pH-induced phase transition and crystallization of soft-oxometalates (SOMs) into polyoxometalates (POMs): a study on crystallization from colloids

2018 ◽  
Vol 74 (11) ◽  
pp. 1274-1283 ◽  
Author(s):  
Shounik Paul ◽  
S. S. Sreejith ◽  
Soumyajit Roy
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Volume Fraction ◽  
Three Dimensional ◽  
Dispersion Phase ◽  
Colloidal Chemistry ◽  
Colloidal Form ◽  
1D Chain ◽  
Light Scattering Measurement

In this work, we demonstrate a simple approach for growing 1D (one-dimensional) inorganic chains of K(C6H16N)3Mo8O26·H2O polyoxometalates (POMs) from its colloidal soft-oxometalate (SOM) phase through the variation of pH. The structure is composed mainly of a 1D inorganic chain with a β-Mo8O26 4− binding node linked using K+ via Mo—O—K linkages, which results in a cuboctahedral geometry for the K+ ions. Crystal structure and Hirshfeld surface studies reveal the role of triethylammonium cations in restricting the growth of the 1D chain into 2D/3D (two-/three-dimensional) structures. During the nucleation process from the heterogeneous SOM phase, some of the intermolecular interactions in the dispersion phase are retained in the crystal structure, which was evidenced from residual O...O interactions. The crystallization of the species from its colloidal form as a function of pH was studied by the use of Raman spectroscopy and it was found that the increase in volume fraction of the β-Mo8O26 4− species in the crystallizing colloidal mixture with the decrease in pH is responsible for the nucleation. This was monitored by time-dependent DLS (dynamic light scattering) measurement and zeta-potential studies, revealing the co-existence of both the crystal and the colloidal forms at pH 3–2. This brings us to the conclusion that in the crystallization of POMs, the colloidal SOM phase precedes the crystalline POM phase which occurs via a phase transition. This work could open up avenues for the study of POM formation from the stand-point of colloidal chemistry and SOMs.

scholarly journals Hydrogen diffusion and the percolation of austenite in nanostructured bainitic steel

2014 ◽  
Vol 470 (2168) ◽  
pp. 20140108 ◽  
Author(s):  
L. C. D. Fielding ◽  
E. J. Song ◽  
D. K. Han ◽  
H. K. D. H. Bhadeshia ◽  
D.-W. Suh
Keyword(s):  
Hydrogen Diffusion ◽  
Volume Fraction ◽  
Three Dimensional ◽  
Bainitic Ferrite ◽  
Effective Diffusivity ◽  
Steel Sample ◽  
Thin Plates ◽  
Heat Treated ◽  
Diffusion Of Hydrogen

The diffusion of hydrogen in austenite is slower than in ferrite. Experiments have been conducted to study the behaviour of hydrogen in a nanostructured steel sample consisting of a mixture of thin plates of bainitic ferrite and intervening films of retained austenite, with the latter phase present in a quantity larger than the percolation threshold, i.e. it has three-dimensional connectivity. The structure was then heat treated to control the fraction of austenite, and hence to study the role of hydrogen when the austenite decomposes below the value required to sustain percolation. The experiments have involved both thermal desorption analysis and permeation, and when combined with theoretical analysis, indicate a significant influence of percolating austenite in hindering the passage of hydrogen into the steel during hydrogen charging, and its permeation through the composite nanostructure. The effect is not as large as might be expected from a simple comparison of independent data on the diffusivities of hydrogen in the two lattices, because the effective diffusivity in ferrite is found to be much smaller than in the defect-free ferrite, owing to trapping effects. The morphology of the austenite is demonstrated to play a role by comparing with a sample containing a larger volume fraction of austenite but present as isolated grains which are ineffective to the permeation of hydrogen.

scholarly journals (NH4)Mg(HSO4)(SO4)(H2O)2 and NaSc(CrO4)2(H2O)2, two crystal structures comprising kröhnkite-type chains, and the temperature-induced phase transition (NH4)Mg(HSO4)(SO4)(H2O)2\rightleftharpoons (NH4)MgH(SO4)2(H2O)2

2021 ◽  
Vol 77 (3) ◽  
pp. 144-151
Author(s):  
Matthias Weil ◽  
Uwe Kolitsch
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Hydrogen Bonds ◽  
Crystal Structures ◽  
Room Temperature ◽  
Classification Scheme ◽  
Three Dimensional ◽  
Structure Type ◽  
Group Symmetry ◽  
Water Molecules

