Crystals

651 KiB

Open AccessEditorial

Acknowledgement to Reviewers of Crystals in 2015

by Crystals Editorial Office

Crystals 2016, 6(1), 15; https://doi.org/10.3390/cryst6010015 - 21 Jan 2016

Cited by 1 | Viewed by 2845

The editors of Crystals would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2015. [...] Full article

3052 KiB

Open AccessArticle

A Family of Nitrogen-Enriched Metal Organic Frameworks with CCS Potential

by Emma Dooris, Craig A. McAnally, Edmund J. Cussen, Alan R. Kennedy and Ashleigh J. Fletcher

Crystals 2016, 6(1), 14; https://doi.org/10.3390/cryst6010014 - 21 Jan 2016

Cited by 13 | Viewed by 5242

Abstract

Materials with enhanced carbon capture capacities are required to advance post-combustive amelioration methods; these are necessary to reduce atmospheric carbon dioxide emissions and the associated rate of global temperature increase. Current technologies tend to be very energy intensive processes with high levels of [...] Read more.

Materials with enhanced carbon capture capacities are required to advance post-combustive amelioration methods; these are necessary to reduce atmospheric carbon dioxide emissions and the associated rate of global temperature increase. Current technologies tend to be very energy intensive processes with high levels of waste produced; this work presents three new metal organic framework materials with embedded Lewis base functionalities, imparted by the nitrogen-rich ligand, demonstrating an affinity for carbon dioxide. Thus, we report the synthesis and characterization of a series of metal organic framework materials using a range of metal centers (Co, Ni, and Zn) with the 1,4-bis(pyridin-4-yl)-1,2,4,5-tetrazine organic linker, in the presence of ammonium hexafluorosilicate. Three distinct crystal structures are reported for Zn-pytz(hydro) 1D chains, and Ni-pytz and Co-pytz isostructural 1D Ladders. Co-pytz shows an uptake of 47.53 mg CO₂/g of sorbent, which equates to 15 wt % based on available nitrogen sites within the structure, demonstrating potential for carbon capture applications. Full article

► Show Figures

Figure 1

Figure 1
(a) Unit Structure of [Zn(pytz(hydrolyzed))2(OH2)2(OCOCH3)2]·H2O; (b) Possible π stacking interactions between 1D chains; Zn (cyan), C (grey), H (white), N (blue), O (red). Full article ">Figure 2
(a) Unit Structure of [Ni(pytz)1.5(NO3)2]·nDCM (n = 2–3); (b) 1D ladder structure; Ni (green), C (grey), H (white), N (blue), O (red). DCM and ligand H atoms omitted for clarity in (b). Full article ">Figure 3
(a) Unit Structure of [Co2(pytz)3(NO3)4]·nDCM (n = 4–6); (b) 1D ladder structure; Co (magenta), C (grey), H (white), N (blue), O (red). DCM and ligand H atoms omitted for clarity in (b). Full article ">Figure 4
Co-pytz (isostructural to Ni(pytz)) view along a-axis; pore window sizes determined for DCM inclusion. DCM and ligand H atoms omitted from image for clarity. Co (purple), C (grey), N (blue), O (red). Full article ">Figure 5
Co-pytz offset layered ladders demonstrating interconnected porosity; front ladder—blue, second—red, third—green. DCM and ligand H atoms omitted from image for clarity. Full article ">Figure 6
Sorption isotherm for CO2 on Co-pytz at 273 K. Full article ">

1570 KiB

Open AccessArticle

Crystal Structures of Two 1,4-Diamino-1,2,4-triazolium Salts

by Gerhard Laus, Klaus Wurst, Volker Kahlenberg and Herwig Schottenberger

Crystals 2016, 6(1), 13; https://doi.org/10.3390/cryst6010013 - 20 Jan 2016

Cited by 2 | Viewed by 5176

Abstract

Bis(1,4-diamino-1,2,4-triazolium) sulfate (1) was obtained from the corresponding chloride by ion metathesis using Ag₂SO₄. Further metathesis with barium 5,5′-azotetrazolate yielded bis(1,4-diamino-1,2,4-triazolium) 5,5′-azotetrazolate (2). Numerous NH···N and NH···O interactions were identified in the crystal structures of [...] Read more.

