Papers by Ana Maria Alte da Veiga
Acta Crystallographica Section C Crystal Structure Communications, 1999
A new orthorhombic phase of the title compound, CI3HI3N3, is reported. There are two symmetryinde... more A new orthorhombic phase of the title compound, CI3HI3N3, is reported. There are two symmetryindependent molecules in the unit cell, as in the monoclinic phase, both having a syn-anti conformation of the phenyl rings with respect to the unsubstituted N atom. This orthorhombic phase differs from the monoclinic one in the hydrogen-bonding scheme and molecular packing. Bond lengths and angles within the guanidine moiety are close to those expected for a central Csp 2 atom with one C=N and two C--N bonds. The anti ring binds to the guanidine moiety as Ca~yI--NH--C and the syn ring as Caryi--N==:C.
Zeitschrift für Kristallographie - New Crystal Structures, 1999
CioH 2 8F6N206Ta,monoclinic,P12/al (No. 13), a = 12.553(3) Ä, b = 6.531(3) Ä, c= 12.587(3) Ä, β =... more CioH 2 8F6N206Ta,monoclinic,P12/al (No. 13), a = 12.553(3) Ä, b = 6.531(3) Ä, c= 12.587(3) Ä, β = 110.25(1)°, V= 968.2 Ä 3 , Ζ = 2, R gt (F) = 0.030, wR(F 2 ) = 0.068, Τ = 293 Κ. The pure metal was dissolved in concentrated fluoridric acid (40%). Reagent grade betaine (Merck, 99.9% purity) was added to the solution and after a few days of slow evaporation small, transparent crystals were formed, from which a good quality specimen was choosen for X-ray analysis. The data-collection was performed with the crystal encapsulated in a sealed glass capilary. Betaine is unusualy high sensitive to radiation damage [1] and the intensity of three control reflections measured each 3 h showed a decay which continuously increased attaining a maximum rate of 3.6°h _1 by the end of the data collection. A polynomial interpolation was used to correct for this decay in the data reduction. The structure was solved by direct methods. The hydrogen atoms of the cation were placed at calculated positions and refined as riding using the SHELXL-97 [2] defaults: d(0-H) = 0.82 Ä, d(C-H) = 0.93 Ä. Those of the solvent water molecule could not be located in a difference synthesis and were placed at tentative positions according to the best geometry for hydrogen bonding and refined subject to the restraint rf(O-H) = 0.86(2) Ä. Examination of the crystal structure with
ChemInform Abstract: Cycloaddition of Trifluoromethyl Azafulvenium Methides: Synthesis of New Trifluoromethylpyrrole‐Annulated Derivatives
ChemInform, 2010
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was e... more ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
The Journal of Physical Chemistry A, 2007
This paper provides an overview of recent progress on structural data on the title compound. Theo... more This paper provides an overview of recent progress on structural data on the title compound. Theoretical work based on quantum mechanical calculations was performed to gain some understanding on the heterocyclic tautomerism potentially exhibited by the compound. The computational studies encompassed a wide range of tautomers/conformers, allowing the determination of the most probable molecular structure. In the gas phase, the nitroimine tautomers are computed to be substantially more stable than the nitramine tautomers. Among three plausible nitroimine forms, special attention was given to 4,6-bis(nitroimino)-1,3,5-triazinan-2-one, whose crystal structure was unequivocally solved by X-ray diffraction. The crystals are orthorhombic, space group Pnma with a ) 6.187(2)Å, b ) 13.252(5)Å, c ) 8.802(4)Å, and Z ) 4. The structure was solved by direct methods and refined to a final R ) 0.0326. The molecule has an approximate mirror plane relating the two symmetry related halves. The nitroimine groups are positioned in a syn-syn conformation. The least-squares (LS) plane of the heterocyclic ring and the nitroimine (dN-NO 2 ) substituent LS plane make an angle of 10.05(11)°. The crystal structure is held together via hydrogen bonds that assemble the molecules in chains running along the b-axis. Every H-atom is involved in bifurcated hydrogen bonds.
Tetrahedron Letters, 2003
isoindoles were prepared from the thermolysis of (3R,9bS)-5-oxo-2,3,5,9b-tetrahydrothiazolo[2,3-a... more isoindoles were prepared from the thermolysis of (3R,9bS)-5-oxo-2,3,5,9b-tetrahydrothiazolo[2,3-a]isoindole-3-carboxylic acids in acetic anhydride. The structure of 3-methylene-2,5-dioxo-3H,9bH-oxazolo[2,3-a]isoindole 6a was determined by X-ray crystallography.
