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Crystals, Volume 11, Issue 1 (January 2021) – 77 articles

Cover Story (view full-size image): Zinc iodate, Zn(IO3)2 has been studied under compression up to 17 GPa by means of synchrotron infrared microspectroscopy measurements. This is the first time this metal iodate is being studied via high-pressure Fourier Transform Infrared microspectroscopy. The experiments allowed the detection of twenty-five phonons below 600 cm−1 for the initial monoclinic low-pressure polymorph of Zn(IO3)2. The pressure response of the modes has been characterized, with several modes exhibiting non-linear responses. The non-linear behavior of modes and the detection of frequency discontinuities have been related to the possible existence of pressure-driven phase transitions. A meticulous analysis of the high-pressure spectra indicates that Zn(IO3)2 undergoes subtle phase transitions around 3 and 8 GPa, which are followed by a more drastic transition around 13 GPa. View t
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Open AccessArticle
Investigating the Potential of Flexible and Pre-Organized Tetraamide Ligands to Encapsulate Anions in One-Dimensional Coordination Polymers: Synthesis, Spectroscopic Studies and Crystal Structures
Crystals 2021, 11(1), 77; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11010077 - 19 Jan 2021
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Abstract
The synthesis of amide-based molecules, possessing pre-organized structures, has received significant attention due to their potential applications as molecular receptors and as components of nanomaterials. In this study, four extended tetraamide ligands incorporating ethylene and propylene spacers, namely 1,2-bis[N,N′-6-(3-pyridylmethylamido)pyridyl-2-carboxyamido]ethane (L1), 1,2-bis[ [...] Read more.
The synthesis of amide-based molecules, possessing pre-organized structures, has received significant attention due to their potential applications as molecular receptors and as components of nanomaterials. In this study, four extended tetraamide ligands incorporating ethylene and propylene spacers, namely 1,2-bis[N,N′-6-(3-pyridylmethylamido)pyridyl-2-carboxyamido]ethane (L1), 1,2-bis[N,N′-6-(4-pyridylmethylamido)pyridyl-2-carboxyamido]ethane (L2), 1,2-bis[N,N′-6-(3-pyridylmethylamido)pyridyl-2-carboxyamido]propane (L3) and 1,2-bis[N,N′-6-(4-pyridylmethylamido)pyridyl-2-carboxyamido]propane (L4), were successfully synthesized. Further, reaction of L2 and L4, incorporating pendant 4-pyridyl donors as the metal coordinating sites, with cadmium salts, produced two close-packed one-dimensional coordination polymers, {[Cd3(L2)4(H2O)10](NO3)6·12H2O·CH3OH}n and {[Cd(SO4)(L4)(H2O)2]·4H2O·CH3OH}n. X-ray crystallography reveals that the flexible tetraamide ligands fold upon themselves in the coordination polymer structure. As a consequence, the anion pocket in {[Cd(SO4)(L4)(H2O)2]·4H2O·CH3OH}n incorporating the ligand with the propylene spacer was blocked from encapsulating charge-balancing anions, which were involved in bridging the di-cadmium units. Interestingly, a strong interaction between the 2,6-pyridine dicarboxamide moiety with the nitrate anions was found in {[Cd3(L2)4(H2O)10](NO3)6·12H2O·CH3OH}n, showing potential for materials made from these ligands to serve as anion receptors. Full article
(This article belongs to the Section Inorganic Crystalline Materials)
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Open AccessArticle
Spectroscopic Investigations, Computational Analysis and Molecular Docking to SAR-Cov-2 Targets Studies of 5,8-Quinolinedione Attached to Betulin Derivatives
Crystals 2021, 11(1), 76; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11010076 - 19 Jan 2021
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Abstract
The 5,8-quinolinedione-betulin hybrids were investigated using spectroscopic methods as well as a variety of quantum chemical calculations in order to characterize their molecular structure. We used FT-IR and NMR spectroscopy supplemented by the density functional theory (DFT) calculations, molecular electrostatic potential (MEP) and [...] Read more.
The 5,8-quinolinedione-betulin hybrids were investigated using spectroscopic methods as well as a variety of quantum chemical calculations in order to characterize their molecular structure. We used FT-IR and NMR spectroscopy supplemented by the density functional theory (DFT) calculations, molecular electrostatic potential (MEP) and molecular orbital (HOMO, LUMO) analyses. The experimental and calculated FT-IR spectra showed a good correlation for all compounds. Analysis of carbonyl band showed that the compounds are the 7-mono substituted. The calculated 1H NMR and 13C NMR spectra of hybrids reproduced well the experimental ones. Identification of C-6 and C-7 carbon atoms of 5,8-quinolinedione revealed the position of betulin moiety at the C-7 of 5,8-quinolinedione. Molecular electrostatic potential maps of hybrids allowed to recognize the electrophilic and nucleophilic regions within the molecules. The molecular docking study was used to examine the interaction between the 5,8-quinolinedione-betulin hybrids and the SARS-CoV-2 protein, like: Mpro and PLpro. The obtained results showed that compounds with the highest Dock Score are good anti-SARS-CoV-2 potential drug candidates. Full article
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Open AccessArticle
One-Step Carbothermal Synthesis of Super Nanoadsorbents for Rapid and Recyclable Wastewater Treatment
Crystals 2021, 11(1), 75; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11010075 - 18 Jan 2021
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Abstract
As a potential magnetic super adsorbent in wastewater treatment, Fe3O4 has been researched intensively up to date. However, its key problem of poor comprehensive magnetic properties is still challenging. In this work, an effective solution to this problem has been [...] Read more.
