Showing papers by "Oscar E. Piro published in 1998"

Solution thermodynamics of geometrical isomers of pyridino calix(4)arenes and their interaction with the silver cation. The X-ray structure of a 1:1 complex of silver perchlorate and acetonitrile with 5,11,17,23-tetra-tert-butyl-[25,26,27,28-tetrakis(2- pyridylmethyl)oxy]calix(4)arene

Abstract: The solubility and derived standard Gibbs energies of solution of three geometrical isomers of pyridinocalix(4)arenes {5,11,17,23-tert-butyl-[25,26,27,28-tetrakis-(n-pyridylmethyl) oxy]-p-tert-butylcalix(4)arene, with n=2, 3, 4} in a variety of solvents at 298.15 K are reported. Solvation effects are assessed from the standard transfer Gibbs energies of these ligands, using acetonitrile as the reference solvent. For the 2-pyridyl derivative in alcohols as the aliphatic chain length of the alcohol increases, the extent of solvent–ligand interaction increases, whereas for the 3- and the 4-pyridyl derivatives the opposite is observed. The protonation constants for the 4-pyridyl derivative in methanol at 298.15 K are reported. The results, compared with corresponding values for the 3-pyridyl derivative show that the basic character of these ligands follows the sequence; 4-pyridyl>3-pyridyl>2-pyridyl calix(4)arene. Thermodynamic parameters for the complexation of these macrocycles (2 and 4-pyridyl derivatives) and the silver cation in acetonitrile show that, as the distance between the phenolic oxygens and the pyridyl nitrogens increases, the strength of complexation decreases. Thermodynamic data for the complexation of silver and the 2-pyridylcalix(4)arene derivative are compared with corresponding values for sodium and this ligand in the same solvent. The results suggest that the 2-pyridyl derivative provides phenolic oxygens and pyridyl nitrogens as the active sites for complexation with silver. This is corroborated by 1H NMR measurements of this ligand and silver in CD3CN at 298 K.The crystal structure of a 1:1 monoacetonitrile and silver complex of the 2-pyridyl derivative with perchlorate as the counter-ion has been determined from XRD data. The substance crystallises in the tetragonal space group P4/n with a=15.580(2) A, c=13.082(2) A, and z=2. The macrocycle is sited on a fourfold symmetry axis and consists of two conical parts, one hydrophobic, filled with an acetonitrile molecule, the other hydrophilic, encapsulating the Ag+ ion through the ethereal oxygen [d(Ag···O)=2.923(3) A] and pyridine nitrogen atoms [d(Ag···N)=2.483(5) A]. The coordination around the Ag+ ion has the form of a distorted Archimedean square antiprism. The ability of the macrocycle to complex the silver cation in its hydrophilic cavity is demonstrated.

Crystal Structure and Spectroscopic Behaviour of a Binuclear Copper(II) Complex of Mefenamic Acid and Dimethylsulfoxide

Abstract: The crystal structure of the binuclear Cu(II) complex [Cu(mef)₂DMSO]₂ (mef = deprotonated N-2,3-dimethylphenyl-anthranilic acid; DMSO = dimethylsulfoxide) has been determined by single-crystal X-ray diffractometry. It crystallizes in the triclinic space group P1 with Z = 1. IR and electronic spectra of the compound are also discussed briefly.

Crystal structure and ir-spectrum of lithium citrate monohydrate, li(c6h7o7).h2o

Abstract: The crystal structure of Li(C6H7O7) · H2O has been determined by single-crystal X-ray diffractometry. It crystallizes in the triclinic space group P 1 with Z = 2. The structure was solved by direct and Fourier methods and refined to R1 = 0.031. Some comparisons with related structures are made. The infrared spectrum of the salt was recorded and briefly discussed. Kristallstruktur und IR-Spektrum von Lithium-Citrat-Monohydrat, Li(C6H7O7) · H2O Die Kristallstruktur von Li(C6H7O7) · H2O wurde rontgenographisch an Einkristallen bestimmt. Es kristallisiert in der triklinen Raumgruppe P 1 mit Z = 2. Die Struktur wurde mit direkten und Fourier Methoden gelost und zu R1 = 0.031 verfeinert. Es werden einige Vergleiche mit verwandten Strukturen gemacht. Das Infrarotspektrum des Salzes wurde aufgenommen und kurz besprochen.

