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Fil: de la Sovera, Victoria. Universidad de la Republica. Facultad de Quimica. Departamento de Quimica Organica; Uruguay

This work focuses on the polynuclear complexes formed by a lanthanide ion (Ln), a bivalent cation (M) and oxydiacetate (oda) as bridging ligand, with general formula [Ln2M3(oda)6(H 2O)6] · xH2O. The complexes can adopt more than one polymorphic structure, being the hexagonal (P6/mcc) and cubic (Fd3c) the most noticeable, as determined by x-ray powder diffraction. The influence of Ln and M on the solid-state structure is discussed. In addition, potentiometric studies are performed to support the existence of polynuclear species in solution. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Four new lead(II) thiosaccharinate complexes: [Pb(tsac)2H2O] (1) (tsac: thiosaccharinate anion), [Pb2(tsac)4(py)4] (2) (py: pyridine), [Pb(tsac)(o-phen)2](tsac)·CH3CN (3) (o-phen: 1,10-phenantroline), and [Pb(tsac)2(bipy)] (4) (bipy: 2,2′-bipyridine) were prepared. The infrared and electronic spectra as well as the thermal analysis of all the compounds were recorded and discussed. The thiosaccharinate anion acts in three different coordination forms, one of then reported for the first time. The crystal structures of complexes 2 and 3 have been determined by single crystal X-ray diffractometry. In complex 2, two monomeric moieties are joined together forming a symmetric bis-μ-sulphur bridged dimer by interaction of two lead(II) atoms through the exocyclic sulphur atoms of two thiosaccharinate ligands. The seven-fold coordination sphere of each lead atom is completed by two pyridine nitrogen atoms and by another sulfur and two nitrogen atoms of the thiosaccharinate anions. In complex 3, the lead(II) atom is coordinated by four nitrogen atoms of two 1,10-phenantroline molecules and by the sulfur and nitrogen atoms of one thiosaccharinate ion. The second anion has an electrostatic interaction with the nucleus.

MMoO4 (M: Ca, Sr, Ba) scheelite nanocrystals of ≤15 nm size are prepared by a vapor diffusion sol-gel method using MoO2(acac)2 dissolved in M(OR)2 (R: -CH2CH2-O-Me for Ca and -CH2CH(Me)-O-Me for Sr and Ba) in a 1:1 molar ratio followed by diffusion of H2O vapor into the solution, thermal aging (80 °C, 1 d, under N2), and vacuum drying at room temperature.

Several new 1,2,5-oxadiazole N-oxide derivatives were synthesized to be tested both as potential selective hypoxic cell cytotoxins and as DNA-binding agents. The compounds prepared included bis(1,2,5-oxadiazole N-oxide) derivatives and oxadiazole rings linked to naphthyl residues. The compounds were tested for their cytotoxicity in oxia and hypoxia and they proved to be non-selective and less active than the parent compounds 3-formyl-4-phenyl-1,2,5-oxadiazole N2-oxide (3) and 3-chloromethyl-4-phenyl-1,2,5-oxadiazole N2-oxide (4). The DNA-affinity assays showed that the compounds tested have poor affinity for this biomolecule.

Capability of [ReIII(tu-S)6]Cl3, where tu = thiourea, as a precursor to other ReIII complexes by ligand substitution in aqueous medium is studied. For the decomposition of [Re(tu-S)6]Cl3, experiments suggest pseudo first order kinetics and observed rate constants vary from 1.3 × 10–2 to 9.6 × 10–2 min–1 in the pH range 2.80–5.04. Experiments in presence of incoming ligand (ethylendiaminetetraacetic acid or diethylentriaminepentaacetic acid) show that ligand substitution is significantly slower than decomposition of the precursor, even when pH and temperature are modified. Similar results were obtained working with [ReIII(Metu-S)6]Cl3, where Metu = N-methylthiourea. Molecular structure of [ReIII(Metu-S)6](PF6)3 · H2O was determined by single crystal X-ray diffractometry. The coordination polyhedron around the Re ion is a distorted octahedron. The six methylthiourea ligands are bonded to the metal through the sulfur atoms [bond lengths range from 2.409(2) to 2.451(2) A]. [ReIII(thioharnstoff-S)6]Cl3 · 4 H2O und [ReIII(N-methylthioharnstoff-S)6]Cl3 als Vorlaufer fur andere ReIII-Komplexe: Eine kinetische Untersuchung in wasrigem Medium. Die Kristallstruktur von [ReIII(N-methylthioharnstoff-S)6](PF6)3 · H2O Es wird die Eignung von [ReIII(tu-S)6]Cl3 (tu = Thioharnstoff) als Vorlaufer fur andere ReIII-Komplexe durch Ligandenaustausch in wasrigem Medium untersucht. Die Dissoziation von [Re(tu-S)6]Cl3 zeigt im pH-Bereich von 2,80–5,04 eine Kinetik Pseudo-Erster-Ordnung mit einer Geschwindigkeitskonstanten im Bereich von 1,3 × 10–2 bis 9,6 × 10–2 min–1. Experimente im Beisein von Liganden (Ethylendiamin-Tetraessigsaure oder DiethylentriaminPentaessigsaure) zeigen auch bei Variation von Temperatur und pH-Wert eine signifikant langsamere Liganden-Substitution als es der Dissoziation des Vorlaufers entspricht. Ahnliche Ergebnisse werden mit [ReIII(Metu-S)6]Cl3 (Metu = N-Methylthioharnstoff) erzielt. Die Molekulstruktur von [ReIII(Metu-S)6](PF6)3 · H2O wird durch Einkristall-Rontgenstrukturanalyse ermittelt. Das Koordinationspolyeder am Re-Ion ist verzerrt oktaedrisch. Die sechs N-Methylthioharnstoff-Liganden sind uber die Schwefel-Atome an das Rhenium-Atom gebunden [Bindungslangen von 2,409(2) bis 2,451(2) A].