As a potential magnetic super adsorbent in wastewater treatment, Fe3O4 has been researched intensively up to date. However, its key problem of poor comprehensive magnetic properties is still challenging. In this work, an effective solution to this problem has been developed by a one-step carbothermal synthesis of Fe3O4 crystals, which are merited with pure-stoichiometry (FeO-phase free), high crystallinity, small-size (~10 nm), strong magnetism and sensitive magnetic response. The unveiled saturation magnetization of Fe3O4 nanoparticles reaches as high as 90.32 emu·g−1, and the fastest magnetic response time is as short as only 5 s. Such magnetic Fe3O4 super adsorbents exhibit outstanding performance when applied as an adsorbent for wastewater treatment. They can quickly and effectively adsorb methylene blue with an adsorption capacity of 62.5 mg·g−1, which is much higher than that of Fe3O4 adsorbents prepared by other methods reported in the literature. Importantly, this capacity is refreshable after removing the adsorbed methylene blue just by ultrasonic cleaning. With such combined outstanding magnetic properties and recyclable adsorption capacity, the problems associated with the conventional adsorbent solid–liquid separation could be resolved, thus making a forward development towards industrial wastewater treatment. Full article
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Open AccessEditorial
Numerical Study of Concrete
Crystals 2021, 11(1), 74; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11010074 - 18 Jan 2021
Viewed by 322
Abstract
This Special Issue, “Numerical Study of Concrete”, consists of 22 research articles [...] Full article
(This article belongs to the Special Issue Numerical Study of Concrete)
Open AccessArticle
The Role of Deposition Temperature in the Photovoltaic Properties of RF-Sputtered CdSe Thin Films
Crystals 2021, 11(1), 73; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11010073 - 17 Jan 2021
Viewed by 334
Abstract
Cadmium selenide (CdSe) thin films were grown on borosilicate glass substrates using the RF magnetron sputtering method. In this study, CdSe thin film was deposited at a deposition temperature in the range of 25 °C to 400 °C. The influence of deposition or [...] Read more.
Cadmium selenide (CdSe) thin films were grown on borosilicate glass substrates using the RF magnetron sputtering method. In this study, CdSe thin film was deposited at a deposition temperature in the range of 25 °C to 400 °C. The influence of deposition or growth temperature on the structural, morphological, and opto-electrical properties of CdSe films was investigated elaborately to achieve a good-quality window layer for solar-cell applications. The crystal structure, surface morphology, and opto-electrical characteristics of sputtered CdSe films were determined using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), UV–Vis spectrophotometry, and Hall effect measurement, respectively. The XRD results revealed the polycrystalline nature of CdSe, with a hexagonal structure having a strong preferential orientation toward the (002) plane. As evident from the FESEM images, the average grain size and surface morphology of the films were dependent on deposition temperatures. The carrier concentration was obtained as 1014 cm−3. The band gap in the range of 1.65–1.79 eV was found. The explored results suggested that sputtered CdSe thin film deposited at 300 °C has the potential to be used as a window layer in solar cells. Full article
(This article belongs to the Special Issue Synthesis, Structure and Property Analysis of Crystalline Layers)
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Open AccessArticle
Evolution of Shape and Volume Fraction of Superconducting Domains with Temperature and Anion Disorder in (TMTSF)2ClO4
Crystals 2021, 11(1), 72; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11010072 - 17 Jan 2021
Viewed by 283
Abstract
In highly anisotropic organic superconductor (TMTSF)2ClO4, superconducting (SC) phase coexists with metallic and spin-density wave phases in the form of domains. Using the Maxwell-Garnett approximation (MGA), we calculate the volume ratio and estimate the shape of these embedded SC [...] Read more.
In highly anisotropic organic superconductor (TMTSF)2ClO4, superconducting (SC) phase coexists with metallic and spin-density wave phases in the form of domains. Using the Maxwell-Garnett approximation (MGA), we calculate the volume ratio and estimate the shape of these embedded SC domains from resistivity data at various temperature and anion disorder, controlled by the cooling rate or annealing time of (TMTSF)2ClO4 samples. We found that the variation of cooling rate and of annealing time affect differently the shape of SC domains. In all cases the SC domains have oblate shape, being the shortest along the interlayer z-axis. This contradicts the widely assumed filamentary superconductivity along the z-axis, used to explain the anisotropic superconductivity onset. We show that anisotropic resistivity drop at the SC onset can be described by the analytical MGA theory with anisotropic background resistance, while the anisotropic Tc can be explained by considering a finite size and flat shape of the samples. Due to a flat/needle sample shape, the probability of percolation via SC domains is the highest along the shortest sample dimension (z-axis), and the lowest along the sample length (x-axis). Our theory can be applied to other heterogeneous superconductors, where the size d of SC domains is much larger than the SC coherence length ξ, e.g., cuprates, iron-based or organic superconductors. It is also applicable when the spin/charge-density wave domains are embedded inside a metallic background, or vice versa. Full article
(This article belongs to the Special Issue Organic Conductors)
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Open AccessCommunication
Comparative Study of Cold Sintering Process and Autoclave Thermo-Vapor Treatment on a ZnO Sample
Crystals 2021, 11(1), 71; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11010071 - 16 Jan 2021
Viewed by 393
Abstract
Analysis of scanning electron microscopy images was used to study the changes in the crystal size distribution of ZnO, which occurred during its processing in an aqueous medium at 220–255 °C and an equilibrium vapor pressure in an autoclave. The results were compared [...] Read more.
