Search Results (14)

Three new complexes of Hg(II), with the general formulas [Hg₂(ox)₂(NA)₄]_n·3nH₂O (1), [Hg(NO₃)₂(NA)₂(H₂O)₂]·2NA (2), and [Hg₂(SO₄)₂(H₂O)₂(NA)₄]·6H₂O (3), where ox = oxalate and NA = nicotinamide, were synthesized and characterized by single crystal X-ray diffraction, elemental analysis, FT-IR, and fluorescence spectra. For complex (2), ¹³C and ¹H NMR spectra were recorded. Thermogravimetric analysis was also performed for complexes (1) and (2). Single crystal X-ray diffraction shows that in the polymeric complex (1) and the binuclear complex (3), the Hg(II) ions are hexacoordinated, whereas in the mononuclear complex (2), Hg(II) is octacoordinated. In complex (1), each oxalate group acts in a µ₄ coordination manner, the basal plan being made up by four oxygen atoms belonging to the two oxalate ligands, while the nicotinamide molecules occupy the axial positions. In complex (2), the nitrate groups coordinate in a bidentate chelating mode, whereas in complex (3), each sulphate ligand acts in a bidentate chelating–bis monodentate bridging manner. Full article

A mononuclear complex [Dy(phenN₆)(HL′)₂]PF₆·CH₂Cl₂ (H₂L′ = R/S-1,1′-binaphthyl-2,2′-diphenol) with local D_6h symmetry was synthesized. Structural determination shows that Dy³⁺ was encapsulated within the coordination cavity of the neutral hexaaza macrocyclic ligand phenN₆, forming a non-planar coordination environment. The axial positions are occupied by two phenoxy groups of binaphthol in the trans form. The local geometry of Dy³⁺ closely resembles a regular hexagonal bipyramid D_6h configuration. The axial Dy-O_phenoxy distances are 2.189(5) and 2.145(5) Å, respectively, while the Dy-N bond lengths in the equatorial plane are in the range of 2.524(7)–2.717(5) Å. The axial O_phthalmoxy-Dy-O_phthalmoxy bond angle is 162.91(17)°, which deviates from the ideal linearity. Under the excitation at 320 nm, the complex exhibits a characteristic emission peak at 360 nm, corresponding to the naphthalene ring. The AC susceptibility measurements under an applied DC field of 1800 Oe show distinct temperature-dependent and frequency-dependent AC magnetic susceptibility, typical of single-molecule magnetic behavior. The Cole–Cole plot in the temperature range of 6.0–28.0 K was fitted using a model incorporating Orbach and Raman relaxation mechanisms, giving an effective energy barrier of U_eff = 300.2 K. Theoretical calculations on complex 1 reveal that the magnetization relaxation proceeds through the first excited Kramers doublets with a calculated magnetization blocking barrier of 404.1 cm⁻¹ (581.4 K). Full article

We report here the synthesis of a series of nine coordinated mononuclear Ln^III complexes [LnL₁Cl₂(DMF)]Cl·2.5DMF and [LnL¹(L₂)₂]Cl·4CH₃OH (Ln^III = Gd^III, Dy^III, Er^III and Yb^III, HL₂ = 9-anthracenecarboxylic acid), where L1 is a hexadentate N₄O₂ Schiff base ligand prepared from the condensation of 1,10-phenanthroline-2,9-dicarbaldehyde and semicarbazone. The X-ray crystal structures of these complexes show the Ln^III ions to possess LnN₄O₂Cl₂ and LnN₄O₄ coordination spheres, which can be considered to be derived from a hexagonal bipyramidal geometry, with the ligand in the equatorial plane and the anions (chloride or 9-antracenecarboxylate) in axial positions, which undergo distortion after coordination of either a molecule of DMF or a bidentate coordination of the 9-anthracenecarboxxylate ligand. All these compounds exhibit field-induced slow magnetization relaxation (SMR). The absence of SMR at zero field due to QTM, as well as the processes involved in the magnetic relaxation under a field of 0.1 T, have been justified on the basis of theoretical calculations and the distortion of the respective coordination spheres. The severe discrepancy between the calculated and experimental thermal energy barriers for the Dy^III complexes seems to indicate that the relaxation occurs with the contribution of spin–vibrational coupling, which is favored by the flexibility of the ligand. Full article

