Crystal structure, optical properties and colouring performance of karrooite MgTi2O5 ceramic pigments

Karrooite, MgTi₂O₅, is a promising ceramic pigment due to its high refractoriness and refractive indices, as well as its ability to host transition metal ions in two crystallographically distinct octahedral sites. The colouring performance was investigated combining X-ray powder diffraction with UV-vis-NIR spectroscopy on karrooite doped with V, Cr, Mn, Fe, Co or Ni (M) according to the formula Mg_1−xTi_2−xM_2xO₅, with x=0.02 and 0.05. Transition metals solubility in the karrooite lattice is not complete and a second phase is always present (geikielite or rutile). Structural data proved that incorporation of different chromophore ions into the karrooite structure affects unit cell parameters, bond length distances and angles, site occupancies and therefore cation order-disorder. Optical spectra exhibit broad absorbance bands of Co(II), Cr(IV), Fe(III), Mn(II), Mn(III), Ni(II), V(IV) with distinct contributions by cations in the M₁ and M₂ sites. Karrooite pigments have colours ranging from orange to brown-tan (Cr, Fe, Mn, V) to green (Co) and yellow (Ni) that are stable in low-temperature (<1050 °C) ceramic glazes and glassy coatings.     

Pseudobrookite ceramic pigments: Crystal structural,optical and technological properties

Pseudobrookite pigments were synthesised by the conventional ceramic route, calcining at 1300 °C four mixtures, with a Fe₂O₃:TiO₂ ratio ranging from 47:53 to 40:60, and were characterised by XRPD, DRS and colouring performance in several ceramic matrices. Titania in moderate excess of the Fe₂TiO₅ stoichiometry, necessary to minimise the occurrence of unreacted precursors, induced lattice parameters smaller than ideal pseudobrookite, in agreement with the different radii of Ti⁴⁺ and Fe³⁺ ions. These pigments exhibit a peculiar, intensely brown coloration originated by several light absorptions in the visible spectrum due to both d⁵ electronic transitions and a magnetically-coupled paired transition between iron ions in adjacent lattice sites. A doubling of the ⁶A₁ → ⁴T₁ and ⁴T₂ bands is related to the occurrence of Fe³⁺ in both octahedral sites of pseudobrookite. Besides, distinct metal–oxygen distances imply different energy absorptions in good accordance with the crystal field theory, despite the strongly covalent character of the Fe–O bonding. Although an entropy-stabilised phase, pseudobrookite persists dispersed in glazes and glassy coatings even after fast firing at 1200 °C, so being suitable as ceramic pigment. However, its colouring performance depends on the chemico-physical properties of ceramic matrices: saturated brown shades achieved in low temperature glasses shift to a lighter brown in opacified glazes and fade to a light gray in wall tile glazes, where the high CaO and ZnO content contributes to rapidly dissolve pseudobrookite.     

Synthesis of zirconium titanate with an ordered M-fergusonite (beta) structure

We report a new zirconium titanate compound (Zr,Ti)O₂ with 27.5-35 mol% titania (TiO₂) formed from the oxides at 35-38 kbar, 1400-1500 °C. Crystal structure investigations at atmospheric conditions with powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed a monoclinic structure related to that of M-fergusonite (beta). Unit-cell dimensions (from 27.5 to 35 mol% TiO₂): a=7.267(20)-7.340(2) Å, b=10.435(3)-10.429(1) Å, c=5.023(11)-5.040(1) Å, β=136.45(12)-137.55(1)°, V=262.44(92)-260.40(12) Å³, Z=4. Rietveld refinement (R_F=1.55) of a sample with 32.8 mol% TiO₂ indicates that site A is 8-fold coordinated, mostly occupied by Zr, while site B has 6-fold average coordination, occupied by Ti and Zr. Site B is at least partly ordered, as indicated by superstructure reflections 0 0 1 and −2 0 1 detected with TEM, reducing the space group from C2/c to C2. Pronounced streaking of selected diffraction spots is linked to the boundaries of lamellar domains in twin orientation, with twin planes either (200) or (20−2). Adjacent lamellae differ slightly in composition, causing subtle asymmetry of the twin diffraction patterns.     