Bis(1,4-diamino-1,2,4-triazolium) sulfate (1) was obtained from the corresponding chloride by ion metathesis using Ag₂SO₄. Further metathesis with barium 5,5′-azotetrazolate yielded bis(1,4-diamino-1,2,4-triazolium) 5,5′-azotetrazolate (2). Numerous NH···N and NH···O interactions were identified in the crystal structures of 1 and 2. Both compounds undergo exothermal decomposition upon heating. Full article

(This article belongs to the Special Issue Nitrogen-Rich Salts)

► Show Figures

Figure 1

Figure 1
Syntheses of 1,4-diamino-1,2,4-triazolium sulfate (1) and 5,5′-azotetrazolate (2). Full article ">Figure 2
Bis(1,4-diamino-1,2,4-triazolium) sulfate (1). (a–d) The four independent cations as hydrogen-bond donors. Symmetry codes: (i) 1+x, y, z; (ii) x, –y, ½ + z; (iii) x, 1 + y, z; (iv) x, –y, –1/2 + z; (v) x, 1 – y, –1/2 + z; (vi) x, –1 + y, z; (vii) –1 + x, y, z; (e) Asymmetric unit. Full article ">Figure 3
Bis(1,4-diamino-1,2,4-triazolium)5,5′-azotetrazolate (2). (a) The cation as hydrogen-bond donor; (b) The anion as hydrogen-bond acceptor; (c) Wave-like arrangement of the ions in the unit cell. Symmetry codes: (i) –x, –1/2 + y, 1/2 – z; (ii) 1 – x, 1 – y, 1 – z; (iii) x, 3/2 – y, –1/2 + z; (iv) –x, 1/2 + y, 1/2 – z; (v) x, 3/2 – y, 1/2 + z. Full article ">Figure 4
DSC and TGA of (a) bis(1,4-diamino-1,2,4-triazolium) sulfate (1) and (b) 5,5′-azotetrazolate (2). Heating rate 10 °C·min−1. Full article ">

3311 KiB

Open AccessArticle

Formation Mechanism of Porous Cu₃Sn Intermetallic Compounds by High Current Stressing at High Temperatures in Low-Bump-Height Solder Joints

by Jie-An Lin, Chung-Kuang Lin, Chen-Min Liu, Yi-Sa Huang, Chih Chen, David T. Chu and King-Ning Tu

Crystals 2016, 6(1), 12; https://doi.org/10.3390/cryst6010012 - 16 Jan 2016

Cited by 32 | Viewed by 9995

Abstract

Electromigration tests of SnAg solder bump samples with 15 μm bump height and Cu under-bump-metallization (UBM) were performed. The test conditions were 1.45 × 10⁴ A/cm² at 185 °C and 1.20 × 10⁴ A/cm² at 0 °C. A porous [...] Read more.

Electromigration tests of SnAg solder bump samples with 15 μm bump height and Cu under-bump-metallization (UBM) were performed. The test conditions were 1.45 × 10⁴ A/cm² at 185 °C and 1.20 × 10⁴ A/cm² at 0 °C. A porous Cu₃Sn intermetallic compound (IMC) structure was observed to form within the bumps after several hundred hours of current stressing. In direct comparison, annealing alone at 185 °C will take more than 1000 h for porous Cu₃Sn to form, and it will not form at 170 °C even after 2000 h. Here we propose a mechanism to explain the formation of this porous structure assisted by electromigration. The results show that the SnAg bump with low bump height will become porous-type Cu₃Sn when stressing with high current density and high temperature. Polarity effects on porous Cu₃Sn formation is discussed. Full article

(This article belongs to the Special Issue Intermetallics)

► Show Figures

Figure 1

11017 KiB

Open AccessArticle

Accelerated Approach for the Band Structures Calculation of Phononic Crystals by Finite Element Method

by Lin Han, Yan Zhang, Xiao-mei Li, Lin-hua Jiang and Da Chen

Crystals 2016, 6(1), 11; https://doi.org/10.3390/cryst6010011 - 14 Jan 2016

Cited by 12 | Viewed by 5099

Abstract

We present here a fast and easily realized computational approach based on the finite element methods with consistent and lumped mass matrices (CM-FEM and LM-FEM, respectively), and the Bloch’s theorem, to calculate the elastic band structures of phononic crystals. Two improvements, the adjustment [...] Read more.