The study of small synthetic models for the highly selective removal of uranyl ions from seawater with amidoxime-containing materials is a valuable means to enhance their recovery capacity, leading to better extractants. An important issue in such efforts is to design bifunctional ligands and study their reactions with trans-{UO₂}²⁺ in order to model the reactivity of polymeric sorbents possessing both amidoximate and another adjacent donor site on the side chains of the polymers. In this work, we present our results concerning the reactions of uranyl and pyrimidine-2-amidoxime, a ligand possessing two pyridyl nitrogens near the amidoxime group. The 1:2:2 {UO₂}²⁺/pmadH₂/external base (NaOMe, Et₃N) reaction system in MeOH/MeCN provided access to complex [UO₂(pmadH)₂(MeOH)₂] (1) in moderate yields. The structure of the complex was determined by single-crystal X-ray crystallography. The U^VI atom is in a distorted hexagonal bipyramidal environment, with the two oxo groups occupying the trans positions, as expected. The equatorial plane consists of two terminal MeOH molecules at opposite positions and two N,O pairs of two deprotonated η² oximate groups from two 1.11000 (Harris notation) pmadH⁻ ligands; the two pyridyl nitrogen atoms and the –NH₂ group remain uncoordinated. One pyridyl nitrogen of each ligand is the acceptor of one strong intramolecular H bond, with the donor being the coordinated MeOH oxygen atom. Non-classical C_aromatic-H⋯X (X=O, N) intermolecular H bonds and π–π stacking interactions stabilize the crystal structure. The complex was characterized by IR and Raman spectroscopies, and the data were interpreted in terms of the known structure of 1. The solid-state structure of the complex is not retained in DMSO, as proven via ¹H NMR and UV/Vis spectroscopic techniques as well as molar conductivity data, with the complex releasing neutral pmadH₂ molecules. The to-date known coordination chemistry of pmadH₂ is critically discussed. An attempt is also made to discuss the technological implications of this work. Full article

The structure and bonding of two novel tungstaboranes which were synthesized using diverse synthetic methods are described. (i) The room-temperature photolysis of [Cp*W(CO)₃Me] with [BH₃·SMe₂] led to the isolation of the hydrogen-rich tungstaborane [Cp*W(CO)₂B₃H₈] (1). Its geometry consists of an arachno butterfly core similar to tetraborane(10) and obeys the Wade-Mingos electron counting rules (n vertices, n + 3 skeletal electron pairs (seps)). (ii) Further, the tungstaborane [(Cp*W)₃(μ-H)₂(μ₃-H)(μ-CO)₂B₄H₄] (4) was isolated by thermolysis reaction of a tungsten intermediate, obtained by low temperature reaction of [Cp*WCl₄] and [LiBH₄·THF] with [Cr(CO)₅·THF]. Compound 4 which seems to have formed by replacement of a BH unit in [(Cp*W)₂B₅H₉] by the isoelectronic fragment {Cp*W(CO)₂}, adopts an oblato-nido hexagonal-bipyramidal core (n vertices, n–1 seps). Both compounds were characterized using multinuclear NMR, IR spectroscopy, mass spectrometry as well as single crystal X-ray diffraction analysis. In addition, density functional theory (DFT) calculations were performed in order to elucidate their bonding and electronic structures. Full article

YMnO₃ is a P-type semiconductor with a perovskite-type structure (ABO₃). It presents two crystalline systems: rhombohedral and hexagonal, the latter being the most stable and studied. In the hexagonal system, Mn³⁺ ions are coordinated by five oxygen ions forming a trigonal bipyramid, and the Y³⁺ ions are coordinated by five oxygen ions. This arrangement favors its ferroelectric and ferromagnetic properties, which have been widely studied since 1963. However, applications based on their optical properties have yet to be explored. This work evaluates the photoelectric response and the photocatalytic activity of yttrium manganite in visible spectrum wavelengths. To conduct this, a rod-obelisk-shaped yttrium manganite with a reduced indirect bandgap value of 1.43 eV in its hexagonal phase was synthesized through the precipitation method. The synthesized yttrium manganite was elucidated by solid-state techniques, such as DRX, XPS, and UV-vis. It was non-toxic as shown by the 100% leukocyte viability of mice BALB/c. Full article

