Positions Of Ions Research Articles

Czochralski growth and characterization of MgAl2O4 single crystals

MgAl2O4 (MALO) single crystals were pulled by the Czochralski method in [111] direction. The crystals were doped with Co (0.06–0.6at% (charge compositions)), because Co2+ ions in tetrahedral positions exhibit non-linear optical properties, and, currently, Co:MALO seems to be the best saturable absorber in the eye-safe region (ca. 1.5µm). By XRD powder technique a stoichiometric MALO was evidenced without admixtures of higher order spinels (MgAl4O7 and MgAl6O10). Also no excessive residual stresses have been discovered by different optical methods, and irrespective of the doping level we did not face any problem of cracking when cutting the crystals into wafers and other structures. In this work we have concentrated our efforts on investigation of thermal properties of MALO. Due to the 2nd order phase transition ca. 650°C they seem to be of crucial importance in future thermal bonding of this material to the lasing host (Yb,Er-glass) expected just about this temperature.

Dimer paramagnetic centers in lead germanate crystals doped with iron and halogen (Cl−, Br−, F−) ions

The dimer complexes Fe3+-Cl−, Fe3+-Br−, and Fe3+-O2− in ferroelectric lead germanate crystals doped with iron and annealed in chlorine-, bromine-, and fluorine-containing atmospheres have been studied using the electron paramagnetic resonance method. These complexes are formed by Fe3+ ions in the trigonal position of lead and their associated anions located in the interstitial channel of the structure. The positions of the charge-compensating anions in the channel have been discussed based on the analysis of the parameters of the spin Hamiltonian and their temperature dependence.

Study of the ion mobility in a Li0.03Na0.97Ta0.4Nb0.6O3 solid solution by raman spectra

We have studied ion mobility in a Li0.03Na0.97Ta0.4Nb0.6O3 solid solution by its Raman spectra. It has been revealed that, as the temperature of the solution is increased to approach the point of the phase transition to a state with a high conductivity with respect to lithium, the lines with frequencies at 77, 118, and 142 cm−1, which refer, respectively, to librations of oxygen octahedra Nb(Ta)O6 as a whole and vibrations of Li and Na ions in octahedra, considerably broaden, decrease in intensity, and smear into the wing of the Rayleigh line. Remaining lines are preserved in the spectrum. We have observed that the width of the line with a frequency of 118 cm−1 depends exponentially on temperature, while the width of the line with a frequency of 142 cm−1 changes linearly with it, which makes it possible to attribute to the line with the frequency of 118 cm−1 to vibrations of Li+ cations, whereas the line with the frequency of 142 cm−1 should be attributed to vibrations of Na+ cations in AO12 cuboctahedra. The average lifetime of Li+ ions in equilibrium positions and the jump barrier have been estimated to be ∼8 × 10−12 s and ∼20 kJ/mol, respectively. This agrees well with the data in the literature on measurements of electric conductivity.

Synthesis, crystal structure, and spectral properties of a series of metal complexes with 3,4-dimethyl-5-(2-pyridyl)-1,2,4-triazole

A series of metal complexes with 3,4-dimethyl-5-(2-pyridyl)-1,2,4-triazole (L), trans-[CoL2(MeOH)2](ClO4)2 (1), trans-[NiL2(MeOH)2](ClO4)2 (2), trans-[CuL2(ClO4)2] (3) and trans-[CoL2(NCS)2] (4) have been synthesized, and their molecular structures determined by X-ray crystallography, UV, IR, TGA/DSC, powder XRD and elemental analyses. Structural analyses indicate that both complexes 1 and 2 have a pseudo-octahedral [MN4O2] core with two ClO4− ions in the trans position. While complexes 3 and 4 show a distorted octahedron containing two trans-coordinated anions in 3 with ClO4− but in 4 with NCS−.