Analysis of scanning electron microscopy images was used to study the changes in the crystal size distribution of ZnO, which occurred during its processing in an aqueous medium at 220–255 °C and an equilibrium vapor pressure in an autoclave. The results were compared with those of ZnO placed in a die for treatment under similar conditions supplemented with mechanical pressure application in the cold sintering process. In both cases, ZnO was treated in the presence of an activating additive: either zinc acetate or ammonium chloride. During autoclaving, a powder consisting of fine ZnO monocrystals was obtained, while the cold sintering process led to ceramics formation. Under vapor pressure and mechanical pressure, the aqueous medium affected ZnO transformation by the same mechanism of solid-phase mobility activation due to the additives’ influence. The higher the content of additives in the medium, and the higher the mechanical pressure, the more pronounced activating effect was observed. Mass transfer during the cold sintering process occurred mainly by the coalescence of crystals, while without mechanical pressure, the predominance of surface spreading was revealed. In the initial ZnO powder, the average crystal size was 0.193 μm. It grew up to 0.316–0.386 μm in a fine-crystalline powder formed in the autoclave and to an average grain size of 0.244–0.799 μm in the ceramics, which relative density reached 0.82–0.96. A scheme explaining the influence of an aqueous medium on the solid-phase mobility of ZnO structure was proposed. It was found that the addition of 7.6 mol% ammonium chloride to the reaction medium causes the processes of compaction and grain growth similar to those observed in ZnO Cold Sintering Process with the addition of 0.925 mol% zinc acetate. Full article
(This article belongs to the Special Issue Advanced Functional Oxide Ceramics)
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Open AccessArticle
A Comparison Study on Multilayered Barrier Oxide Structure in Charge Trap Flash for Synaptic Operation
Crystals 2021, 11(1), 70; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11010070 - 16 Jan 2021
Viewed by 392
Abstract
A synaptic device that contains weight information between two neurons is one of the essential components in a neuromorphic system, which needs highly linear and symmetric characteristics of weight update. In this study, a charge trap flash (CTF) memory device with a multilayered [...] Read more.
A synaptic device that contains weight information between two neurons is one of the essential components in a neuromorphic system, which needs highly linear and symmetric characteristics of weight update. In this study, a charge trap flash (CTF) memory device with a multilayered high-κ barrier oxide structure on the MoS2 channel is proposed. The fabricated device was oxide-engineered on the barrier oxide layers to achieve improved synaptic functions. A comparison study between two fabricated devices with different barrier oxide materials (Al2O3 and SiO2) suggests that a high-κ barrier oxide structure improves the synaptic operations by demonstrating the increased on/off ratio and symmetry of synaptic weight updates due to a better coupling ratio. Lastly, the fabricated device has demonstrated reliable potentiation and depression behaviors and spike-timing-dependent plasticity (STDP) for use in a spiking neural network (SNN) neuromorphic system. Full article
(This article belongs to the Special Issue Functional Oxide Based Thin-Film Materials (Volume II))
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Open AccessArticle
Modulation Effect of Hardness on the Friction Coefficient and Its Mechanism Analysis of ZrB2/Mo Multilayers Synthesized by Magnetron Sputtering
Crystals 2021, 11(1), 69; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11010069 - 16 Jan 2021
Viewed by 334
Abstract
ZrB2/Mo multilayers were prepared by the magnetron sputtering technique on Si (100) and Al2O3 (001) substrates. The friction behavior and wear mechanism of the multilayers were tested at variable modulation ratios (tZrB2:tMo) [...] Read more.
ZrB2/Mo multilayers were prepared by the magnetron sputtering technique on Si (100) and Al2O3 (001) substrates. The friction behavior and wear mechanism of the multilayers were tested at variable modulation ratios (tZrB2:tMo) of 1:1 to 8:1 at different temperatures. Under the influence of an effective modulation ratio and temperature, the friction coefficient and hardness of ZrB2/Mo multilayers showed an almost opposite change rule, that is, the higher the hardness, the lower the friction coefficient. The hardness and elastic modulus reached the maximum value (26.1 GPa and 241.99 GPa) at tZrB2:tMo = 5:1 and the corresponding friction coefficient was 0.86. Meanwhile, the hardness and average friction coefficient at 500 °C were, respectively, 8.9 GPa and 1.23. First-principles calculations of the interface model of ZrB2 (001)/Mo (110) showed that the ionic bonds and covalent bonds at the interface can effectively improve the viscosity of the multilayer and the stability of the interface, and thus increase the hardness. This also indicated that the variation of the friction coefficient was mainly determined by the stability of the interface in the ZrB2/Mo multilayers. Full article
(This article belongs to the Special Issue First-Principles Simulation—Nano-Theory)
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Open AccessReview
The Formation and Control of Ice Crystal and Its Impact on the Quality of Frozen Aquatic Products: A Review
Crystals 2021, 11(1), 68; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11010068 - 15 Jan 2021
Viewed by 386
Abstract
Although freezing has been used to delay the deterioration of product quality and extend its shelf life, the formation of ice crystals inevitably destroys product quality. This comprehensive review describes detailed information on the effects of ice crystals on aquatic products during freezing [...] Read more.
Although freezing has been used to delay the deterioration of product quality and extend its shelf life, the formation of ice crystals inevitably destroys product quality. This comprehensive review describes detailed information on the effects of ice crystals on aquatic products during freezing storage. The affecting factors (including nucleation temperature, freezing point, freezing rate, and temperature fluctuation) on the size, number, distribution, and shape of ice crystals are also elaborated in detail. Meanwhile, the corresponding technologies to control ice crystals have been developed based on these affecting factors to control the formation of ice crystals by inhibiting or inducing ice crystallization. In addition, the effects of ice crystals on the water, texture, and protein of aquatic products are comprehensively discussed, and the paper tries to describe their underlying mechanisms. This review can provide an understanding of ice crystallization in the aquatic products during freezing and contribute more clues for maintaining frozen food quality. Full article
(This article belongs to the Special Issue Crystallization Processes: Food and Pharmaceutical Crystals)
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Open AccessArticle
Acoustic Emission Study on the Damage Evolution of a Corroded Reinforced Concrete Column under Axial Loads
Crystals 2021, 11(1), 67; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11010067 - 15 Jan 2021
Viewed by 343
Abstract
In this paper, the damage of a reinforced concrete (RC) column with various levels of reinforcement corrosion under axial loads is characterized using the acoustic emission (AE) technique. Based on the AE rate process theory, a modified damage evolution equation of RC associated [...] Read more.
