Calcium Halides Research Articles

DFT based study of copper calcium halide perovskite nanomaterials for optoelectronic and energy applications

The mechanical, electronic, optical, and thermoelectric analyses of CuCaX3 (X = Cl, Br, I) have been done using DFT based TB-mBJ approach. The stability of CuCaX3 (X = Cl, Br, I) has been confirmed from the enthalpy of formation; values for CuCaCl3, CuCaBr3, and CuCaI3 are −1.07 eV, −1.55 eV, and −2.15 eV, respectively. The phonon spectra plot is also discussed, and the phonon dispersion analysis confirms that the CuCaX3 systems are dynamically stable since no imaginary modes are observed. The modified Becke-Johnson exchange potential is used to evaluate the opto-electronic and thermo-electric properties. By replacing anions (Cl to I), the band gap of the studied material in the visible region has been tailored, from 2.9 eV to 2.65 eV, for renewable energy devices. In addition, various optical properties such as dielectric constant, refraction, absorption, optical conductivity, and optical loss factor have been analyzed for optoelectronic applications. With the replacement of anions (Cl to I), the peaks of maximum intensities shifted to lower energy to values of 7.2 eV, 6.2 eV and 5 eV for CuCaCl3, CuCaBr3 and CuCaI3 respectively. Furthermore, the BoltzTrap code has been used to discuss thermal conductivity, power factor, Hall coefficient, specific capacitance and electron densities in detail for thermoelectric applications. The CuCaX3 family of perovskites has been found to have bandgaps falling in the visible region for light-emitting diodes (LEDs). These also exhibit high thermal efficiency, making them potential multifunctional candidates for optoelectronic and energy harvesting applications.

Novel Fluoride- and Chloride-containing Bioactive Glasses for Use in Air Abrasion

ObjectivesTo investigate the degradation, fluorapatite formation, biological safety and cutting efficiency on dentine of the mixed fluoride- and chloride-containing bioactive glasses (BGs). MethodsTwo series of mixed fluoride- and chloride-containing glasses (GPFCl and GPF2.3Cl series) were synthesized using a melt-quench method. Glass transition temperature (Tg) and the bioactivity in term of glass degradation and fluorapatite formation were evaluated in Tris buffer solution. The cutting efficiency of the powdered BGs (GPF2.3Cl series) on dentine via air abrasion was investigated using white light profilometry and scanning electron microscope. The cytotoxicity of GPF2.3Cl series on human periodontal ligament stem cells (hPLSCs) and oral fibroblasts (OFB) were examined by MTT. ResultsThese BGs are highly degradable and able to form fluorapatite within 3h of immersion. The formation of CaF2 was also found in the high fluoride-containing BGs. The faster glass degradation was evidenced in the BGs with higher chloride. A significant reduction of Tg from 790°C to 463°C was seen with increasing in calcium halide content. Air abrasion on dentine using the low and intermediate chloride-containing glasses demonstrates clear depressions, while no depression was found using the high chloride-containing glass. Moreover, the studied BGs showed no cytotoxicity to hPLSCs and OFB. ConclusionsThe glasses with mixed fluoride and chloride integrate the benefits from the presence of both, showing rapid glass degradation, fast fluorapatite formation, excellent biocompatibility and controllable hardness to provide a selective cutting efficiency on dentine. Clinical SignificanceThe developed BGs air abrasive with tunable hardness by varying chloride content can selectively cut different dental tissues. In clinic, a relatively hard BG is of great interest for caries preparation, while a soft glass is attractive for tooth cleaning.

CsPb(Br/Cl)3 Perovskite Nanocrystals with Bright Blue Emission Synergistically Modified by Calcium Halide and Ammonium Ion.

Colloidal cesium lead halide (CsPbX3, X = Cl, Br, and I) perovskite nanocrystals (NCs) demonstrate supreme optical properties in the spectra region of infrared, red, and green. High-performance blue-emitting counterparts are still eagerly required for next-generation full-color displays. However, it is challenging to obtain efficient blue perovskite NCs, especially in a deep blue region with an emission wavelength of around 460 nm or shorter. Herein, calcium halide and ammonium ions are applied simultaneously to modify the CsPb(Br/Cl)3 NCs in situ to reduce surface defects, finally remarkably enhancing the photoluminescence quantum yield (PLQY) from 13% to 93% with an emission peak at 455 nm and the Commission Internationale de l’Eclairage (CIE) coordinates at (0.147, 0.030), which is close to the requirement of the Rec.2020 standard and also meets the requirement of blue emission in DCI-P3. Bright white emission and a wide color gamut are also achieved by combining the commercial red-emitting and green-emitting phosphors. The combination of time-resolved PL spectra and femtosecond transient absorption results discloses the reason for PLQY improvement as suppressing the nonradiative recombination.