SBN60, strontium-barium niobate at 100 K

The title compound, Sr0.6Ba0.4Nb2O6 (strontium barium niobium oxide), belongs to the group of strontium–barium niobates with varying composition of Sr and Ba. Their general formula can be written as SrxBa1 - xNb2O6. Below the Curie temperature, T c, these materials indicate ferroelectric properties. The Curie temperature for SBN60 is equal to 346±0.5 K so the structure is in the ferroelectric phase at the measurement temperature of 100 K. Characteristic for this family of compounds is the packing along the z-axis. The NbO6 corner-sharing octa­hedra surround three types of vacancy tunnels with penta­gonal, square and triangular shapes. The Sr2+ ions partially occupy two unique sites, the first one located inside the penta­gon and the second one in the square tunnels. Consequently, they are situated on the mirror plane and the inter­section of two glide planes, respectively. The site inside the penta­gonal tunnel is additionally disordered so that the same position is shared by Ba2+ and Sr2+ ions whereas another part of the Ba2+ ion occupies a different position (relative occupancies 0.43:0.41:0.16). One of the NbV atoms and three of the O2− ions occupy general positions. The second NbV atom is located on the inter­section of the mirror planes. Two remaining O2− ions are located on the same mirror plane. Only the NbV atom and one of the O2− ions which is located on the mirror plane are not disordered. Each of the remaining O2− ions is split between two sites, with relative occupancies of 0.52:0.48 (O2− ions in general positions) and 0.64:0.36 (O2− ion on the mirror plane).

Synthesis, Crystal Structure, and Spectral Properties of Two Manganese(II) and Zinc(II) Complexes with 3,4-Dimethyl-5-(2-pyridyl)-1,2,4-triazole

Two complexes, cis-[MnL2(NCS)2] (1) and cis-[ZnL2(NCS)2] (2) with asymmetrical substituted triazole ligands [L = 3,4-dimethyl-5-(2-pyridyl)-1,2,4-triazole], were synthesized and characterized by elemental analysis, UV/Vis and FT-IR spectroscopy as well as thermogravimetric analyses (TGA), powder XRD, and single-crystal X-ray diffraction. In the complexes, each L molecule adopts a chelating bidentate mode by the nitrogen atoms of pyridyl and triazole. Both complexes have a similar distorted octahedral [MN6] core (M = Mn2+ and Zn2+) with two NCS– ions in the cis position.

Studies on influence of aluminium ions on the bioactivity of B2O3–SiO2–P2O5–Na2O–CaO glass system by means of spectroscopic studies

Bioactive multi component glasses of the composition of 27.4B2O3–6.4SiO2–2.5P2O5–25.5Na2O–(38.2−x)CaO: xAl2O3 (x between 0 and 3.2) were synthesized, by melt quenching technique and their bioactivity was investigated as a function of Al2O3 concentration. Initially, optical absorption and infrared spectra were recorded and analyzed in order to have some pre-understanding over structural aspects of the glasses. For understanding the bioactivity, the samples were immersed in simulated body fluid (SBF) solution for prolonged times (∼30 days) and the weight loss measurements were carried out. The spectroscopic studies were repeated on the post immersed samples. From the comparison of the analysis of the spectroscopic data of both pre-immersed and post-immersed samples together with the information on variation of pH value of residual solution as a function of immersion time, it is concluded that the participation of aluminium ions in tetrahedral positions is hindrance for the formation of HA layer and for the bioactivity of the samples.

Bis[μ-3,5-bis(pyridin-2-yl)pyrazolato]bis[(hexafluorophosphato)copper(II)

The title dinuclear complex mol­ecule, [Cu2(C13H9N4)2(PF6)2], lies about an inversion center. The CuII atom shows a square-pyramidal coordination geometry with the basal plane formed by four N atoms of the two bis-chelating 3,5-bis­(pyridin-2-yl)pyrazolate ions and with one F atom of the hexa­fluoro­phosphate ion in the apical position. Mol­ecules are stacked in a column along the a axis through C—H⋯F hydrogen bonds. The columns are further linked by other C—H⋯F hydrogen bonds, forming a three-dimensional network.

