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Crystals
Volume 8
Issue 10
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Crystals, Volume 8, Issue 10 (October 2018) – 30 articles

Cover Story (view full-size image): The Hydrated KNbWO6 pyrochlore contains a main covalent framework of (NbV,WVI)O6 octahedra sharing vertices (in green), forming large cavities wherein K, H, and O’ are distributed at 32e, 96g, and 32e Wyckoff sites, respectively. Detail: A2O’sub-lattice of K and water molecules are highlighted as purple tetrahedra. Only ¼ of the vertices are actually occupied by K atoms (some atoms are hidden for the sake of clarity). View this paper
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8 pages, 2099 KiB  
Article
Influence of Sputtered ZnO and Al:ZnO Top Layers on Magneto-Optic Responses of Yttrium Iron Garnet Films
by Shinichiro Mito, Satsuki Kikuchi, Yasutoshi Ito, Nana Ota and Mitsuteru Inoue
Crystals 2018, 8(10), 396; https://doi.org/10.3390/cryst8100396 - 22 Oct 2018
Viewed by 3365
Abstract
Zinc oxide (ZnO) is a promising material for combining with magneto-optic (MO) materials because it can propagate stable exciton-polaritons, with velocities considerably lower than that of photons in a vacuum. This study investigated the influence of sputtered ZnO and Al:ZnO top layers on [...] Read more.
Zinc oxide (ZnO) is a promising material for combining with magneto-optic (MO) materials because it can propagate stable exciton-polaritons, with velocities considerably lower than that of photons in a vacuum. This study investigated the influence of sputtered ZnO and Al:ZnO top layers on MO responses of a bismuth-substituted yttrium iron garnet (Bi:YIG) film. The ZnO top layer modulated the Faraday rotation and magnetic circular dichroism (MCD) of the Bi:YIG around the exciton resonance wavelength of ZnO at 369 nm. Furthermore, Al-substituted ZnO, which is a conductive ZnO, also changed the MO effects around the exciton resonance wavelength. These results imply that the exciton-polaritons in ZnO affect the MO interaction, because of their considerably low group velocity. The results suggest potential for controlling the MO response via excitons. Full article
(This article belongs to the Special Issue Spin-dependent Optical, Plasmonic, Confinement and High-frequency Phenomena and Applications—Mini-symposium, ETOPIM11)
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18 pages, 7345 KiB  
Article
Highly Visible Photoluminescence from Ta-Doped Structures of ZnO Films Grown by HFCVD
by Víctor Herrera, Tomás Díaz-Becerril, Eric Reyes-Cervantes, Godofredo García-Salgado, Reina Galeazzi, Crisóforo Morales, Enrique Rosendo, Antonio Coyopol, Román Romano and Fabiola G. Nieto-Caballero
Crystals 2018, 8(10), 395; https://doi.org/10.3390/cryst8100395 - 22 Oct 2018
Cited by 7 | Viewed by 4034
Abstract
Tantalum-doped ZnO structures (ZnO:Ta) were synthesized, and some of their characteristics were studied. ZnO material was deposited on silicon substrates by using a hot filament chemical vapor deposition (HFCVD) reactor. The raw materials were a pellet made of a mixture of ZnO and [...] Read more.
Tantalum-doped ZnO structures (ZnO:Ta) were synthesized, and some of their characteristics were studied. ZnO material was deposited on silicon substrates by using a hot filament chemical vapor deposition (HFCVD) reactor. The raw materials were a pellet made of a mixture of ZnO and Ta2O5 powders, and molecular hydrogen was used as a reactant gas. The percentage of tantalum varied from 0 to 500 mg by varying the percentages of tantalum oxide in the mixture of the pellet source, by holding a fixed amount of 500 mg of ZnO in all experiments. X-ray diffractograms confirmed the presence of zinc oxide in the wurtzite phase, and metallic zinc with a hexagonal structure, and no other phase was detected. Displacements to lower angles of reflection peaks, compared with those from samples without doping, were interpreted as the inclusion of the Ta atoms in the matrix of the ZnO. This fact was confirmed by energy dispersive X-ray spectrometry (EDS), and X-ray diffraction (XRD) measurements. From scanning electron microscopy (SEM) images from undoped samples, mostly micro-sized semi-spherical structures were seen, while doped samples displayed a trend to grow as nanocrystalline rods. The presence of tantalum during the synthesis affected the growth direction. Green photoluminescence was observed by the naked eye when Ta-doped samples were illuminated by ultraviolet radiation and confirmed by photoluminescence (PL) spectra. The PL intensity on the Ta-doped ZnO increased from those undoped samples up to eight times. Full article
(This article belongs to the Special Issue Functional Oxide Based Thin-Film Materials)
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8 pages, 3342 KiB  
Article
Effectiveness of Light Source on Detecting Thin Film Transistor
by Fu-Ming Tzu and Jung-Hua Chou
Crystals 2018, 8(10), 394; https://doi.org/10.3390/cryst8100394 - 21 Oct 2018
Cited by 4 | Viewed by 3177
Abstract
Light sources tend to affect images captured in any automatic optical inspection (AOI) system. In this study, the effectiveness of metal-halide lamps, quartz-halogen lamps, and LEDs as the light sources in AOI systems for the detection of the third and fourth layers electrodes [...] Read more.
Light sources tend to affect images captured in any automatic optical inspection (AOI) system. In this study, the effectiveness of metal-halide lamps, quartz-halogen lamps, and LEDs as the light sources in AOI systems for the detection of the third and fourth layers electrodes of thin-film-transistor liquid crystal displays (TFT-LCDs) is examined experimentally. The results show that the performance of LEDs is generally comparable or better than that of metal-halide and quartz-halogen lamps. The best optical performance is by the blue LED due to its spectrum compatibility with the time-delay-integration charged-coupled device (TDI CCD) sensor and its better spatial resolution. The images revealed by the blue LED are sharper and more distinctive. Since current LEDs are more energy efficient and environmentally friendly, using LEDs as the light source for AOI is very beneficial. As the blue LED performs the best, it should be adopted for AOI using TDI CCD sensors. Full article
(This article belongs to the Special Issue Thin Film Transistor)
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2 pages, 2950 KiB  
Correction
Correction: Taberman, H. Radiation Damage in Macromolecular Crystallography—An Experimentalist’s View. Crystals 2018, 8, 157
by Helena Taberman
Crystals 2018, 8(10), 393; https://doi.org/10.3390/cryst8100393 - 20 Oct 2018
Cited by 1 | Viewed by 2587
Abstract
The author wishes to make the following corrections to this paper [1]:[...] Full article
(This article belongs to the Special Issue Recent Advances in Protein Crystallography)
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8 pages, 2170 KiB  
Article
Cocrystal Assembled by Pyrene Derivative and 1,4-Diiodotetrafluorobenzene via a C=O···I Halogen Bond
by Qi Feng, Wenhui Huan, Jiali Wang, Fang Guo, Jiadan Lu, Guowang Diao and Yaqi Shan
Crystals 2018, 8(10), 392; https://doi.org/10.3390/cryst8100392 - 17 Oct 2018
Cited by 7 | Viewed by 3239
Abstract
Cocrystal formation is a strategy used to modify the solid-state properties of a given molecule. In this study, a new cocrystal assembled by 1,4-Diiodotetrafluorobenzene (1,4-DITFB) and a pyrene derivative, 1-acetyl-3-phenyl-5-(1-pyrenyl)-pyrazoline (APPP), was synthesized. Due to the twisted structure of APPP, the crystal structure [...] Read more.
