Showing papers by "Oscar E. Piro published in 2002"

Selective interaction of lower rim calix[4]arene derivatives and bivalent cations in solution. Crystallographic evidence of the versatile behavior of acetonitrile in lead(II) and cadmium(II) complexes.

Abstract: The interaction of lower rim calix(4)arene derivatives containing ester (1) and ketone (2) functional groups and bivalent (alkaline-earth, transition- and heavy-metal) cations has been investigated in various solvents (methanol, N,N-dimethylformamide, acetonitrile, and benzonitrile). Thus, 1 H NMR studies in CD 3 -OD, C 3 D 7 NO, and CD 3 CN show that the interaction of these ligands with bivalent cations (Mg 2+ , Ca 2+ , Sr 2+ , Ba 2+ , Hg 2+ , Pb 2+ , Cd 2+ ) is only observed in CD 3 CN. These findings are corroborated by conductance measurements in these solvents including benzonitrile, where changes upon the addition of the appropriate ligand (1 or 2) to the metal-ion salt only occur in acetonitrile. Thus, in this solvent, plots of molar conductance against the ligand/metal cation ratio reveal the formation of 1:1 complexes between these ligands and bivalent cations. Four metal-ion complex salts resulting from the interaction of 1 and 2 with cadmium and lead, respectively, were isolated and characterized by X-ray crystallography. All four structures show an acetonitrile molecule sitting in the hydrophobic cavity of the ligand. The mode of interaction of the neutral guest in the cadmium(II) complexes differs from each other and from that found in the lead(II) complexes and provides evidence of the versatile behavior of acetonitrile in binding processes involving calix(4)arene derivatives. The thermodynamics of complexation of these ligands and bivalent cations in acetonitrile is reported. Thus, the selective behavior of 1 and 2 for bivalent cations is for the first time demonstrated. The role of acetonitrile in the complexation process in solution is discussed on the basis of 1 H NMR and X-ray crystallographic studies. It is suggested that the complexation of 1 and 2 with bivalent cations is likely to involve the ligand-solvent adducts rather than the free ligand. Plots of complexation Gibbs energies against the corresponding data for cation hydration show a selectivity peak which is explained in terms of the predominant role played by cation desolvation and ligand binding energy in complex formation involving metal cations and macrocycles in solution. A similar peak is found in terms of enthalpy suggesting that for most cations (except Mg 2+ ) the selectivity is enthalpically controlled. The ligand effect on the complexation process is quantitatively assessed. Final conclusions are given highlighting the role of the solvent in complexation processes involving calix(4)arene derivatives and metal cations.

Photoinduced charge separation in R–CO2–Re(CO)3(2,2′-bipyridine) complexes. Two emitting charge transfer excited states

Abstract: Excited state properties of the newly prepared complexes R–CO2–Re(CO)3(2,2′-bipy), where R–CO2− = naphthalene-2-carboxylate, anthracene-9-carboxylate, pyrene-1-carboxylate and acetate, were investigated by steady state and time resolved spectroscopy The X-ray structure revealed that the R containing ligand is coordinated through the carboxylate group to Re(I) Results showed that two emitting excited states play a major role in the photophysics of the complexes The fast component of the complexes luminescence was associated with the charge transfer excited state, MLCT, Re-to-2,2′-bipyridine, while experimental evidence led to the long lived component being attributed to a ligand-to-ligand charge transfer excited state This emissive LLCT excited state can also evolve to a photodissociative state which ultimately produces the complex decarboxylation On the other hand, the carboxylate bridge was shown to be able to impede connection between R and the Re(CO)3(2,2′-bipy) chromophore

Structural and Single Crystal EPR Studies of the Complex Copper L‐Glutamine: A Weakly Exchange‐Coupled System with syn‐anti Carboxylate Bridges