Synthesis, characterization, and catalytic performance of bifunctional titanium silicalite-1

A series of bifunctional Ti-molecular sieves (M-TS-1, M = Al, B, or Fe) containing different trivalent ions (Al3+, B3+, or Fe3+), with MFI topology, were synthesized using tetrapropylammonium bromide, silica sol, and n-butylamine as a template, base, and Si source, respectively. The simultaneous presence of Ti and trivalent ions in lattice positions provided catalysts with activity in both oxidation and acid-catalyzed reactions. The samples were characterized using X-ray diffraction, Fourier-transform infrared spectroscopy, ultraviolet-visible spectroscopy, NH3 temperature-programmed desorption, inductively coupled plasma atomic emission spectroscopy, and N2 adsorption-desorption isotherms. The results showed that the numbers and strength of acid sites of TS-1 were enhanced by the incorporation of trivalent ions. Using selective oxidation of ethylene as the probe reaction, the catalytic properties of M-TS-1 were investigated. The results showed that Al-TS-1 and B-TS-1 had better catalytic properties; conversion and utilization of H2O2 reached 95% and 90%, respectively, and the yield of ethylene glycol plus its monomethyl ether was greater than 10%.

What Makes Copper-Exchanged SSZ-13 Zeolite Efficient at Cleaning Car Exhaust Gases?

Recently, the outstanding properties of Cu-SSZ-13 (a zeolite in the chabazite structure) for the selective catalytic reduction of nitrous oxides were discovered. However, the true nature of the active site is still not answered satisfactorily. In this work, we identify the active site for the given reaction from first-principles simulations of the total energy of Cu(II) ions in various positions in combination with previously published catalytic activity as a function of the copper exchange level. This attribution is confirmed by the simulation of vibrational properties of CO adsorbed to the reduced Cu(I) species. The relation between energetic considerations, vibrational calculations, and experiment allows a clear statement about the distribution of active sites in the catalyst. We furthermore discuss the structural properties of the active site leading to the high stability under reaction conditions over a large temperature range. The insights from this work allow a more targeted catalyst design and represent a step toward an industrial application of copper-exchanged zeolites in cleaning car exhaust gases.

Cis-Dichloridotetrakis(dimethyl sulfoxide-κO)chromium(III) chloride dimethyl sulfoxide monosolvate

The structure of the title compound, [CrCl2(C2H6OS)4]Cl·C2H6OS, consists of a CrIII ion coordinated by four O atoms of dimethyl sulfoxide (DMSO) ligands and two chloride ions in cis positions, forming a distorted CrCl2O4 octa­hedron. An isolated Cl− counter-anion and a positionally disordered DMSO mol­ecule [occupancy ratio 0.654 (4):0.346 (4)] are also present. In the structure, the complex cations inter­act with the Cl− counter-anions and the DMSO solvent mol­ecules via weak C—H⋯Cl and C—H⋯O inter­actions, forming a three-dimensional network.

Dopant depends on morphological and electrochemical characteristics of LiMn 2– X Mo X O4 cathode nanoparticles

For the first time, solid solutions of LiMn2–X Mo X O4 nanoparticles were synthesized by combustion method at 700 °C in air. The synthesized LiMn2–X Mo X O4 (X = 0.0–0.2) nanoparticles were characterized by X-ray powder diffraction, Fourier transform infrared spectroscopy (FT-IR), Field emission-scanning electron microscopy, and Particle size analysis. The unit-cell constant is increasing from 8.237 to 8.293 A with the increase of Mo, the presence of Mo at X ≤ 0.05 in LiMn2–X Mo X O4 nanoparticles retained the spinel structure (Fd-3m), whereas on increasing the Mo (X ≥ 0.05 %), the ordering of Li+ ions in both octahedral and tetrahedral cationic position leads to the lowering of symmetry (P4132). On increasing the Mo content, prominent peak splitting and broadening are observed at 600–500 and 830 cm−1 for Li–Mn–O and Mo–O respectively in the FT-IR spectra. The TG/DTA spectrum reveals that the convenient formation of Li mangano-molybdate is at 700 °C. The voltammograms of all the samples show two redox peaks centered around 4 V except for the sample with higher Mo doping (X = 0.2). The sample with X = 0.03 shows higher redox peak current values. A marginal increase of 146 Ω R ct value was found for the LiMn1.97Mo0.03O4 nanomaterial after 10th cycle which is rather high for the rest of the materials. A discharge capacity retention of 88 % at 50th cycle is observed for X = 0.03 sample, while the other samples exhibit drastically reduced capacity. The LiMn1.97Mo0.03O4 nanoparticle can able to deliver higher and constant discharge capacity, and it may be a good alternative for the existing cathode materials.