Crystal structure and optical properties of new 0D-hybrid hydroxyfluorotitanates

New 0D hybrid organic–inorganic hydroxyfluorotitanates result from the microwave assisted reactions in autoclaves of TiF₄ with organic amines (3-5 diamino-1,2,4,triazol (guaz), ethylenediamine (en) and diethylenetriamine (dien)) and concentrated aqueous HF in ethanol at 190 °C for 1 h. Four compounds, [Hguaz]₂·(TiF_4.9(OH)_1.1) (I), [H₂guaz]·(TiF_4.8(OH)_1.2) (II), [H₂en]·(TiF_4.3(OH)_1.7) (III) and [H₂dien]·(Ti(F,OH)₆)·2H₂O (IV) are prepared and characterized. All structures are built up from isolated (Ti(F,OH)₆)²⁻ anions interacting with mono- or di-protonated amines which local symmetry dictates the long range stacking of the Ti(F,OH)₆ octahedra. Insertion of crystallized water molecules is only observed for IV. The experimental optical gaps of I, II and III have been measured at about 3.4 eV and compare well with the theoretical values estimated from the examination of density of state diagrams. The optical thresholds are mainly due to O(2p) → Ti(3d) electronic transitions, the F(2p) → Ti(3d) charge transfers occurring at higher energy.     

Synthesis, crystal structure and optical limiting properties of some W---Se---Cu clusters

A nest-shaped cluster [(C₄H₉)₄N]₂[WOSe₃Cu₃Br_1.67Cl_1.33] (1) and a cage-shaped cluster [(C₄H₉)₄N]₃[WSe₄Cu₃Br₂Cl₂] (2) were synthesized and their structures were determined by single-crystal X-ray diffraction. It was found that cluster 1 showed better optical limiting properties under an 8 ns pulsed laser at 532 nm but poorer optical limiting properties under a 35 ps pulsed laser compared with its analogue [(C₄H₉)₄N]₂[MoOS₃Cu₃BrCl₂]. The influence of the peripheral ligands of the cluster to the optical limiting properties was also discussed.     

ZnS nanosheets: Egg albumin and microwave-assisted synthesis and optical properties

ZnS nanosheets were prepared via egg albumin and microwave-assisted method. The phases, crystalline lattice structures, morphologies, chemical and optical properties were characterized by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), field-emission scanning electron microscope(FE-SEM), selected area electron diffraction (SAED), Fourier transform infrared (FTIR) spectroscopy, ultraviolet–visible (UV–Vis) spectroscopy and fluorescence(FL) spectrometer and growth mechanism of ZnS nanosheets was investigated. The results showed that all samples were pure cubic zinc blende with polycrystalline structure. The width of ZnS nanosheets with a rectangular nanostructure was in the range of 450–750 nm. The chemical interaction existed between egg albumin molecules and ZnS nanoparticles via the amide/carboxylate group. The band gap value calculated was 3.72 eV. The band at around 440 nm was attributed to the sulfur vacancies of the ZnS nanosheets. With increasing volumes of egg albumin, the photoluminescence (PL) intensity of ZnS samples firstly increased and then decreased, attributed to concentration quenching.     

Li2Si3O7: Crystal structure and Raman spectroscopy

The crystal structure of metastable Li₂Si₃O₇ was determined from single crystal X-ray diffraction data. The orthorhombic crystals were found to adopt space group Pmca with unit cell parameters of , and . The content of the cell is Z=4. The obtained structural model was refined to a R-value of 0.035. The structure exhibits silicate sheets, which can be classified as [Si₆O₁₄] using the silicate nomenclature of Liebau. The layers are build up from zweier single chains running parallel to c. Raman spectra are presented and compared with other silicates. Furthermore, the structure is discussed versus Na₂Si₃O₇.     