Abstract: We report the molecular structure and a single crystal EPR study at 9.8 and 33.9 GHz of a new copper(II) compound with the amino acid L-Glutamine, Cu[NH2CO2CH(CH2)2CONH2]2. The CuII ion is in an elongated octahedral environment equatorially trans-coordinated by two glutamine molecules acting as bidentate ligands through the nitrogen atom and one oxygen atom of each amino acid group, and axially by two carboxylate oxygen atoms of two neighboring glutamine molecules. Copper ions are arranged in layers connected by syn-anti carboxylate bridges that provide equatorial and apical ligands to the copper ions. Neighboring layers are connected by long chemical paths, which include two amino acid side chains connected by H bonds. Single crystal EPR spectra show a single exchange-collapsed resonance at both microwave frequencies for any magnetic field orientation. The evaluation of the molecular g-tensor from the angular variation of the EPR line position yielded g⊥ = 2.051 and g|| = 2.248, which indicates a d ground orbital for the Cu ions. The angular variation of the EPR line width displays a contribution that is typical of a 2-D magnetic system, and another contribution depending on the microwave frequency, which is attributed to the incomplete collapse of the resonances corresponding to magnetically nonequivalent copper ions. A quantitative analysis of the line width data allowed us to estimate a mean exchange coupling constant |J/k| = 0.42(2) K, which is assigned to the syn-anti carboxylate chemical path that connects neighboring copper ions within a layer. The results are discussed and compared with those observed in similar systems. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Two thiourea-containing gold(I) complexes.

Abstract: The crystal structures of two salts of bis­(thio­urea)­gold(I) complexes, namely bis­(thio­urea-κS)­gold(I) chloride, [Au(CH4N2S)2]Cl, (I), and bis­[bis­(thio­urea-κS)­gold(I)] sulfate, [Au(CH4N2S)2]2SO4, (II), have been determined. The chloride salt, (I), is isomorphous with the corresponding bromide salt, although there are differences in the bonding. The AuI ion is located on an inversion centre and coordinated by two symmetry-related thio­urea ligands through the lone pairs on their S atoms [Au—S 2.278 (2) A and Au—S—C 105.3 (2)°]. The sulfate salt, (II), crystallizes with four independent [Au(CH4N2S)2]+ cations per asymmetric unit, all with nearly linear S—Au—S bonding. The cations in (II) have similar conformations to that found for (I). The Au—S distances range from 2.276 (3) to 2.287 (3) A and the Au—S—C angles from 173.5 (1) to 177.7 (1)°. These data are relevant in interpreting different electrochemical processes where gold–thio­urea species are formed.

New lower rim calix(4)arene derivatives with mixed pendent arms and their complexation properties for alkali-metal cations. Structural, electrochemical, and thermodynamic characterization

Abstract: The synthesis and characterization (1H NMR) of two new lower rim calix(4)arene derivatives containing mixed pendent arms, namely, 5,11,17,23-tetrakis(1,1-dimethylethyl)-25,27-bis[2-(methylthio)etho...

On a Novel Synthesis of 2-Sulfonatobenzoic Acid by Oxidation of Thiosalicylic Acid Catalyzed by Copper(II): a Structural Study

Abstract: The oxidation of thiosalicylic acid in methanol into 2-sulfonatobenzoic acid was successfully achieved by the reaction with pyridine-N-oxide in aerobic media containing a copper(II) catalysts. The 100 K structure of the tetraphenylphosphonium 2-sulfonatobenzoic acid [P(C6H5)4]C6H4SO3COOH (I) has been determined by X ray diffraction methods. The anion shows a novel conformation with a strong intramolecular COOH · · · OSO2 bond. The oxidation reaction also produces [P(C6H5)4]2[Cu2Cl6] (II), as assessed by single crystal X-ray measurements. When water is added to the reaction medium, the compound I is reformed. Nevertheless, instead of compound II, chloro tetrapyridine-N-oxide copper(II) chloride monohydrate [Cu(C5H5NO)4Cl]Cl · H2O (III) is obtained. The crystal structure of this new copper complex has been determined and is also reported here. The copper ion is in a CuO4Cl pyramidal coordination with the oxygen atoms of four C5H5NO ligands at the square basis (average Cu—O distance of 1.98(1) A) and a chlorine ion (d(Cu—Cl) = 2.4585(4) A) at the pyramid apex. Vibrational studies of the three compounds have been performed. Compound III has also been characterized by diffuse reflectance and UV-vis spectroscopy and by its thermal and magnetic behavior. Eine neuartige Synthese der 2-Sulfobenzoesaure durch Oxydation von Thiosalizylsaure in Gegenwart eines Kupfer(II)-Katalysators — Untersuchungen zur Struktur erhaltener Verbindungen Die Oxidation von Thiosalizylsaure in Methanol zu 2-Sulfobenzoesaure gelang durch die Reaktion mit Pyridin-N-oxid unter aeroben Bedingungen in Gegenwart eines Kupfer(II)-Katalysators. Die Struktur von Tetraphenylphosphonium-2carb oxy-benzosulfonat [P(C6H5)4]C6H4SO3COOH (I) bei 100 K wurde durch Rontgenbeugung bestimmt. Das Anion hat eine neuartige Konformation mit einer starken intramolekularen COOH · · · OSO2-Bindung. Wie durch Einkristall-Rontgenuntersuchungen festgestellt wurde, liefert die Oxidation auch [P(C6H5)4]2[Cu2Cl6] (II). Unter Zusatz von Wasser zum Reaktionsmedium wird I zuruckgebildet. Daneben entsteht an Stelle von Verbindung II das Monohydrat des Tetrakispyridin-N-oxid-chloro-Kupfer(II)-chlorids [Cu(C5H5NO)4Cl]Cl · H2O (III). Die Kristallstruktur dieses neuen Kupferkomplexes wurde bestimmt, und uber sie wird hier ebenfalls berichtet. Das Kupferion befindet sich in einer pyramidalen CuO4Cl-Umgebung in der die Sauerstoffatome der vier C5H5NO-Liganden die quadratische Basis bilden (mittlerer Cu—O Abstand 1.98(1)A), und ein Chloridion (Cu—Cl = 2.4585(4)A) befindet sich an der Spitze der Pyramide. Die drei Verbindungen wurden schwingungsspektroskopisch untersucht. Verbindung III wurde auch UV-VIS-spektroskopisch mittels diffuser Reflexionsspektroskopie sowie durch sein thermisches und magnetisches Verhalten charakterisiert.