Dehydrohalogenation of halobenzenes and C(sp3)-X (X = F, OPh) bond activation by a molecular calcium hydride

The molecular calcium hydride, [(BDI)CaH] 2 (BDI = HC{(Me)CN-2,6-i-Pr 2 C 6 H 3 } 2 ), effects the slow hydrodehalogenation of C 6 H 5 X (X = I, Br) to provide benzene and the respective dimeric calcium halides, [(BDI)CaX] 2 . Although a similar reaction with fluorobenzene was non-discriminating, the analogous hydrogenation of chlorobenzene was observed, albeit this process yields the calcium hydride-chloride as the alkaline earth-containing product. Assessment of the bromide- and chloride-based processes by density functional theory (DFT) calculations, imply that the reactions take place with the retention of the dimeric calcium structures throughout. Both systems invoke an S N Ar-type displacement of the halide, via barriers (in the range 32–34 kcal mol −1 for C 6 H 5 Br and 31.1–32.9 kcal mol −1 for C 6 H 5 Cl), which vary only marginally during the transformation of the initial hydride and halide-hydride intermediates. The isolation of the calcium hydride-chloride is ascribed, therefore, to its more rapid crystallisation and depletion from solution. Also reported is the reactivity of [(BDI)CaH] 2 with α,α,α-trifluorotoluene and anisole, which yield the corresponding dicalcium hydride-fluoride and phenoxide derivatives, respectively, rather than the products of directed ortho metalation.

The Effect of Calcium and Halide Ions on the Gramicidin A Molecular State and Antimicrobial Activity.

Gramicidin A (gA) forms several convertible conformations in different environments. In this study, we investigated the effect of calcium halides on the molecular state and antimicrobial activity of gramicidin A. The molecular state of gramicidin A is highly affected by the concentration of calcium salt and the type of halide anion. Gramicidin A can exist in two states that can be characterized by circular dichroism (CD), mass, nuclear magnetic resonance (NMR) and fluorescence spectroscopy. In State 1, the main molecular state of gramicidin A is as a dimer, and the addition of calcium salt can convert a mixture of four species into a single species, which is possibly a left-handed parallel double helix. In State 2, the addition of calcium halides drives gramicidin A dissociation and denaturation from a structured dimer into a rapid equilibrium of structured/unstructured monomer. We found that the abilities of dissociation and denaturation were highly dependent on the type of halide anion. The dissociation ability of calcium halides may play a vital role in the antimicrobial activity, as the structured monomeric form had the highest antimicrobial activity. Herein, our study demonstrated that the molecular state was correlated with the antimicrobial activity.

Stable single-layers of calcium halides (CaX2, X = F, Cl, Br, I).

By means of density functional theory based first-principles calculations, the structural, vibrational, and electronic properties of 1H- and 1T-phases of single-layer CaX2 (X = F, Cl, Br, or I) structures are investigated. Our results reveal that both the 1H- and 1T-phases are dynamically stable in terms of their phonon band dispersions with the latter being the energetically favorable phase for all single-layers. In both phases of single-layer CaX2 structures, significant phonon softening occurs as the atomic radius increases. In addition, each structural phase exhibits distinctive Raman active modes that enable one to characterize either the phase or the structure via Raman spectroscopy. The electronic band dispersions of single-layer CaX2 structures reveal that all structures are indirect bandgap insulators with a decrease in bandgaps from fluorite to iodide crystals. Furthermore, the calculated linear elastic constants, in-plane stiffness, and Poisson ratio indicate the ultra-soft nature of CaX2 single-layers, which is quite important for their nanoelastic applications. Overall, our study reveals that with their dynamically stable 1T- and 1H-phases, single-layers of CaX2 crystals can be alternative ultra-thin insulators.

