alkyl-1,4-bis(substituted salicylidene)isothiosemicarbazide and a tetramer with S-methyl-1,4-bis(salicylidene)isothiosemicarbazide, {[FeL]₂O}₂I₃·I₂, were investigated by cyclic voltammetry at glassy carbon electrode inDMF. Studies were carried out in the presence of either a weak (phenol) or a strong (HClO₄ aq.) acid. The stoichimoetry of the reaction, changes in the general voltammetric pattern and the electrode reaction mechanism were discussed. These studies served as the basis for three-electrode amperometric titrations to determine the content of several of these complexes.

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Voltammetrische und titrimetrische Untersuchung der Säure-Base-Eigenschaften einiger -oxo dimerer Eisen(III)-Komplexe inDMF-Lösungen

Zusammenfassung Die Säure-Base-Eigenschaften einiger dimerer -oxo-Eisen(III)-Komplexe [FeL]₂O mit Liganden auf Basis von 1,4-bis(substituierten Salicyliden)S-(alkyl)isothiosemicarbaziden sowie eines tetrameren Komplexes mit 1,4-Bis(salicyliden)S-methylisothiosemicarbazid, {[FeL]₂O}₂I₃·I₂, wurden mittels zyklischer Voltammetrie an der Glaskohlenstoffelektrode inDMF-Lösungen untersucht. Die Messungen wurden in Gegenwart entweder einer schwachen (Phenol) oder einer starken (HClO₄ aq.) Säure ausgeführt. Die Stöchiometrie der Reaktion, die Änderungen der voltammetrischen Kurven und der Elektroden-Reaktionsmechanismus wurden diskutiert. Diese Untersuchungen stellten eine Basis für Drei-Elektroden amperometrische Titrationen dar, die für die Bestimmung des Gehalts einiger dieser Komplexe angewendet wurden.

     

Properties of long superconducting variable thickness bridges

We have studied the properties of long (lengthL20m) superconducting threads (Pb of Sn) formed by pulse electrical breakdown in monocrystalline silicon. These variable thickness bridges have well defined dc and ac Josephson effects in wide temperature range. Some interesting results on the quasiparticle subharmonic gap structures are also reported.The authors would like to express their thanks to J.Móza and A.Neasová for technical assistance.     

Einfluß der Alkylgruppen auf die Struktureigenschaften der Cyanato-Kupfer(II)-Komplexe mit Alkylpyridinen

New cyanato-copper(II) complexes of the type Cu(NCO)₂ L ₂ (L=2,3-, 2,5-, 3,4- or 3,5-lutidine, 3- or 4-ethylpyridine) and Cu(NCO)₂ L (L=2,3- or 2,5-lutidine, 2-ethylpyridine) were prepared. Solid state electronic, ESR and IR spectral results show, that Cu(NCO)₂ L ₂ complexes have tetragonal structures varying from pseudooctahedral to practically planar forms, also involving a square-pyramidal arrangement. The -form of Cu(NCO)₂(2-picoline)₂ was isolated and found to be a distortion isomer of the known -form. According to physical results, Cu(NCO)₂ L complexes exhibit highly distorted five-coordinate structures. Further knowledge about the influence of type, number and position ofL ligand alkyl groups on the structure-bonding properties of cyanato-copper(II) complexes was obtained.

18. Mitt.:Valach, F., Dunaj-Juro, M., Handlovi, M., J. Cryst. Mol. Struct.10, 61 (1980).     

Highly diastereoselective synthesis of trans-2,5-disubstituted tetrahydrofurans

trans-2,5-Disubstituted tetrahydrofurans were obtained as major diastereomers (trans/cis ratio 90:10-100:0) when acetylated gamma-lactols derived from (S)-glutamic acid were treated with titanium enolates of N-acetyl (R)-oxazolidin-2-thiones. A simple transesterification allowed us to obtain the corresponding methyl esters and recover the chiral auxiliary.     