In this work, ZnO nanocrystals (NCs) have been effectively synthesized by a simple, efficient and cost-effective method using coconut husk extract as a novel fuel. The synthesized NCs are characterized by UV-Vis, XRD, FT-IR, SEM, EDX, Raman and PL studies. The obtained ZnO were found to be UV-active with a bandgap of 2.93 eV. The X-ray diffraction pattern confirms the crystallinity of the ZnO with hexagonally structured ZnO with a crystallite size of 48 nm, while the SEM analysis reveals the hexagonal bipyramid morphology. Photocatalytic activities of the synthesized ZnO NCs are used to degrade methylene blue and metanil yellow dyes. Full article

Observations of the surface domain structure (Kerr-effect), optical metallography, scanning electron microscopy (SEM-SE), and electron microprobe analysis (EPMA-SEM), measurements of major and minor magnetic hysteretic loops were used to study pseudo-single-crystal samples of (Sm,Zr)(Co,Cu,Fe)_z alloys subjected to heat treatments to the high-coercivity state, which are used in fabricating sintered permanent magnets. Correlations between the chemical composition, hysteretic properties, structural components, domain structure, and phase state were determined for the concentration ranges that ensure wide variations of 4f-/4d-/3d-element ratio in the studied samples. The phase state formed by collinear and coherent phase components determines the high coercive force and ultimate magnetic hysteresis loops of the pseudo-single crystals. It was found that the 1:5 phase with the hexagonal structure (P6/mmm) is the matrix of the alloys for (Sm,Zr)(Co,Cu,Fe)_z permanent magnets; the matrix undergoes phase transformations in the course of all heat treatments for the high-coercivity state. The heterogeneity observed with optical magnifications, namely, the observation of main structural components A and B, is due to the alternation, within the common matrix, of regions with modulated quasi-spherical precipitates and regions with hexagonal bipyramids (cellular phase) although, traditionally, many investigators consider the cellular phase as the matrix. It is shown that the relationship of volume fractions of structural components A and B that account for more than 0.9 volume fraction of the total, which is due to the integral chemical composition of the alloys, determines the main hysteretic performances of the samples. The Zr-rich phases, such as 5:19, 2:7, and 6:23, and a structural component with the variable stoichiometry (Sm(Co,Cu,Fe)_3.5–5) that is almost free of Zr and contains up to 33 at% Cu, were found only within structural component A in quantities sufficient for EPMA analysis. Full article

Single crystals of Ba ${}_{26}$ Ru ${}_{12}$ O ${}_{57}$ were grown by the floating zone method. The crystal structure is formed by an alternating stacking of pseudo-hexagonal Ru single layers and double layers. The Ru ions within the double layers are dimerized (Ru ${}_2$ O ${}_9$ ) whereas the Ru ions within the single layers arrange in a distorted Kagome lattice of trigonal bipyramidally coordinated RuO ${}_5$ polyhedra. Additionally, this Kagome lattice is “decorated” with RuO ${}_6$ octahedra that are situated in the central free spaces within this Kagome lattice. According to the composition, the oxidation state of most of the Ru ions should be formally close to 5+. Full article

Lanthanide-doped hexagonal β-NaYF₄ crystals have received much attention in recent years due to their excellent photoluminescence properties. However, lanthanide-doped β-NaYF₄ crystals with micron and submicron scales as well as uniform morphology have received less attention. In this study, Eu³⁺-doped β-NaYF₄ (β-NaYF₄:Eu³⁺) crystals of micron and submicron size scales were synthesized using the solvothermal method with ethylene glycol as the solvent. The β-NaYF₄:Eu³⁺ crystals were highly crystallized. A comparison of the characteristics of the β-NaYF₄:Eu³⁺ crystals synthesized with and without the use of oleic acid as a surfactant was conducted. It was found that the utilization of oleic acid as a surfactant during their synthesis greatly decreased their particle size from micron to submicron scale, while adding a small amount of ethanol further reduced their particle size. In addition, they exhibited much smoother surfaces and more uniform morphologies, which were hexagonal prism bipyramids. The microstructural characteristics and photoluminescence properties of the β-NaYF₄:Eu³⁺ crystals were studied in detail. Results showed that β-NaYF₄:Eu³⁺ crystals prepared with the aid of oleic acid as a surfactant during their synthesis exhibited stronger photoluminescence. Full article