In this paper, the damage of a reinforced concrete (RC) column with various levels of reinforcement corrosion under axial loads is characterized using the acoustic emission (AE) technique. Based on the AE rate process theory, a modified damage evolution equation of RC associated with the axial load and different corrosion rates is proposed. The experimental results show that the measured AE signal parameters during the loading process are closely related to the damage evolution of the RC column as well as the reinforcement corrosion level. The proposed modified damage evolution equation enables dynamic analysis for the damage of corrosion on a RC column under axial loading for a further real-time quantitative evaluation of corrosion damage on reinforced concrete. Full article
(This article belongs to the Special Issue Advances in Sustainable Concrete System)
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Open AccessArticle
“Fuzzy Band Gaps”: A Physically Motivated Indicator of Bloch Wave Evanescence in Phononic Systems
Crystals 2021, 11(1), 66; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11010066 - 15 Jan 2021
Viewed by 409
Abstract
Phononic crystals (PCs) have been widely reported to exhibit band gaps, which for non-dissipative systems are well defined from the dispersion relation as a frequency range in which no propagating (i.e., non-decaying) wave modes exist. However, the notion of a band gap is [...] Read more.
Phononic crystals (PCs) have been widely reported to exhibit band gaps, which for non-dissipative systems are well defined from the dispersion relation as a frequency range in which no propagating (i.e., non-decaying) wave modes exist. However, the notion of a band gap is less clear in dissipative systems, as all wave modes exhibit attenuation. Various measures have been proposed to quantify the “evanescence” of frequency ranges and/or wave propagation directions, but these measures are not based on measurable physical quantities. Furthermore, in finite systems created by truncating a PC, wave propagation is strongly attenuated but not completely forbidden, and a quantitative measure that predicts wave transmission in a finite PC from the infinite dispersion relation is elusive. In this paper, we propose an “evanescence indicator” for PCs with 1D periodicity that relates the decay component of the Bloch wavevector to the transmitted wave amplitude through a finite PC. When plotted over a frequency range of interest, this indicator reveals frequency regions of strongly attenuated wave propagation, which are dubbed “fuzzy band gaps” due to the smooth (rather than abrupt) transition between evanescent and propagating wave characteristics. The indicator is capable of identifying polarized fuzzy band gaps, including fuzzy band gaps which exists with respect to “hybrid” polarizations which consist of multiple simultaneous polarizations. We validate the indicator using simulations and experiments of wave transmission through highly viscoelastic and finite phononic crystals. Full article
(This article belongs to the Special Issue Emerging Trends in Phononic Crystals)
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Open AccessArticle
Textures of Nematic Liquid Crystal Cylindric-Section Droplets Confined by Chemically Patterned Surfaces
Crystals 2021, 11(1), 65; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11010065 - 15 Jan 2021
Viewed by 301
Abstract
The director fields adopted by nematic liquid crystals (LCs) that are confined by the surface to form long, thin droplets are investigated using polarising optical microscopy. Samples are produced by de-wetting of the LC on a surface patterned with alternating high-surface energy and [...] Read more.
The director fields adopted by nematic liquid crystals (LCs) that are confined by the surface to form long, thin droplets are investigated using polarising optical microscopy. Samples are produced by de-wetting of the LC on a surface patterned with alternating high-surface energy and low-surface energy stripes of 10–30 μm width. The droplets obtained are expected to adopt a profile which is that of a longitudinal section of a cylinder and, as this suggests, the director fields observed are variants in the case where the LC is constrained in a cylindrical capillary or fibre. Hence, when there is normal anchoring at the air interface, the textures observed are related to the well-known escaped radial texture (for the nematic LC mixture E7) or plane polar texture (for the LC mixture MLC6609). More surprising is the observation that the nematic LC mixture MLC7023, which is anchored in a planar or tilted manner at the air interface, also gives what appears to be an escaped radial director field. As an exploration of the possibility of using these systems in creating sensors, the effects of adding a chiral dopant and of adding water to the substrates are also investigated. Full article
(This article belongs to the Special Issue Pattern Formation and Defects in Liquid Crystals)
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Open AccessArticle
Pyroelectric Properties of Bismuth Borate BZBO Single Crystals
Crystals 2021, 11(1), 64; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11010064 - 15 Jan 2021
Viewed by 331
Abstract
Pyroelectric properties of orthorhombic Bi2ZnB2O7 (BZBO) crystals were investigated by using the charge integration method. The primary and the secondary pyroelectric coefficients of BZBO crystals were found to be 6.4 and −6.5 µC/(m2·°C), respectively. The pyroelectric [...] Read more.
Pyroelectric properties of orthorhombic Bi2ZnB2O7 (BZBO) crystals were investigated by using the charge integration method. The primary and the secondary pyroelectric coefficients of BZBO crystals were found to be 6.4 and −6.5 µC/(m2·°C), respectively. The pyroelectric performance was evaluated by different figure of merits (FOMs), where BZBO crystals possessed relatively high current responsivity Fi (10.38 pm/V), and detectivity Fd (11.31 × 10−5/Pa1/2). In addition, the temperature dependent behaviours of primary pyroelectric coefficients and FOMs were studied from 15 °C to 155 °C; the pyroelectric properties were found to decrease with increases in temperature. Full article
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Open AccessArticle
Temperature Characterization of Liquid Crystal Dielectric Image Line Phase Shifter for Millimeter-Wave Applications
Crystals 2021, 11(1), 63; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11010063 - 14 Jan 2021
Viewed by 363
Abstract
In this paper we investigate the temperature dependent behavior of a liquid crystal (LC) loaded tunable dielectric image guide (DIG) phase shifter at millimeter-wave frequencies from 80 GHz to 110 GHz for future high data rate communications. The adhesive, necessary for [...] Read more.