Exploring halide destabilised calcium hydride as a high-temperature thermal battery

CaH2 is a metal hydride with a high energy density that decomposes around 1100 °C at 1 bar of H2 pressure. Due to this high decomposition temperature, it is difficult to utilise this material as a thermal battery for the next generation of concentrated solar power plants, where the currently targeted operational temperature is between 600 and 800 °C. In this study, CaH2 has been mixed with calcium halide salts (CaCl2, CaBr2 and CaI2) and annealed at 450 °C under 100 bar of H2 pressure to form CaHCl, CaHBr and CaHI. These hydride-halide salts incur a thermodynamic destabilisation of their hydrogen release, compared to CaH2, so that they can operate between 600 and 800 °C within practical operating pressures (1–10 bar H2) for thermochemical energy storage. The as-synthesised metal hydrides were studied by in-situ synchrotron X-ray diffraction, temperature programmed desorption and pseudo pressure composition isothermal analysis. Each of the calcium hydride-halide salts decomposed to form calcium metal and a calcium halide salt after hydrogen release. In comparison to pure CaH2, their decomposition reactions were faster when heated up to 850 °C, and the experimental values of the desorbed hydrogen gas were very close to the theoretical ones. All samples after their decomposition showed signs of sintering, which hindered their rehydrogenation reaction.

Direct Synthesis of Heavy Grignard Reagents: Challenges, Limitations, and Derivatization

The direct synthesis of organocalcium compounds (heavy Grignard reagents) by the reduction of organyl halides with activated calcium powder succeeded in a straightforward manner for organic bromides and iodides that are bound at sp2 -hybridized carbon atoms. Extension of this strategy to alkyl halides was very limited, and only the reduction of trialkylsilylmethyl bromides and iodides with activated calcium allowed the isolation of the corresponding heavy Grignard reagents. Substitution of only one hydrogen atom of the methylene moiety by a phenyl or methyl group directed this reduction toward the Wurtz-type coupling and the formation of calcium halide and the corresponding C-C coupling product. The stability of the methylcalcium and benzylcalcium derivatives in ethereal solvents suggests an unexpected reaction behavior of the intermediate organyl halide radical anions. Quantum chemical calculations verify a dependency between the ease of preparative access to organocalcium complexes and the C-I bond lengths of the organyl iodides. The bulkiness of the trialkylsilyl group is of minor importance. Chloromethyltrimethylsilane did not react with activated calcium; however, halogen-exchange reactions allowed the isolation of [Ca(CH2 SiMe3 )(thf)3 (μ-Cl)]2 . Furthermore, the metathetical approach of reacting [Ca(CH2 SiMe3 )I(thf)4 ] with KN(SiMe3 )2 and the addition of N,N,N',N'',N''-pentamethyldiethylenetriamine (pmdeta) allowed the isolation of heteroleptic [CaCH2 SiMe3 {N(SiMe3 )2 }(pmdeta)]. In the reaction of this derivative with phenylsilane, the trimethylsilylmethyl group proved to be more reactive than the bis(trimethylsilyl)amido substituent.

Extraction of metal bromides from chloride brines with mixtures of molecular iodine and tributyl phosphate

The process of recovery by direct extraction of metal bromides from calcium chloride brines using mixtures of molecular iodine with tributyl phosphate has been studied. It was found that iodine significantly increases the recovery of the bromides of alkali and alkaline earth metals due to the formation of hydrophobic iodine complexes with the halide anions. Bromides of calcium and lithium are the most selectively extracted. The extracted complexes significantly dissociate into ions in the organic phase. The extraction of calcium halide over a wide range of its concentration in an aqueous solution results in the extraction of a mixed chloride-bromide salt. This is due to a significant difference in the separation factors for bromide and chloride ions in the interphase exchange reactions for the halide ions of the inner and outer coordination spheres of the extracted complex.

Tritopic ion-pair receptors based on anion–π interactions for selective CaX2binding

Selective ion-pair binding of CaX2 (X = Br-, I-) was realized by a tritopic receptor containing homoditopic anion-π binding sites and a pentaethylene glycol site. The receptor formed an unusual solvent-separated ion-pair complex with CaI2 and a contact one with CaBr2, and can be applied to selectively dissolve calcium halides in organic solvents.

Ionic co-crystals of enantiopure and racemic histidine with calcium halides

Ionic co-crystals (ICCs) of l- and dl-histidine with CaCl2, CaBr2 and CaI2 were prepared by mechanochemical and solution methods and were structurally characterized by either single crystal or powder X-ray diffraction methods.

Hydrolysis of molten CaCl<sub>2</sub>-CaF<sub>2</sub> with additions of CaO

Calcium halide based molten salts have recently attracted interest for a number of applications such as direct reduction of oxides for metal production and as liquefying agent in cyclic sorption processes for CO2 by CaO from dilute flue gases (Ca-looping). A fundamental aspect of these melts is the possible hydrolysis reaction upon exposure to gaseous H2O forming corrosive and poisonous hydrogen halides. In this work experiments have been performed investigating the formation of HCl and HF from a molten salt consisting of a 13.8 wt% CaF2 in CaCl2 eutectic exposed to a flowing gas consisting of 10 vol% H2O in N2. Hydrolysis has been investigated as function of content of CaO and temperature. HCl and HF are shown to be formed at elevated temperatures; HCl forms to a substantially larger extent than HF. Addition of CaO has a marked, limiting effect on the hydrolysis. Thermodynamic modeling of the reaction indicates activity coefficients for CaO above unity in the system. For cyclic CO2-capture based on thermal swing, it is advisable to keep the temperature in the carbonation (absorption) reactor well below 850 ℃ while maintaining a high CaO content if molten CaCl2 is employed. Similar conclusions can be drawn with regards to CaF2.

