Silvina Pagola

• PhD, Chemistry
• Professor (Assistant) at Old Dominion University

The direct-space methods software Powder Structure Solution Program (PSSP) [Pagola & Stephens (2010). J. Appl. Cryst.43, 370–376] has been migrated to the Windows OS and the code has been optimized for fast runs. WinPSSP is a user-friendly graphical user interface that allows the input of preliminary crystal structure information, integrated intens...

Tetrathiafulvalene-chloranil (TTF-CA) was synthesized by two methods, liquid assisted grinding (LAG) and vapor digestion (VD), which largely reduce the use of reaction solvents. The effects of the small quantities of LAG solvent and solvent vapors in VD toward the formation of a particular TTF-CA product polymorph were studied from both tetrathiafu...

This work describes the computer program PSSP (powder structure solution program) for the crystal structure solution of molecular solids from X-ray powder diffraction data. This direct-space structure solution program uses the simulated annealing global optimization algorithm to minimize the difference between integrated intensities calculated from...

Despite the worldwide public health impact of malaria, neither the mechanism by which the Plasmodium parasite detoxifies and sequesters haem, nor the action of current antimalarial drugs is well understood. The haem groups released from the digestion of the haemoglobin of infected red blood cells are aggregated into an insoluble material called hae...

Quininium aspirinate is mechanochemically prepared as a crystalline solid by liquid-assisted grinding, or as an amorphous phase (as determined by X-ray powder diffraction), by neat grinding or neat ball milling. Our previous work demonstrated using FT-IR spectroscopy that a mechanochemical reaction had occurred in the mechanically treated neat mixt...

This study successfully implemented microcrystal electron diffraction (microED) and X-ray powder diffraction (XRPD) for the crystal structure determination of a new phase, TAF-CNU-1, Ni(C 8 H 4 O 4 )·3H 2 O, solved by microED from single microcrystals in the powder and refined at the kinematic and dynamic electron diffraction theory levels. This ni...

Although known since antiquity, mechanochemistry has remained dormant for centuries. Nowadays, mechanochemistry is a flourishing research field at the simultaneous stages of gathering data and (often astonishing) observations, and scientific argumentation toward their analysis, for which the combination of interdisciplinary expertise is necessary....

Quinine (an anti­malarial) and aspirin (a nonsteroidal anti-inflammatory drug) were combined into a new drug–drug salt, quininium aspirinate, C20H25N2O2⁺·C9H7O4⁻, by liquid-assisted grinding using stoichiometric amounts of the reactants in a 1:1 molar ratio, and water, EtOH, toluene, or heptane as additives. A tetra­hydro­furan (THF) solution of th...

A poster shared at the Undergraduate Research Conference of the Virginia Academy of Science on 11/07/20

Ice-templating technique enables the synthesis of novel ceramic materials with directional, anisotropic pores, and the templated structure is highly tunable. Another factor that also drives interest in ice-templated ceramics is that for a comparable level of porosity, the uniaxial compressive strength of these materials can be significantly greater...

This report describes aspects of our previous studies of the mechanochemical synthesis of charge transfer complexes of the electron donor tetrathiafulvalene, which are relevant to the use of laboratory X-ray powder diffraction for ex situ monitoring of mechanochemical reactions toward investigating their mechanisms. In particular, the reaction of t...

The crystal and molecular structure of fenspiride, a bronchodilator and anti-inflammatory drug, are reported. Fenspiride crystallizes in the monoclinic system, with two crystallographically independent molecules in the general position of the space group P 2 1 / n (No. 14) and Z = 8. Rietveld refined unit cell parameters are a = 11.52013(8) Å, b =...

Two polymorphs of tetrathiafulvalene chloranilic acid (TTF-CAH2) have been synthesized by mechanochemistry. The previously known “ionic” polymorph (form I), was prepared by liquid assisted grinding (LAG) using various highly polar solvents; as well as protic, but moderately polar solvents, such as alcohols of one to four carbon atoms. A new TTF-CAH...