In this paper we investigate the temperature dependent behavior of a liquid crystal (LC) loaded tunable dielectric image guide (DIG) phase shifter at millimeter-wave frequencies from 80 GHz to 110 GHz for future high data rate communications. The adhesive, necessary for precise fabrication, is analyzed before temperature dependent behavior of the component is shown, using the nematic LC-mixture GT7-29001. The temperature characterization is conducted by changing the temperature of the LC DIG’s ground plane between 10C and 80 C. The orientation of the LC molecules, and therefore the effective macroscopic relative permittivity of the DIG, is changed by inserting the temperature setup in a fixture with rotatable magnets. Temperature independent matching can be observed, while the insertion loss gradually increases with temperature for both highest and lowest permittivity of the LC. At 80 C the insertion loss is up to 1.3dB higher and at 10C it is 0.6dB lower than the insertion loss present at 20 C. In addition, the achievable differential phase is reduced with increasing temperature. The impact of molecule alignment to this reduction is shown for the phase shifter and an estimated 85% of the anisotropy is still usable with an LC DIG phase shifter when increasing the temperature from 20 C to 80 C. Higher reduction of differential phase is present at higher frequencies as the electrical length of the phase shifter increases. A maximum difference in differential phase of 72 is present at 110 GHz, when increasing the temperature from 20 C to 80 C. Nevertheless, a well predictable, quasi-linear behavior can be observed at the covered temperature range, highlighting the potential of LC-based dielectric components at millimeter wave frequencies. Full article
(This article belongs to the Special Issue Nematic Liquid Crystals)
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Open AccessArticle
Mechanical Properties of Graphene Oxide Coupled by Multi-Physical Field: Grain Boundaries and Functional Groups
Crystals 2021, 11(1), 62; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11010062 - 14 Jan 2021
Viewed by 242
Abstract
Graphene and graphene oxide (GO) usually have grain boundaries (GBs) in the process of synthesis and preparation. Here, we “attach” GBs into GO, a new molecular configuration i.e., polycrystalline graphene oxide (PGO) is proposed. This paper aims to provide an insight into the [...] Read more.
Graphene and graphene oxide (GO) usually have grain boundaries (GBs) in the process of synthesis and preparation. Here, we “attach” GBs into GO, a new molecular configuration i.e., polycrystalline graphene oxide (PGO) is proposed. This paper aims to provide an insight into the stability and mechanical properties of PGO by using the molecular dynamics method. For this purpose, the “bottom-up” multi-structure-spatial design performance of PGO and the physical mechanism associated with the spatial structure in mixed dimensions (combination of sp2 and sp3) were studied. Also, the effect of defect coupling (GBs and functional groups) on the mechanical properties was revealed. Our results demonstrate that the existence of the GBs reduces the mechanical properties of PGO and show an “induction” role during the tensile fracture process. The presence of functional groups converts in-plane sp2 carbon atoms into out-of-plane sp3 hybrid carbons, causing uneven stress distribution. Moreover, the mechanical characteristics of PGO are very sensitive to the oxygen content of functional groups, which decrease with the increase of oxygen content. The weakening degree of epoxy groups is slightly greater than that of hydroxyl groups. Finally, we find that the mechanical properties of PGO will fall to the lowest values due to the defect coupling amplification mechanism when the functional groups are distributed at GBs. Full article
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Open AccessArticle
Prospects of Using Small Scale Testing to Examine Different Deformation Mechanisms in Nanoscale Single Crystals—A Case Study in Mg
Crystals 2021, 11(1), 61; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11010061 - 14 Jan 2021
Viewed by 374
Abstract
The advent of miniaturised testing techniques led to excessive studies on size effects in materials. Concomitantly, these techniques also offer the capability to thoroughly examine deformation mechanisms operative in small volumes, in particular when performed in-situ in electron microscopes. This opens the feasibility [...] Read more.
The advent of miniaturised testing techniques led to excessive studies on size effects in materials. Concomitantly, these techniques also offer the capability to thoroughly examine deformation mechanisms operative in small volumes, in particular when performed in-situ in electron microscopes. This opens the feasibility of a comprehensive assessment of plasticity by spatially arranging samples specifically with respect to the crystal unit cell of interest. In the present manuscript, we will showcase this less commonly utilised aspect of small-scale testing on the case of the hexagonal metal Mg, where, besides dislocation slip on different slip planes, twinning also exists as a possible deformation mechanism. While it is close to impossible to examine individual deformation mechanisms in macroscale tests, where local multiaxial stress states in polycrystalline structures will always favour multiple mechanisms of plasticity, we demonstrate that miniaturised uniaxial experiments conducted in-situ in the scanning electron microscope are ideally suited for a detailed assessment of specific processes. Full article
(This article belongs to the Special Issue Crystal Plasticity at Micro- and Nano-scale Dimensions)
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Open AccessArticle
Origins of a Low-Sulfur Superalloy Al2O3 Scale Adhesion Map
Crystals 2021, 11(1), 60; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11010060 - 13 Jan 2021
Viewed by 315
Abstract
Low-sulfur single-crystal Ni-base superalloys have demonstrated excellent cyclic oxidation resistance due to improved Al2O3 scale adhesion. This derives from preventing deleterious interfacial sulfur segregation that occurs at common ppm levels of S impurity. Multiple hydrogen-annealing desulfurization treatments were employed to [...] Read more.