Liquid crystalline metal-free phthalocyanines designed for charge and exciton transport

A joint theoretical and experimental study of the electronic and structural properties of liquid crystalline metal-free phthalocyanines bearing a strong potential for charge and exciton transport has been performed. The synthesis of such compounds has been triggered by quantum chemical calculations showing that: (i) hole transport is favored in metal-free phthalocyanines by their extremely low reorganization energy (0.045 eV) and large electronic splittings; and (ii) the efficiency of energy transfer along the one-dimensional discotic stacks is weakly affected by rotational disorder due to the two-dimensional character of the molecules. We have synthesized two metal-free phthalocyanines with different branched aliphatic chains on the gram scale to allow for a full characterization of their solid-state properties. The two compounds self-organize in liquid crystalline mesophases, as evidenced by optical microscopy, differential scanning calorimetry, X-ray powder diffraction, and molecular dynamics simulations. They exhibit a columnar rectangular mesophase at room temperature and a columnar hexagonal mesophase at elevated temperature.     

Crystal structures of 4,11-pregnadiene-3,20-dione and 21-methyl-20-oxa-4-pregnene-3,20-dione

The structures of the title compounds were solved by direct methods and refined by anisotropic full-matrix least-squares methods. 4,11-Pregnadiene-3,20-dione, C₂₁H₂₈O₂(1) crystallizes in the monoclinic space groupP2₁ (Z=2). The unit cell parametersa, b, c (Å), and (°) were: 12.319(2), 7.700(2), 9.717(2), 109.41(2). TheA- andC-rings exhibit intermediate sofa-halfchair conformations. TheB-ring has a chair conformation and theD-ring assumes an intermediate envelope-half-chair conformation. The progesterone side chain has a typical conformation; the C16–C17–C20–O20 torsion angle is –15.1(4)°. 21-Methyl-20-oxa-4-pregnene-3,20-dione, C₂₁H₃₀O₃ (2) crystallizes in the orthorhombic space groupP2₁2₁2₁ (Z=4). The unit cell parametersa, b, c (Å) were: 12.926(2), 19.447(4), 7.313(1). The progesterone side chain has an unusual conformation; the C16–C17–C20–O20 torsion angle is 174.6(4)°. TheA-ring has a 1, 2-half-chair conformation, ringsB andC exhibit chair conformations and ringD is in a 13,14-half-chair conformation.     

Structure of 11α-hydroxy-progesterone,C21H30O3

The structure of the title compound, C₂₁H₃₀O₃, was determined by X-rays.M _r =330.5, orthorhombic,P2₁2₁2₁,a=8.4451(9),b=10.7074(8),c=20.1525(40) Å,V=1822(8) ų,Z=4,D _x =1.205 mg m^–3. CuK radiation (1.54184 Å),(CuK)=5.85 cm^–1,F(000)=720. FinalR=0.054R _w =0.049 for 1774 unique reflections. The structure was solved usingMultan. TheA ring adopts an intermediate sofa-half-chair conformation and is bent toward the face of the steroid skeleton. RingsB andC have typical chair conformations, and theD ring has a slightly distorted half-chair conformation. The progesterone side chain has a typical conformation, and the C16-C17-C20-O20 torsion angle is –17.9°. An intermolecular hydrogen bond is formed between the hydroxyl group and the progesterone side chain.     

Structure of 6β-acetoxyprogesterone,C23H32O4

The X-ray crystal structure of 6-acetoxyprogesterone, C₂₃H₃₂O₄, has been determined. This compound crystallizes in space groupP2₁2₁2₁ witha=13.195(3),b=15.035(4),c=10.705(3) Å,V=2139.8(9) ų,M _r=372.5,Z=4,D _x=1.156g cm^–3; MoK radiation (=0.7107 Å),=0.72 cm^–1,F(000)=808;R=0.069, andR _w=0.052 for 1292 reflections. RingA adopts a normal 1,2-half-chair conformation. The side chain is typical for a 20-ketosteroid conformation.     

Structure of 17α-methyl-testosterone semihydrate,C20H30O2·1/2 H2O

The crystal structure of 17-methyltestosterone hemihydrate, C₂₀H₃₀O₂·1/2H₂O, has been determined:M _r =312.5, space groupP2₁2₁2₁2₁,a=6.374(2),b=12.807(2),c=43.398(5)Å,V _c =3543(2)ų,Z=8,D _x =1.172 mg^–3, CuK radiation ( = 1.54184 Å),(CuK)=5.5 cm^–1,F(000)=1376. The structure was solved usingMultan. The final conventionalR=0.053 (R _w =0.052) for 3634 reflections. The structure contains two crystallographically independent molecules in the asymmetric part of the unit cell that have almost identical geometry.