On the limited electroactivity of Li2NiTiO4 nanoparticles in lithium batteries

The electroactivity of the rock-salt structure Li2NiTiO4 in lithium batteries containing LiBOB as electrolyte salt was examined. The compound exhibits a random distribution of the metal ions in octahedral 4a positions. The combined use of electrochemical impedance spectroscopy, step potential spectroscopy and thermogravimetric analysis revealed that the electrode undergoes various changes during the charging process. Thus, Ni(II) is initially oxidised to Ni(IV) through Ni(III) as an intermediate state over the region from OCV to 4.6V versus Li+/Li, which provides a high capacity (180mAhg−1). Upon charging, however, highly charged Ni(IV) ions hinder charge carrier motion in both ions and electrons. In fact, the lithium diffusion coefficient was also very low (DLi+≈10−17 cm2 s−1), which suggests a low ionic conductivity. From impedance studies, it seems that a quite stable polymer film is formed in the electrolyte/electrode interface during the first charge. The region between 4.6 and 4.8V exhibited an additional capacity of 23mAhg−1 that was assigned to the release of oxygen if the electrolyte oxidation at this stage is discarded. The electrode impedance increased three times after one cycle, which is consistent with irreversible rearrangement of lithium ions during the first oxidation process. Furthermore, a very resistive solid electrolyte interface is developed after a few cycles. Therefore, the capacity fading observed can be ascribed to deterioration of both, the electrolyte and the electrode conduction properties, by effect of hindered lithium and electron motion.

Bis(1,2,3-benzotriazolium) sulfate dihydrate

In the asymmetric unit of the title hydrated salt, 2C6H6N3 +·SO4 2−·2H2O, there are two independent sulfate ions, one lying on a twofold axis, and the other in a general position. There are three independent benzotriazolium cations and three independent water mol­ecules. The sulfate ion in a general position forms hydrogen-bonded chains of stoichiometry SO4 2−·3H2O in the b-axis direction. The sulfate on the twofold axis is unhydrated and accepts hydrogen bonds from four surrounding benzotriazoles. The benzotriazolium cations form two types of stacks along b. One stack contains only one type of independent cation, related by inversion centers. The other stack contains two alternating independent cations and no symmetry. The two types of stacks have orientations which are rotated by about 79° in the ac plane. 12 symmetrically distinct hydrogen bonds of type N—H⋯O(sulfate), N—H⋯O(water), O—H⋯O(sulfate) and O—H⋯O(water), with donor–acceptor distances in the range 2.5490 (13)–2.7871 (12) Å, form a three-dimensional array.

Bis(3-azaniumylpyridin-1-ium) hexachloridostannate(IV) dichloride

The asymmetric unit of the title compound, (C5H8N2)2[SnCl6]Cl2, consists of one 3-aza­niumylpyridin-1-ium dication and one chloride ion in a general position and a hexa­chloridostannate(IV) dianion lying about a centre of inversion. The [SnCl6]2− anion exhibits almost perfect octa­hedral geometry. The 3-aza­niumylpyridin-1-ium and chloride ions are connected via medium–strong charge-supported N—H⋯Cl hydrogen bonds, forming undulating layers in the (110) plane. The [SnCl6]2− ions are located between these layers and occupy cavities formed by two facing layer puckers.

Bromido(1,4,7,10,13-pentaazacyclohexadecane)cobalt(III) dibromide dihydrate

The title salt, [CoBr(C11H27N5)]Br2·2H2O, contains a complex cation with mirror symmetry and two Br− counter-anions that are likewise located on the mirror plane. The central CoIII atom of the complex cation has one Br− ion in an axial position, one N atom of the penta­dentate macrocyclic ligand in the other axial position and four N atoms of the ligand in equatorial positions, defining a distorted octa­hedral coordination geometry. The macrocyclic ligand is coordinated to the CoIII atom within a 5, 6, 5 arrangement of chelate rings in the equatorial plane of the four N atoms. Due to symmetry, the configuration of the chiral N atoms is 1RS, 4SR, 10RS, 13SR. In the crystal, N—H⋯Br, O—H⋯Br and N—H⋯O hydrogen bonds between the complex cation, anions and lattice water mol­ecules generate a three-dimensional network.