Low-sulfur single-crystal Ni-base superalloys have demonstrated excellent cyclic oxidation resistance due to improved Al2O3 scale adhesion. This derives from preventing deleterious interfacial sulfur segregation that occurs at common ppm levels of S impurity. Multiple hydrogen-annealing desulfurization treatments were employed to produce a continuum of levels demonstrating this oxidative transition, using 1 h cyclic oxidation at 1100 °C for 500 h to 1000 h. The sulfur content was determined by glow discharge mass spectrometry. The complete gravimetric database of 25 samples is revealed and correlated with sulfur content. Maximum adhesion (i.e., no weight loss) was achieved at ≤ 0.3 ppmw S, significant spallation (20–30 mg/cm2) above 2 ppmw, with transitional behavior between 0.3 and 2 ppmw S. A map suggested that adhesion was enabled when the total sulfur reservoir was less than one S atom per Ni interface atom. Equilibrium models further suggest that segregation may be minimized (~1% at 0.2 ppmw bulk), regardless of section thickness. 1st order adhesion effects have thus been demonstrated for PWA 1480 having no Y, Zr, or Hf reactive element dopants and no possibility of confounding reactive element effects. The results are compared with 2nd generation PWA 1484, Rene’N5, N6, and CMSX-4® SLS, all having Hf dopants. Full article
(This article belongs to the Special Issue Recent Advances in Metallurgy and Properties of Superalloys)
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Open AccessArticle
Efficient Photocatalytic Degradation of RhB by Constructing Sn3O4 Nanoflakes on Sulfur-Doped NaTaO3 Nanocubes
Crystals 2021, 11(1), 59; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11010059 - 13 Jan 2021
Viewed by 321
Abstract
Band structure engineering and heterojunction photocatalyst construction are efficient approaches to improve the separation of photo-induced electrons and holes, along with enhancing light response ability. By sulfur doping, sodium tantalite (NaTaO3) showed an improved photocatalytic property for the degradation of Rhodamine [...] Read more.
Band structure engineering and heterojunction photocatalyst construction are efficient approaches to improve the separation of photo-induced electrons and holes, along with enhancing light response ability. By sulfur doping, sodium tantalite (NaTaO3) showed an improved photocatalytic property for the degradation of Rhodamine B (RhB). Sn3O4 nanoflakes were constructed on the surface of NaTaO3 nanocubes, forming a surface heterostructure via a simple hydrothermal process, initially. This heterostructure endows the photocatalyst with an enhanced charge separation rate, resulting in an improved photocatalytic degradation of RhB. Moreover, a possible mechanism over Sn3O4/NaTaO3 and the photodegradation pathway of RhB were proposed as the combined effect of photo-induced electrons and holes. This facile process for band structure engineering and heterostructure construction provides the possibility for the practical application of high-efficiency photocatalysts. Full article
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Open AccessArticle
Single-Longitudinal-Mode Laser at 1123 nm Based on a Twisted-Mode Cavity
Crystals 2021, 11(1), 58; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11010058 - 13 Jan 2021
Viewed by 291
Abstract
A single-longitudinal-mode (SLM) Neodymiun-doped Yttrium Aluminium Garnet (Nd:YAG) laser at 1123 nm was first demonstrated with a twisted-mode (TM) cavity. By eliminating the spatial hole burning phenomenon, a stable SLM 1123 nm laser output was obtained. An efficient TM cavity was designed based [...] Read more.
A single-longitudinal-mode (SLM) Neodymiun-doped Yttrium Aluminium Garnet (Nd:YAG) laser at 1123 nm was first demonstrated with a twisted-mode (TM) cavity. By eliminating the spatial hole burning phenomenon, a stable SLM 1123 nm laser output was obtained. An efficient TM cavity was designed based on the Brewster plate with high reflection under s-polarization radiation. At an incident pump power of 7.65 W, the maximum output power of 689 mW was obtained. The corresponding optical conversion efficiency was about 9%. The center wavelength was 1122.58 nm and the line-width was <140 MHz. Full article
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Open AccessArticle
First-Principles Study on Redox Magnetism and Electrochromism of Cyclometalated Triarylamine-Core Triruthenium Complex
Crystals 2021, 11(1), 57; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11010057 - 13 Jan 2021
Viewed by 242
Abstract
Spin electronic states and optical properties of a circular ruthenium (Ru) terpyridine complex with a triarylamine core (CTTC) are theoretically investigated by first-principles calculations within an all-electron numerical orbital scheme based on spin density functional theory (SDFT), which demonstrate five well-defined redox states [...] Read more.
Spin electronic states and optical properties of a circular ruthenium (Ru) terpyridine complex with a triarylamine core (CTTC) are theoretically investigated by first-principles calculations within an all-electron numerical orbital scheme based on spin density functional theory (SDFT), which demonstrate five well-defined redox states for electrochromic functions. Atomic structure of CTTC molecule is obtained by geometric optimization, and its electronic structure with a decreasing semiconductor band-gap exhibits five consecutive single-electron redox states of Ru-coordinated centers. Except for CTTC in (Ru)3+4 redox state exhibiting a net spin of 2.25 (ћ/2), the other redox states are almost zero in total spin. Density distribution and energy-splitting of spin states indicate that the ferromagnetic coupling of Ru cations coordinating with terpyridine/triarylamine ligands originates dominantly from the spin polarization of Ru 4d-orbitals coordinated by N- and C-2p electrons of triarylamine. CTTC molecule in each redox state represents a well-discriminated absorption in visible region, with the highest characteristic peaks locating at 24.2, 20.2, 21.3, and 19.3/21.7 (103 cm−1) and a manifold of peaks at 13.4~25.3 (103 cm−1) for +2~+6 redox states, respectively. Theoretical electronic structure and optics of CTTC complex are used to evaluate the underlying physical mechanism of realizing a multi-color visible electrochromism by four couples of redox pairs, which is suggested to be applied for monitoring electrical information. Full article
(This article belongs to the Special Issue First-Principles Simulation—Nano-Theory)
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Open AccessArticle
Alkali Uranyl Borates: Bond Length, Equatorial Coordination and 5f States
Crystals 2021, 11(1), 56; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11010056 - 12 Jan 2021
Viewed by 401
Abstract
Three uranyl borates, UO2B2O4, LiUO2BO3 and NaUO2BO3, have been prepared by solid state syntheses. The influence of the crystallographic structure on the splitting of the empty 5f and 6d states [...] Read more.