Synthesis, band structure, and optical properties of Ba2ZnV2O8

A novel compound Ba₂ZnV₂O₈ has been synthesized in high temperature solution reaction and its crystal structure has been characterized by means of single crystal X-ray diffraction analysis. It crystallizes in monoclinic system and belongs to space group P2₁/c with a=7.9050(16), b=16.149(3), , β=90.49(3). It builds up from 1-D branchy chains of [ZnV₂O₈⁴⁻]_∞, and the Ba²⁺ cations are located in the space among these chains. The IR spectrum, ultraviolet-visible diffuse reflection integral spectrum and fluorescent spectra of this compound have been investigated. The calculated results of energy band structure by the density functional theory method show that the solid-state compound of Ba₂ZnV₂O₈ is an insulator with direct band gap of 3.48 eV. The calculated total and partial density of states indicate that the top valence bands are contributions from the mixings of O-2p, V-3d, and Zn-3d states and low conduction bands mostly originate from unoccupied antibonding states between the V-3d and O-2p states. The V-O bonds are mostly covalence characters and Zn-O bonds are mostly ionic interactions, and the ionic interaction strength is stronger between the Ba-O than between the Zn-O. The refractive index of n_x, n_y, and n_z is estimated to be 1.7453, 1.7469, and 1.7126, respectively, at wavelength of 1060 nm for Ba₂ZnV₂O₈ crystal.     

A sodium gadolinium phosphate with two different types of tunnel structure: Synthesis, crystal structure, and optical properties of Na3GdP2O8

A sodium gadolinium phosphate crystal, Na₃GdP₂O₈, has been synthesized by a high-temperature solution reaction, and it exhibits a new structural family of the alkali-metal-rare-earth phosphate system. Although many compounds with formula M₃LnP₂O₈ have been reported, but they were shown to be orthorhombic [R. Salmon, C. Parent, M. Vlasse, G. LeFlem, Mater. Res. Bull. 13 (1978) 439] rather than monoclinic as shown in this paper. Single-crystal X-ray diffraction analysis shows the structure to be monoclinic with space group C2/c and the cell parameters: a=27.55 (25), b=5.312 (4), c=13.935(11) Å, β=91.30(1)°, and V=2038.80 Å³, Z=4. Its structure features a three-dimensional GdP₂O₈³⁻ anionic framework with two different types of interesting tunnels at where Na atoms are located by different manners. The framework is constructed by Gd polyhedra and isolated PO₄ tetrahedra. It is different from the structure of K₃NdP₂O₈ [R. Salmon, C. Parent, M. Vlasse, G. LeFlem, Mater. Res. Bull. 13 (1978) 439] with space group P2₁/m that shows only one type of tunnel. The emission spectrum and the absorption spectrum of the compound have been investigated. Additionally, the calculations of band structure, density of states, dielectric constants, and refractive indexes have been also performed with the density functional theory method. The obtained results tend to support the experimental data.     

Preparation of optical active single-handed helical barium titanate nanotubes and characterization of dielectric properties

Left and right-handed helical barium titanate nanotubes are prepared with the impregnation of Ba(OH)_2 into single-handed helical titania nanotubes.Wide angle X-ray diffraction pattern and transmission electron microscopy image indicate that they are constructed by nanoparticles with a partially crystalline structure.The diffuse reflertance circular dichroism spectra indicate that they exhibit optical activity which was proposed to originate from chiral defects on the inner surfaces of the nanotubes.Both the dielectric constant and tanδ decrease with increasing the frequency.At 10 and 100 Hz,one dielectric constant peak at 9.6℃ and one tanδ peak at 5.0℃ are observed at -120℃ to 180℃.     