Crystal Structure and Spectroscopic Behaviour of Oxoetoxo-bis(5,7-dichloro-8-hydroxyquinolinato)vanadium(V)

Abstract: The title compound, a new example of an inorganic ester-like complex, was characterized by spectroscopic and X-ray crystallographic methods. It crystallizes in the triclinic space group P1 (a=9.413(2), b=10.595(3), c=11.783(2) A, α=103.59(2), β=101.98(2), γ=99.40(2)°, Z=2). The structure was solved employing 2902 independent reflections with I>2σ(I) by direct and Fourier methods and refined by a full-matrix least-squares fit to R 1=0.049. Infrared and Raman spectra of the solid compound and the electronic absorption spectra of its acetonitrilic and ethanolic solutions were recorded and are briefly discussed.

X-ray diffraction studies and solution thermodynamics of 5,7,17,23-para-tert-butyl-25,26,27,28-tetra(diethylamine)ethoxy-calix(4)arene

Abstract: The crystal structure of 5,7,17,23-para-tert-butyl-25,26,27,28-tetra(diethylamine)ethoxycalix(4)arene has been determined from X-ray diffraction data. The substance crystallises in the space group P21/a with a = 14.103(2), b = 34.250(5), c = 14.486(2) A, β = 105.15(1)°, and Z = 4. The macrocycle consists of two distorted conical parts, one hydrophobic the other hydrophilic, linked through their smaller rims. The larger bore of the hydrophobic cavity has transversal dimensions of about 5.90 × 5.90 A while the hydrophilic cavity reaches apertures of 5.06 × 10.39 A at the aminoethyl nitrogen atom positions. The solubility of this ligand at several temperatures in various solvents has been determined and the data were used to derive its solution Gibbs energies in these solvents at 288.15, 298.15 and 313.15 K. The enthalpy of solution for this calix(4)arene derivative in five solvents was measured calorimetrically at 298.15 K. Thermodynamic parameters of transfer are calculated using benzonitrile as the reference solvent. It is shown that the transfer Gibbs energy among these solvents is almost 0 kJ mol−1 as a result of an enthalpy–entropy compensation effect, where the most significant enthalpic and entropic changes are found in transfers to protic solvents.

Molecular structure of trans-[Co(NH3)4(NH2CH3)Cl](ClO4)2

Abstract: The title compound crystallizes in the orthorhombic space group Pnma, with a = 7.9209(5), b = 9.818(1), c = 16.867(2) A, and Z = 4. The structure was solved employing 1864 independent x-ray reflections with I>2σ(I) by Patterson and difference Fourier techniques and refined by full-matrix least-squares to R = 0.036. The trans-[CO(NH3)4(NH2CH3)Cl](ClO4)2 molecule is on a crystallographic mirror plane. The cobalt ion is in an elongated octahedral coordination with four equatorial ammonia ligands [average Co–N distance equal to 1.966(2) A], an axial methylamine [Co–N=1.965(3)A], and an axial chlorine ion [Co–Cl=2.2771(9)A]. Kinetic steric effects of the complex are interpreted in terms of structural results.

Crystal structure and EPR spectra of glycilglycilglycinocopper(II)bromide sesquihydrate

Abstract: The title compound, Cu(glyglygly)Br·1·5H2O, crystallizes in the space group C2/c, with a = 21.468(7), b = 6.716(5), c = 16.166(6) A, β = 98.39°, and Z = 8. The tripeptide is bonded to one Cu(II) ion through the nitrogen [Cu–N=1.97(1)A] and oxygen [Cu–O=2.019(8)A] atoms of the amino end glycine residue and to another Cu(II) through one oxygen atom [Cu–O=1.931(9)A] of the terminal carboxyl group. This give rise to covalently bonded and infinite ···–Cu–tripeptide–Cu–··· chains. These chains are linked to one another by a network of H-bonds involving the water molecules and bromide ions. The Cu(II) ion is in a distorted tetragonal pyramidal coordination polyhedron. At the corner of the base of the pyramid are the terminal glycine nitrogen and oxygen atoms of one tripeptide, a carboxylic oxygen of another tripeptide and a bromide ion. The fivefold coordination is completed with a water molecule at the top of the pyramid [Cu–Ow=2.286(9)A]. For all orientations of the applied magnetic field the single crystal EPR spectra display a single anisotropic exchange collapsed resonance without hyperfine structure. Its position was measured in three perpendicular planes and the crystal g-tensor evaluated from the data. This tensor is interpreted in terms of the contributing Cu(II) complexes in the unit cell to deduce the principal values g1 = 2.273, g2 = 2.050 and g3 = 2.131 for the molecular gyromagnetic tensor. We also discuss the magnitude of the exchange interaction between neighboring copper ions in the lattice on the basis of the features in the EPR spectra and the structural information.