Synthesis, 2009
Microwave-assisted 1,3-dipolar cycloaddition of the azomethine ylide generated by ring opening of... more Microwave-assisted 1,3-dipolar cycloaddition of the azomethine ylide generated by ring opening of a N-vinylaziridine gave new N-vinyl derivatives of pyrrolidine, 3-pyrroline, octahydropyrrolo [3,4-c]pyrrole and 1,2,4-triazolidine.
Zeitschrift für Kristallographie - New Crystal Structures, 1998
Zeitschrift für Kristallographie - New Crystal Structures, 2001
, a = 8.314(8) Ä, b = 5.777(1) k,c= 18.680(6) Ä, β = 95.83(5)°, V= 892.5 A 3 , Z= 4, R & (F) = 0.... more , a = 8.314(8) Ä, b = 5.777(1) k,c= 18.680(6) Ä, β = 95.83(5)°, V= 892.5 A 3 , Z= 4, R & (F) = 0.059, wRreftF 2 ) = 0.162, T= 293 K. An alcoholic solution of 10 mmol of manganese chloride tetrahydrate was added to a water solution of 10 mmol of sarcosine and left at room temperature. After several months small transparent crystals were grown from the solution, many were tested using Laue methods, but only crystals of poor quality were found.
Zeitschrift für Kristallographie - New Crystal Structures, 2001
C26H28F5N6V, monoclinic, C12/cl (No. 15), a = 21.036(4) A, b = 10.704(1) A, c = 12.481(2) Ä, β = ... more C26H28F5N6V, monoclinic, C12/cl (No. 15), a = 21.036(4) A, b = 10.704(1) A, c = 12.481(2) Ä, β = 103.86(2)°, V= 2728.7 Ä 3 , Z = 4, R gt (F) = 0.073, wR^F 2 ) = 0.217, Γ=293 K. The pure metal was dissolved in concentrated fluoric acid (40%). Diphenylguanidine (Aldrich, 98% purity) dissolved in ethanol was added to the solution and slow evaporation of the solvent at room temperature was allowed for several weeks. The remaining solid was then dissolved in ethanol and after a few weeks small, green crystals were formed, from which a good quality specimen was choosen for X-ray analysis.
Journal of Sol-Gel Science and Technology, 2011
Silica based materials were synthesized using ethyltrimethoxysilane (ETMS) and/or methyltrimethox... more Silica based materials were synthesized using ethyltrimethoxysilane (ETMS) and/or methyltrimethoxysilane (MTMS) precursors by sol-gel technology, in order to ascertain if their properties are suitable for aerospace applications. When ETMS was used alone and in equimolar ETMS/MTMS mixtures, no gel formation took place and a resin-like precipitate was observed. After drying, a compact tablet was formed. When mixtures of 25% ETMS/ 75% MTMS and MTMS alone were used, gel formation occurred and xerogels were produced upon drying. Chemical and structural characterization of the obtained materials was performed using Elemental Analysis, FTIR, XRD and SEM. Bulk density, specific surface area, contact angle and the thermal behavior were also evaluated. For materials from ETMS, the chemical structure grows preferentially in one direction and, in the case of MTMS the growth follows a 3D pattern. The use of ETMS precursor leads to a significant increase in the product density, accompanied by a decrease in the specific surface area. It also leads to a decrease in the thermal stability limit of the synthesized materials. Then, ETMS precursor is less appropriate than MTMS precursor for space applications. However, ETMS co-precursor in mixtures with MTMS contributes to the increase in the hydrophobic character of the synthesized materials.
Journal of Physics and Chemistry of Solids, 2011
Iron(III) oxyhydroxide xerogels were prepared through sol-gel technology, using iron(III) nitrate... more Iron(III) oxyhydroxide xerogels were prepared through sol-gel technology, using iron(III) nitrate nonahydrate as precursor, ethanol as solvent and ammonium hydroxide as gelation agent. This base is used for propylene oxide substitution, which was the gelation agent in previous works. The synthesis of a gel using the NH 4 OH gelation agent is an innovative result with this type of precursor, since with metal salts the addition of a strong base commonly results in precipitation of the solid. The gel synthesis was achieved by controlling the base addition time. The dried material has a residual amount of organic impurities, in contrast with the significant amount detected in xerogels prepared using propylene oxide. The iron phase prevailing in the produced xerogels can be defined as γ-FeO(OH) (Lepidocrocite), according to FTIR and Mössbauer analyses. The xerogels are formed by large clusters of well connected nanocrystallites of this phase. XRD revealed a crystalline phase retained inside the iron oxyhydroxide amorphous structure, which corresponds to NH 4 NO 3 and results from the combination of NO 3 -and NH 4 + ions in solution. The produced xerogel has a promising composition to be an oxidizing composite for the energetic materials area.