Cocrystal formation is a strategy used to modify the solid-state properties of a given molecule. In this study, a new cocrystal assembled by 1,4-Diiodotetrafluorobenzene (1,4-DITFB) and a pyrene derivative, 1-acetyl-3-phenyl-5-(1-pyrenyl)-pyrazoline (APPP), was synthesized. Due to the twisted structure of APPP, the crystal structure is greatly different with some large π-conjugated compounds, which exhibits edge-to-face π-stacked arrangement between 1,4-DITFB and pyrene rings, rather than the face-to-face π-stacked arrangement. Hirshfeld surface analysis and the shift of characteristic vibration band of the carbonyl group in FT-IR spectroscopy suggest the formation of a C=O···I halogen bond. Full article
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10 pages, 1918 KiB  
Brief Report
Refolding, Characterization, and Preliminary X-ray Crystallographic Studies on the Campylobacter concisus Plasmid-Encoded Secreted Protein Csep1p Associated with Crohn’s Disease
by Mohammad Mizanur Rahman, Bradley Goff, Li Zhang and Anna Roujeinikova
Crystals 2018, 8(10), 391; https://doi.org/10.3390/cryst8100391 - 16 Oct 2018
Cited by 1 | Viewed by 4316
Abstract
Colonization of Campylobacter concisus in the gastrointestinal tract can lead to the development of inflammatory bowel disease (IBD). Plasmid-encoded C. concisus-secreted protein 1 (Csep1p) was recently identified as a putative pathogenicity marker associated with active Crohn’s disease, a clinical form [...] Read more.
Colonization of Campylobacter concisus in the gastrointestinal tract can lead to the development of inflammatory bowel disease (IBD). Plasmid-encoded C. concisus-secreted protein 1 (Csep1p) was recently identified as a putative pathogenicity marker associated with active Crohn’s disease, a clinical form of IBD. Csep1p shows no significant full-length sequence similarity to proteins of known structure, and its role in pathogenesis is not yet known. This study reports a method for extraction of recombinantly expressed Csep1p from Escherichia coli inclusion bodies, refolding, and purification to produce crystallizable protein. Purified recombinant Csep1p behaved as a monomer in solution. Crystals of Csep1p were grown by the hanging drop vapour diffusion method, using polyethylene glycol (PEG) 4000 as the precipitating agent. A complete data set has been collected to 1.4 Å resolution, using cryocooling conditions and synchrotron radiation. The crystals belong to space group P62 or P64, with unit cell parameters a = b = 85.8, c = 55.2 Å, α = β = 90, and γ = 120°. The asymmetric unit appears to contain one subunit, corresponding to a packing density of 2.47 Å3 Da−1. Full article
(This article belongs to the Special Issue Biological Crystallization)
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9 pages, 5502 KiB  
Article
Dihalogen and Pnictogen Bonding in Crystalline Icosahedral Phosphaboranes
by Jindřich Fanfrlík and Drahomír Hnyk
Crystals 2018, 8(10), 390; https://doi.org/10.3390/cryst8100390 - 13 Oct 2018
Cited by 16 | Viewed by 3178
Abstract
Noncovalent interactions in the single crystal of 3,6-Cl2-closo-1,2-P2B10H8 and in the crystal of closo-1,7-P2B10Cl10•toluene were analyzed by means of quantum chemical computations. The crystal packing in the [...] Read more.
Noncovalent interactions in the single crystal of 3,6-Cl2-closo-1,2-P2B10H8 and in the crystal of closo-1,7-P2B10Cl10•toluene were analyzed by means of quantum chemical computations. The crystal packing in the second crystal was dominated by numerous B-Cl···Cl-B dihalogen and strong B-P···π pnictogen bonds, the latter of which were characterized by a small length of 3.08 Å and a large interaction energy value, exceeding −10 kcal mol−1. Full article
(This article belongs to the Special Issue σ- and π-Hole Interactions in Crystals)
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18 pages, 11954 KiB  
Article
A Phosphonic Acid Anchoring Analogue of the Sensitizer P1 for p-Type Dye-Sensitized Solar Cells
by Y. Maximilian Klein, Nathalie Marinakis, Edwin C. Constable and Catherine E. Housecroft
Crystals 2018, 8(10), 389; https://doi.org/10.3390/cryst8100389 - 12 Oct 2018
Cited by 10 | Viewed by 3843
Abstract
We report the synthesis and characterization of the first example of an organic dye, PP1, for p-type dye-sensitized solar cells (DSCs) bearing a phosphonic acid anchoring group. PP1 is structurally related to the benchmarking dye, P1, which possesses a carboxylic acid [...] Read more.
We report the synthesis and characterization of the first example of an organic dye, PP1, for p-type dye-sensitized solar cells (DSCs) bearing a phosphonic acid anchoring group. PP1 is structurally related to the benchmarking dye, P1, which possesses a carboxylic acid anchor. The solution absorption spectra of PP1 and P1 are similar (PP1 has λmax = 478 nm and εmax = 62,800 dm3 mol−1 cm−1), as are the solid-state absorption spectra of the dyes adsorbed on FTO/NiO electrodes. p-Type DSCs with NiO as semiconductor and sensitized with P1 or PP1 perform comparably. For PP1, short-circuit current densities (JSC) and open-circuit voltages (VOC) for five DSCs lie between 1.11 and 1.45 mA cm−2, and 119 and 143 mV, respectively, compared to ranges of 1.55–1.80 mA cm−2 and 117–130 mV for P1. Photoconversion efficiencies with PP1 are in the range 0.054–0.069%, compared to 0.065–0.079% for P1. Electrochemical impedance spectroscopy, open-circuit photovoltage decay and intensity-modulated photocurrent spectroscopy have been used to compare DSCs with P1 and PP1 in detail. Full article
(This article belongs to the Special Issue Metal Phosphonates and Phosphinates)
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10 pages, 406 KiB  
Review
The Neutron Macromolecular Crystallography Instruments at Oak Ridge National Laboratory: Advances, Challenges, and Opportunities
by Flora Meilleur, Leighton Coates, Matthew J. Cuneo, Andrey Kovalevsky and Dean A. A. Myles
Crystals 2018, 8(10), 388; https://doi.org/10.3390/cryst8100388 - 11 Oct 2018
Cited by 25 | Viewed by 5066
Abstract
The IMAGINE and MaNDi instruments, located at Oak Ridge National Laboratory High Flux Isotope Reactor and Spallation Neutron Source, respectively, are powerful tools for determining the positions of hydrogen atoms in biological macromolecules and their ligands, orienting water molecules, and for differentiating chemical [...] Read more.