The crystal structure of the mineral kröhnkite, Na2Cu(SO4)2(H2O)2, contains infinite chains composed of [CuO4(OH2)2] octahedra corner-linked with SO4 tetrahedra. Such or similar tetrahedral–octahedral `kröhnkite-type' chains are present in the crystal structures of numerous compounds with the composition AnM(XO4)2(H2O)2. The title compounds, (NH4)Mg(HSO4)(SO4)(H2O)2, ammonium magnesium hydrogen sulfate sulfate dihydrate, and NaSc(CrO4)2(H2O)2, sodium scandium bis(chromate) dihydrate, are members of the large family with such kröhnkite-type chains. At 100 K, (NH4)Mg(HSO4)(SO4)(H2O)2 has an unprecedented triclinic crystal structure and contains [MgO4(OH2)2] octahedra linked by SO3(OH) and SO4 tetrahedra into chains extending parallel to [\overline{1}10]. Adjacent chains are linked by very strong hydrogen bonds between SO3(OH) and SO4 tetrahedra into layers parallel to (111). Ammonium cations and water molecules connect adjacent layers through hydrogen-bonding interactions of medium-to-weak strength into a three-dimensional network. (NH4)Mg(HSO4)(SO4)(H2O)2 shows a reversible phase transition and crystallizes at room temperature in structure type E in the classification scheme for structures with kröhnkite-type chains, with half of the unit-cell volume for the resulting triclinic cell, and with disordered H atoms of the ammonium tetrahedron and the H atom between two symmetry-related sulfate groups. IR spectroscopic room-temperature data for the latter phase are provided. Monoclinic NaSc(CrO4)2(H2O)2 adopts structure type F1 in the classification scheme for structures with kröhnkite-type chains. Here, [ScO4(OH2)2] octahedra (point group symmetry \overline{1}) are linked by CrO4 tetrahedra into chains parallel to [010]. The Na+ cations (site symmetry 2) have a [6 + 2] coordination and connect adjacent chains into a three-dimensional framework that is consolidated by medium–strong hydrogen bonds involving the water molecules. Quantitative structural comparisons are made between NaSc(CrO4)2(H2O)2 and its isotypic NaM(CrO4)2(H2O)2 (M = Al and Fe) analogues.

Hybrid materials based on transition metal–BTC–benzimidazole: solvent assisted crystallographic and structural switching

CrystEngComm ◽  
2018 ◽  
Vol 20 (41) ◽  
pp. 6602-6612 ◽  
Author(s):  
Ranjay K. Tiwari ◽  
J. N. Behera
Keyword(s):  
Crystal Structure ◽  
Transition Metal ◽  
Structure Analysis ◽  
Hybrid Materials ◽  
Coordination Polymers ◽  
Three Dimensional ◽  
Hierarchical Structures ◽  
Crystal Structure Analysis ◽  
Solvothermal Condition ◽  
1D Chain

Five transition metal–BTC–BIm based coordination polymers with hierarchical structures were synthesized under hydro/solvothermal condition. Crystal structure analysis of the compounds showed that 1 forms a 1D chain, 2 and 3 have 2D layers, while 4 and 5 have three-dimensional architectures.

scholarly journals Crystal structure of the fluorescent protein fromDendronephthyasp. in both green and photoconverted red forms

2016 ◽  
Vol 72 (8) ◽  
pp. 922-932 ◽  
Author(s):  
Nadya V. Pletneva ◽  
Sergei Pletnev ◽  
Alexey A. Pakhomov ◽  
Rita V. Chertkova ◽  
Vladimir I. Martynov ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonding ◽  
Blue Light ◽  
Considerable Increase ◽  
Fluorescent Protein ◽  
Fluorescent Proteins ◽  
Three Dimensional ◽  
Red Shift ◽  
Peptide Backbone

The fluorescent protein fromDendronephthyasp. (DendFP) is a member of the Kaede-like group of photoconvertible fluorescent proteins with a His62-Tyr63-Gly64 chromophore-forming sequence. Upon irradiation with UV and blue light, the fluorescence of DendFP irreversibly changes from green (506 nm) to red (578 nm). The photoconversion is accompanied by cleavage of the peptide backbone at the Cα—N bond of His62 and the formation of a terminal carboxamide group at the preceding Leu61. The resulting double Cα=Cβbond in His62 extends the conjugation of the chromophore π system to include imidazole, providing the red fluorescence. Here, the three-dimensional structures of native green and photoconverted red forms of DendFP determined at 1.81 and 2.14 Å resolution, respectively, are reported. This is the first structure of photoconverted red DendFP to be reported to date. The structure-based mutagenesis of DendFP revealed an important role of positions 142 and 193: replacement of the original Ser142 and His193 caused a moderate red shift in the fluorescence and a considerable increase in the photoconversion rate. It was demonstrated that hydrogen bonding of the chromophore to the Gln116 and Ser105 cluster is crucial for variation of the photoconversion rate. The single replacement Gln116Asn disrupts the hydrogen bonding of Gln116 to the chromophore, resulting in a 30-fold decrease in the photoconversion rate, which was partially restored by a further Ser105Asn replacement.

