Showing papers by "Oscar E. Piro published in 2008"

Structure and thermal reactivity of Zn(II) salts of isocinchomeronic acid (2,5-pyridinedicarboxylic acid)

Abstract: The synthesis, an improved refined crystal and molecular structure re-determination, and the thermal decomposition behavior of two Zn(II) derivatives of isocinchomeronic acid (2,5-pyridinedicarboxylic acid or H22,5-pydc) are presented. [Zn(2,5-pydc)(H2O)3Zn(2,5-pydc)(H2O)2]2 (1) crystallizes in the triclinic P-1 space group with a = 7.106(2), b = 11.450(2), c = 11.869(1) A, α = 107.29(1), β = 104.08(1), γ = 90.32(2)°, and Z = 2. [Zn(2,5-pydc)(H2O)2] · H2O (2) is orthorhombic (P212121 space group), with a = 7.342(1), b = 9.430(1), c = 13.834(2) A, and Z = 4. The structures were refined to agreement R 1-factors of 0.0315 (1) and 0.0336 (2). Complex (1) is arranged as molecular Zn4(2,5-pydc)4(H2O)10 tetramers, the cages of which define channels that remain unblocked by anions. Compound (2) is polymeric with Zn(2,5-pydc)(H2O)2 and Zn(2,5-pydc)(H2O)3 units linked through bridging ligands. Both compounds were synthesized under mild conditions in aqueous media, without need to resort to hydrothermal media. Changing the pH from 4.51 to 5.75 suffices to direct the chemical processes toward the orthorhombic compound rather than to the triclinic one.

Combined crystallographic and solution molecular dynamics study of allosteric effects in ester and ketone p-tert-butylcalix[4]arene derivatives and their complexes with acetonitrile, Cd(II), and Pb(II).

Abstract: We describe here a procedure to bridge the gap in the field of calixarene physicochemistry between solid-state atomic-resolution structural information and the liquid-state low-resolution thermodynamics and spectroscopic data. We use MD simulations to study the kinetics and energetics involved in the complexation of lower rim calix[4]arene derivatives (L), containing bidentate ester (1) and ketone (2) pendant groups, with acetonitrile molecule (MeCN) and Cd(2+) and Pb(2+) ions (M(2+)) in acetonitrile solution. On one hand, we found that the prior inclusion of MeCN into the calix to form a L(MeCN) adduct has only a weak effect in preorganizing the hydrophilic cavity toward metal ion binding. On the other hand, the strong ion-hydrophilic cavity interaction produces a wide open calix which enhances the binding of one MeCN molecule (allosteric effect) to stabilize the whole (M(2+)) L(MeCN) bifunctional complex. We reach two major conclusions: (i) the MD results for the (M(2+)) 1(MeCN) binding are in close agreement with the "endo", fully encapsulated, metal complex found by X-ray diffraction and in vacuo MD calculations, and (ii) the MD structure for the more flexible 2 ligand, however, differs from the also endo solid-state molecule. In fact, it shows strong solvation effects at the calixarene lower bore by competing MeCN molecules that share the metal coordination sphere with the four CO oxygens of an "exo" (M(2+)) 2(MeCN) complex.

A New Supramolecular Assembly Obtained by Reaction Between Thiosaccharin and Pyridine

Abstract: The crystal structure of pyridinium thiosaccharinate thiosaccharin, [HNC5H5]+ [(tsac)(Htsac)]− (Htsac = C7H5NO2S2, the thiosaccharin molecule), was determined by single-crystal X-ray diffraction. Both, the thiosaccharinate anion, the corresponding neutral molecule and the pyridinium cation are nearly planar and arranged in the solid state in an almost parallel fashion, hence giving rise to a layered supramolecular structure. The anion shows small but significant modifications in the bonding of the thioamide group as compared with the neutral molecule. The crystal is further stabilized by an extensive H-bonding network. The FTIR spectrum of the compound is briefly commented.