Reduction of Bromo- and Iodo-2,6-bis(diphenylphosphanylmethyl)benzene with Magnesium and Calcium

Arylmagnesium and -calcium reagents are easily accessible; however, ether degradation processes limit storability, especially of the calcium-based heavy Grignard reagents. Ortho-bound substituents with phosphanyl donor sites usually block available coordination sites and stabilize such complexes. The reaction of bromo-2,6-bis(diphenylphosphanylmethyl)benzene (1a) with magnesium in tetrahydrofuran yields [Mg{C6H3-2,6-(CH2PPh2)2}2] (2) after recrystallization from 1,2-dimethoxyethane. However, the similarly performed reduction of bromo- (1a) and iodo-2,6-bis(diphenylphosphanylmethyl)benzene (1b) with calcium leads to ether cleavage and subsequent degradation products. α-Deprotonation of tetrahydrofuran (THF) yields 1,3-bis(diphenylphosphanylmethyl)benzene. Furthermore, the insoluble THF adducts of dimeric calcium diphenylphosphinate halides, [(thf)3Ca(X)(µ-O2PPh2)]2 [X = Br (3a), I (3b)], precipitate verifying ether decomposition and cleavage of P–C bonds. Ether adducts of calcium halides (such as [(dme)2(thf)CaBr2] (4)) form, supporting the initial Grignard reaction and a subsequent Schlenk-type dismutation reaction.

Benz–amidinato Stabilized a Monomeric Calcium Iodide and a Lithium Calciate(II) Cluster featuring Group 1 and Group 2 Elements

AbstractSoluble calcium halides reported so far are mostly dimeric in nature. The halides occupy the bridging position and thus provide additional coordination to the metal. We obtained a monomeric calcium iodide [{PhC(NiPr)2}CaI(thf)3] (1) from the reaction of [PhC(NiPr)2]Li with CaI2 in THF. The compound has been stabilized by electronic donation and steric shielding from the amidinate ligand as well as coordination of three THF molecules. 1 does not show any propensity towards ligand exchange reaction. When the same reaction is carried out in diethyl ether instead of THF, it led to the formation of a Li calciate(II) cluster of composition L2Ca4I8Li4O (L=PhC(NiPr)2) (2) with an encapsulated O2− in the middle of a tetrahedron spanned by four Ca2+ ions. 2 represents a metal‐rich halide comprising of both alkali and alkaline earth metals which is quite unprecedented. Another notable aspect is that the amidinate ligand binds to the calcium atom in chelating bidentate mode in 1, whereas in 2 each N atom of the amidinate ligands binds to two Ca atoms leading to bridging bis‐chelating coordination mode.

Incidental Polymorphism, Non-Isomorphic and Isomorphic Substitution in Calcium-Valine Coordination Polymers

Five coordination polymers with the stoichiometry CaX2(valine)2(H2O)2 (X = Cl, Br) were obtained from the corresponding calcium halides and either racemic and enantiopure valine. In all cases the zwitterionic amino acid is exclusively O coordinated and the halides act as counteranions for the resulting one-dimensional cationic chains. The enantiopure chloride shows dimorphism; both forms differ in connectivity from the bromide. In contrast to this structural variability for L-valine, the derivatives of the racemic amino acid are isomorphous.

Crystal structures of coordination polymers from CaI2 and proline.

