A5Sn2As6 (A = Sr, Eu). Synthesis, crystal and electronic structure, and thermoelectric properties

Two new ternary Zintl phases, Sr(5)Sn(2)As(6) and Eu(5)Sn(2)As(6), have been synthesized, and their structures have been accurately determined through single-crystal X-ray diffraction. Both compounds crystallize in orthorhombic space group Pbam (No. 55, Z = 2) with cell parameters of a = 12.482(3)/12.281(5) ?, b = 14.137(3)/13.941(5) ?, and c = 4.2440(10)/4.2029(16) ? for Sr(5)Sn(2)As(6) (R1 = 0.0341; wR2 = 0.0628) and Eu(5)Sn(2)As(6) (R1 = 0.0324; wR2 = 0.0766), respectively. Their structure belongs to the Sr(5)Sn(2)P(6) type, which can be closely related to the Ca(5)Ga(2)As(6) type. Electronic band structure calculations based on the density functional theory reveal an interesting electronic effect in the structure formation of these two types of Zintl phases, which substantially affect their corresponding electronic band structure. Related studies on the thermal stability, magnetism, and thermoelectric properties of Eu(5)Sn(2)As(6) are presented as well.     

Synthesis and crystal structure of Sr(2)AlH(7): a new structural type of alkaline earth aluminum hydride

The title hydride and its deuteride were successfully synthesized. The heavy atom structure and hydrogen positions were determined respectively by X-ray powder diffraction and time-of-flight neutron powder diffraction. They crystallize with a new monoclinic structure in space group I2 (No. 5); cell parameters: a = 12.575(1) A, b = 9.799(1) A, c = 7.9911(8) A, beta = 100.270(4) degrees (hydride), a = 12.552(1) A, b = 9.7826(8) A, c = 7.9816(7) A, beta = 100.286(4) degrees (deuteride), Z = 8. Sr(2)AlH(7) is the first example that consists of isolated [AlH(6)] units and infinite one-dimensional twisted chains of edge-sharing [HSr(4)] tetrahedra along the crystallographic c axis.     

Synthesis, crystal and electronic structures, and properties of the new pnictide semiconductors A2CdPn2 (A = Ca, Sr, Ba, Eu; Pn = P, As)

A series of ternary Zintl phases, Ca(2)CdP(2), Ca(2)CdAs(2), Sr(2)CdAs(2), Ba(2)CdAs(2), and Eu(2)CdAs(2), have been synthesized through high temperature metal flux reactions, and their structures have been characterized by single-crystal X-ray diffraction. They belong to the Yb(2)CdSb(2) structure type and crystallize in the orthorhombic space group Cmc2(1) (No. 36, Z = 4) with cell dimensions of a = 4.2066(5), 4.3163(5), 4.4459(7), 4.5922(5), 4.4418(9) ?; b = 16.120(2), 16.5063(19), 16.904(3), 17.4047(18), 16.847(4) ?; c = 7.0639(9), 7.1418(8), 7.5885(11), 8.0526(8), 7.4985(16) ? for Ca(2)CdP(2) (R1 = 0.0152, wR2 = 0.0278), Ca(2)CdAs(2) (R1 = 0.0165, wR2 = 0.0290), Sr(2)CdAs(2) (R1 = 0.0238, wR2 = 0.0404), Ba(2)CdAs(2) (R1 = 0.0184, wR2 = 0.0361), and Eu(2)CdAs(2) (R1 = 0.0203, wR2 = 0.0404), respectively. Among these, Ca(2)CdAs(2) was found to form with another closely related structure, depending on the experimental conditions--monoclinic space group Cm (No. 8, Z = 10) with lattice constants a = 21.5152(3) ?, b = 4.30050(10) ?, c = 14.3761(2) ? and β = 110.0170(10)° (R1 = 0.0461, wR2 = 0.0747). UV/vis optical absorption spectra for both forms of Ca(2)CdAs(2) show band gaps on the order of 1.0 eV, suggesting semiconducting properties, which have also been confirmed through electronic band structure calculations based on the density-functional theory. Results from differential scanning calorimetry measurements probing the thermal stability and phase transitions in the two Ca(2)CdAs(2) polymorphs are discussed. Magnetic susceptibility measurements for Eu(2)CdAs(2), indicating divalent Eu(2+) cations, are presented as well.     