We present here a fast and easily realized computational approach based on the finite element methods with consistent and lumped mass matrices (CM-FEM and LM-FEM, respectively), and the Bloch’s theorem, to calculate the elastic band structures of phononic crystals. Two improvements, the adjustment of the introduction of Bloch’s theorem as well as weighting treatment of consistent and lumped mass matrices, are performed. Numerical simulations show that convergence speed is accelerated obviously. Furthermore, the method is verified by analytical solutions in specified homogeneous cases. It is concluded that compared with CM-FEM or LM-FEM, the present method gives higher precision results with sparser mesh and takes less time. Full article

(This article belongs to the Special Issue Phononic Crystals)

► Show Figures

Figure 1

6813 KiB

Open AccessReview

A Review on the Properties of Iron Aluminide Intermetallics

by Mohammad Zamanzade, Afrooz Barnoush and Christian Motz

Crystals 2016, 6(1), 10; https://doi.org/10.3390/cryst6010010 - 14 Jan 2016

Cited by 159 | Viewed by 17547

Abstract

Iron aluminides have been among the most studied intermetallics since the 1930s, when their excellent oxidation resistance was first noticed. Their low cost of production, low density, high strength-to-weight ratios, good wear resistance, ease of fabrication and resistance to high temperature oxidation and [...] Read more.

Iron aluminides have been among the most studied intermetallics since the 1930s, when their excellent oxidation resistance was first noticed. Their low cost of production, low density, high strength-to-weight ratios, good wear resistance, ease of fabrication and resistance to high temperature oxidation and sulfurization make them very attractive as a substitute for routine stainless steel in industrial applications. Furthermore, iron aluminides allow for the conservation of less accessible and expensive elements such as nickel and molybdenum. These advantages have led to the consideration of many applications, such as brake disks for windmills and trucks, filtration systems in refineries and fossil power plants, transfer rolls for hot-rolled steel strips, and ethylene crackers and air deflectors for burning high-sulfur coal. A wide application for iron aluminides in industry strictly depends on the fundamental understanding of the influence of (i) alloy composition; (ii) microstructure; and (iii) number (type) of defects on the thermo-mechanical properties. Additionally, environmental degradation of the alloys, consisting of hydrogen embrittlement, anodic or cathodic dissolution, localized corrosion and oxidation resistance, in different environments should be well known. Recently, some progress in the development of new micro- and nano-mechanical testing methods in addition to the fabrication techniques of micro- and nano-scaled samples has enabled scientists to resolve more clearly the effects of alloying elements, environmental items and crystal structure on the deformation behavior of alloys. In this paper, we will review the extensive work which has been done during the last decades to address each of the points mentioned above. Full article

(This article belongs to the Special Issue Intermetallics)

► Show Figures

Figure 1

907 KiB

Open AccessEditorial

Crystal Dislocations

by Ronald W. Armstrong

Crystals 2016, 6(1), 9; https://doi.org/10.3390/cryst6010009 - 6 Jan 2016

Cited by 1 | Viewed by 6197

Abstract

Crystal dislocations were invisible until the mid-20th century although their presence had been inferred; the atomic and molecular scale dimensions had prevented earlier discovery. Now they are normally known to be just about everywhere, for example, in the softest molecularly-bonded crystals as well [...] Read more.

Crystal dislocations were invisible until the mid-20th century although their presence had been inferred; the atomic and molecular scale dimensions had prevented earlier discovery. Now they are normally known to be just about everywhere, for example, in the softest molecularly-bonded crystals as well as within the hardest covalently-bonded diamonds. The advent of advanced techniques of atomic-scale probing has facilitated modern observations of dislocations in every crystal structure-type, particularly by X-ray diffraction topography and transmission electron microscopy. The present Special Issue provides a flavor of their ubiquitous presences, their characterizations and, especially, their influence on mechanical and electrical properties. Full article

(This article belongs to the Special Issue Crystal Dislocations)

► Show Figures

Figure 1

1716 KiB

Open AccessCommunication

Enantiopure Radical Cation Salt Based on Tetramethyl-Bis(ethylenedithio)-Tetrathiafulvalene and Hexanuclear Rhenium Cluster

by Flavia Pop, Patrick Batail and Narcis Avarvari

Crystals 2016, 6(1), 8; https://doi.org/10.3390/cryst6010008 - 5 Jan 2016

Cited by 7 | Viewed by 4562

Abstract

Electrocrystallization of the (S,S,S,S) enantiomer of tetramethyl-bis(ethylenedithio)-tetrathiafulvalene donor 1 in the presence of the dianionic hexanuclear rhenium (III) cluster [Re₆S₆Cl₈]²⁻ affords a crystalline radical cation salt formulated as [(S)-1]₂ [...] Read more.

