Three-frequency resonances in dynamical systems

We investigate numerically and experimentally dynamical systems having three interacting frequencies: a discrete mapping (a circle map), an exactly solvable model (a system of coupled ordinary differential equations), and an experimental device (an electronic oscillator). We compare the hierarchies of three-frequency resonances we find in each of these systems. All three show similar qualitative behaviour, suggesting the existence of generic features in the parameter-space organization of three-frequency resonances.Comment: See home page http://lec.ugr.es/~julya

Crystallographic and theoretical studies on a coupled chain of AF binuclear Cu(II)-fluoraspirinate complexes

We present here the low temperature (116K) crystal and molecular structure of poly-[μ-pyrazine{tetrakis-fluoraspirinate-dicopper(II)}]diacetonitrile, for short [Cu(Fasp)4Cu(pyz)]n, a 5-halogenated derivative of pharmacologically relevant copper aspirinates. We also discuss the theoretically expected magnetic and thermodynamic behavior of this interesting system for molecular magnetism.Instituto de Física La Plat

Low temperature crystal structure of natural diosgenone

The molecular structure of diosgenone, a natural steroidal sapogenin, closely related to diosgenin and isolated from Solanum nudum, was solved by single crystal X-ray diffractometry at 120 K and refined by full-matrix least-squares to an agreement factor, R1 = 0.054. It crystallizes in the monoclinic space group P21, with a = 15.1870(4) Å, b = 7.2710(2) Å, c = 21.2840(6) Å, β = 99.251(1)°, and four molecules in the unit cell (Z = 4). The results constitute the first structural report on a steroidal sapogenin from the diosgenin group.Facultad de Ciencias ExactasCentro de Química Inorgánic

A combined experimental and theoretical study of the supramolecular self-assembly of the natural benzopyran 2,2-dimethyl-3-hydroxy-6-acetyl-chromane and its isomeric benzofuran 10,11-dihydro-10-hydroxytremetone

Epoxidation of 4HMBA, the main metabolite of the medicinal plant Sencecionutans, produces an unstable epoxide eventually giving rise to a mixture of four derivatives, three of them previously reported as natural products. The epoxide product easily undergoes an intra-molecular attack of the phenolic hydroxyl against the epoxide group carbons to produce either a benzofuran or a chromane derivative. When dissolved in methanol-water mixture at room temperature the epoxide is completely solvolyzed to give the corresponding diol (hydrolysis) or vicinal hydroxyl-methoxy (methanolysis) derivative. All the compounds involved in the above reactions were characterized by IR, Raman, H NMR and UV–vis spectroscopies, and by mass spectrometry. Density functional theory (DFT) computations were used to optimize the structure conformations. The optimized structures were further subjected to a Natural Bond Orbital (NBO) and electrostatic potentials analysis. The crystal structures of the title compounds (for short, 3 and 4 respectively) were determined by X-ray diffraction methods. Compound 3 crystallizes in the triclinic P-1 space group with a = 6.4289 (6) Å, b = 8.7120 (6) Å, c = 10.952 (1) Å, α = 92.280 (7)°, β = 95.738 (7)°, γ = 103.973 (7)°, and Z = 2 molecules per unit cell and 4 in the monoclinic P21/c space group with a = 11.2891 (6) Å, b = 9.1902 (4) Å, c = 12.4272 (7) Å. Β = 113.689 (7)°, and Z = 4. In 3 neighboring molecules are linked to each other by OH⋯O (keto) bonds giving rise to a polymeric structure. In 4 the OH group is a bifurcate H-bond donor. It forms a weak intra-molecular OH⋯O (furan) bond and also a much stronger inter-molecular OH⋯O (keto) bond giving rise to a zig-zag polymeric structure. A detailed analysis of the solid state molecular interactions of compounds 3 and 4 has been performed using Hirshfeld surface analysis and their associated 2D fingerprint plots.Instituto de Física La Plat

Structural, Spectroscopic, and Thermal Behaviour of Bis-(thiosaccharinate)- aqua-cadmium(II)

The crystal structure of the title complex, [Cd(tsac)2(H2O)], has been determined by single crystal X-ray diffraction methods. It crystallizes in the monoclinic space group C2/c (a = 12.236(3), b = 8.919(3), c = 16.655(3) A, β = 96.18(2)°, Z = 4). The molecular structure was solved from 1705 independent reflections with I > σ(I) and refined to R1 = 0.0489. Infrared and Raman spectra of the complex were recorded and are briefly discussed. Its thermal behaviour was investigated by thermogravimetry and differential thermal analysis.Instituto de Física La PlataCentro de Química Inorgánic

Second generation of α-tocopherol analogs-nitric oxide donors: Synthesis, physicochemical and biological characterization.