Synthesis, crystal structure and optical properties of BiMgVO5

The new vanadate BiMgVO₅ has been prepared and its structure has been determined by single crystal X-ray diffraction: space group P2₁/n, , , , β=107.38(5)°, wR₂=0.0447, R=0.0255. The structure consists of [Mg₂O₁₀] and [Bi₂O₁₀] dimers sharing their corners with [VO₄] tetrahedra. The ranges of bond lengths are 2.129-2.814 Å for Bi-O; 2.035-2.167 Å for Mg-O and 1.684-1.745 Å for V-O. V-O bond lengths determined from Raman band wavenumbers are between 1.679 and 1.747 Å. An emission band overlapping the entire visible region with a maximum around 650 nm is observed.     

Synthesis,Structure and Raman Data of the New Binuclear Zirconium Complex [Ph4P]2[(ZrCl4Py)2O], with a Zr‐O‐Zr Bridge

The new Zirconium(IV) coordination compound [Ph₄P]₂[(ZrCl₄Py)₂O] (Ph = phenyl, Py = pyridine) was synthesized by dissolving ZrCl₄, [Ph₄P]Cl and a stoichiometric amount of NaOH/Na mixture in pyridine or pyridine/organic solvent mixtures. The title phase was obtained as colourless crystals. The crystal structure of [Ph₄P]₂[(ZrCl₄Py)₂O] was determined. It crystallizes monoclinic, P2₁/c, Z = 4, a = 13.412(2), b = 13.461(2), c = 16.442(3) Å, β = 102.72(1)°. The structure consists of isolated tetraphenylphosphonium cations and [(ZrCl₄Py)₂O]^2? complex anions. The centrosymmetric complex anion contains a linear Zr–O–Zr bridge. Each Zr atom is coordinated by one oxygen dianion, the N atom of one pyridine ring and four chloro ligands in a distorted octahedral geometry. The Raman spectrum of [Ph₄P]₂[(ZrCl₄Py)₂O] is also reported. Most of the observed frequencies can be assigned to vibrations of the tetraphenylphosphonium cations and the pyridine rings.     

Syntheses, crystal and electronic structure, and some optical and transport properties of LnCuOTe (Ln=La, Ce, Nd)

Three new compounds, LaCuOTe, CeCuOTe, and NdCuOTe, have been synthesized from the respective rare-earth elements, CuO, and a KI flux at 1023 K. The compounds, which have the ZrSiCuAs structure type, are isostructural to LaCuOS, and crystallize in space group P4/nmm of the tetragonal system with two formula units in cells of dimensions at 153 K of , , for LaCuOTe; , , for CeCuOTe; and , , for NdCuOTe. The structure of LnCuOTe (Ln=La, Ce, Nd) is composed of alternating PbO-like [Ln₂O₂] and anti-PbO-like [Cu₂Te₂] layers stacked perpendicular to [0 0 1]. The experimental optical band gaps of LaCuOTe and NdCuOTe are 2.31 and 2.26 eV, respectively. At 298 K the electrical conductivity of LaCuOTe is 1.65 S/cm and the Hall mobility is +80.6 cm² V⁻¹ s⁻¹. The positive values of the Seebeck and Hall coefficients indicate p-type electrical conduction. First-principles theoretical calculations were performed on LaCuOQ (Q=S, Se, Te). In LaCuOTe, Cu 3d and Te 5p orbitals dominate the states near the valence band maximum; the states near the conduction band minimum are composed of Cu 4s, Te 5p, and La 5d orbitals. The larger dispersion of Cu 3d orbitals and the presence of Te 5p orbitals near the valence band maximum are responsible for the larger hole mobility of LaCuOTe compared to LaCuOS and LaCuOSe.     