Electrocrystallization of the (S,S,S,S) enantiomer of tetramethyl-bis(ethylenedithio)-tetrathiafulvalene donor 1 in the presence of the dianionic hexanuclear rhenium (III) cluster [Re₆S₆Cl₈]²⁻ affords a crystalline radical cation salt formulated as [(S)-1]₂·Re₆S₆Cl₈, in which the methyl substituents of the donors adopt an unprecedented all-axial conformation. A complex set of intermolecular TTF···TTF and cluster···TTF interactions sustain an original tridimensional architecture. Full article

► Show Figures

Graphical abstract

4623 KiB

Open AccessArticle

Electrostatic Potentials, Intralattice Attractive Forces and Crystal Densities of Nitrogen-Rich C,H,N,O Salts

by Peter Politzer, Pat Lane and Jane S. Murray

Crystals 2016, 6(1), 7; https://doi.org/10.3390/cryst6010007 - 4 Jan 2016

Cited by 26 | Viewed by 5760

Abstract

The computed electrostatic potentials on C,H,N,O molecular solids and nitrogen-rich C,H,N,O salts are used in analyzing and comparing intralattice attractive forces and crystal densities in these two categories of compounds. Nitrogen-rich C,H,N,O salts are not an assured path to high densities. To increase [...] Read more.

The computed electrostatic potentials on C,H,N,O molecular solids and nitrogen-rich C,H,N,O salts are used in analyzing and comparing intralattice attractive forces and crystal densities in these two categories of compounds. Nitrogen-rich C,H,N,O salts are not an assured path to high densities. To increase the likelihood of high densities, small cations and large anions are suggested. Caution is recommended in predicting benefits of nitrogen-richness for explosive compounds. Full article

(This article belongs to the Special Issue Nitrogen-Rich Salts)

► Show Figures

Figure 1

Figure 1
Computed electrostatic potential on 0.001 au molecular surface of 5-nitrotetrazole (1). Color ranges, in kcal/mol, are: red, greater than 30; yellow, between 30 and 15; green, between 15 and 0; blue, negative (less than 0). Circles show positions of atoms; NO2 group is on the left. Most positive potential is 73 kcal/mol by the hydrogen; most negative are −29 kcal/mol by the ring nitrogen at the bottom right. Full article ">Figure 2
Computed electrostatic potential on 0.001 au molecular surface of 3-nitro-1,2,4-triazole (2). Color ranges, in kcal/mol, are: red, greater than 30; yellow, between 30 and 15; green, between 15 and 0; blue, negative (less than 0). Circles show positions of atoms; NO2 group is on the lower right. Most positive potential is 71 kcal/mol by the N-H hydrogen; most negative are −33 to −39 kcal/mol by the ring nitrogens and the NO2 oxygens. Full article ">Figure 3
Computed electrostatic potential on 0.001 au anionic surface of 5-nitrotetrazolate anion (3). Color ranges, in kcal/mol, are: yellow, between −60 and −80; green, between −80 and −100; blue, more negative than −100. Circles show positions of atoms; NO2 group is on the left. Most negative potentials are −126 kcal/mol by the ring nitrogens closest to the carbon bearing the NO2 group. Full article ">Figure 4
Computed electrostatic potential on 0.001 au anionic surface of 3-nitro-1,2,4-triazolate anion (4). Color ranges, in kcal/mol, are: red, less negative than −60; yellow, between −60 and −80; green, between −80 and −100; blue, more negative than −100. Circles show positions of atoms; NO2 group is on the lower right. Most negative potentials are −133 and −136 kcal/mol by the ring nitrogens closest to the carbon bearing the NO2 group. Full article ">Figure 5
Computed electrostatic potential on 0.001 au cationic surface of NH4+ cation. Color ranges, in kcal/mol, are: red, greater than 178; yellow, between 178 and 174; green, between 174 and 168; blue, less than 168. Circles show positions of atoms. Most positive potentials are 181 kcal/mol by hydrogens. Full article ">Figure 6
Computed electrostatic potential on 0.001 au cationic surface of 5-nitrotetrazolium cation (5). Color ranges, in kcal/mol, are: red, greater than 150; yellow, between 150 and 120; green, between 120 and 90; blue, less than 90. Circles shown positions of atoms; NO2 group is on the left. Most positive potentials are 174 kcal/mol by hydrogens. Full article ">Figure 7
Crystal density distributions of C,H,N,O molecular compounds (purple) and nitrogen-rich C,H,N,O ionic compounds (green). Vertical axes are percentages. Full article ">Figure 8
Computed electrostatic potential on 0.001 au cationic surface of NH3OH + cation. Color ranges, in kcal/mol, are: red, greater than 165; yellow, between 165 and 140; green, between 140 and 110; blue, less than 110. Circles show positions of atoms; OH group is on the left. Most positive potential is 190 kcal/mol by the OH hydrogen. Full article ">