Three uranyl borates, UO2B2O4, LiUO2BO3 and NaUO2BO3, have been prepared by solid state syntheses. The influence of the crystallographic structure on the splitting of the empty 5f and 6d states have been probed using High Energy Resolved Fluorescence Detected X-ray Absorption Spectroscopy (HERFD-XAS) at the uranium M4-edge and L3-edge respectively. We demonstrate that the 5f splitting is increased by the decrease of the uranyl U-Oax distance, which in turn correlates with an increased bond covalency. This is correlated to the equatorial coordination change of the uranium. The role of the alkalis as charge compensating the axial oxygen of the uranyl is discussed. Full article
(This article belongs to the Special Issue Crystal Chemistry of Uranyl Compounds)
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Open AccessArticle
Low-Cost High-Performance SnO2–Cu Electrodes for Use in Direct Ethanol Fuel Cells
Crystals 2021, 11(1), 55; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11010055 - 11 Jan 2021
Viewed by 463
Abstract
The high cost of Pt-based electrode materials limits the commercialization of fuel cells and their subsequent application in renewable energy production. It is thus necessary to develop economical, high-performance electrodes alongside biofuels to reduce the pollution associated with the production of energy. Tin [...] Read more.
The high cost of Pt-based electrode materials limits the commercialization of fuel cells and their subsequent application in renewable energy production. It is thus necessary to develop economical, high-performance electrodes alongside biofuels to reduce the pollution associated with the production of energy. Tin dioxide–copper foil (SnO2–Cu) electrode materials are herein developed using an electrodeposition process. Cyclic voltammetry, chronoamperometry, and potentiodynamic polarization methods are used to electrochemically characterize the electrode materials, with the results revealing that their excellent catalytic properties result in them delivering a high current. The surface morphologies of the developed electrodes are examined using scanning electron microscopy, with the results showing that upon an increase in the deposition time, a finer deposit of SnO2 is formed on the surface of the Cu foil. Consequently, electrochemical oxidation using an enhanced surface area of the material leads to it exhibiting a high current and excellent corrosion resistance. Powder X-ray diffraction was used to confirm the successful depositing of SnO2 on the surface of Cu. The fuel cell fabricated using the SnO2–Cu electrode is promising for use in clean energy generation, as it can be prepared at low cost compared to conventionally used electrodes. Full article
(This article belongs to the Special Issue Advanced Functional Oxide Ceramics)
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Open AccessArticle
Long Term Evaluation of Biodegradation and Biocompatibility In-Vivo the Mg-0.5Ca-xZr Alloys in Rats
Crystals 2021, 11(1), 54; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11010054 - 11 Jan 2021
Viewed by 362
Abstract
Biodegradable alloys in Mg have the advantages of traditional metallic materials and those of biodegradable polymers with superior strength, lower density and ideal rigidity for fixing bone fractures. The biocompatibility and biodegradability of the five concentrations of Mg-0.5Ca-xZr alloys used were assessed using [...] Read more.
Biodegradable alloys in Mg have the advantages of traditional metallic materials and those of biodegradable polymers with superior strength, lower density and ideal rigidity for fixing bone fractures. The biocompatibility and biodegradability of the five concentrations of Mg-0.5Ca-xZr alloys used were assessed using clinical and laboratory examinations that followed over time: tissue reaction, histological and imaging (RX, CT and SEM) evolution at 1, 2, 4 and 8 weeks after implant. The main purpose of this study was to investigate in vivo the long-term effect of Mg-0.5Ca-xZr alloys in rats. The results confirmed that Mg-0.5Ca-xZr alloys are biocompatible and biodegradable and are recommended to be used as possible materials for new orthopedics devices. Full article
(This article belongs to the Special Issue Biomaterials Characterization for Medical Applications)
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Open AccessArticle
Thermal Stability of Nanocrystalline Gradient Inconel 718 Alloy
Crystals 2021, 11(1), 53; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11010053 - 11 Jan 2021
Viewed by 410
Abstract
Gradient structures containing nanograins in the surface layer have been introduced into Inconel 718 (IN718) nickel-based alloy using the surface mechanical grinding treatment technique. The thermal stability of the gradient IN718 alloy was investigated. Annealing studies reveal that nanograins with a grain size [...] Read more.
Gradient structures containing nanograins in the surface layer have been introduced into Inconel 718 (IN718) nickel-based alloy using the surface mechanical grinding treatment technique. The thermal stability of the gradient IN718 alloy was investigated. Annealing studies reveal that nanograins with a grain size smaller than 40 nm exhibited significantly better thermal stability than those with larger grain size. Transmission electron microscopy analyses reveal that the enhanced thermal stability was attributed to the formation of grain boundaries with low energy configurations. This study provides new insight on strategies to improve the thermal stability of nanocrystalline metals. Full article
(This article belongs to the Special Issue Crystal Plasticity at Micro- and Nano-scale Dimensions)
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Open AccessEditorial
Early Career Stars of the Decade
Crystals 2021, 11(1), 52; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11010052 - 11 Jan 2021
Viewed by 346
Abstract
The field of liquid crystals is constantly reinventing itself, evolving from measurements of elastic constants and devices such as the simple nematic twist cell in the 1970s to topological defects, nanoparticle inclusions, and smart sensors today [...] Full article
(This article belongs to the Special Issue Early Career Stars of the Decade)
Open AccessArticle
Solution-Based Synthesis of Sulvanite Cu3TaS4 and Cu3TaSe4 Nanocrystals
Crystals 2021, 11(1), 51; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11010051 - 10 Jan 2021
Viewed by 396
Abstract
Sulvanites have the parent formula Cu3MCh4. The metal M belongs to group 5 and Ch is a chalcogen. The tantalum sulvanites Cu3TaS4 and Cu3TaSe4 are predicted to have wide band gaps and p-type [...] Read more.