The crystal structure of divainillin (systematic name: 6,6′-dihy­droxy-5,5′-di­meth­oxy-[1,1′-biphen­yl]-3,3′-dicarbaldehyde), C16H14O6, was determined from laboratory powder X-ray diffraction data using the software EXPO2013 (direct methods) and WinPSSP (direct-space approach). Divanillin mol­ecules crystallize in the ortho­rhom­bic space group Pb...

The crystal structure of the purpureo salt, [Co(NH 3 ) 5 Cl]Cl 2 , first reported in 1963 and later revised in 1968 (in both cases from single-crystal diffraction) in the space group Pnma (No. 62), has been recently re-examined from synchrotron X-ray powder diffraction using direct methods and the software EXPO2013. The comparison of the Rietveld a...

This work reports the long sought crystal structures of the title members of the intriguing series of 3d transition metal dichloride monohydrates. The double chain structure which results from rearrangement of the well-known pseudo-octahedral coordination geometry and single chains in the corresponding metal chloride dihydrate is extremely unusual....

We report the conversion between three crystalline polymorphs of a capped amino acid, N-acetyl-l-phenylalanyl-NH2, using mechanochemistry, with conversion between the α and γ polymorphs being reversible, depending on the milling conditions used. Solvent drop grinding of the α and β polymorphs with water yields the γ polymorph, whereas dry grinding...

We report the crystal structure analysis of the glucocorticoid drug amcinonide from high-resolution X-ray powder diffraction data, with an uncommonly large number of atoms (142, including H) and Z′ = 2; which was carried out through the stepwise location of the rigid and flexible fragments of the asymmetric unit, using the knowledge of steroidal co...

Pb2[Fe(CN)6]�4H2O was synthesized by mixing aqueous solutions of lead(II) nitrate and potassium ferrocyanide. Its crystal structure was solved ab initio from synchrotron powder X-ray diffraction data using the direct methods and refined by the Rietveld method. Thermal analysis (TGA and DTA), Fourier Transform Infrared Spectroscopy (FTIR) and scanni...

Presented here are susceptibility data for fully deuterated forms of the title materials, and comparison with normal hydrogen forms. Also shown is the first structure determination for any monohydrate compound, for the Mn system with the simplest magnetic behavior to analyze. Interesting similarities and contrasts appear relative to normal hydrogen...

This work describes the computer program PSSP (powder structure solution program) for the crystal structure solution of molecular solids from X-ray powder diffraction data. This direct-space structure solution program uses the simulated annealing global optimization algorithm to minimize the difference between integrated intensities calculated from...

In 2-ethoxy­benzamide, C9H11NO2, the amide substituents are linked into centrosymmetric head-to-head hydrogen-bonded dimers. Additional hydrogen bonds between adjacent dimers give rise to ribbon-like packing motifs, which extend along the c axis and possess a third dimension caused by twisting of the 2-ethoxy­phenyl substituent with respect to the...

A matter of technique: For a new steroidal lactol, jaborosalactol 24 (1), isolated from Jaborosa parviflora, NMR spectroscopy residual dipolar couplings and powder X-ray diffraction analysis independently gave the same stereochemistry at C23-C26. Conventional NMR spectroscopic techniques, such as NOE and ³J coupling-constant analysis failed to unam...

The crystal structure of the title compound (systematic name: methyl 3,4,5-trihydroxy­benzoate), C8H8O5, is composed of essentially planar mol­ecules [maximum departures from the mean carbon and oxygen skeleton plane of 0.0348 (10) Å]. The H atoms of the three hydroxyl groups, which function as hydrogen-bond donors and acceptors simultaneously, are...

High resolution X-ray powder diffraction has been used to obtain the crystal structure of sideroxylin (4H-1-Benzopyran-4-one,5-hydroxy-2-(4- hydroxyphenyl)-7-methoxy-6,8-dimethyl) monohydrate, (C18H 16O5).H2O, isolated from the bioactive ethyl acetate extract of Miconia ioneura Griseb (Melastomataceae) leaves. The crystal structure was determined u...