The IMAGINE and MaNDi instruments, located at Oak Ridge National Laboratory High Flux Isotope Reactor and Spallation Neutron Source, respectively, are powerful tools for determining the positions of hydrogen atoms in biological macromolecules and their ligands, orienting water molecules, and for differentiating chemical states in macromolecular structures. The possibility to model hydrogen and deuterium atoms in neutron structures arises from the strong interaction of neutrons with the nuclei of these isotopes. Positions can be unambiguously assigned from diffraction studies at the 1.5–2.5 Å resolutions, which are typical for protein crystals. Neutrons have the additional benefit for structural biology of not inducing radiation damage to protein crystals, which can be critical in the study of metalloproteins. Here we review the specifications of the IMAGINE and MaNDi beamlines and illustrate their complementarity. IMAGINE is suitable for crystals with unit cell edges up to 150 Å using a quasi-Laue technique, whereas MaNDi provides neutron crystallography resources for large unit cell samples with unit cell edges up to 300 Å using the time of flight (TOF) Laue technique. The microbial culture and crystal growth facilities which support the IMAGINE and MaNDi user programs are also described. Full article
(This article belongs to the Special Issue Neutron Diffractometers for Single Crystals and Powders)
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14 pages, 5410 KiB  
Article
Study of Detector-Grade CdMnTe:In Crystals Obtained by a Multi-Step Post-Growth Annealing Method
by Pengfei Yu, Yongren Chen, Wei Li, Wenfei Liu, Bin Liu, Jie Yang, Kun Ni, Lijun Luan, Jiahong Zheng, Zhuo Li, Min Bai, Guodong Sun, Hui Li and Wanqi Jie
Crystals 2018, 8(10), 387; https://doi.org/10.3390/cryst8100387 - 11 Oct 2018
Cited by 10 | Viewed by 2837
Abstract
A multi-step annealing method was successfully applied to inclusions reduction and resistivity improvement of CdMnTe:In (CMT:In) single crystals with high resistivity, including a Cd atmosphere annealing step followed by a Te atmosphere annealing step. After the Cd atmosphere annealing step, the density of [...] Read more.
A multi-step annealing method was successfully applied to inclusions reduction and resistivity improvement of CdMnTe:In (CMT:In) single crystals with high resistivity, including a Cd atmosphere annealing step followed by a Te atmosphere annealing step. After the Cd atmosphere annealing step, the density of Te inclusions was reduced distinctly, and it could be also decreased in the subsequent step of re-annealing under Te atmosphere. Both the resistivity and IR transmittance decreased notably after Cd atmosphere annealing, whereas they increased tremendously after re-annealing under a Te atmosphere. The reduction of full-width at-half-maximum (FWHM) and the increase of the intensity of the X-ray rocking curve indicated an improvement of the crystal quality. Meanwhile, after Cd atmosphere annealing, the increase of the intensity of the (D0,X) peak and the disappearance of the (A0,X) peak in photoluminescence (PL) measurements suggested further that the crystal quality was improved. The detector performance was enhanced obviously after annealing. The higher the annealing temperature, the better the performance was. The detector fabricated by CMT:In slice (Cd atmosphere annealing at 1073 K for 240 h and Te atmosphere re-annealing at 773 K for 120 h) with 9.43% energy resolution and 1.25 × 10−3 cm2/V μτ value had the best detector performance. Full article
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15 pages, 8588 KiB  
Article
Frequency Conversion in KTP Crystal and Its Isomorphs
by Sergey Gagarskiy, Sergey Grechin, Pioter Druzhinin, Kiyoshi Kato, David Kochiev, Pavel Nikolaev and Nobihuro Umemura
Crystals 2018, 8(10), 386; https://doi.org/10.3390/cryst8100386 - 10 Oct 2018
Cited by 15 | Viewed by 6733
Abstract
We report the results of an analysis of the functional capabilities of the KTP crystal and its isomorphs for nonlinear-optical frequency conversion of all types of interactions in the transparency range of the crystal. The possibility of implementing angle, wavelength (frequency), and temperature-noncritical [...] Read more.
We report the results of an analysis of the functional capabilities of the KTP crystal and its isomorphs for nonlinear-optical frequency conversion of all types of interactions in the transparency range of the crystal. The possibility of implementing angle, wavelength (frequency), and temperature-noncritical phase matching is shown. Full article
(This article belongs to the Special Issue KTP Crystal for Nonlinear Optical and Electrooptic Applications)
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10 pages, 15696 KiB  
Article
Dynamic Fracture Mechanism of Quasicrystal-Containing Al–Cr–Fe Consolidated Using Spark Plasma Sintering
by Ruitao Li, Zhiyong Wang, Zhong Li, Khiam Aik Khor and Zhili Dong
Crystals 2018, 8(10), 385; https://doi.org/10.3390/cryst8100385 - 10 Oct 2018
Cited by 1 | Viewed by 3437
Abstract
The potential applications of quasicrystals (QCs) in automotive and aerospace industries requires the investigation of their fracture and failure mechanisms under dynamic loading conditions. In this study, Al–Cr–Fe powders were consolidated into pellets using spark plasma sintering at 800 °C for 30 min. [...] Read more.