Crystal Structure and Vibrational Behaviour of Tetraaqua-di(nicotinamide)M(II)-Saccharinates, with M(II) = Co, Ni, Zn

Abstract: The crystal structures of [M(nic) 2 (H 2 O) 4 ](sac) 2 (nic = nocotinamide; sac = saccharinate anion) with M = Co(II), Ni(II) and Zn(II), have been determined at 116 K by single-crystal X-ray diffractometry. The compounds crystallize in the triclinic space group P1 with Z = 1, and the M(II) cations present a slightly distorted MN 2 O 4 octahedral environment, with equatorially coordinated water molecules and axially pyridine N-bound nicotinamide ligands. The saccharinate anions act as counteranions, and are not part of the first coordination sphere. Some comparisons with related structures have been made and the most important features of their IR spectra discussed.

Crystal Structure and Vibrational Behaviour of Aqua Di(saccharinato)di(nicotinamide)copper(II)

Abstract: The crystal structure of [Cu(sac) 2 (nic) 2 (H 2 O)] (sac = saccharinate anion; nic = nicotinamide) has been determined by single-crystal X-ray diffraction. It crystallizes in the monoclinic space group C2/c with Z = 4 and the Cu(II) ion presents a CuN 4 O square pyramidal coordination. Some comparisons with related structures are made and the most important features of its IR spectrum were also discussed.

Characterization of a Novel CuII/4, 4'-Bipyridine Coordination Polymer Containing Square Grids

Abstract: In an attempt to obtain new square grid polymers we could prepare the copper(II) complex [Cu(4, 4'-bipy)2 (H2O)2](sac)2 · DMF (4, 4'-bipy = 4, 4'-bipyridine; sac = anion of saccharin; DMF = dimethylformamide) Its structure was determined by single crystal X-ray diffraction methods It crystallizes in the orthorhombic space group Pcnb (a = 144994(2), b = 158128(3), c = 166850(2) A, Z = 4) and is a square grid polymer with the saccharinate anions sandwiched between the complex layers and the DMF molecules filling the square holes UV-vis, diffuse reflectance and IR spectra, room temperature magnetic susceptibility and the thermal behaviour were also investigated Charakterisierung eines neuartigen, viereckige Gitter enthaltenden CuII/4, 4'-Bipyridin Koordinationspolymer Bei Versuchen neue viereckige Gitter-Polymere zu erhalten, gelang es den Kupfer(II)-Komplex [Cu(4, 4'-bipy)2(H2O)2] (sac)2 · DMF (4, 4'-bipy = 4, 4'-Bipyridin; sac = Anion des Saccharins; DMF = Dimethylformamid) darzustellen Seine Struktur wurde rontgenographisch an Einkristallen bestimmt Er kristallisiert in der orthorhombischen Raumgruppe Pcnb (a = 144994(2), b = 158128(3), c = 166850(2) A, Z = 4) und bildet ein viereckiges Polymer-Gitter mit den Saccharinat-Anionen zwischen den Komplex-Schichten und mit den DMF-Molekulen in viereckigen Lucken UV-vis-, Reflexions- und IR-Spektren, sowie die magnetische Suszeptibilitat (bei Raumtemperatur) und das thermische Verhalten, wurden auch untersucht

A liquid crystal derived from ruthenium(II,III) and a long-chain carboxylate.