Ca(SCN)2 and Ca(SCN)2 · 2 H2O: Crystal Structure, Thermal Behavior and Vibrational Spectroscopy

2002 ◽  
Vol 57 (12) ◽  
pp. 1419-1426 ◽  
Author(s):  
Claudia Wickleder ◽  
Patrick Larsen
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Hydrogen Bonding ◽  
Single Crystals ◽  
Three Dimensional ◽  
Water Molecules ◽  
Dimensional Network ◽  
Thermal Investigations ◽  
Unknown Structure ◽  
Ir And Raman

The dehydration of Ca(SCN)2∙4H2O yields single crystals of Ca(SCN)2 ∙ 2 H2O as well as of Ca(SCN)2. Ca(SCN)2 ∙ 2 H2O crystallizes with a hitherto unknown structure (orthorhombic, Pnma, Z = 4, a = 1280.1(2), b = 790.3(1), c = 726.9(1) pm, Rall = 0.0430). The Ca2+ ions are surrounded by four SCN− ions and four water molecules. The polyhedra are connected to chains along [010] via common oxygen atoms. The SCN− ions connect these chains to a three-dimensional network so that each thiocyanate group is linked to two Ca2+ ions. Hydrogen bonding with sulfur atoms as acceptors is observed. The crystal structure of Ca(SCN)2 (monoclinic, C2/c, Z = 4, a = 961.7(2), b = 642.4(2), c = 787.2(2) pm, Rall = 0.0673) consists of alternating layers of Ca2+ and SCN− ions. The cations are surrounded by four sulfur and four nitrogen atoms in form of a square antiprism. According to 3∞[Ca(SCN)8/4] each SCN− ion connects four Ca2+ ions with each other. Thermal investigations show a phase transition of Ca(SCN)2 ∙ 4 H2O followed by dehydration to Ca(SCN)2 which finally decomposes yielding CaS. IR and Raman measurements have been performed and the resulting frequencies assigned and discussed.

scholarly journals Crystal structure and Hirshfeld surface analysis of dimethyl (3aS,6R,6aS,7S)-2-(2,2,2-trifluoroacetyl)-2,3-dihydro-1H,6H,7H-3a,6:7,9a-diepoxybenzo[de]isoquinoline-3a1,6a-dicarboxylate

2018 ◽  
Vol 74 (11) ◽  
pp. 1599-1604 ◽  
Author(s):  
Zeliha Atioğlu ◽  
Mehmet Akkurt ◽  
Flavien A. A. Toze ◽  
Pavel V. Dorovatovskii ◽  
Narmina A. Guliyeva ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Surface Analysis ◽  
Dominant Role ◽  
Three Dimensional ◽  
Chair Conformation ◽  
Hirshfeld Surface ◽  
Hirshfeld Surface Analysis ◽  
Piperidine Ring ◽  
Dimensional Network

The title molecule, C18H16F3NO7, comprises a fused cyclic system containing four five-membered (two dihydrofuran and two tetrahydrofuran) rings and one six-membered (piperidine) ring. The five-membered dihydrofuran and tetrahydrofuran rings adopt envelope conformations, and the six-membered piperidine ring adopts a distorted chair conformation. Intramolecular O...F interactions help to stabilize the conformational arrangement. In the crystal structure, molecules are linked by weak C—H...O and C—H...F hydrogen bonds, forming a three-dimensional network. The Hirshfeld surface analysis confirms the dominant role of H...H contacts in establishing the packing.

scholarly journals (E)-5-(4-Chlorobenzylidene)-1-phenyl-4,5,6,7-tetrahydro-1H-indazol-4-one: crystal structure and Hirshfeld surface analysis

IUCrData ◽  
2021 ◽  
Vol 6 (11) ◽  
Author(s):  
C. Selva Meenatchi ◽  
S. Athimoolam ◽  
J. Suresh ◽  
S. Raja Rubina ◽  
R. Ranjith Kumar ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Title Compound ◽  
Three Dimensional ◽  
Heterocyclic Ring ◽  
Membered Ring ◽  
Hirshfeld Surface ◽  
Dihedral Angles ◽  
Compound C ◽  
Hirshfeld Surfaces

In the title compound, C20H15ClN2O, the non-aromatic six-membered ring adopts a distorted envelope conformation with methylene-C atom nearest to the five-membered ring being the flap atom. The dihedral angle between the phenyl and chlorobenzene rings is 74.5 (1)°. The heterocyclic ring forms dihedral angles of 37.9 (1) and 64.3 (1)° with the phenyl and chlorobenzene rings, respectively. In the crystal, weak C—H...O interactions feature predominantly within the three-dimensional architecture. The intermolecular interactions are further analysed with the calculation of the Hirshfeld surfaces highlighting the prominent role of C—H...O interactions, along with H...H (36.8%) and C...H/H...C (26.5%) contacts.