The potential applications of quasicrystals (QCs) in automotive and aerospace industries requires the investigation of their fracture and failure mechanisms under dynamic loading conditions. In this study, Al–Cr–Fe powders were consolidated into pellets using spark plasma sintering at 800 °C for 30 min. The microhardness and dynamic failure properties of the samples were determined using nanoindentation and split-Hopkinson pressure bar technique, respectively. Scanning electron microscopy and transmission electron microscopy were employed to analyze fracture particles. The dynamic failure strength obtained from the tests is 653 ± 40 MPa. The dynamic failure process is dominated by transgranular fracture mechanisms. The difficulty in the metadislocation motion in the dynamic loading leads to the high brittleness of the spark plasma sintered (SPSed) Al–Cr–Fe materials. Full article
(This article belongs to the Special Issue Structure and Properties of Quasicrystals)
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9 pages, 2946 KiB  
Article
Structural and Magnetic Studies of Cr3+ Substituted Nickel Ferrite Nanomaterials Prepared by Sol-Gel Auto-Combustion
by Jinpei Lin, Yun He, Xianglin Du, Qing Lin, Hu Yang and Hongtao Shen
Crystals 2018, 8(10), 384; https://doi.org/10.3390/cryst8100384 - 9 Oct 2018
Cited by 23 | Viewed by 4604
Abstract
The present study envisages the preparation of chromium substituted Nickel ferrite NiCrxFe2−xO4 (x = 0~1.0) powders by a sol-gel auto-combustion method. X-ray diffraction analysis (XRD) showed that the specimens with x > 0.2 exhibited a single-phase spinel [...] Read more.
The present study envisages the preparation of chromium substituted Nickel ferrite NiCrxFe2−xO4 (x = 0~1.0) powders by a sol-gel auto-combustion method. X-ray diffraction analysis (XRD) showed that the specimens with x > 0.2 exhibited a single-phase spinel structure, and that more content of Cr within a specimen is favorable for the synthesis of pure Ni-Cr ferrites. The lattice parameter decreased with an increase in the Cr concentration. The sample without calcining exhibited a good crystallinity. Scanning Electron Microscopy (SEM) showed the formation of ferrite powders nano-particles, and that the substitution of Cr weakened the agglomeration between the particles. Mössbauer spectra of NiCrxFe2−xO4 showed two normal Zeeman-split sextets that displayed a ferrimagnetic behavior. Furthermore, the spectra indicated that iron was in the Fe3+ state, and the magnetic hyperfine field at the tetrahedral tended to decrease with an increase in the Cr substitution. The saturation magnetization decreased by the Cr3+ ions, and reached a minimum value (Ms = 4.46 emu/g). With an increase in the annealing temperature, the coercivity increased initially, which later decreased. Full article
(This article belongs to the Special Issue Ceramic Conductors)
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10 pages, 2392 KiB  
Article
Continuous Crystalline Membranes of a Ni(II)-Based Pillared-Layer Metal-Organic Framework In Situ Grown on Nickel Foam with Two Orientations
by Yu-Qi Wu, Lin-Hua Xie, Xi Qin, Yu-Xiu Sun, Ya-Bo Xie and Jian-Rong Li
Crystals 2018, 8(10), 383; https://doi.org/10.3390/cryst8100383 - 8 Oct 2018
Cited by 9 | Viewed by 5641
Abstract
The membranes of a pillared-layer structure Metal-Organic Framework (MOF), [Ni(HBTC)(4,4′-bipy)] (HBTC = 1,3,5-Benzenetricarboxylic acid, 4,4′-bipy = 4,4′-bipyridine), have been in situ fabricated on Nickel foam substrate. The orientations of MOF crystals in the membranes can be controlled by the molar ratio of ligand [...] Read more.
The membranes of a pillared-layer structure Metal-Organic Framework (MOF), [Ni(HBTC)(4,4′-bipy)] (HBTC = 1,3,5-Benzenetricarboxylic acid, 4,4′-bipy = 4,4′-bipyridine), have been in situ fabricated on Nickel foam substrate. The orientations of MOF crystals in the membranes can be controlled by the molar ratio of ligand H3BTC to 4,4′-bipyridine. Scanning electron microscope images and powder X-ray diffraction patterns were used to characterize the membranes and confirm the orientations of their MOF layers. Control experiments have revealed that the presence of homologous metal element Nickel in both the MOF and the substrate and the presence of the neutral 4,4′-bipyridine in the reaction system are necessary for in situ growth of the well-intergrown MOF membranes. This work provides a successful example of directly growing continuous MOF layers on porous metallic substrate with desired orientations by a facile approach. Full article
(This article belongs to the Special Issue MOF-Based Membranes)
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16 pages, 6897 KiB  
Article
Evolution of Spin-Crossover Transition in Hybrid Crystals Involving Cationic Iron Complexes [Fe(III)(3-OMesal2-trien)]+ and Anionic Gold Bis(dithiolene) Complexes Au(dmit)2 and Au(dddt)2
by Nataliya G. Spitsyna, Yuri N. Shvachko, Denis V. Starichenko, Erkki Lahderanta, Anton A. Komlev, Leokadiya V. Zorina, Sergey V. Simonov, Maksim A. Blagov and Eduard B. Yagubskii
Crystals 2018, 8(10), 382; https://doi.org/10.3390/cryst8100382 - 3 Oct 2018
Cited by 5 | Viewed by 3907
Abstract
Hybrid ion-pair crystals involving hexadentate [Fe(III)(3-OMesal2-trien)]+ spin-crossover (SCO) cationic complexes and anionic gold complexes [Au(dmit)2]− (1) (dmit = 4,5-dithiolato-1,3-dithiole-2-thione) and [Au(dddt)2]− (2) (dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate) were synthesized and studied by [...] Read more.
Hybrid ion-pair crystals involving hexadentate [Fe(III)(3-OMesal2-trien)]+ spin-crossover (SCO) cationic complexes and anionic gold complexes [Au(dmit)2]− (1) (dmit = 4,5-dithiolato-1,3-dithiole-2-thione) and [Au(dddt)2]− (2) (dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate) were synthesized and studied by single-crystal X-ray diffraction, P-XRD, and SQUID magnetometry. Our study shows that both complexes have similar 1:1 stoichiometry but different symmetry and crystal packing. Complex 1 has a rigid structure in which the SCO cations are engaged in strong π-interplay with molecular surrounding and does not show SCO transition while 2 demonstrates a reversible transition at Tsco = 118 K in a much “softer”, hydrogen-bonded structure. A new structural indicator of spin state in [Fe(sal2-trien)]+ complexes based on conformational analysis has been proposed. Aging and thermocycling ruined the SCO transition increasing the residual HS fraction from 14 to 41%. Magnetic response of 1 is explained by the AFM coupled dimers S = 5/2 with J1 = −0.18 cm−1. Residual high-spin fraction of 2, apart from a contribution of the weak dimers with J12 = J34 = −0.29 cm−1, is characterized by a stronger interdimer coupling of J23 = −1.69 cm−1, which is discussed in terms of possible involvement of neutral radicals [Au(dddt)2]. Full article
(This article belongs to the Special Issue Synthesis and Applications of New Spin Crossover Compounds)
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10 pages, 2104 KiB  
Article
Na4Yb(CO3)3F: A New UV Nonlinear Optical Material with a Large Second Harmonic Generation Response
by Qiaoling Chen, Min Luo and Chensheng Lin
Crystals 2018, 8(10), 381; https://doi.org/10.3390/cryst8100381 - 30 Sep 2018
Cited by 5 | Viewed by 3714
Abstract
A new nonlinear optical crystals fluoride carbonate, Na4Yb(CO3)3F, has been synthesized by mild hydrothermal method. The Na4Yb(CO3)3F crystallizes in the noncentrosymmetric space group Cc (no. 9) with the lattice parameters a [...] Read more.