In the title compound, [Cu(CN)(C4H5N3)]n or [Cu(μ-CN)(μ-PyzNH2)]n (PyzNH2 is 2-amino­pyrazine), the CuI center is tetra­hedrally coordinated by two cyanide and two PyzNH2 ligands. The CuI–cyano links give rise to [Cu–CN]∞ chains running along the c axis, which are bridged by bidentate PyzNH2 ligands. The three-dimensional framework can be described...

In the title compound, [Cu(CN)(C4H5N3)]n or [Cu(μ-CN)(μ-PyzNH2)]n (PyzNH2 is 2-aminopyrazine), the CuI center is tetrahedrally coordinated by two cyanide and two PyzNH2 ligands. The CuI–cyano links give rise to [Cu–CN]∞ chains running along the c axis, which are bridged by bidentate PyzNH2 ligands. The three-dimensional framework can be described a...

The crystal structure of Nd[Fe(CN)6]·4H2O has been refined by Rietveld analysis using high resolution synchrotron powder X-ray diffraction data. It belonged to the orthorhombic crystal system, Cmcm space group, with cell parameters: a=7.473952(1)Å, b=12.919104(2)Å and c=13.800549(2)Å. The change in space group from P63/m which is observed in the pe...

This study was designed to investigate the physical characteristics and crystalline structure of 2-hydroxy-N-[3(5)-pyrazolyl]-1,4-naphthoquinone-4-imine (PNQ), a new active compound against Trypanosoma cruzi, the causative agent of American trypanosomiasis. Methods used included differential scanning calorimetry, thermogravimetry, hot stage microsc...

The crystal structure of 2-isopropyl-5-methyl-1,4-benzoquinone (thymoquinone) and its thermal behavior--as necessary physical and chemical properties--were determined in order to enhance the current understanding of thymoquinone chemical action by using high resolution x-ray powder diffraction, Fourier transform infrared spectroscopy (FTIR), and 3...

Sr 2 CoWO 6 perovskite has been prepared in polycrystalline form by solid-state reaction at 1150 °C. This material has been studied by high-resolution synchrotron X-ray and neutron powder diffraction (NPD), magnetic measurements, and differential scanning calorimetry (DSC). At room temperature, the crystal structure is tetragonal, space group I4/m,...

Double-cell perovskites RBaFe 2O 5+ w ( R= Nd and Sm) are synthesized in the -0.03<w<0.47 portion of the nonstoichiometry range. The ideal composition with w=0 has di- and tri-valent iron in equal proportions and exhibits a charge-ordering Verwey transition upon cooling, preceded by a weaker premonitory transition. Both transitions are detectable b...

BaFeO2.8−δ with a crystal structure different from any of those previously reported in the system BaFeOy (2.5≤y≤3.0) was prepared by a low-temperature method of synthesis, based on the oxidative thermal decomposition of BaFe[(CN)5NO]·3H2O. The structure was solved ab initio by high-resolution synchrotron X-ray powder diffraction and refined by Riet...

The low-temperature properties of HoNi2B2C strongly depend on its thermodynamic state established via thermal treatment. We present high resolution x-ray powder diffraction data taken on a pair of polycrystalline samples with identical chemical composition (HoNi2B2.1C) but annealed at different temperatures, namely, at 800 and at 1100 °C. Their sup...

A unique polyurethane (PU) elastomer containing inorganic polyhedral oligomeric silsesquioxane (POSS) molecules as molecular reinforcements in the hard segment was investigated by means of wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) techniques. The mechanical properties of POSS...

BaFeO2.8-delta with a crystal structure different from any of those previously reported in the system BaFeOy (2.5

The solutions of the molecular crystal structures: (I) 2-amino-4, 5-dimetoxyacetophenone (C10H13NO3); (II) 1, 4-benzenedimethanol (C8H10O2); and (III) 3-aminoquinoline (C6H8N2), were obtained using the simulated annealing technique on synchrotron X-ray powder diffraction patterns. In this procedure we use the knowledge of the molecular geometry whi...