Synthesis,structures and luminescence of two new Europium(II) Silicate-Chlorides,Eu2SiO3Cl2 and Eu5SiO4Cl6

Eu₂SiO₃Cl₂ and Eu₅SiO₄Cl₆ were prepared by reaction of EuCl₂ with EuSiO₃ and Eu₂SiO₄, respectively, Sr₂SiO₃Cl₂: Eu²⁺ from mixtures of SrCO₃, Eu₂O₃, SrCl₂ · 6H₂O and SiO₂ under reducing conditions. The crystal structures of Eu₂SiO₃Cl₂ [a = 1118.7(5), c = 952.6(1) pm, tetragonal, I4/m, Z = 8, R = 3.3, R_w = 3.0%] and Eu₅SiO₄Cl₆ [a = 900.4(1), b = 1401.7(2), c = 1112.3(2) pm, β = 103.51(1)°, monoclinic, C2/c, Z = 4, R = 3.6, R_w = 2.6%] were determined from four-circle diffractometer data and compared with related compounds. The luminescence properties were investigated at 300 K and at 4.2 K; all compounds show intense bluish-green photoluminescence. Sr₂SiO₃Cl₂:Eu²⁺ shows thermoluminescence.     

Synthesis, crystal and electronic structures of the new quaternary phases A5Cd2Sb5F (A = Sr, Ba, Eu), and Ba5Cd2Sb5O(x) (0.5<x<0.7)

A new family of quaternary fluoro-antimonides A(5)Cd(2)Sb(5)F (A = Sr, Ba, Eu) and oxyantimonides Ba(5)Cd(2)Sb(5)O(x) (0.5相似文献   

Synthesis,crystal structures and properties of two copper(II) 2-aminomethylbenzimidazole complexes

Two new Cu^II complexes, [Cu(Hambi)₂(ClO₄)₂] and [Cu(Hambi)₂(dca)₂] (Hambi = 2-aminomethylbenzimidazole) have been prepared and characterized by X-ray diffraction, electronic paramagnetic resonance (e.p.r.) and i.r. analyses. Both complexes exhibit an elongated octahedral coordination environment with two Hambi ligands situated at the equatorial positions in a trans fashion [Cu—N bond distances range from 1.940(9) to 2.031(9) Å]. In the second complex, a new coordination mode, in which dicyanamide coordinates to copper(II) as a monodentate ligand with the amide nitrogen atom, was observed.     

K3Eu5(PO4)6: hydrothermal synthesis,crystal structure and photoluminescence properties

An anhydrous orthophosphate, K₃Eu₅(PO₄)₆ (tripotassium pentaeuropium hexaphosphate), has been prepared by a high‐temperature solid‐state reaction combined with hydrothermal synthesis, and its crystal structure was determined by single‐crystal X‐ray diffraction analysis (SC‐XRD). The results show that the compound crystallizes in the monoclinic space group C2/c and the structure features a three‐dimensional framework of [Eu₅(PO₄)₆]_∞, with the tunnel filled by K⁺ ions. The IR spectrum, UV–Vis spectrum and luminescence properties of polycrystalline samples of K₃Eu₅(PO₄)₆, annealed at temperatures of 650, 700, 750, 800 and 850 °C, were investigated. Although with a full Eu³⁺ concentration (9.96 × 10²¹ ions cm^?3), the self‐activated phosphor K₃Eu₅(PO₄)₆ shows s strong luminescence emission intensity with a quantum yield of 37%. Under near‐UV light excitation (393 nm), the series of samples shows the characteristic emissions of Eu³⁺ ions in the visible region from 575 to 715 nm. The sample sintered at 800 °C gives the strongest emission and its lifetime sintered at 800 °C (1.88 ms) is also the longest of all.     

Synthesis, characterization and luminescence properties of SrLa2(MoO4)4:Eu phosphors

SrLa₂(MoO₄)₄ (SLM) phosphors doped with Eu³⁺ ions were prepared by a sol–gel combustion method using citric acid as a fuel/reductant and nitrates as oxidants. The crystallization processes were tracked by means of X-ray diffraction and thermo-gravimetric analysis and differential scanning calorimetry. The size and shape of the products were characterized using a scanning electron microscope, while the luminescent spectra of these resulting phosphors were recorded using a photoluminescence (PL) spectrophotometer. PL studies reveal that the emission intensity of SLM:Eu phosphors was strongly related to sintering temperature as well as the doping concentration of Eu³⁺ ions. The present phosphor has a strong excitation at 395 and 459 nm, indicating that it could serve as a promising red-emitting candidate for near-UV and GaN-based blue light-emitting diode chips.     