A new nonlinear optical crystals fluoride carbonate, Na4Yb(CO3)3F, has been synthesized by mild hydrothermal method. The Na4Yb(CO3)3F crystallizes in the noncentrosymmetric space group Cc (no. 9) with the lattice parameters a = 8.018(3), b = 15.929(5), c = 13.950(5) Å and β = 101.425(6)°. The compound Na4Yb(CO3)3F has a high density of [CO3] groups. The structure can be described as one-dimensional [Na5Yb(CO3)2F2] chains connected by [CO3] groups, forming an intricate three-dimensional (3D) framework. Other Na+ and Yb3+ cations are located in the cavities of 3D network. The powder second harmonic generation (SHG) measurement shows that Na4Yb(CO3)3F features a large SHG response, about 4.3 times that of KH2PO4 (KDP), and is a phase-matchable material. In addition, its UV-Vis-NIR diffuse reflectance spectral data indicate that Na4Yb(CO3)3F has a large optical gap about 4.72 eV, which corresponds to the UV cut-off edge of 263 nm. Full article
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6 pages, 5000 KiB  
Article
A Crystallographic Study on the Growth of Partially Faceted MnSn2 Phase during Solidification Process
by Lei Li, Yuantong Bi, Chunyan Ban, Haitao Zhang, Tie Liu, Xiangjie Wang, Claude Esling and Jianzhong Cui
Crystals 2018, 8(10), 380; https://doi.org/10.3390/cryst8100380 - 29 Sep 2018
Cited by 4 | Viewed by 3818
Abstract
The growth of MnSn2 phase during the solidification process of Sn-Mn alloy was crystallographically investigated. The results show that the non-faced spherical caps of the MnSn2 crystals follow the continuous growth mechanism to grow rapidly along the <001> direction, while the [...] Read more.
The growth of MnSn2 phase during the solidification process of Sn-Mn alloy was crystallographically investigated. The results show that the non-faced spherical caps of the MnSn2 crystals follow the continuous growth mechanism to grow rapidly along the <001> direction, while the side surfaces the two-dimensional nucleation mechanism to form the low index {100} and {110} facets. An interface structure analysis indicates that the atom planes within the {100} interplanar spacing period (IPSP) has a lower average reticular density than those within the {011} IPSP. This leads to the faster growth rates and thus the shortening and disappearance of the {100} side facets. As a consequence, the partially faceted (i.e., non-faceted spherical caps and faceted side surfaces) MnSn2 crystals follow an octagonal-base/spherical-cap geometric model (few crystals possess square bases) in three dimensions. Full article
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26 pages, 9865 KiB  
Review
Current Trends in the Development of Microwave Reactors for the Synthesis of Nanomaterials in Laboratories and Industries: A Review
by Sylwia Dąbrowska, Tadeusz Chudoba, Jacek Wojnarowicz and Witold Łojkowski
Crystals 2018, 8(10), 379; https://doi.org/10.3390/cryst8100379 - 27 Sep 2018
Cited by 129 | Viewed by 11942
Abstract
Microwave energy has been in use for many applications for more than 50 years, from communication, food processing, and wood drying to chemical reactions and medical therapy. The areas, where microwave technology is applied, include drying, calcination, decomposition, powder synthesis, sintering, and chemical [...] Read more.
Microwave energy has been in use for many applications for more than 50 years, from communication, food processing, and wood drying to chemical reactions and medical therapy. The areas, where microwave technology is applied, include drying, calcination, decomposition, powder synthesis, sintering, and chemical process control. Before the year 2000, microwaves were used to produce ceramics, semiconductors, polymers, and inorganic materials; in next years, some new attempts were made as well. Nowadays, it has been found that microwave sintering can also be applied to sintered powder and ceramics and is more effective than conventional sintering. Particularly interesting is its use for the synthesis of nanomaterials. This review identifies the main sources of microwave generation, the delivery mechanisms of microwave energy, and the typical designs and configurations of microwave devices, as well as the measurement and construction material problems related to microwave technology. We focus our attention on the configurations, materials, optimized geometries, and solvents used for microwave devices, providing examples of products, especially nanoparticles and other nanomaterials. The identified microwave devices are divided into four groups, depending on the scale, the maximum pressure developed, the highest temperature for sintering, or other special multi-functions. The challenges of using microwave energy for the synthesis of nanopowders have been identified as well. The desirable characteristics of microwave reactors in the synthesis of nanostructures, as well as their superiority over conventional synthetic methods, have been presented. We have also provided a review of the commercial and self-designed microwave reactors, digestors, and sintering furnaces for technology for synthesis of nanomaterials and other industries. Full article
(This article belongs to the Special Issue Microwave-Assisted Synthesis of Nanocrystals and Nanostructures)
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14 pages, 2116 KiB  
Article
NMR Crystallography of the Polymorphs of Metergoline
by Jiri Czernek, Martina Urbanova and Jiri Brus
Crystals 2018, 8(10), 378; https://doi.org/10.3390/cryst8100378 - 25 Sep 2018
Cited by 16 | Viewed by 4490
Abstract
Two polymorphs of the drug compound metergoline (C25H29N3O2) were investigated in detail by solid-state NMR measurements. The results have been analysed by an advanced procedure, which uses experimental input together with the results of quantum [...] Read more.