The role of different nonspecific interactions and halogen contacts in the crystal structure organization of 5-chloroisatoic anhydride

2018 ◽  
Vol 74 (3) ◽  
pp. 372-380
Author(s):  
Dorota Pogoda ◽  
Agnieszka Matera-Witkiewicz ◽  
Marcin Listowski ◽  
Jan Janczak ◽  
Veneta Videnova-Adrabinska
Keyword(s):  
Crystal Structure ◽  
Weak Interactions ◽  
Three Dimensional ◽  
Lone Pair ◽  
One Dimensional ◽  
Π Interactions ◽  
Dimensional Network ◽  
Nonspecific Interactions

The crystal structure of 6-chloro-2,4-dihydro-1H-3,1-benzoxazine-2,4-dione (5-chloroisatoic anhydride), C8H4ClNO3, has been determined and analysed in terms of connectivity and packing patterns. The compound crystallizes in the noncentrosymmetric space groupPna21with one molecule in the asymmetric unit. The role of different weak interactions is discussed with respect to three-dimensional network organization. Molecules are extended into one-dimensional helical arrangements, making use of N—H...O hydrogen bonds and π–π interactions. The helices are further organized into monolayersviaweak C—H...O and lone pair–π interactions, and the monolayers are packed into a noncentrosymmetric three-dimensional architecture by C—Cl...π interactions and C—H...Cl and Cl...Cl contacts. A Hirshfeld surface (HS) analysis was carried out and two-dimensional (2D) fingerprint plots were generated to visualize the intermolecular interactions and to provide quantitative data for their relative contributions. In addition, tests of the antimicrobial activity andin vitrocytotoxity effects against fitoblast L929 were performed and are discussed.

Ferrostalderite, CuFe2TlAs2S6, a new mineral from Lengenbach, Switzerland: occurrence, crystal structure, and emphasis on the role of iron in sulfosalts

2016 ◽  
Vol 80 (1) ◽  
pp. 175-186 ◽  
Author(s):  
Cristian Biagioni ◽  
Luca Bindi ◽  
Fabrizio Nestola ◽  
Ralph Cannon ◽  
Philippe Roth ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Three Dimensional ◽  
New Mineral ◽  
Crystal Data ◽  
Chemical Formula ◽  
Crystal Chemical Formula ◽  
New Mineral Species ◽  
Reflectance Data ◽  
The Ideal

AbstractThe new mineral species ferrostalderite, CuFe2TlAs2S6, was discovered in the Lengenbach quarry, Binn Valley, Wallis, Switzerland. It occurs as minute, metallic, black, equant to prismatic crystals, up to 50 mu;m, associated with dolomite, realgar, baumhauerite (?) and pyrite. Minimum and maximum reflectance data for COM wavelengths in air are [λ (nm): R (%)]: 471.1: 24.2/25.4; 548.3: 23.7/24.7; 586.6: 22.9/23.8; 652.3: 21.0/22.0. Electron microprobe analyses give (wt.%): Cu 6.24(25), Ag 4.18(9), Fe 9.95(83), Zn 4.46(91), Hg 1.22(26), Tl 26.86(62), As 19.05(18), Sb 0.63(6),S 25.39(47), total 97.98(72). On the basis of 12 atoms per formula unit, the chemical formula of ferrostalderite is Cu0.75(2)Ag0.30(1)Fe1.36(10)Zn0.52(11)Hg0.05(1)Tl1.00(1)[As1.94(4)Sb0.04(1)]∑1.98(4)S6.04(4). The new mineral is tetragonal, space group I4̄2 m, with a = 9.8786(5), c = 10.8489(8) Å, V = 1058.71(11) Å3, Z = 4. The main diffraction lines of the calculated powder diagram are [d (in Å), intensity, hkl]: 4.092, 70, 211; 3.493, 23, 220; 3.396, 35, 103; 3.124, 17, 310; 2.937, 100, 222; 2.656, 19, 321; 2.470, 19, 400; 2.435, 33, 303. The crystal structure of ferrostalderite has been refined by Xray single-crystal data to a final R1= 0.050, on the basis of 1169 reflections with F0 > 4σ(F0). It shows a three dimensional framework of (Cu,Fe)-centred tetrahedra (1M1 + 2 M2), with channels parallel to [001] hosting disymmetric TlS6and (As,Sb)S3 polyhedra. Ferrostalderite is derived from its isotype stalderiteM1CuM2Zn2TlAs2S6through the homovalent substitution M2Zn2+ → M2Fe2+. The ideal crystal-chemical formula of ferrostalderite isM1CuM2Fe2TlAs2S6.

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