Fluorescence Features of Samarium Ion in PbO-B2O3-SiO2-Al2O3 Glass System

The glasses of the composition 30PbO-65B2O3-0.5SiO2-(4.5–x)Al2O3-xSm2O3 with x varying from 0 to 2 mol% have been synthesized. Optical absorption and photoluminescence spectra in the spectral range 300-2200 nm and 450-700 nm, respectively, were studied at ambient temperature. The Judd-Ofelt theory was applied to characterize these spectra. The analysis of the results indicated that the glasses containing maximum concentration of Al3+ ions in octahedral positions is preferable for achieving the highest luminescence efficiency.

Synthesis and characterization of Tetrakis-μ-[N-phenylanthranilato](O,O′)-bis[(4-vinylpyridine copper(II)] complex

Abstract The complex, tetrakis-μ-[2-(phenylamino)ben-zoato](O,O′)-bis[4-vinylpyridine copper(II)] (1) was synthesized by the reaction of N-phenylanthranilic acid and copper powder in the presence of 4-vinylpyridine and crystallized from ethanol-dichloromethane-n-hexane mixture (1 : 1 : 1). The crystal structure of 1 contains one binuclear cage complex and each dimer locate on a crystallographic inversion centre (triclinic, P-1 space group). In the compound, two Cu(II) ions are bridged by four µ2-O : O′ N-phenylanthranilato (NPA) ligands, forming a cage structure, and 4-vinylpyridine ligands are bonded through their N atoms to the Cu(II) ions in terminal positions to form square pyramidal environment around Cu(II) ions. The Cu(II) ions in apart of 2.6298(14) Å, are bridged by the carboxylate groups of four N-phenylanthranilate ligands. The complex molecules show three dimensional supramolecular networks by O—H···O, C—H···O, C—H···π and π···π interactions.

Synthesis, crystal structure, and spectroscopic characterization of two new binuclear complexes of manganese(II) and vanadium(V) with dipicolinate ligands containing 2-aminopyrimidinium as a counter cation

Two new binuclear complexes, formulated as [(Hamp)[Mn(μ-dipic)Cl(H2O)2]]2 and [(Hamp)[V(μ-O)(O)(dipic)]·H2O]2 (dipicH2 = pyridine-2,6-dicarboxylic (dipicolinic) acid; amp = 2-aminopyrimidine), were synthesized by a hydrothermal process and characterized by elemental analysis, IR spectroscopy, thermal analysis, and X-ray single crystal diffraction. Both compounds contain two Hamp cations and a dinuclear manganese(II) or vanadium(V) anion complex. In addition, the vanadium complex contains two lattice water molecules. Two manganese(II) ions are bridged by pyridine-2,6-dicarboxylate ions in the manganese complex, and they are both coordinated by O,N,O of the tridentate dipicolinate ligand, one oxygen of another dipicolinate ligand, one chlorine, and two water molecules in a distorted pentagonal-bipyramidal geometry. Vanadium(V) ions are coordinated octahedrally by O,N,O of the tridentate dipicolinate ligand, one oxo ion, and two bridging μ-O ions in cis position in the vanadium complex. The crystal structures of both complexes are stabilized by a complex network of hydrogen bonds comprising water molecules, counter ion, and carboxyl groups of dipic2−.

Syntheses, Crystal Structures and Magnetic Properties of Cr(NCNH2)4Cl2 and Mn(NCNH2)4Cl2

The two isotypic compounds Cr(NCNH2)4Cl2 and Mn(NCNH2)4Cl2 have been synthesized and characterized by X-ray diffraction. They crystallize in the cubic space group Im3̄m (Z = 6) with a = 12:643(2) Å for Cr(NCNH2)4Cl2 and a = 12:821(1) Å for Mn(NCNH2)4Cl2. The divalent transition metal ions are octahedrally coordinated by four H2NCN molecules in equatorial and two chloride ions in axial positions. The magnetic susceptibility data of the four Curie-paramagnetic compounds Cr(NCNH2)4Cl2, Mn(NCNH2)4Cl2, Co(NCNH2)4Cl2, and Ni(NCNH2)4Cl2 have been analyzed in greater detail, including many-body quantum theory.