1380 KiB

Open AccessArticle

Constructor Graphs as Useful Tools for the Classification of Hydrogen Bonded Solids: The Case Study of the Cationic (Dimethylphosphoryl)methanaminium (dpmaH⁺) Tecton

by Guido J. Reiss

Crystals 2016, 6(1), 6; https://doi.org/10.3390/cryst6010006 - 31 Dec 2015

Cited by 3 | Viewed by 5839

Abstract

The structural chemistry of a series of dpmaH (dpmaH = (dimethylphosphoryl)methanaminium) salts has been investigated using constructor graph representations to visualize structural dependencies, covering the majority of known dpmaH salts. It is shown that the structurally related α-aminomethylphosphinic acid [...] Read more.

The structural chemistry of a series of dpmaH (dpmaH = (dimethylphosphoryl)methanaminium) salts has been investigated using constructor graph representations to visualize structural dependencies, covering the majority of known dpmaH salts. It is shown that the structurally related α-aminomethylphosphinic acid can be integrated in the systematology of the dpmaH salts. Those dpmaH salts with counter anions that are weak hydrogen bond acceptors (ClO₄⁻, SnCl₆²⁻, IrCl₆²⁻,I⁻) tend to form head-to-tail hydrogen bonded moieties purely consisting of dpmaH⁺ cations as the primarily structural motif. In structures with weak to very weak hydrogen bonds between the dpmaH⁺ cations and the counter anions, the anions fill the gaps in the structures. In salts with medium to strong hydrogen bond acceptor counter ions (Cl⁻, NO₃⁻, PdCl₄²⁻), the predominant structural motif is a double head-to-tail hydrogen bonded (dpmaH⁺)₂ dimer. These dimeric units form further NH···X hydrogen bonds to neighboring counter anions X, which results in one-dimensional and two-dimensional architectures. Full article

(This article belongs to the Special Issue Analysis of Hydrogen Bonds in Crystals)

► Show Figures

Figure 1

Figure 1
(Upper part): Structure of (dpmaH)2[SnCl6] with view along [100]; (Lower part): modified constructor graph of the polymeric, cationic (dpmaH+)n substructure. Full article ">Figure 2
(a) Showing the primary structural motif of a four-membered, hydrogen bonded ring (N–H···I hydrogen bonds to the adjacent iodide counter anions are omitted); (b) modified constructor graph of the tetrameric (dpmaH+)4 ring unit. Full article ">Figure 3
(a) part of the hydrogen bonded chain structure and modified constructor graph of dpmaH[ClO4]; (b) hydrogen bonded strands in the structure of dpmaHX·dpma (X = [ClO4]− [<a href="#B24-crystals-06-00006" class="html-bibr">24</a>], I− [<a href="#B25-crystals-06-00006" class="html-bibr">25</a>]) and its modified constructor graph (the dpma molecule is shown as brick-shaped icon composed of a black circle and a red dot; red colored circle indicates a composite tecton); (c) hydrogen bonded strands constructed from head-to-tail connected {dpmaH}+[HSO4]− ion pairs [<a href="#B26-crystals-06-00006" class="html-bibr">26</a>] and the corresponding modified constructor graph (brick-shaped icon composed of a black circle and a red minus sign is shown for the HSO4− anion; red colored circle indicates a composite tecton). Full article ">Figure 4
Hydrogen bonding pattern of the zwitterionic α-aminomethylphosphinic acid [<a href="#B27-crystals-06-00006" class="html-bibr">27</a>] and its modified constructor graph. Full article ">Figure 5
Hydrogen bonded structure of dpmaHCl containing (dpmaH+)2 dimers and chloride counter anions; a modified constructor graph for a section of the chain is shown. Full article ">Figure 6
(a) the hydrogen bonded layered structure of dpmaH[NO3] and the corresponding constructor graph is shown; (b) the hydrogen bonded chain structure of (dpmaH)2[PdCl4] and the corresponding modified constructor graph is shown. Full article ">Figure 7
Hydrogen bonding functionality of the dpmaH+ tecton (left part) and the corresponding icon useable in constructor graphs (right part). Full article ">