Postprin

Estructura molecular y resonancia paramagnética electrónica en cristales de bis (L-valinato) cobre, Cu[H₂NCHC0₂CH(CH₃)₂]₂.H₂0

Se presenta un estudio magneto-estructural del compuesto bis (L-valinato) cobre (II) monohidratado, Cu (L-Val)₂.H₂0, empleando RPE y difracción de rayos X. El compuesto cristaliza en el grupo espacial C2 con a = 21.314 (5) Å, b = 9.586 (2)Å, c = 7.417 (2) Å, b = 108.89° y z = 4. Los cobres se encuentran en una coordinación piramidal de base cuadrada con dos valinas, y el oxígeno de la molécula de agua. Se ubican en el cristal formando capas paralelas al plano (100). Se realizaron mediciones de RPE en monocristales de Cu(L-Val))₂.H₂0, en banda X (9.7 GHz) y a temperatura ambiente. Se midió la posición y el ancho de la única resonancia observada, en tres planos mutuamente perpendiculares. La resonancia se debe al colapso por intercambio de las resonancias de dos iones cobre magnéticamente no equivalentes. Las componentes del tensor molecular fueron calculadas suponiendo simetría axial alrededor de los cobres. Se obtuvo g// = 2.254 y g⊥ =2.061, que indican un orbital d (x²-y²) para el electrón desapareado. La variación angular del ancho de línea se debe a la contribución de la interacción dipolar angostada por intercambio en una red magnética bidimensional y al colapso incompleto de la interacción hiperfina.Facultad de Ciencias Exacta

Reactivity and spectroscopy of the {Ru'(DMAP) IND.5'} fragment: an {Ru'(N'H IND.3') IND.5} analogue

Reaction of trans-Ru(DMSO)4Cl2 with DMAP (DMAP = 4-dimethylaminopyridine) yields the yellow [Ru(DMAP)6]2+ cation in good yield. The crystal and molecular structure of [Ru(DMAP)6]Cl2·6CH3CH2OH was determined by X-ray diffraction methods. The complex crystallizes in the trigonal R3̅ space group with a = b = 16.373(1), c = 20.311(1) Å, γ = 120°, and Z = 3 molecules per unit cell. The reaction of [Ru(DMAP)6]2+ in aerobic water gives the red [RuIII(DMAP)5(OH)]2+ cation. This complex shows a chemical behavior similar to [RuIII(NH3)5Cl]2+ and allows the preparation of a family of [Ru(DMAP)5L]n+ complexes. Their electronic properties indicate that the {RuII(DMAP)5} fragment is a weaker π-donor than {RuII(NH3)5}. Our density functional theory (DFT) calculations show that in {RuII(DMAP)5} the DMAP ligands can compete for the π electron density of the ruthenium making the fragment a weaker π-donor.CONICETANPCyTFAPES

Three-frequency resonances in dynamical systems

We investigate numerically and experimentally dynamical systems having three interacting frequencies: a discrete mapping (a circle map), an exactly solvable model (a system of coupled ordinary differential equations), and an experimental device (an electronic oscillator). We compare the hierarchies of three-frequency resonances we find in each of these systems. All three show similar qualitative behaviour, suggesting the existence of generic features in the parameter-space organization of three-frequency resonances.Facultad de IngenieríaInstituto de Investigaciones en Electrónica, Control y Procesamiento de Señale

Crystallographic and theoretical studies on a coupled chain of AF binuclear Cu(II)-fluoraspirinate complexes

We present here the low temperature (116K) crystal and molecular structure of poly-[μ-pyrazine{tetrakis-fluoraspirinate-dicopper(II)}]diacetonitrile, for short [Cu(Fasp)4Cu(pyz)]n, a 5-halogenated derivative of pharmacologically relevant copper aspirinates. We also discuss the theoretically expected magnetic and thermodynamic behavior of this interesting system for molecular magnetism.Instituto de Física La Plat