Abstract: The title compound, catena-poly[[tetrakis(μ-decanoato-κ2O:O′)diruthenium(II,III)(Ru—Ru)]-μ-octanesulfonato-κ2O:O′], [Ru2(C10H19O2)4(C8H17O3S)], is an octane­sulfonate derivative of the mixed-valence complex diruthenium tetradecanoate. The equatorial carboxyl­ate ligands are bidentate, bridging two Ru atoms to form a dinuclear structure. Each of the two independent dinuclear metal complexes in the asymmetric unit is located at an inversion centre. The octane­sulfonate anion bridges the two dinuclear units through axial coordination. The alkyl chains of the carboxyl­ate and sulfonate ligands are arranged in a parallel manner. The global structure can be seen as infinite chains of polar moieties separated by a double layer of non-polar alkyl groups, without interdigitation of the alkyl chains.

Novel Synthesis of 3,4,4-Trisubstituted Thiadiazolines from 3,4-Diphenyl-1,2,5-Thiadiazole 1,1-Dioxide. Competition with the Intra-Molecular Aryl-Aryl Cyclization of 3,4-Diphenyl-1,2,5-Thiadiazole 1,1-Dioxide

Abstract: 3,4-Diphenyl-1,2,5-thiadiazole 1,1-dioxide (1) reacted. in the presence ol anhydrous aluminum trichloride, with aromatic nucleophiles possessing electron donor substituent groups to give novel (2a-e, Figure 1) 3,4,4-trisubstituted 1,2,5-thiadiazoline 1,1-dioxides in good yield. In the presence of aluminum trichloride, but without the addition of nucleophiles, a slower, but practically quantitative intramolecular cyclization reaction (Scholl reaction 1 ) of 1 to phenanthro[9,10-c]-1,2,5-thiadiazole 1,1-dioxide (3), took place. Both reactions occur through the intermediation of a strong electrophile formed by 1 and aluminum trichloride. Spectral data and structure (through single-crystal X-ray diffraction, with the exception ol 2c) were measured for all new compounds.

Low temperature crystal structure of natural diosgenone.

Abstract: 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 P2(1), with a = 15.1870(4) A, b = 7.2710(2) A, c = 21.2840(6) A, beta = 99.251(1) degrees, and four molecules in the unit cell (Z = 4). The results constitute the first structural report on a steroidal sapogenin from the diosgenin group.

A complex containing three different kinds of Ru—N bonds: ethoxydinitronitrosyl(N,N,N′,N′-tetramethylethylenediamine-κ2N,N′)ruthenium(II)

Abstract: The octahedral title compound, [Ru(C2H5O)(NO)(NO2)2(C6H16N2)], crystallizes in the rhombohedral space group P31 with an ethoxy ligand axially coordinated trans to the nitro­syl ligand. The RuII ion is equatorially coordinated by a tetramethylethylenediamine group acting as a bidentate ligand, and to two nitro moieties whose planes are tilted with respect to the mean equatorial plane. Each nitro­gen ligand bonded to the metallic centre has a different hybridization state.

A pyrazine bis-adduct of a binuclear rhodium(II) carboxylate containing 3,4,5-triethoxybenzoate as the equatorial ligand.

Abstract: The title compound, tetrakis(μ-3,4,5-triethoxy­benzoato-κ2O:O′)­bis­[(pyrazine-κN)­rhodium(II)](Rh—Rh), [Rh2(C13H17O5)4(C4H4N2)2], crystallizes on an inversion centre in the triclinic space group P \overline 1. The equatorial carboxyl­ate ligands bridge the two RhII atoms, giving a binuclear lantern-like structure. The pyrazine mol­ecules occupy the two axial coordination sites. The phenyl rings are tilted by ca 10° with respect to the attached carboxyl­ate groups. The pyrazine planes have a torsion angle of ca 19° around the Rh—N bond with respect to the plane of the nearer carboxyl­ate group and are not coplanar with the Rh—Rh bond.