4128 KiB

Open AccessReview

Recent Advances in the Synthesis of High Explosive Materials

by Jesse J. Sabatini and Karl D. Oyler

Crystals 2016, 6(1), 5; https://doi.org/10.3390/cryst6010005 - 29 Dec 2015

Cited by 98 | Viewed by 34852

Abstract

This review discusses the recent advances in the syntheses of high explosive energetic materials. Syntheses of some relevant modern primary explosives and secondary high explosives, and the sensitivities and properties of these molecules are provided. In addition to the synthesis of such materials, [...] Read more.

This review discusses the recent advances in the syntheses of high explosive energetic materials. Syntheses of some relevant modern primary explosives and secondary high explosives, and the sensitivities and properties of these molecules are provided. In addition to the synthesis of such materials, processing improvement and formulating aspects using these ingredients, where applicable, are discussed in detail. Full article

(This article belongs to the Special Issue Energetic Materials)

► Show Figures

Figure 1

1448 KiB

Open AccessArticle

Synthesis, Crystal Structure, DFT Study and Antifungal Activity of 4-(5-((4-Bromobenzyl) thio)-4-Phenyl-4H-1,2,4-Triazol-3-yl)pyridine

by Jin-Xia Mu, Zhi-Wen Zhai, Ming-Yan Yang, Zhao-Hui Sun, Hong-Ke Wu and Xing-Hai Liu

Crystals 2016, 6(1), 4; https://doi.org/10.3390/cryst6010004 - 25 Dec 2015

Cited by 16 | Viewed by 4783

Abstract

The title compound 4-(5-((4-bromobenzyl)thio)-4-phenyl-4H-1,2,4-triazol-3-yl)pyridine (C₂₀H₁₅BrN₄S) was synthesized, and its structure was confirmed by ¹H NMR, MS and elemental analyses and single-crystal X-ray structure determination. It crystallizes in the triclinic space group P-1 with a [...] Read more.

The title compound 4-(5-((4-bromobenzyl)thio)-4-phenyl-4H-1,2,4-triazol-3-yl)pyridine (C₂₀H₁₅BrN₄S) was synthesized, and its structure was confirmed by ¹H NMR, MS and elemental analyses and single-crystal X-ray structure determination. It crystallizes in the triclinic space group P-1 with a = 7.717(3), b = 9.210(3), c = 13.370(5) Å, α = 80.347(13), β = 77.471(13), γ = 89.899(16)°, V = 913.9(6) Å³, Z = 2 and R = 0.0260 for 3145 observed reflections with I > 2σ(I). A Density functional theory (DFT) (B3LYP/6-31G) calculation of the title molecule was carried out. The full geometry optimization was carried out using a 6-31G basis set, and the frontier orbital energy. Atomic net charges are discussed. Calculated bond lengths and bond angles were found to differ from experimental values, and the compound exhibits moderate antifungal activity. Full article

► Show Figures

Figure 1

2403 KiB

Open AccessArticle

[FHF]⁻—The Strongest Hydrogen Bond under the Influence of External Interactions

by Sławomir J. Grabowski

Crystals 2016, 6(1), 3; https://doi.org/10.3390/cryst6010003 - 25 Dec 2015

Cited by 30 | Viewed by 8470

Abstract

A search through the Cambridge Structural Database (CSD) for crystal structures containing the [FHF]⁻ anion was carried out. Forty five hydrogen bifluoride structures were found mainly with the H-atom moved from the mid-point of the F…F distance. However several [FHF]⁻ systems [...] Read more.