A new ReV oxo complex with tetramethylthiourea, [ReO(Me4tu)4](PF6)3, has been synthesized by reduction of perrhenate with tin(II) chloride in strongly acidic solution in the presence of excess tetramethylthiourea. The complex has been characterized by elemental analysis and electronic and FTIR spectroscopy. The molecular structure of the compound was determined by X-ray diffraction methods. The coordination polyhedron is a regular square pyramid with the substituted thiourea sulfur atoms in the equatorial positions [d(Re–S) = 2.339(3) A] and the oxo ligand located in the summit [d(Re–O) = 1.63(2) A]. Computational methods were employed to analyze the geometric and electronic structures of tetramethylthiourea and thiourea. Quantum mechanical studies suggest steric hindrance as the reason for the stabilization of the ReO3+ center instead of the ReIII one.

The new title compounds are prepared by solid state reactions of Y2O3, Eu2O3, Nd2O3, La2O3, Fe2O3, and V2O3 (argon, 1623 K, several 12 h periods).

The structures and absolute stereochemistries of two chamigrene-type metabolites (spiro­[5.5]­un­decane derivatives) isolated from the red algae Laurencia scoparia are described. One, a non-sesquiterpene named maĩlione (8-bromo-9-hydroxy-7,7-di­methyl-11-methyl­ene­spiro­[5.5]­undec-1-en-3-one), C14H19BrO2, was detected previously in Laurencia cartilaginea, while the other, the sesquiterpene isorigidol (8-bromo-3,7,7-tri­methyl-11-methyl­ene­spiro­[5.5]-undec-1-ene-3,9-diol), C15H23BrO2, is a new isomer of rigidol, first isolated from Laurencia rigida. The A rings of these spiro­cyclic compounds show the same carbon skeleton. However, the relative stereochemistry of the 8-Br and 9-OH substituents is different. While maĩlione displays the usual syn (or cis) relative stereochemistry of the bromo­hydroxy vicinal group, isorigidol shows an anti (or trans) arrangement. The 8-Br and 9-OH groups are both in equatorial positions in isorigidol, while the 9-OH group is axial in maĩlione, as in most chamigrenes. The absolute configurations of the chiral centers were determined as 6S, 8S and 9R in maĩlione, and 3R, 6S, 8S and 9S in isorigidol.

LaxSr1−xMnO2.6+δ (x=0.1–0.4) compounds have been obtained by low-temperature annealing of stoichiometric materials in hydrogen. La0.1Sr0.9MnO2.6+δ (δ=0.15) and La0.3Sr0.7MnO2.6, tetragonal (P4/m), and La0.2Sr0.8MnO2.6, pseudo-tetragonal monoclinic (P2/m), structures are isostructural with oxygen-vacancy-ordered Sr5Mn5O13 ( a = b ≈ 5 a P , c≈aP). La0.4Sr0.6MnO2.6 shows cubic perovskite structure with disordered oxygen vacancies. In the vacancy-ordered (LaxSr1−x)5Mn5O13 phases four out of five Mn cations are Mn3+ and show a typical Jahn-Teller elongated pyramidal coordination while the fifth one Mn(4−5x)+, in octahedral environment, shows decreasing formal charge from Mn4+ (x=0) to Mn2.5+ x=0.3. This unusual selective doping of the octahedral site produces structural strain due to increasing size of the Mn(4−5x)+ and, in the case of (La0.2Sr0.8)5Mn5O13, the unusual compressed octahedral arrangement of oxygen atoms around it. The coordination geometry implies that either the d x 2 - y 2 orbital is occupied, which would be a rare example of inverted occupancy of eg orbitals in manganites, or that disordered Mn3+ apically elongated MnO6 octahedra are present with normal electronic configuration d t 2 g 3 d x 2 - y 2 0 d z 2 1 , and the observed bond distances are the average of the long and intermediate in-plane Mn–O bonds. Several structural features favor the second case.

Bulk SrMnO {sub x} samples with oxygen contents 2.5{

Several new 1,2,5-oxadiazole N-oxide derivatives were synthesized to be tested both as potential selective hypoxic cell cytotoxins and as DNA-binding agents. The compounds prepared included bis(1,2,5-oxadiazole N-oxide) derivatives and oxadiazole rings linked to naphthyl residues. The compounds were tested for their cytotoxicity in oxia and hypoxia and they proved to be non-selective and less active than the parent compounds 3-formyl-4-phenyl-1,2,5-oxadiazole N2-oxide (3) and 3-chloromethyl-4-phenyl-1,2,5-oxadiazole N2-oxide (4). The DNA-affinity assays showed that the compounds tested have poor affinity for this biomolecule.

The title macrocycle, C(31)H(30)O(5), is comprised of two bibenzyl ether moieties linked cyclically by spacers which each consist of two-carbon alkyl chains. The observed conformation of the macrocycle may be partly stabilized by intramolecular C-H.O close contacts. The packing appears to be directed by van der Waals forces. This work explains the occurrence of a signal found in the (1)H NMR spectra of both marchantinquinone and marchantin M trimethyl ether at delta = 5. 49 and 5.56 p.p.m., respectively. The shift in the position of the expected peak can be explained by the proximity of an H atom belonging to one of the aromatic rings to another ring in the same molecule.