Two polymorphs of the drug compound metergoline (C25H29N3O2) were investigated in detail by solid-state NMR measurements. The results have been analysed by an advanced procedure, which uses experimental input together with the results of quantum chemical calculations that were performed for molecular crystals. In this way, it was possible to assign the total of 40 1H–13C correlation pairs in a highly complex system, namely, in the dynamically disordered polymorph with two independent molecules in the unit cell of a large volume of 4234 Å3. For the simpler polymorph, which exhibits only small-amplitude motions and has just one molecule in the unit cell with a volume of 529.0 Å3, the values of the principal elements of the 13C chemical shift tensors were measured. Additionally, for this polymorph, a set of crystal structure predictions were generated, and the {13C, 1H} isotropic and 13C anisotropic chemical shielding data were computed while using the gauge-including projector augmented-wave approach combined with the “revised Perdew-Burke-Ernzerhof“ exchange-correlation functional (GIPAW-RPBE). The experimental and theoretical results were combined in an application of the newly developed strategy to polymorph discrimination. This research thus opens up new routes towards more accurate characterization of the polymorphism of drug formulations. Full article
(This article belongs to the Special Issue NMR Crystallography)
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7 pages, 1580 KiB  
Article
Interference Induced Enhancement of Magneto-Optical Effect in Pt/TbCo Hetero-Structured Films
by Syougo Iemoto, Satoshi Sumi, Pham Van Thach, Hiroyuki Awano and Masamitsu Hayashi
Crystals 2018, 8(10), 377; https://doi.org/10.3390/cryst8100377 - 24 Sep 2018
Cited by 4 | Viewed by 3218
Abstract
Magnetic films with a heavy metal layer show strong interfacial interaction of spin-orbit. Spin-orbit interaction is one of the key technologies for spintronics. In this paper, we measured magneto-optical Kerr spectra of Pt/TbCo hetero-structure films on a thermally oxidized silicon substrate (0.3 mm); [...] Read more.
Magnetic films with a heavy metal layer show strong interfacial interaction of spin-orbit. Spin-orbit interaction is one of the key technologies for spintronics. In this paper, we measured magneto-optical Kerr spectra of Pt/TbCo hetero-structure films on a thermally oxidized silicon substrate (0.3 mm); A: Pt (3 nm)/TbCo (6 nm)/Pt (3 nm), B: Si3N4 (10 nm)/TbCo (6 nm)/Pt (3 nm), and C: Pt (3 nm)/TbCo (6 nm)/Si3N4 (10 nm). Magneto-optical Kerr spectra of each sample were measured with a wavelength range of 300–700 nm, and were compared to the simulated spectra using the effective refractive index method. In the sample A, which has a symmetric structure, the simulated spectra are consistent with the measured ones. On the other hand, in the samples B and C, with an asymmetric structure, there are some differences between the simulated spectra and the measured ones in a lower photon energy region. This may be caused by interfacial effects of the spin-orbit interaction. Full article
(This article belongs to the Special Issue Spin-dependent Optical, Plasmonic, Confinement and High-frequency Phenomena and Applications—Mini-symposium, ETOPIM11)
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16 pages, 3980 KiB  
Article
Solvent Effects on the Spin-Transition in a Series of Fe(II) Dinuclear Triple Helicate Compounds
by Alexander R. Craze, Mohan M. Bhadbhade, Cameron J. Kepert, Leonard F. Lindoy, Christopher E. Marjo and Feng Li
Crystals 2018, 8(10), 376; https://doi.org/10.3390/cryst8100376 - 23 Sep 2018
Cited by 11 | Viewed by 4833
Abstract
This work explores the effect of lattice solvent on the observed solid-state spin-transition of a previously reported dinuclear Fe(II) triple helicate series 1–3 of the general form [FeII2L3](BF4)4(CH3CN)n, [...] Read more.
This work explores the effect of lattice solvent on the observed solid-state spin-transition of a previously reported dinuclear Fe(II) triple helicate series 1–3 of the general form [FeII2L3](BF4)4(CH3CN)n, where L is the Schiff base condensation product of imidazole-4-carbaldehyde with 4,4-diaminodiphenylmethane (L1), 4,4′-diaminodiphenyl sulfide (L2) and 4,4′-diaminodiphenyl ether (L3) respectively, and 1 is the complex when L = L1, 2 when L = L2 and 3 when L = L3 (Craze, A.R.; Sciortino, N.F.; Bhadbhade, M.M.; Kepert, C.J.; Marjo, C.E.; Li, F. Investigation of the Spin Crossover Properties of Three Dinuclear Fe(II) Triple Helicates by Variation of the Steric Nature of the Ligand Type. Inorganics. 2017, 5 (4), 62). Desolvation of 1 and 2 during measurement resulted not only in a decrease in T1/2 and completeness of spin-crossover (SCO) but also a change in the number of steps in the spin-profile. Compounds 1 and 2 were observed to change from a two-step 70% complete transition when fully solvated, to a single-step half complete transition upon desolvation. The average T1/2 value of the two-steps in the solvated materials was equivalent to the single T1/2 of the desolvated sample. Upon solvent loss, the magnetic profile of 3 experienced a transformation from a gradual SCO or weak antiferromagnetic interaction to a single half-complete spin-transition. Variable temperature single-crystal structures are presented and the effects of solvent molecules are also explored crystallographically and via a Hirshfeld surface analysis. The spin-transition profiles of 1–3 may provide further insight into previous discrepancies in dinuclear triple helicate SCO research reported by the laboratories of Hannon and Gütlich on analogous systems (Tuna, F.; Lees, M. R.; Clarkson, G. J.; Hannon, M. J. Readily Prepared Metallo-Supramolecular Triple Helicates Designed to Exhibit Spin-Crossover Behaviour. Chem. Eur. J. 2004, 10, 5737–5750 and Garcia, Y.; Grunert, C. M.; Reiman, S.; van Campenhoudt, O.; Gütlich, P. The Two-Step Spin Conversion in a Supramolecular Triple Helicate Dinuclear Iron(II) Complex Studied by Mössbauer Spectroscopy. Eur. J. Inorg. Chem. 2006, 3333–3339). Full article
(This article belongs to the Special Issue Synthesis and Applications of New Spin Crossover Compounds)
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28 pages, 19453 KiB  
Review
Basic Concepts and Recent Advances of Crystallographic Orientation Determination of Graphene by Raman Spectroscopy
by Yucheng Lan, Mobolaji Zondode, Hua Deng, Jia-An Yan, Marieme Ndaw, Abdellah Lisfi, Chundong Wang and Yong-Le Pan
Crystals 2018, 8(10), 375; https://doi.org/10.3390/cryst8100375 - 21 Sep 2018
Cited by 26 | Viewed by 11076
Abstract
Graphene is a kind of typical two-dimensional material consisting of pure carbon element. The unique material shows many interesting properties which are dependent on crystallographic orientations. Therefore, it is critical to determine their crystallographic orientations when their orientation-dependent properties are investigated. Raman spectroscopy [...] Read more.