Syntheses, crystal structures and optical spectroscopy of Ln2(SO4)3·8H2O (Ln=Ho, Tm) and Pr2(SO4)3·4H2O

The lanthanide sulphate octahydrates Ln₂(SO₄)₃·8H₂O (Ln=Ho, Tm) and the respective tetrahydrate Pr₂(SO₄)₃·4H₂O were obtained by evaporation of aqueous reaction mixtures of trivalent rare earth oxides and sulphuric acid at 300 K. Ln₂(SO₄)₃·8H₂O (Ln=Ho, Tm) crystallise in space group C2/c (Z=4, a_Ho=13.4421(4) Å, b_Ho=6.6745(2) Å, c_Ho=18.1642(5) Å, β_Ho=102.006(1) Å³ and a_Tm=13.4118(14) Å, b_Tm=6.6402(6) Å, c_Tm=18.1040(16) Å, β_Tm=101.980(8) Å³), Pr₂(SO₄)₃·4H₂O adopts space group P2₁/n (a=13.051(3) Å, b=7.2047(14) Å, c=13.316(3) Å, β=92.55(3) Å³). The vibrational and optical spectra of Ho₂(SO₄)₃·8H₂O and Pr₂(SO₄)₃·4H₂O are also reported.     

W/Cu(Ag)/S complexes containing bridging diphosphine ligands: Synthesis,structures and optical properties

The substitution reactions of [Et₄N]₂[WOS₃MCN] (M = Cu, Ag) with dppe (dppe = 1,2-bis(diphenylphosphino) ethane) in DMF afforded a tetranuclear cluster [Et₄N]₂[WOS₃Cu(dppe)]₂ · H₂O (1) and a polymer [WEE′S₂Ag(dppe)]₂ · CH₃CN (3) (E = 0.636S + 0.364O, E′ = 0.581O + 0.419S), respectively. Treatment of 1 with AgI at elevated temperature yielded polymeric complex [WS₄Cu₂(dppe)₂]_n (2). X-ray single crystal structural analyses revealed that in both 1 and 2, the W/Cu/S cluster units are linked by two dppe ligands to form a 10-membered [–Cu–P–C–C–P–]₂ ring. In the polymeric structure of 2, the W and Cu atoms form a helical chain whereas in 3 the cluster units (WEE′S₂Ag) are bridged by dppe ligands affording a zig-zag chain structure. The optical absorption spectra and the solid-state photoluminescent properties of the title complexes are also studied.     

A 1-D chain praseodymium complex with chelidamic acid: synthesis,structure, and optical properties

The title compound [Pr(C₇H₃NO₅)(C₇H₄NO₅)(H₂O)₂] _n · 1.25nH₂O (1) or [Pr(HChel)(H₂Chel)(H₂O)₂] _n · 1.25nH₂O, where H₃Chel is 4-hydroxypyridine-2,6-dicarboxylic (chelidamic) acid, was synthesized by reaction of chelidamic acid, PrCl₃ · 6H₂O and H₂O under hydrothermal conditions, and characterized by X-ray single-crystal diffraction. The crystal structure of 1 reveals that Pr is nine-coordinate with distorted tricapped trigonal prismatic coordination. Coordination polyhedra are interlinked into a 1-D chain, further linked by hydrogen bonds into a 3-D network. Fluorescence spectra exhibit strong green luminescence with maximum emission at 530 nm when excited with λ _ex = 475 nm, originating from π–π* of the ligand.     

Synthesis, structure and optical limiting properties of organoruthenium-chalcogenide clusters

Treatment of Ru₃(CO)₁₂ with Ph₃PS affords the compounds [Ru₃(μ₃-S)₂(CO)_9 − n(PPh₃)_n] (n = 1 (1a), 2 (2a)) and [Ru₃(μ₃-S)(μ₃-CO)(CO)₇(PPh₃)₂] (3a) as the major products. Single crystal X-ray diffraction studies of [Ru₃(μ₃-S)₂(CO)₈(PPh₃)] and [Ru₃(μ₃-S)(μ₃-CO)(CO)₇(PPh₃)₂] show these two classes of compounds to contain square pyramidal Ru₃S₂ and trigonal pyramidal Ru₃S metal cores, respectively, with the latter being isostructural to the analogous selenide cluster compound. The clusters [Ru₃(μ₃-E)₂(CO)_9 − n(PPh₃)_n] (E = S, n = 1; E = Se, n = 2) readily undergo ligand displacement reactions with PPh₃ to afford the compounds [Ru₃(μ₃-E)₂(CO)₆(PPh₃)₃] (E = S, 5a; E = Se 5b). The mixed chalcogenide cluster, [Ru₃(μ₃-S)(μ₃-Se)(CO)₇(PPh₃)₂] (6), was prepared from the reaction of [Ru₃(μ₃-S)(μ₃-CO)(CO)₇(PPh₃)₂] and SePPh₃. The optical limiting properties of the complexes 1a,b, 2a,b, 5a,b have been measured by the Z-scan technique employing 40 ns pulses at 523 nm; power limiting was observed for all clusters under our experimental conditions.     