Sulvanites have the parent formula Cu3MCh4. The metal M belongs to group 5 and Ch is a chalcogen. The tantalum sulvanites Cu3TaS4 and Cu3TaSe4 are predicted to have wide band gaps and p-type conductivity and show promise in optoelectronic applications. Their potential as p-type transparent conductors or efficient photocatalysts for visible-light water splitting is a valuable incentive to explore these materials in their nanoscale form, toward bottom-up processing opportunities. Reported herein are the first syntheses of nanosized Cu3TaS4 and Cu3TaSe4 sulvanites, which preserve the parent cubic crystal structure but show that morphology at the nanoscale is dependent of the reaction conditions. The two solution-based methods for synthesizing the tantalum S and Se sulvanites result in Cu3TaS4 or Cu3TaSe4 nanocrystals (NCs) with prismatic morphology, or, in the case of Cu3TaSe4, could lead to core-shell spherical nanostructures. The Cu3TaS4 NCs and Cu3TaSe4 NCs have good absorption in the UV-Vis region, while the Cu3TaSe4 core-shell NCs possess broad absorption bands not only in the UV-Vis but also in the near-infrared region. Photoluminescence measurements of Cu3TaS4 and Cu3TaSe4 reveal optical bandgaps of 2.54 and 2.32 eV, respectively, consistent with the values measured in bulk. Additionally, the current–voltage (I-V) curve of Cu3TaS4 NCs proves its electrical conductivity. Full article
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Open AccessArticle
LiNbO3-Tm3+ Crystal. Material for Optical Cooling
Crystals 2021, 11(1), 50; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11010050 - 09 Jan 2021
Viewed by 380
Abstract
The possibilities of LiNbO3-Tm3+ crystals for optical cooling based on anti-Stokes luminescence in the wavelength range of 1818–2200 nm are investigated. The concentration dependences of the final temperature of the crystal have been determined under continuous (CW) excitation at wavelengths [...] Read more.
The possibilities of LiNbO3-Tm3+ crystals for optical cooling based on anti-Stokes luminescence in the wavelength range of 1818–2200 nm are investigated. The concentration dependences of the final temperature of the crystal have been determined under continuous (CW) excitation at wavelengths of 1822–1977 nm with a pump intensity Fp=5×1021 cm2s1. It was shown that significant cooling with ∆T = 22 K, 19 K, and 16.4 K can be achieved, respectively, with excitation at wavelengths 1977, 1967, and 1948 nm. Full article
(This article belongs to the Section Crystal Engineering)
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Open AccessArticle
Analysis of Multi-Hit Crystals in Serial Synchrotron Crystallography Experiments Using High-Viscosity Injectors
Crystals 2021, 11(1), 49; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11010049 - 09 Jan 2021
Viewed by 341
Abstract
Serial Synchrotron Crystallography (SSX) is rapidly emerging as a promising technique for collecting data for time-resolved structural studies or for performing room temperature micro-crystallography measurements using micro-focused beamlines. SSX is often performed using high frame rate detectors in combination with continuous sample scanning [...] Read more.
Serial Synchrotron Crystallography (SSX) is rapidly emerging as a promising technique for collecting data for time-resolved structural studies or for performing room temperature micro-crystallography measurements using micro-focused beamlines. SSX is often performed using high frame rate detectors in combination with continuous sample scanning or high-viscosity or liquid jet injectors. When performed using ultra-bright X-ray Free Electron Laser (XFEL) sources serial crystallography typically involves a process known as ’diffract-and-destroy’ where each crystal is measured just once before it is destroyed by the intense XFEL pulse. In SSX, however, particularly when using high-viscosity injectors (HVIs) such as Lipidico, the crystal can be intercepted multiple times by the X-ray beam prior to exiting the interaction region. This has a number of important consequences for SSX including whether these multiple-hits can be incorporated into the data analysis or whether they need to be excluded due to the potential impact of radiation damage. Here, we investigate the occurrence and characteristics of multiple hits on single crystals using SSX with lipidico. SSX data are collected from crystals as they tumble within a high viscous stream of silicone grease flowing through a micro-focused X-ray beam. We confirmed that, using the Eiger 16M, we are able to collect up to 42 frames of data from the same single crystal prior to it leaving the X-ray interaction region. The frequency and occurrence of multiple hits may be controlled by varying the sample flow rate and X-ray beam size. Calculations of the absorbed dose confirm that these crystals are likely to undergo radiation damage but that nonetheless incorporating multiple hits into damage-free data should lead to a significant reduction in the number of crystals required for structural analysis when compared to just looking at a single diffraction pattern from each crystal. Full article
(This article belongs to the Special Issue Time Resolved Crystallography)
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Open AccessArticle
H-Bonds, π-Stacking and (Water)O-H/π Interactions in (µ4-EDTA)Bis(Imidazole) Dicopper(II) Dihydrate
Crystals 2021, 11(1), 48; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11010048 - 08 Jan 2021
Viewed by 279
Abstract
We synthesized and studied the polymeric compound {[Cu24-EDTA)(Him)2] 2H2O}n (1). The single-crystal structure is reported along with an in depth characterization of its thermal stability (TGA), spectral properties (FT-IR, Vis-UV and RSE), [...] Read more.
We synthesized and studied the polymeric compound {[Cu24-EDTA)(Him)2] 2H2O}n (1). The single-crystal structure is reported along with an in depth characterization of its thermal stability (TGA), spectral properties (FT-IR, Vis-UV and RSE), and magnetic behavior. The crystal consists of infinite 2D-networks built by centrosymmetric dinuclear motifs, constructed by means of a bridging anti,syn-carboxylate group from each asymmetric unit. Each layer guides Him ligands toward their external faces. They are connected by intermolecular (Him)N-H···O(carboxylate) bonds and antiparallel π–π stacking between symmetry related pairs of Him ligands, and then pillared in a 3D-network with parallel channels, where disordered water molecules are guested. About half of the labile water is lost from these channels over a wide temperature range (r.t. to 210 °C) before the other one, most strongly retained by the cooperating action of (water)O1-H(1A)···O(carboxylate) and (water) O1-H(1B)···π(Him) interactions. The latter is lost when organic ligands start to burn. ESR spectra and magnetic measurements indicated that symmetry related Cu(II) centers connected by the bridging carboxylate groups behave magnetically not equivalently, enabling an exchange interaction larger than their individual Zeeman energies. Full article
(This article belongs to the Special Issue σ- and π-Hole Interactions (Volume II))
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