Showing papers by "Oscar E. Piro published in 2012"

Water-Soluble (Pterin)rhenium(I) Complex: Synthesis, Structural Characterization, and Two Reversible Protonation–Deprotonation Behavior in Aqueous Solutions

Abstract: A new water-soluble complex, Re(CO)3(pterin)(H2O), was synthesized and characterized by 1H NMR and FTIR spectroscopy, and by a combination of three mass spectrometry techniques: MALDI, probe electrospray ionisation (PESI), and ESI. Because, unlike most metal-pterin complexes, the ReI complex is quite soluble in water, appropriate single crystals could be obtained for structural X-ray analysis. We report here the first solid state molecular structure containing a pterin ligand coordinated to the Re(CO)3 core. This determination revealed that strong H bonds between the hydrogen atom of the 2-amino group and crystallization water molecules give rise to a polymeric arrangement of Re(CO)3(pterin)(H2O) complexes in the lattice. Protonation studies in aqueous solutions of the ReI complex showed two acid-base equilibriums with pKa1 = 3.9 and pKa2 = 8.8. pKa1 was assigned to the protonation equilibrium at N3 of the pterin ligand in the complex and pKa2 could be ascribed to the deprotonation of a coordinated water molecule.

Structural, spectral and potentiometric characterization, and antimicrobial activity studies of [Zn(phen)2(cnge)(H2O)](NO3)2 · H2O

Abstract: An octahedral Zn complex with o-phenanthroline (o-phen) and cyanoguanidine (cnge) has been synthesized and characterized. The crystal structural data show the formation of a ZnN5O core where the metal coordinates to two mutually perpendicular o-phenanthrolines as bidentate ligands [Zn–N bond lengths in the 2.124(2)–2.193(2) A range], the cyanide nitrogen of a cnge [d(Zn–N) = 2.092(2) A, ∠(Zn–N–C) = 161.1(2)°], and a water molecule [d(Zn–Ow) = 2.112(2) A]. Spectral data (FT-IR, Raman, and fluorescence) and speciation studies are in agreement with the structure found in the solid state and the one proposed to exist in the solution. To evaluate the changes in the microbiological activity of Zn, antibacterial studies were carried out by observing the changes in minimum inhibitory concentration of the complex, the ligands, and the metal against five different bacterial strains. The antibacterial activity of Zn improved upon complexation in three of the tested strains.

Spectroscopic, structural, and conformational properties of (Z)-4,4,4-trifluoro-3-(2-hydroxyethylamino)-1-(2-hydroxyphenyl)-2-buten-1-one, C12H12F3NO3: a trifluoromethyl-substituted β-aminoenone.

Abstract: The (Z)-4,4,4-trifluoro-3-(2-hydroxyethylamino)-1-(2-hydroxyphenyl)-2-buten-1-one (C12H12F3NO3) compound was thoroughly studied by IR, Raman, UV–visible, and 13C and 19F NMR spectroscopies. The solid-state molecular structure was determined by X-ray diffraction methods. It crystallizes in the P21/c space group with a = 12.1420(4) A, b = 7.8210(3) A, c = 13.8970(5) A, β = 116.162(2)°, and Z = 4 molecules per unit cell. The molecule shows a nearly planar molecular skeleton, favored by intramolecular OH···O and NH···O bonds, which are arranged in the lattice as an OH···O bonded polymer coiled around crystallographic 2-fold screw-axes. The three postulated tautomers were evaluated using quantum chemical calculations. The lowest energy tautomer (I) calculated with density functional theory methods agrees with the observed crystal structure. The structural and conformational properties are discussed considering the effect of the intra- and intermolecular hydrogen bond interactions.

Crystal structure and spectroscopic properties of polymeric adducts of the tetra-μ-haloaspirinate-dicopper(II)

Abstract: Eight new copper(II) complexes with halo-aspirinate anions have been synthesized: [Cu2(Fasp)4(MeCN)2] · 2MeCN (1), [Cu2(Clasp)4(MeCN)2] · 2MeCN (2), [Cu2(Brasp)4(MeCN)2] · 2MeCN (3), {[Cu2(Fasp)4(Pyrz)] · 2MeCN} n (4), {[Cu2(Clasp)4(Pyrz)] · 2MeCN} n (5), [Cu2(Brasp)4(Pyrz)] n (6), [Cu2(Clasp)4(4,4′-Bipy)] n (7), and [Cu2(Brasp)4(4,4′-Bipy)] n (8) (Fasp: fluor-aspirinate; Clasp: chloro-aspirinate; Brasp: bromo-aspirinate; MeCN: acetonitrile; Pyrz: pyrazine; 4,4′-Bipy: 4,4′-bipyridine). The crystal structure of two 2 and 4 have been determined by X-ray diffraction methods. All compounds have been studied employing elemental analysis, IR, and UV-Visible spectroscopic techniques. The results have been compared with previous data reported for complexes with similar structures.

Structural and Spectroscopic Properties of Two New IsostructuralComplexes of Lapacholate with Cobalt and Copper

Abstract: The molecular structures of two isostructural complexes of lapacholate (Lap) anion and dimethylformamide (DMF), M(Lap)2(DMF)2 with M: Co Cu, were determined by X-ray diffraction methods The substances crystallize in the triclinic space group with one molecule per unit cell and cell constants (3), (3), (4) A, (2), (2), and (2)° for the Co complex and (2), (4), (4), (2), (2), and (2)° for the Cu complex The structures were solved from 2933 (Co) and 2888 (Cu) reflections with (I) and refined by full matrix least squares to agreement R1-factors of 0041 (Co) and 0033 (Cu) The metal M(II) ion is sited on a crystallographic inversion center in a MO6 distorted octahedral environment This ion is coordinated equatorially to two lapacholate anions through their adjacent carbonyl and phenol oxygen atoms [M–O bond distances of 2134(1) and 2008(1) A (Co) and 2301(1) and 1914(1) A (Cu)] and axially to two DMF molecules through oxygen atoms [M–O bond lengths of 2143(1) A (Co) and 2069(1) A (Cu)] The solid state IR transmittance and solution electronic absorption spectra of both Co and Cu compounds are also reported and compared to each other and to the corresponding spectra of other members of the lapacholate metal family of complexes