A search through the Cambridge Structural Database (CSD) for crystal structures containing the [FHF]⁻ anion was carried out. Forty five hydrogen bifluoride structures were found mainly with the H-atom moved from the mid-point of the F…F distance. However several [FHF]⁻ systems characterized by D_∞h symmetry were found, the same as this anion possesses in the gas phase. The analysis of CSD results as well as the analysis of results of ab initio calculations on the complexes of [FHF]⁻ with Lewis acid moieties show that the movement of the H-atom from the central position depends on the strength of interaction of this anion with external species. The analysis of the electron charge density distribution in complexes of [FHF]⁻ was performed with the use of the Quantum Theory of Atoms in Molecules (QTAIM) approach and the Natural Bond Orbitals (NBO) method. Full article

(This article belongs to the Special Issue Analysis of Hydrogen Bonds in Crystals)

► Show Figures

Figure 1

Figure 1
Molecular graphs of selected systems analyzed here, big circles correspond to atoms, continuous and broken lines to bond paths while small, green circles to bond critical points. Full article ">Figure 2
The fragments of the crystal structures of (a) bis(tetramethylammonium) di-fluoro-dioxoiodide (FAJHAA); (b) tetramethylammonium hydrogen difluoride (KELRIC01). Full article ">Figure 3
The fragment of the crystal structure of diphenylguanidinium hydrogen difluoride (IBOWOL). Full article ">Figure 4
The fragment of the crystal structure of tetramethylammonium dihydrogen trifluoride (GIBGOB01). Full article ">Figure 5
The dependence between the F-H and H...F distances in the [FHF]− species interacting with Lewis acid centers; open circles—theoretical results, full circles—experimental data taken from the Cambridge Structural Database (CSD); R2 is the squared correlation coefficient (for this figure and other ones presented in this study). The solid line passing through the structures of the D∞h and C2v symmetries is presented. Full article ">Figure 6
The second order polynomial relationship between the F-H distance and the deformation energy. Two cases of [FHF]−…Li+ and [FHF]−…Na+ are not included in this relation, however they are presented in the figure (squares). Full article ">Figure 7
The relationships between the electron shift, Eltrans (in au), and (a) ρFH—electron density at the BCP of the F-H of [FHF]−; (b) ρH…F—electron density at BCP of the H…F of [FHF]−; (c) ρF…H—electron density at BCP of the external [FHF]−—Brønsted acid contact. Full article ">Figure 8
The molecular graphs of [FHF]−, [FHF]−...Li+, [FHF]−...HCCH, [FHF]−...HF and [FHF]−...H3O+. Solid and broken lines correspond to bond paths, big circles to attractors, and small green circles to BCPs, isolines of laplacian of electron density are presented; positive values are depicted in solid lines and negative values in broken lines. Full article ">

2460 KiB

Open AccessArticle

Structural Elucidation of α-Cyclodextrin-Succinic Acid Pseudo Dodecahydrate: Expanding the Packing Types of α-Cyclodextrin Inclusion Complexes

by Sofiane Saouane and Francesca P. A. Fabbiani

Crystals 2016, 6(1), 2; https://doi.org/10.3390/cryst6010002 - 24 Dec 2015

Cited by 5 | Viewed by 9025

Abstract

This paper reports a new packing type of α-cyclodextrin inclusion complexes, obtained here with succinic acid under low-temperature crystallization conditions. The structure of the 1:1 complex is characterized by heavy disorder of the guest, the solvent, and part of the host. The crystal [...] Read more.