Journal of Molecular Structure, 2003
3-Amino-1-propanol (3AP) was investigated by differential scanning calorimetry, and low temperatu... more 3-Amino-1-propanol (3AP) was investigated by differential scanning calorimetry, and low temperature powder X-ray diffraction and Raman spectroscopy. Within the range of temperatures studied (2 150-25 8C), 3AP was found to be able to crystallize in two monotropic polymorphs. Fast cooling rates produce an amorphous state that, on heating, crystallizes into the metastable polymorph. At higher temperatures, this metastable crystalline phase converts into the stable crystal. Using intermediate cooling rates, 3AP crystallizes as the metastable polymorph, the solid l solid transition leading to conversion of this form into the stable polymorph occurring during the subsequent heating. Slower cooling rates enable formation of the stable crystal on cooling. The two crystalline polymorphs were structurally characterized by powder X-ray diffraction and Raman spectroscopy. It was concluded that different conformations are assumed by the individual molecules of 3AP in the two crystalline varieties, with the molecules assuming the all-trans configuration in the metastable crystalline state and having the heavy atom backbone trans but the NH 2 and OH groups gauche in the stable crystal.
Journal of Molecular Catalysis A: Chemical, 2003
A series of easily obtained pyrrolidine-based -amino alcohols derived from tartaric acid and pri... more A series of easily obtained pyrrolidine-based -amino alcohols derived from tartaric acid and primary amines was synthesized and used as chiral ligands in the enantioselective alkylation of benzaldehyde. Using diethylzinc, 1-phenyl-1-propanol was obtained with enantiomeric excesses of up to 80% when (3S,4S)-N-(1-naphthylmethyl)-3,4-dihydroxypyrrolidine was used. The nature of the N-substituent on the ligand, as well as the reaction temperature proved to significantly influence reaction product distribution as well as the enantiomeric excess of the chiral alcohol.
The Journal of Chemical Physics, 2011
Poly(ester amide)s (PEAs) are lacking in structural and spectroscopic information. This paper rep... more Poly(ester amide)s (PEAs) are lacking in structural and spectroscopic information. This paper reports a structural and spectroscopic characterization of Nα-benzoyl-L-argininate ethyl ester chloride (BAEEH+·Cl−), an important amino acid derivative and an adequate PEAs’ model compound. Crystals of BAEEH+·Cl− obtained by slow evaporation in an ethanol/water mixture were studied by different complementary techniques. X-ray analysis shows that BAEEH+·Cl− crystallizes in the chiral space group P21. There are two symmetry independent cations (and anions) in the unit cell. The two cations have different conformations: in one of them, the angle between the least-squares planes of the phenyl ring and the guanidyl group is 5.1(2)º, and in the other the corresponding angle is 13.3(2)º. There is an extensive network of H-bonds that assembles the ions in layers parallel to the ab plane. Experimental FT-IR and Raman spectra of BAEEH+·Cl− were recorded at room temperature in the 3750–600 cm−1 and 3...
Journal of Chemical Crystallography, 2007
2-Methoxy-5-phenylaniline, a promissor monomer for PANI studies, has been characterized by single... more 2-Methoxy-5-phenylaniline, a promissor monomer for PANI studies, has been characterized by single-crystal X-ray diffraction at two temperatures: orthorhombic, space group P2 1 2 1 2 1 , Z = 12 with a = 5.9900(2) A ˚, b = 20.4873(6) A ˚, c = 26.3727(8) A ånd R = 0.0868 for 293(2) K and a = 5.8337(9) A ˚, b = 20.4428(31) A ˚, c = 26.0773(40) A ˚and R = 0.0669 for 120(2) K. There are three independent molecules in the unit cell. One of them is approximately planar, the other two have the phenyl rings rotated. At room temperature the two latter molecules are joined in dimers through H-bonds and at low temperature the same molecules are joined in columns that run along the a-axis.