The compounds tetrakis(trimethylsilyl)methane C[Si(CH(3))(3)](4) (TC) and tetrakis(trimethylsilyl)silane Si[Si(CH(3))(3)](4) (TSi) have crystal structures with the molecules in a cubic closed-packed (c.c.p.) stacking. At room temperature both structures have space group Fm{\bar 3}m (Z = 4) with a = 13.5218 (1) Å, V = 2472.3 (1) Å(3) for TSi, and a...

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and...

The compounds tetrakis(trimethylsilyl)methane C[Si(CH3)3]4 (TC) and tetrakis(trimethylsilyl)silane Si[Si(CH3)3]4 (TSi) have crystal structures with the molecules in a cubic closed-packed (c.c.p.) stacking. At room temperature both structures have space group (Z = 4) with a = 13.5218 (1) Å, V = 2472.3 (1) Å3 for TSi, and a = 12.8902 (2) Å, V = 2141....

The strain state of epitaxial Cu(50 Å)/Ni(tNi)/Cu(2000 Å)/Si(001) films as a function of the nickel film thickness (30Å<~tNi<~2000Å) has been studied using Bragg diffraction and grazing-incidence diffraction with a synchrotron x-ray source. For 30Å<~tNi<~150Å both the in-plane and out-of-plane nickel strains show a phenomenological (1/t)2/3 power d...

The reaction of [MII(OH2)6](NO3)2 (M = Co, Ni) and [N(CN)2]- leads to formation of isomorphous M[N(CN)2]2 [M = Co (2a), Ni (3)], respectively, while the reaction of [CoII(OH2)6](NO3)2 in 1% pyridine (py) solution with [N(CN)2]- leads to the formation of Co[N(CN)2]2py2. The structure of 2a, α-Co[N(CN)2]2, was determined from the Rietveld analyses of...

The crystal structure of the isomorphous phases Mg{sub 5}Nb{sub 4}O{sub 15} and Mg{sub 5}Ta{sub 4}O{sub 15} was refined from neutron powder diffraction data. These compounds are isostructural with pseudobrookite, Fe{sub 2}TiO{sub 5}. The two kinds of metal sites of this structure are randomly occupied by Mg(II) and Nb(V) or Ta(V). The structure con...

The crystal structure of the columbite-type phase MgNb2O6has been refined from powder neutron diffraction data. The compound is orthorhombic, space groupPbcn(60),Z=4, with unit cell parametersa=14.1875(1),b=5.7001(1),c=5.0331(1) Å. The structure contains chains of NbO6octahedra sharing edges along thecaxis, which are arranged in double layers throu...

Both X-ray and neutron diffraction data were analyzed by the Rietveld method, taking as starting structural model that of the Ba5Ta4O15 structure. The results of such an analysis show that the progressive elimination of oxygen ions produce only small changes in the structure. A decrease in the unit-cell parameters as the number of oxygen vacancies...

Quite often the literature cites superconductors with high critical temperature as having an anharmonic lattice close to a structural phase transition. It is then of interest to find materials, with distorted perovskite structure, that reveal bare phonon behavior expected for such an environment. Here we discuss layered Ba5Nb4O15 and Ba5Ta4O15-x (0...

We report low-temperature, far-infrared reflectivity, and Raman-scattering measurements for layered Ba5Nb4O15. We find that this material is characterized by a strong anharmonic lattice where the symmetric stretching vibration of the empty octahedra, a singular feature of this layer compound, splits into two narrow Raman-active bands. We assign the...

Both X-ray and neutron diffraction data were analyzed by the Rietveld method, taking as starting structural model that of the Ba5Ta4O15 structure, The results of such an analysis show that the progressive elimination of oxygen ions produce only small changes in the structure. A decrease in the unit-cell parameters as the number of oxygen vacancies...

Ba5Nb4O15-x oxides were studied by infrared, electrical resistivity and thermogravimmetric analysis (TGA). FIR reflectivity measurementsreveal a strong ionic compound that has well defined features in groups that we assign to oxygen stretching, bending and lattice phonons splitted by the lower symmetry of this layered compound. For the sample with...