This paper reports a new packing type of α-cyclodextrin inclusion complexes, obtained here with succinic acid under low-temperature crystallization conditions. The structure of the 1:1 complex is characterized by heavy disorder of the guest, the solvent, and part of the host. The crystal packing belongs to the known channel-type structure; the basic structural unit is composed of cyclodextrin trimers, as opposed to the known isolated molecular or dimeric constructs, packed along the c-axis. Each trimer is made of crystallographically independent molecules assembled in a stacked vase-like cluster. A multi-temperature single-crystal X-ray diffraction analysis reveals the presence of dynamic disorder. Full article

(This article belongs to the Special Issue Analysis of Hydrogen Bonds in Crystals)

► Show Figures

Graphical abstract

Graphical abstract
Full article ">Figure 1
Diagrams and numbering schemes of: (a) α-cyclodextrins; (b) α-D-glucopyranose; (c) succinic acid (SA): the mean distance O(3)–O(4) was computed from 72 structures of SA in the Cambridge Structural Database (CSD), the width of SA is the (mean distance O(3)–O(4) plus twice the van der Waals radius of an oxygen atom. Full article ">Figure 2
Crystal packing of α-CD molecules viewed along the b-axis. H atoms, disorder of α-CD C, SA and water molecules have been omitted for clarity. Symmetry-equivalent molecules are color coded. Full article ">Figure 3
Projection of α-CD∙SA structure along the b-axis. The crystallographically-independent CD molecules are named A, B and C, see main text for details. H atoms, SA and water molecules have been omitted for clarity. The distances refer to gap in Å between the least-square planes formed by all O(4) atoms involved in the glycosidic bonds. Full article ">Figure 4
H-bonded motif formed by SA molecules in the asymmetric unit viewed (a) along the a-axis and (b) along the b-axis. O–O contacts are represented by dashed green lines. H-atoms (in b), α-CD and water molecules have been omitted for clarity. SA molecules are contained in the cavities of the crystallographically-independent CD molecules named A, B and C, see main text for details. Full article ">Figure 5
The evolution of the normalized unit-cell parameters as function of temperature (errors at 3σ level) taken from the structures in <a href="#app1-crystals-06-00002" class="html-app">Supplementary Table S1</a>, see <a href="#app1-crystals-06-00002" class="html-app">Supplementary Information</a> for details. Full article ">Figure 6
SHELXLE Fobs-Fcalc maps (at 0.40 e−/Å3) of α-CD∙SA inclusion complex at 100 K and the respective solvent region at the bottom (right-hand side in the picture) of the vase-like cluster at the different temperatures showing the decrease of the signal as a function of increasing temperature. A similar decrease, not shown here, is observed for the other side. Full article ">Figure 7
Fobs-Fcalc maps in green showing the electron density before (a) and after (b) modeling SA inside α-CD B molecule. The peaks Q1 and 3 × (Q4) are forming a tetrahedron. H-atoms and the rest of the structure have been omitted for clarity. Displacement ellipsoids are drawn at the 50% probability level. Full article ">

785 KiB

Open AccessArticle

Diffusivity and Mobility of Adsorbed Water Layers at TiO₂ Rutile and Anatase Interfaces

by Niall J. English

Crystals 2016, 6(1), 1; https://doi.org/10.3390/cryst6010001 - 22 Dec 2015

Cited by 15 | Viewed by 5014

Abstract

Molecular-dynamics simulations have been carried out to study diffusion of water molecules adsorbed to anatase-(101) and rutile-(110) interfaces at room temperature (300 K). The mean squared displacement (MSD) of the adsorbed water layers were determined to estimate self-diffusivity therein, and the mobility of [...] Read more.

Molecular-dynamics simulations have been carried out to study diffusion of water molecules adsorbed to anatase-(101) and rutile-(110) interfaces at room temperature (300 K). The mean squared displacement (MSD) of the adsorbed water layers were determined to estimate self-diffusivity therein, and the mobility of these various layers was gauged in terms of the “swopping” of water molecules between them. Diffusivity was substantially higher within the adsorbed monolayer at the anatase-(101) surface, whilst the anatase-(101) surface’s more open access facilitates easier contact of adsorbed water molecules with those beyond the first layer, increasing the level of dynamical inter-layer exchange and mobility of the various layers. It is hypothesised that enhanced ease of access of water to the anatase-(101) surface helps to rationalise experimental observations of its comparatively greater photo-activity. Full article

(This article belongs to the Special Issue Analysis of Hydrogen Bonds in Crystals)

► Show Figures

Figure 1

Journal Menu

Journal Browser

Crystals, Volume 6, Issue 1 (January 2016) – 15 articles

Further Information

Guidelines

MDPI Initiatives

Follow MDPI