Completing our reports concerning the reaction products from calcium halides and the amino acid proline, two different solids were found for the reaction of l- and dl-proline with CaI2. The enanti-opure amino acid yields the one-dimensional coordination polymer catena-poly[[aqua-μ3-l-proline-tetra-μ2-l-proline-dicalcium] tetra-iodide 1.7-hydrate], {[Ca2(C5H9NO2)5(H2O)]I4·1.7H2O} n , (1), with two independent Ca(2+) cations in characteristic seven- and eightfold coordination. Five symmetry-independent zwitterionic l-proline mol-ecules bridge the metal sites into a cationic polymer. Racemic proline forms with Ca(2+) cations heterochiral chains of the one-dimensional polymer catena-poly[[di-aquadi-μ2-dl-proline-calcium] diiodide], {[Ca(C5H9NO2)2(H2O)2]I2} n , (2). The centrosymmetric structure is built by one Ca(2+) cation that is bridged towards its symmetry equivalents by two zwitterionic proline mol-ecules. In both structures, the iodide ions remain non-coordinating and hydrogen bonds are formed between these counter-anions, the amino groups, coordinating and co-crystallized water mol-ecules. While the overall composition of (1) and (2) is in line with other structures from calcium halides and amino acids, the diversity of the carboxyl-ate coordination geometry is quite surprising.

Effect of the calcium halides, CaCl2 and CaBr2, on hydrogen desorption in the Li–Mg–N–H system

Calcium-halide-doped lithium amide–magnesium hydride samples were prepared both by hand-grinding and ball-milling 2LiNH2–MgH2–xCaX2 (x=0, 0.1, and 0.15; X=Cl or Br). The addition of calcium halides reduced the hydrogen desorption temperature in all samples. The ball-milled undoped sample (2LiNH2–MgH2) began to desorb hydrogen at around 125°C and peaked at 170°C. Hydrogen desorption from the 0.15mol CaCl2-containing sample began ca 30°C lower than that of the undoped sample and peaked at 150°C. Both the onset and peak temperatures of the CaBr2 sample (x=0.15) were reduced by 15°C compared to the chloride. Kissinger’s method was used to calculate the effective activation energy (Ea) for the systems: Ea for the 0.15mol CaCl2-containing sample was found to be 91.8kJmol−1 and the value for the 0.15mol CaBr2-containing sample was 78.8kJmol−1.

The Unusual Coordination Sphere in the Octaammine Calcium(II) Ions of [Ca(NH3)8]Br2 and [Ca(NH3)8]I2 and the Thermal Decomposition of the Iodide to [Ca(NH3)6]I2

We report on the synthesis and crystal structure of the octaammine calcium(II) halides [Ca(NH3)8]Br2, and [Ca(NH3)8]I2, which were synthesized by the reaction of the respective calcium( II) halides with dry liquid ammonia. The compounds form colorless crystals which crystallize isotypically at 123 K with Z = 4 in the orthorhombic space group Pnma with a = 12:0478(3), b = 7:4406(2), c = 15:7216(4) Å, V = 1409:33(6) Å3 for the bromide, and a = 12:1113(4), b = 7:7706(3), c = 16:7145(6) Å, V = 1573:0(1) Å3 for the iodide. Instead of the expected tetragonal antiprism for the eightfold-coordinated Ca2+ ions, we observed a coordination polyhedron best described as a twofold capped trigonal prism. After evaporation of the liquid ammonia and warming of [Ca(NH3)8]I2 to room temperature, [Cu(NH3)6]I2 was obtained as a colorless powder. The hexaammine calcium(II) iodide crystallizes isotypically to [Mn(NH3)6]I2 (CaF2 type) in the cubic space group Fm3̅m with a = 11:18580(6) Å, V = 1399:59(1) Å3, Z = 4 at 293 K

Preparation of Self-Assembled Chitin Nanofibers by Regeneration from Ion Gels Using Calcium Halide · dihydrate/Methanol Solutions

Preparation of Self-Assembled Chitin Nanofibers by Regeneration from Ion Gels Using Calcium Halide · dihydrate/Methanol Solutions

Synthesis and structural characterization of a calcium coordination polymer based on a μ 3 -bridging tetradentate binding mode of glycine#

A new coordination polymer namely [[Ca6(H–gly)12(H2O)18]Cl12·6H2O]n (1) (H–gly = glycine) has been isolated from the calcium chloride–glycine–water system and structurally characterized. Each Ca(II) in 1 is eight-coordinated and is bonded to eight oxygen atoms three of which are from terminal water molecules and five oxygen atoms from four symmetry related zwitterionic glycine ligands. The H–gly ligands exhibit two different binding modes viz. a monodentate carboxylate ligation and a μ3-tetradentate bridging carboxylate binding mode, which results in the formation of a one-dimensional coordination polymer. In the infinite chain the Ca(II) atoms are organized in a zigzag fashion. A comparative study reveals a rich and diverse structural chemistry of calcium halide–glycine compounds. The synthesis and structural characterization of a new coordination polymer namely [[Ca6(H–gly)12(H2O)18]Cl12·6H2O]n (1) (H-gly = glycine) isolated from the calcium chloride–glycine–water system is reported.