3-D Hydrogen-bonded networks of metal complexes with chelidamic acid and 1,10-phenanthroline: syntheses,structures, and optical properties

The title complexes, (C₁₂H₈N₂) ? [La(C₇H₃NO₅)(C₇H₄NO₅) ? 3H₂O] ? 1.75H₂O (1), (C₁₂H₈N₂) ? [Pr(C₇H₃NO₅)(C₇H₄NO₅) ? 3H₂O] ? 2H₂O (2), (C₁₂H₈N₂)[Nd(C₇H₃NO₅)(C₇H₄NO₅) ? 3H₂O] ? 2.25H₂O (3), and (C₁₂H₈N₂) ? [Fe(C₇H₃NO₅)(C₇H₄NO₅)] ? 2H₂O (4), were synthesized and characterized by single-crystal X-ray diffraction. The crystal structures of 1–3 reveal that they are isomorphous, among which the metal atoms are all nine-coordinate with distorted tricapped trigonal prismatic coordination geometries. The Fe is six-coordinate with a distorted octahedron by two chelidamic acid ligands in 4. Complexes 1–4 are formed into 3-D networks by H-bonds and π–π stacking interactions. The fluorescence spectra of 1–3 were investigated and all exhibit strong luminescence.     

Semicarbazones and thiosemicarbazones,XII: Crystal structure of salicylaldehyde semicarbazone

Summary The crystal and molecular structure of salicylaldehyde semicarbazone was obtained by single crystal X-ray diffraction. The O atom of the semicarbazone fragment isanti to the N atom of the hydrazinic group. The distribution of bond lengths in the semicarbazone fragment indicates delocalization of the -electrons. The crystal structure is stabilized by intra- and intermolecular hydrogen bonds.

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Semicarbazone und Thiosemicarbazone, 12. Mitt.: Die Kristallstruktur des Salicylaldehyd-Semicarbazons

Zusammenfassung Die Kristallstruktur und die molekulare Struktur des Salicylaldehyd-Semicarbazons wurde über Einkristall-Röntgenstreuung ermittelt. Das O-Atom des Semicarbazonteils stehtanti zum N-Atom der Hydrazin-Gruppierung. Die Bindungslängen in der Semicarbazoneinheit zeigen eine Delokalisierung der -Elektronen an. Die Geometrie der Verbindung wird durch stabilisierende intra- und intermolekulare Wasserstoffbrückenbindungen bestimmt.

     

Synthesis, crystal structure and optical properties of an indium phosphate K3In3P4O16

An alkali-metal indium phosphate crystal, K₃In₃P₄O₁₆, has been synthesized by a high-temperature solution reaction and exhibits a new structure in the family of the alkali-metal indium phosphates system. Single-crystal X-ray diffraction analysis shows the structure to be monoclinic with space group P2₁/n, and the following cell parameters: a=9.7003(18), b=9.8065(18), c=15.855(3) Å, β=90.346(3)°, V=1508.2(5) Å³, Z=4, R=0.0254. It possesses three-dimensional anionic frameworks with tunnels occupied by K⁺ cations running along the a-axis. The emission and absorption spectra of the compound have been investigated. Additionally, the calculations of energy band structure, density of states, dielectric constants and refractive indexes have been performed with the density functional theory method. Also, the two-photon absorption spectrum is simulated by two-band model. The obtained results tend to support the experimental data.