Journal of Chemical Crystallography, 2007
Crystal structure of diphenylacetic acid has been solved by X-ray diffraction. The crystals are m... more Crystal structure of diphenylacetic acid has been solved by X-ray diffraction. The crystals are monoclinic, space group P2 1 /c, with a = 12.254(4) A ˚, b = 7.2260(8) A ˚, c = 17.521(4) A ˚, b = 133.38(1)°, Mr = 212.24, V = 1127.6(5) A ˚3, Z = 4 and R = 0.045. A strong hydrogen bond links the molecules in dimers. The dimers are connected by weaker C-HÁÁÁp and pÁÁÁp interactions. A calculation was performed for the isolated molecule and for the dimer within the Hartree-Fock (HF) level with a 6-311G(d) basis set. In both calculations, the minimum of the energy is achieved with the phenyl rings assuming a more symmetric arrangement around the central carboxylic plane than is experimentally observed.
Zeitschrift für Kristallographie - New Crystal Structures, 2005
A few drops of phosphorous acid were added to a aqueous solution of L-tryptophan. Within few mont... more A few drops of phosphorous acid were added to a aqueous solution of L-tryptophan. Within few months transparent single crystals of prismatic shape grew from the solution. The single crystal used for the X-ray study was checked prior to data collection by Laue photographs. All Η atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms using SHELXL-97 defaults . Examination of the crystal structure with PLATON [2] showed that there are no solvent-accessible voids in the crystal lattice. Due to the lack of significant anomalous dispersion at the Mo£a wavelength, the well-known absolute configuration of the L-tryptophanium cations was chosen to fix the enantiomer. The Flack parameter was found to be 0.5(2).
Acta Crystallographica Section A Foundations of Crystallography, 2007
Cell parameters using Nonius Kappa CCD at 173 K (Å and °) are: (I) 14.071(2), 14.071(2), 39.993(4... more Cell parameters using Nonius Kappa CCD at 173 K (Å and °) are: (I) 14.071(2), 14.071(2), 39.993(4), 90.0, 90.0 and 90.0; (II) 21.114(4), 4.972(1), 25.710(4), 90.0, 94.27(3) and 90.0; (III) 10.708(3), 19.143(3), 29.027(4), 90.0, 94.70(3) and 90.0; (IV) 10.937(2), 27.320(5), 15.120(3), 90.0, 105.23(3) and 90.0. Slightly distorted coordination spheres are tetrahedral in four-coordinated compounds (I) and (II) and octahedral in six-coordinated compounds (III) and (IV). Bond distances (Å) within the coordination spheres for Co-O vary from 1.927(3) to 1.947(3) in (I), from 1.889(3) to 1.906(3) in (II), 1.897(2) in (III) and from 1.878(2) to 1.901(2) in (IV) and for Co-N from 1.940(4) to 2.019(4) in (I), from 1.982(4) to 1.984( ) in (II), from 1.962(2) to 1.994(2) in (III) and from 1.947(2) to 1.963(2) in (IV). The values are comparable to those found in some similar compounds [1][2][3]. Salicylaldimines can be prepared from salicylaldehyde and respective aliphatic or aromatic amines heating overnight. Crystal structure and magnetic properties of mononuclear Co(II) and Ni(II) complexes B.
Zeitschrift für Kristallographie - New Crystal Structures, 1999
C20H26N4O4, orthorhombic, P2\2\2\ (No. 19), a = 9.266(3) Â, b = 14.659(5) k,c = 30.70(2) Â, V= 41... more C20H26N4O4, orthorhombic, P2\2\2\ (No. 19), a = 9.266(3) Â, b = 14.659(5) k,c = 30.70(2) Â, V= 4170.4 À 3 , Z= 8, R&(F) = 0.067, Rv,(F 2 ) = 0.179, Τ = 293 Κ. The title compound was prepared by reacting equimolar amounts of L-arginine (Aldrich, 98%) and diphenylacetic acid (Aldrich, 99%) in aqueous solution. Crystals were grown from an ethanol/water (1:1) solution by slow evaporation over a period of a few weeks.
Acta Crystallographica Section C: Crystal Structure Communications, 2006
ÁC 2 Cl 3 O 2 À , crystallizes in the P4 1 space group with two glycinium cations and two trichlo... more ÁC 2 Cl 3 O 2 À , crystallizes in the P4 1 space group with two glycinium cations and two trichloroacetate anions in the asymmetric unit. The glycinium cations have nearly C s point-group symmetry which is only broken by the H atoms of the amine group. The trichloroacetate anions show typical bond lengths and angles, one of the trichloromethyl groups being disordered. Chains of alternating anions and cations run along the c axis. Within these chains, consecutive anion±cation pairs are bound via strong hydrogen bonds involving the carboxylate anions and the carboxyl or amine groups of the cations. Weaker hydrogen bonds bind neighbouring chains together.
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Papers by Ana Maria Alte da Veiga