Graphene is a kind of typical two-dimensional material consisting of pure carbon element. The unique material shows many interesting properties which are dependent on crystallographic orientations. Therefore, it is critical to determine their crystallographic orientations when their orientation-dependent properties are investigated. Raman spectroscopy has been developed recently to determine crystallographic orientations of two-dimensional materials and has become one of the most powerful tools to characterize graphene nondestructively. This paper summarizes basic aspects of Raman spectroscopy in crystallographic orientation of graphene nanosheets, determination principles, the determination methods, and the latest achievements in the related studies. Full article
(This article belongs to the Special Issue Graphene Mechanics)
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8 pages, 1810 KiB  
Communication
Crystal Structure of the Protonated Germanide Cluster [HGe9]3−
by Corinna Lorenz and Nikolaus Korber
Crystals 2018, 8(10), 374; https://doi.org/10.3390/cryst8100374 - 21 Sep 2018
Cited by 5 | Viewed by 4218
Abstract
A single crystal X-ray diffraction study of the new compound [Rb([2.2.2]crypt)]2[Rb([18]crown−6)][HGe9]·4NH3 revealed the presence of the first protonated nine-atom germanide cluster [HGe9]3−. It forms from Rb4Ge9 in liquid ammonia, so that [...] Read more.
A single crystal X-ray diffraction study of the new compound [Rb([2.2.2]crypt)]2[Rb([18]crown−6)][HGe9]·4NH3 revealed the presence of the first protonated nine-atom germanide cluster [HGe9]3−. It forms from Rb4Ge9 in liquid ammonia, so that [Ge9]4− can be considered as the base and [HGe9]3− its formally conjugated acid. The H atom is attached to a germanium vertex atom of the basal square plane, as it is known for [RGe9]3− (R = C5H9, Mes, etc.) or [HE9]3− (E = Si, Sn). In addition, the proton could be located unambiguously in the Fourier difference map. [HGe9]3− also represents a nido cluster species with 22 cluster-bonding electrons, which can be considered the most stable structure for nine-atom cluster species for all group 14 elements. Full article
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11 pages, 4723 KiB  
Article
Propylene-Selective Thin Zeolitic Imidazolate Framework Membranes on Ceramic Tubes by Microwave Seeding and Solvothermal Secondary Growth
by Jingze Sun, Chen Yu and Hae-Kwon Jeong
Crystals 2018, 8(10), 373; https://doi.org/10.3390/cryst8100373 - 21 Sep 2018
Cited by 13 | Viewed by 5535
Abstract
Zeolitic imidazolate framework (ZIF-8) membranes have attracted tremendous interest for their high-resolution kinetic separation of propylene/propane mixtures. Current polycrystalline ZIF-8 membranes are supported mostly on planar ceramic substrates (e.g., alumina disks) because of their high thermal, chemical, and mechanical stabilities and facile manufacturing [...] Read more.
Zeolitic imidazolate framework (ZIF-8) membranes have attracted tremendous interest for their high-resolution kinetic separation of propylene/propane mixtures. Current polycrystalline ZIF-8 membranes are supported mostly on planar ceramic substrates (e.g., alumina disks) because of their high thermal, chemical, and mechanical stabilities and facile manufacturing in the labs. Planar supports are, however, not scalable for practical separation applications owing to their low packing density (typically 30–500 m2/m3). On the other hand, ceramic tubes provide order-of-magnitude higher packing densities than planar supports (i.e., much higher membrane areas per module). Here, we report polycrystalline ZIF-8 membranes with thicknesses of ~1.2 μm grown on the bore side of commercially-available ceramic tubes using the microwave seeding and secondary growth technique. The tubular ZIF-8 membranes showed excellent propylene/propane separation factors of ~80, exceeding all currently-reported ZIF-8 membranes on ceramic tubes. It was found that the secondary growth time was critical to enhance the propylene/propane separation factor of the membranes. Membranes were also grown on the shell side of tubular supports, showing the versatility of our technique. Full article
(This article belongs to the Special Issue MOF-Based Membranes)
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12 pages, 8073 KiB  
Article
Synthesis, Crystal Structure, and Properties of a New Coordination Polymer Built from N/O-Donor Mixed Ligands
by Mei-An Zhu, Shuai-Shuai Han, Feng Deng, Jia-Le Li and Shui-Sheng Chen
Crystals 2018, 8(10), 372; https://doi.org/10.3390/cryst8100372 - 21 Sep 2018
Viewed by 3039
Abstract
The coordination polymer, namely, [Cd(H2L)(nobda)]n (1) was prepared by the reaction of Cd(NO3)2·4H2O with 4-amino-1,2-benzenedicarboxylic acid (H2nobda) and 1,4-di(1H-imidazol-4-yl)benzene (H2L), and characterized by single-crystal X-ray diffraction, [...] Read more.
The coordination polymer, namely, [Cd(H2L)(nobda)]n (1) was prepared by the reaction of Cd(NO3)2·4H2O with 4-amino-1,2-benzenedicarboxylic acid (H2nobda) and 1,4-di(1H-imidazol-4-yl)benzene (H2L), and characterized by single-crystal X-ray diffraction, elemental analysis, infrared (IR) spectroscopy, thermogravimetric analysis, and powder X-ray diffraction (PXRD). The carboxylic acid of H2nobda ligands was completely deprotonated to be nobda2− anions, which act as tridentate ligand to connect the Cd2+ to form two-dimensional (2D) network, while the neutral H2L ligands serve as a linear didentate bridge to connect two adjacent Cd2+ ions upper and down the 2D layer. The adjacent 2D layers were further linked into the three-dimensional (3D) supramolecular polymer by the weak interactions such as hydrogen bonds and π−π stacking interactions. The ultraviolet-visible (UV-vis) absorption spectra and luminescent properties in the solid state at room temperature have been investigated. Full article
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15 pages, 7133 KiB  
Article
Comparison of the Mesomorphic Behaviour of 1:1 and 1:2 Mixtures of Charged Gay-Berne GB(4.4,20.0,1,1) and Lennard-Jones Particles
by Tommaso Margola, Katsuhiko Satoh and Giacomo Saielli
Crystals 2018, 8(10), 371; https://doi.org/10.3390/cryst8100371 - 20 Sep 2018
Cited by 14 | Viewed by 4210
Abstract
We present a Molecular Dynamics study of mixtures of charged Gay-Berne (GB) ellipsoids and spherical Lennard-Jones (LJ) particles as models of ionic liquids and ionic liquid crystals. The GB system is highly anisotropic (GB(4.4,20.0,1,1)) and we observe a rich mesomorphism, with ionic nematic [...] Read more.