Synthesis, crystal structures and triboluminescence of a pair of Eu(III)-based enantiomers

Using the chiral ligands L_SS (+)-4,5-pinene bipyridine and L_RR (−)-4,5-pinene bipyridine (Scheme 1), two novel Eu(III)-based complexes with the formula [Eu(DBM)₃L] (L_SS in 1, L_RR in 2, DBM = dibenzoylmethanate) have been successfully synthesized and characterized by X-ray single crystal determination and spectroscopic methods. The crystal structure analysis of 1 and 2 reveal that they crystallize in the chiral space group P2₁ of the monoclinic system. The central Eu(III) ion is eight-coordinated in a geometrical environment intermediate between a square antiprism and a dodecahedron. The CD spectra reflect that complexes 1 and 2 are enantiomers. When ground in daylight, complexes 1 and 2 exhibit brilliant triboluminescence at room temperature.     

Structure and Luminescence Characteristics of Europium Activated Strontium Silicates Sr（Eu ,Bi）SiO3 and Sr（Eu ,Bi）2SiO4

Sr2SiO4 ： Eu^3 , Bi^3 and SrSiO3 ：Eu^3 , Bi^3 samples were synthesized at high temperature and high pressure. The effect of high pressure on the structure and luminescence properties of the samples were stud-ied. As a comparison, the samples were also prepared by the method of sol-gel at high temperature and atmo-spheric pressure. The SrSiO3 ： Eu^3 , Bi^3 prepared at atmosphere has a hexagonal phase structure; in the pressure range of 2. 34—4. 10 GPa, it is transformed into a pseudo-orthorhombic structure (monoclinic), and in the pressure range of 4. 10—4. 15 GPa, the structure change of Sr2SiO4 ： Eu^3 , Bi^3 has not been ob-served, it maintains the monoclinic structure of the samples synthesized at an atmospheric pressure. High pressure makes the luminescence properties of the samples changed obviously. The intensity and the relative quantum luminescent efficiency decrease, the half-width increases obviously and the red shift occurs. The changes of the luminescence properties result from the pressure-induced changes of the crystal structures.     

Synthesis,crystal structures,metal-atom distribution and magnetic properties of Cr5−xTixSe8 (x ≈ 2, 3, 4)

The non-stoichiometric chromium titanium selenides Cr_5−xTi_xSe₈ (x ≈ 2, 3, 4) were prepared applying high-temperature solid-state reactions. The crystal structures have been refined with X-ray and neutron powder diffraction data applying the Rietveld method. The compounds crystallize in the space group F2/m (monoclinic, non-standard setting of C2/m) with four formula units per unit cell. The structures of all phases are related to the NiAs-type structure with ordered metal vacancies in every second metal-atom layer. Among the four different metal-atom sites two are fully occupied and the remaining two are only partially occupied. The MSe₆ octahedra share edges within layers and faces between layers. Consequently, long M–M separations occur in the layers whereas short M–M contacts result between M atoms of face-sharing octahedra. The lattice parameters of the samples and the M–M/M–Se bonds exhibit a remarkable deviation from Végard's rule which is caused by the distribution of Ti and Cr atoms over the independent crystallographic sites. The refinement of neutron diffraction data reveals that for x ≈ 2, 3, Ti atoms are located on three metal sites and only for x ≈ 4 the fourth position is also occupied by Ti. For all compositions a pronounced preference of Ti for sites within the full metal-atom layers is observed. Furthermore, a significant depletion of one partially occupied metal-atom site is accompanied by an increase of occupancy of the other partially occupied metal-atom site. The magnetic properties in the high-temperature range show Curie–Weiss behavior with negative paramagnetic Curie temperatures θ indicating strong antiferromagnetic exchange interactions which get weaker with increasing Ti content. The zero-field-cooled and field-cooled susceptibility curves diverge at low temperatures suggesting spin-glass behavior. The freezing temperature is lowered with increasing Ti content.     

Synthesis and crystal structure of new titanyl phosphate Sr2TiO(PO4)2

New strontium titanyl phosphate Sr₂TiO(PO₄)₂ (1) was synthesized and characterized by X-ray powder diffraction, electron diffraction, high-resolution electron microscopy, and band structure calculations. Titanyl phosphate 1 is isostructural with vanadyl phosphate Sr₂VO(PO₄)₂ and has a layered structure. The titanium atoms are shifted from the centers of the TiO₆ octahedra and form short (1.74 Å) titanyl bonds. The structure of 1 is an unusual example of the disordered orientation of the chains formed by TiO₆ octahedra in complex titanium phosphates.     