A natural barioferrite, BaFe³⁺₁₂O₁₉, from a larnite–schorlomite–gehlenite vein of paralava within gehlenite hornfels of the Hatrurim Complex at Har Parsa, Negev Desert, Israel, was investigated by Raman spectroscopy, electron probe microanalysis, and single-crystal X-ray analyses acquired over the temperature range of 100–400 K. The crystals are up to 0.3 mm × 0.1 mm in size and form intergrowths with hematite, magnesioferrite, khesinite, and harmunite. The empirical formula of the barioferrite investigated is as follows: (Ba_0.85Ca_0.12Sr_0.03)_∑1(Fe³⁺_10.72Al_0.46Ti⁴⁺_0.41Mg_0.15Cu²⁺_0.09Ca_0.08Zn_0.04Mn²⁺_0.03Si_0.01)_∑11.99O₁₉. The strongest bands in the Raman spectrum are as follows: 712, 682, 617, 515, 406, and 328 cm⁻¹. The structure of natural barioferrite (P6₃/mmc, a = 5.8901(2) Å, c = 23.1235(6) Å, V = 694.75(4) ų, Z = 2) is identical with the structure of synthetic barium ferrite and can be described as an interstratification of two fundamental blocks: spinel-like S-modules with a cubic stacking sequence and R-modules that have hexagonal stacking. The displacement ellipsoids of the trigonal bipyramidal site show elongation along the [001] direction during heating. As a function of temperature, the mean apical Fe–O bond lengths increase, whereas the equatorial bond lengths decrease, which indicates dynamic disorder at the Fe2 site. Full article

The newly designed butterfly-shaped hetero-tetranuclear Cu^II-Na^I coordination compound, [Cu₃(HL)₂Na]∙Pic (Pic⁻ is abbreviation of picrate) (1) which is derived from a naphthalenediol-based bis(Salamo)-type chelating ligand H₄L have been synthesized and characterized by elemental analyses, UV-vis spectra, IR spectra analysis, and Hirshfeld surface analysis. X-ray crystallographic analyses revealed that the coordination compound 1 is a novel hetero-tetranuclear Cu^II-Na^I bis(Salamo)-type coordination compound and it differs from heterotrinuclear Cu^II-Na^I bis(Salamo)-type coordination compound reported earlier. The Cu1 and Cu3 atoms are tetra-coordinated with geometries of distorted square pyramid, while Cu2 atom are hexa-coordinated with the geometry of a distorted octahedron. The Na^I atom is octa-coordinated with the geometry of a distorted hexagonal bipyramid. Furthermore, the supramolecular structure and Hirshfeld surface analyses have been discussed in detail. Full article

Crystals of congruently melting noncentrosymmetric (NCS) mixed alkali metal nitrate, Rb₂Na(NO₃)₃, have been grown through solid state reactions. The material possesses layers with NaO₈ hexagonal bipyramids and NO₃ triangular units. Rb⁺ cations are residing in the interlayer space. Each NaO₈ hexagonal bipyramid shares its corners and edges with two and three NO₃ units, respectively, in order to fulfill a highly dense stacking in the unit cell. The NaO₈ groups share their six oxygen atoms in equatorial positions with three different NO₃ groups to generate a NaO₆-NO₃ layer with a parallel alignment. The optimized arrangement of the NO₃ groups and their high density in the structure together produce a strong second-harmonic generation (SHG) response. Powder SHG measurements indicate that Rb₂Na(NO₃)₃ has a strong SHG efficiency of five times that of KH₂PO₄ (KDP) and is type I phase-matchable. The calculated average nonlinear optical (NLO) susceptibility of Rb₂Na(NO₃)₃ turns out to be the largest value among the NLO materials composed of only [NO₃]⁻ anion. In addition, Rb₂Na(NO₃)₃ exhibits a wide transparency region ranging from UV to near IR, which suggests that the compound is a promising NLO material. Full article

Imaginary cubes are three dimensional objects which have square silhouette projections in three orthogonal ways just as a cube has. In this paper, we study imaginary cubes and present assembly puzzles based on them. We show that there are 16 equivalence classes of minimal convex imaginary cubes, among whose representatives are a hexagonal bipyramid imaginary cube and a triangular antiprism imaginary cube. Our main puzzle is to put three of the former and six of the latter pieces into a cube-box with an edge length of twice the size of the original cube. Solutions of this puzzle are based on remarkable properties of these two imaginary cubes, in particular, the possibility of tiling 3D Euclidean space. Full article