We present a Molecular Dynamics study of mixtures of charged Gay-Berne (GB) ellipsoids and spherical Lennard-Jones (LJ) particles as models of ionic liquids and ionic liquid crystals. The GB system is highly anisotropic (GB(4.4,20.0,1,1)) and we observe a rich mesomorphism, with ionic nematic and smectic phases in addition to the isotropic mixed phase and crystalline phases with honeycomb structure. The systems have been investigated by analyzing the orientational and translational order parameters, as well as radial distribution functions. We have directly compared 1:1 mixtures, where the GB and LJ particles have a charge equal in magnitude and opposite in sign, and 1:2 mixtures where the number of LJ particles is twice as large compared to the GB and their charge half in magnitude. The results highlight the role of the long-range isotropic electrostatic interaction compared to the short-range van der Waals anisotropic contribution, and the effect of the stoichiometry on the stability of ionic mesophases. Full article
(This article belongs to the Special Issue Ionic Liquid Crystals)
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16 pages, 29266 KiB  
Article
Quasicrystal Tilings in Three Dimensions and Their Empires
by Dugan Hammock, Fang Fang and Klee Irwin
Crystals 2018, 8(10), 370; https://doi.org/10.3390/cryst8100370 - 20 Sep 2018
Cited by 3 | Viewed by 6231
Abstract
The projection method for constructing quasiperiodic tilings from a higher dimensional lattice provides a useful context for computing a quasicrystal’s vertex configurations, frequencies, and empires (forced tiles). We review the projection method within the framework of the dual relationship between the Delaunay and [...] Read more.
The projection method for constructing quasiperiodic tilings from a higher dimensional lattice provides a useful context for computing a quasicrystal’s vertex configurations, frequencies, and empires (forced tiles). We review the projection method within the framework of the dual relationship between the Delaunay and Voronoi cell complexes of the lattice being projected. We describe a new method for calculating empires (forced tiles) which also borrows from the dualisation formalism and which generalizes to tilings generated projections of non-cubic lattices. These techniques were used to compute the vertex configurations, frequencies and empires of icosahedral quasicrystals obtained as a projections of the D 6 and Z 6 lattices to R 3 and we present our analyses. We discuss the implications of this new generalization. Full article
(This article belongs to the Special Issue Structure and Properties of Quasicrystals)
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25 pages, 771 KiB  
Review
Non-Platinum Metal Complexes as Potential Anti-Triple Negative Breast Cancer Agents
by Eva María Domínguez-Martís, Diego Gabriel Mosteiro-Miguéns, Lucía Vigo-Gendre, David López-Ares, Manuel Freire-Garabal, María Jesús Núñez-Iglesias and Silvia Novío
Crystals 2018, 8(10), 369; https://doi.org/10.3390/cryst8100369 - 20 Sep 2018
Cited by 13 | Viewed by 4253
Abstract
Breast cancer (BC) is the most common cancer in women worldwide, with a mortality rate that has been forecasted to rise in the next decade. This is especially worrying for people with triple-negative BC (TNBC), because of its unresponsiveness to current therapies. Different [...] Read more.
Breast cancer (BC) is the most common cancer in women worldwide, with a mortality rate that has been forecasted to rise in the next decade. This is especially worrying for people with triple-negative BC (TNBC), because of its unresponsiveness to current therapies. Different drugs to treat TNBC have been assessed, and, although platinum chemotherapy drugs seem to offer some hope, their drawbacks have motivated extensive investigations into alternative metal-based BC therapies. This paper aims to: (i) describe the preliminary in vitro and in vivo anticancer properties of non-platinum metal-based complexes (NPMBC) against TNBC; and (ii) analyze the likely molecular targets involved in their anticancer activity. Full article
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11 pages, 3340 KiB  
Article
The Crystal Structure of Defect KBB’O6 Pyrochlores (B,B’: Nb,W,Sb,Te) Revisited from Neutron Diffraction Data
by Sergio F. Mayer, Horacio Falcón, María Teresa Fernández-Díaz and José Antonio Alonso
Crystals 2018, 8(10), 368; https://doi.org/10.3390/cryst8100368 - 20 Sep 2018
Cited by 10 | Viewed by 4224
Abstract
Three defect pyrochlores KNbWO6·xH2O, KNbTeO6 and KSbWO6 were synthesized by solid state reaction at 750 °C, from stoichiometric mixtures of K2C2O4, Sb2O3, Nb2O [...] Read more.
Three defect pyrochlores KNbWO6·xH2O, KNbTeO6 and KSbWO6 were synthesized by solid state reaction at 750 °C, from stoichiometric mixtures of K2C2O4, Sb2O3, Nb2O5, WO3 and 20% excess TeO2. A neutron powder diffraction (NPD) data analysis allowed unveiling some structural features. They are all defined in the cubic F d 3 ¯ m space group symmetry, with α = 10.5068(1) Å, 10.2466(1) Å and 10.2377(1) Å, respectively. Difference Fourier synthesis for KNbWO6·xH2O clearly showed the presence of crystallization water, with extra O’ oxygen and H+ atoms that were located from NPD data. These O’ oxygen atoms are placed at 32e Wyckoff sites, conforming a K2O’ sublattice interpenetrated with the covalent framework constituted by (Nb,W)O6 octahedra. The H+ ions coordinate the O’ atoms at partially occupied 96g Wyckoff sites while K+ ions shift also along 32e sites, but closer to the 16c special site (0,0,0). By contrast, extra H2O molecules are absent in the other two pyrochlores: in KNbTeO6 and KSbWO6 K+ ions are shifted along 32e (x,x,x) sites further away from the origin than for the previous material, and the higher covalency of the octahedral network determines more compact structures, with shorter B–O distances and narrower B–O–B angles in the proposed AB2O6 defect pyrochlore structure. Full article
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12 pages, 5023 KiB  
Article
Size-Controllable Synthesis of Zeolitic Imidazolate Framework/Carbon Nanotube Composites
by Fang Fu, Bin Zheng, Lin-Hua Xie, Huiling Du, Shuangming Du and Zhenhua Dong
Crystals 2018, 8(10), 367; https://doi.org/10.3390/cryst8100367 - 20 Sep 2018
Cited by 34 | Viewed by 6834
Abstract
Composite materials that combine the unique properties of zeolitic imidazolate frameworks (ZIFs) and carbon nanotubes (CNTs) can give rise to novel applications. Here, ZIF-8/CNT composites were successfully prepared with and without the addition of an agent template. The size of the ZIF-8 crystals [...] Read more.
Composite materials that combine the unique properties of zeolitic imidazolate frameworks (ZIFs) and carbon nanotubes (CNTs) can give rise to novel applications. Here, ZIF-8/CNT composites were successfully prepared with and without the addition of an agent template. The size of the ZIF-8 crystals in the composite materials was controlled by varying the template, feeding order, and concentration of reactants. Thus, ZIF-8 crystals with a wide variety of sizes (from nano- to micrometer size, which is range that differs by a factor of 10) were obtained, depending on the conditions. This size-controllable synthesis of ZIF-8 was achieved by modifying the number of nucleation sites on the CNTs, as revealed by density functional theory (DFT) calculations. This work provides an efficient method for preparing ZIF-8/CNT composites with controllable size and can pave the way for the synthesis of other metal-organic framework (MOF)/CNT composite materials. Full article
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