Synthesis, crystal structures and magnetic properties of 2,3,6,7-tetrakis(2-cyanoethylthio)tetrathiafulvalene salts

The synthesis of the protected TTF tetrathiolate 2,3,6,7-tetrakis(2-cyanoethylthio)tetrathiafulvalene (TCE-TTF), as well as those of five new radical cation salts [TCE-TTF](X), X⁻ = PF₆⁻, CF₃SO₃⁻, BF₄⁻, obtained by electrocrystallization technique is presented. Five crystal structures of these materials based on their fully oxidized donor molecules are described. The flexibility of the cyanoethylene arm yields two conformations cis and trans to the molecule. Then compounds with PF₆⁻ and BF₄⁻ anions crystallized as two different phases. All these materials are insulators, and the magnetic studies of one phase of [TCE-TTF](PF₆) revealed an antiferromagnetic behavior.     

Synthesis,crystal structure,and magnetic properties of K4Mn3(HPO4)4(H2PO4)2

A new layered compound, K₄Mn₃(HPO₄)₄(H₂PO₄)₂ (1), has been synthesized under hydrothermal conditions. It crystallizes in the monoclinic space group P2₁/n with a = 8.874(2) Å, b = 6.554(1) Å, c = 18.075(4) Å, and β = 93.39(3)°. The structure consists of zigzag [Mn₃O₁₄]_n chains of edge-sharing MnO₆ octahedrons and MnO₇ pentagonal bi-pyramids, which form layers of formula [Mn₃(HPO₄)₄(H₂PO₄)₂]^4? in the ab plane via H₂PO₄ and HPO₄ units with vertex-sharing. Potassium ions lie between these layers. Magnetic measurements indicate Curie–Weiss behavior above 6 K for 1. A Heisenberg model, with alternating exchange interactions J₁J₁J₂… within the chain and exchange interactions J₃J₃… between the chains, is proposed to describe the magnetic behavior.     

Sr2CeO4:Eu,Gd的微波合成与荧光性质

用微波法合成了Gd3 和Eu3 共掺杂的Sr2CeO4荧光体.Gd3 对Sr2CeO4:Eu的发光起不同的作用:当Eu3 浓度较低(掺杂浓度为1 mol%)时,Gd3 离子起猝灭作用;当Eu3 浓度较高(掺杂浓度为8 mol%)时,Gd3 离子起敏化作用,尤其是Gd3 离子掺杂浓度为3 mol%时,Eu3 的5D0→7F2(614 nm)跃迁发射增强为Sr2CeO4:Eu荧光强度的145%.     

Sr5(PO4)3Cl:Eu2+蓝色荧光粉合成新方法的研究

Sr5 (PO4)3Cl:Eu2+是一种重要的蓝色发射荧光材料,通常采用高温固相反应法来制备.本文利用Sr5(PO4)3(OH)与Sr5(PO4)3Cl结构相同的特点,采用沉淀法合成出羟基磷酸锶铕前体,经过氯化铵和助熔剂作用下的固相氯代反应合成出Sr5(PO4)3Cl:Eu2+荧光粉.考察了pH值与原料比例等对沉淀反应过程及产物的影响,并讨论了氯化铵作用下的氯代过程以及助熔剂对产物荧光粉形貌的作用机制.研究结果表明,本合成方法条件易控,且合成产物Sr5 (PO4)3Cl:Eu2+的物相纯度高,尺寸分布均匀,形貌规则,发光性能优良.     

Synthesis, crystal structures and photoluminescent properties of lanthanide supramolecular complexes with 4-oxo-1(4H)-quinolineacetate

Five new lanthanide supramolecular complexes, namely, [Sm(oqa)₂(H₂O)₄]₂ (ClO₄)₂·(bpy)₂ (1), [Ln(oqa)₃]·2H₂O [Ln=Sm(2), Gd(3)] and [Ln(oqa)₂(NO₃)(H₂O)] [Ln=Pr(4), Eu(5)] (oqa=4-oxo-1(4H)-quinolineacetate, bpy=4,4′-bipyridine), have been synthesized under hydrothermal conditions. These complexes exhibit three typical structure features. Complex 1 possesses a dimeric structure, which is further connected together through hydrogen bonds and π-π attractions, forming a 3D supramolecular framework. Compounds 2-3 are isomorphous and contain 1D ring-like chains, which are further interconnected by the oqa ligands into 2D sheet-like structures. 4 and 5 exhibit eight-connected 3D network of 4²⁴·6⁴-bcu topology. The various coordination modes of carboxylate ligands and the selection of the counterions have clearly affected the topological structures. Furthermore, the solid-state luminescent properties of complexes 1, 2 and 5 were investigated at room temperature and they show intense, characteristic emissions in the visible region.     

Synthesis, crystal structures and magnetic properties of tricyanomethanide-containing copper(II) complexes

The preparation, crystal structures and magnetic properties of the copper(II) complexes of formula [Cu(pyim)(tcm)(2)](n) (1), [Cu(bpy)(tcm)(2)](n) (2), [Cu(4)(bpz)(4)(tcm)(8)] (3), {[Cu(terpy)(tcm)].tcm}(n) (4) and {[Cu(2)(tppz)(tcm)(4)].3/2H(2)O}(n) (5) [pyim = 2-(2-pyridyl)imidazole, tcm = tricyanomethanide, bpy = 2,2'-bipyridine, bpz = 2,2'-bipyrazine, terpy = 2,2':6',2'-terpyridine and tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine] are reported. Complexes, 1, 2 and 4 are uniform copper(II) chains with single- (1 and 4) and double-(2) micro-1,5-tcm bridges with values of the intrachain copper-copper separation of 7.489(1) (1), 7.520(1) and 7.758(1) (2) and 7.469(1) A (4). Each copper atom in 1, 2 and 4 is five-coordinate with bidentate pyim (1)/bpy (2) and tridentate terpy (4) ligands and nitrile-nitrogen atoms from bridging (1,2 and 4) and terminal (1) tcm groups building a distorted square pyramidal surrounding. The structure of 3 is made up of neutral centrosymmetric rectangles of (2,2'-bipyrazine)copper(II) units at the corners, the edges being built by single- and double-micro-1,5-tcm bridges with copper-copper separations of 7.969(1) and 7.270(1) A, respectively. Five- and six-coordinated copper atoms with distorted square pyramidal and elongated octahedral environments occur in . Compound 5 is a neutral copper(II) chain with regular alternating bis-tridentate tppz and double micro-1,5-tcm bridges, the intrachain copper-copper distances being 6.549(7) and 7.668(1) A, respectively. The two crystallographically independent copper atoms in 5 have an elongated octahedral geometry with three tppz nitrogen atoms and a nitrile-nitrogen atom from a bridging tcm group in the equatorial positions, and two nitrile nitrogen atoms from a terminal and a bridging tcm ligand occupying the axial sites. The investigation of the magnetic properies of 1-5 in the temperature range 1.9-295 K has shown the occurrence of weak ferro- [J = +0.11(1) cm(-1) (2)] and antiferromagnetic interactions [J = -0.093(1) (1), -0.083(1) (4), -0.04(1) and 1.21(1) cm(-1) (3)] across the micro-1,5-tcm bridges and intermediate antiferromagnetic coupling [-J = 37.4(1) cm(-1) (5)] through bis-tridentate tppz. The values of the magnetic interactions are analyzed through simple orbital symmetry considerations and compared with those previously reported for related systems.     

Synthesis,properties and crystal structures of nitrobenzoatocopper(II) complexes with pyrazinecarboxamide

The synthesis, spectral characterization and crystal structures of two nitrobenzoatocopper(II) complexes, namely [Cu(2-O₂Nbz)₂(pca)₂(H₂O)₂] (1) and [Cu(3,5-(O₂N)₂bz)₂(pca)₂(H₂O)₂] (2) (where 2-O₂Nbz = 2-nitrobenzoate, 3,5-(O₂N)₂bz = 3,5-dinitrobenzoate, pca = pyrazinecarboxamide), are reported. Complexes 1 and 2 consist of centrosymmetric molecules with the Cu(II) atom monodentately coordinated by a pair of anionic 2-nitrobenzoato (1) or 3,5-dinitrobenzoato (2) ligands and a pair of pyrazinecarboxamide ligands, forming a nearly tetragonal basal plane, and by a pair of water ligands that complete the tetragonal–bipyramidal coordination polyhedron. The molecules of both complexes are linked by N–H⋯O and O–H⋯O hydrogen bonds and lie in planes, which have different orientations depending on the space group. Similar experiments with 3-nitrobenzoic acid resulted in the isolation of the hydrolysis product [Cu(pyzCOO)₂] _n (3) (pyzCOO = pyrazinecarboxylate). The known crystal structure of complex 3 has been re-determined at low temperature with significantly higher precision. The crystal packing and C–H⋯O/C–H⋯N hydrogen bonds are discussed.