Structure determination of KScS2, RbScS2 and KLnS2 (Ln = Nd,Sm, Tb,Dy, Ho,Er, Tm and Yb) and crystal–chemical discussion

The title structures of KScS₂ (potassium scandium sulfide), RbScS₂ (rubidium scandium sulfide) and KLnS₂ [Ln = Nd (potassium neodymium sufide), Sm (potassium samarium sulfide), Tb (potassium terbium sulfide), Dy (potassium dysprosium sulfide), Ho (potassium holmium sulfide), Er (potassium erbium sulfide), Tm (potassium thulium sulfide) and Yb (potassium ytterbium sulfide)] are either newly determined (KScS₂, RbScS₂ and KTbS₂) or redetermined. All of them belong to the α‐NaFeO₂ structure type in agreement with the ratio of the ionic radii r³⁺/r⁺. KScS₂, the member of this structural family with the smallest trivalent cation, is an extreme representative of these structures with rare earth trivalent cations. The title structures are compared with isostructural alkali rare earth sulfides in plots showing the dependence of several relevant parameters on the trivalent cation crystal radius; the parameters thus compared are c, a and c/a, the thicknesses of the S—S layers which contain the respective constituent cations, the sulfur fractional coordinates z(S²⁻) and the bond‐valence sums.     

Hierarchical Nanotubes Constructed by Co9S8/MoS2 Ultrathin Nanosheets Wrapped with Reduced Graphene Oxide for Advanced Lithium Storage

Nanostructured hybrid metal sulfides have attracted intensive attention due to their fascinating properties that are unattainable by the single‐phased counterpart. Herein, we report an efficient approach to construct cobalt sulfide/molybdenum disulfide (Co₉S₈/MoS₂) wrapped with reduced graphene oxide (rGO). The unique structures constructed by ultrathin nanosheets and synergetic effects benefitting from bimetallic sulfides provide improved lithium ions reaction kinetics, and they retain good structural integrity. Interestingly, the conductive rGO can facilitate electron transfer, increase the electronic conductivity and accommodate the strain during cycling. When evaluated as anode materials for lithium‐ion batteries (LIBs), the resultant reduced graphene oxide‐coated cobalt sulfide/molybdenum disulfide (Co₉S₈/MoS₂@rGO) nanotubes deliver high specific capacities of 1140, 948, 897, 852, 820, 798 and 784 mAh g^?1 at the various discharging current densities of 0.2, 0.5, 1, 2, 3, 4 and 5 A g^?1, respectively. In addition, they can maintain an excellent cycle stability with a discharge capacity of 807 mAh g^?1 at 0.2 A g^?1 after 70 cycles, 787 mAh g^?1 at 1 A g^?1 after 180 cycles and 541 mAh g^?1 at 2 A g^?1 after 200 cycles. The proposed method may offer fundamental understanding for the rational design of other hybrid functional composites with high Li‐storage properties.     

NaZr2N2SCl: Ein flußmittelstabilisiertes Derivat von Zirconium(IV)–Nitridsulfid (Zr2N2S)

NaZr₂N₂SCl: A Flux‐Stabilized Derivative of Zirconium(IV) Nitride Sulfide (Zr₂N₂S) The oxidation of zirconium metal with elemental sulfur and sodium azide (NaN₃) should give access to zirconium(IV) nitride sulfide, Zr₂N₂S, which could crystallize isotypically with the trigonal rare‐earth(III) oxide sulfides M₂O₂S (M = Y, La–Lu). Appropriate molar admixtures of these reactants together with NaCl added as flux were heated for seven days at 850 °C in torch‐sealed evacuated silica tubes. As main product, however, pale yellow platelets with the composition NaZr₂N₂SCl (trigonal, R 3 m; a = 363.56(3), c = 2951.2(4) pm; Z = 3) emerged as single crystals. This pseudo‐quaternary compound crystallizes isotypically with e. g. Li_xEr₂H_yCl₂ (x ≤ 1, y ≤ 2) in a (doubly) stuffed ZrBr‐type structure and contains at least structural domains of the hypothetical Ce₂O₂S‐analogous Zr₂N₂S. Zr⁴⁺ resides in monocapped trigonal anti‐prismatic sevenfold coordination of the anions (d(Zr–N) = 218 (3 ×) and 220 pm (1 ×), d(Zr–S/Cl) = 266 pm, 3 ×). Closest packed double‐layers of Zr⁴⁺ with all tetrahedral interstices occupied with N^3– are sandwiched by layers of isoelectronic S^2– and Cl^– anions. These anionic six‐layer slabs (S/Cl–Zr–N–N–Zr–S/Cl) pile up parallel (001) in a cubic closest packed fashion. Charge balance and structural consistence occurs between these layers by intercalation of Na⁺ within octahedral voids (d(Na–S/Cl) = 282 pm, 6 ×) of double‐layers of the indistinguishable heavy anions (S^2– and Cl^–).     

Synthesis of mercury rare earth ternary sulfides

Three new mercury rare earth sulfides have been synthesized by heating a mixture of the sesquisulfide of rare earth and cinnabar at 800°c for 25 h in an evacuated (10^?4 Torr) sealed quartz tube. Their general formula, Ln₄HgS₇ (Ln = Tm, Yb and Lu), was determined by chemical analysis. These sulfides are tetragonal. Lattice parameters for Ln = Tm, Yb and Lu are: a = 11.09(2), 11.07(3) and 11.03(2)Å, c = 8.38(5), 8.35(2) and 8.33(2)Å respectively. These compounds are stable toward air and moisture at room temperature, but are oxidized slowly at elevated temperature. Thermogravimetric curves show that Tm₄HgS₇, Yb₄HgS, and Lu₄HgS₇ are decomposed and oxidized at 500°, 650° and 450°C respectively.     

Preparation,characterization, and properties of two rare earth organic frameworks with 1H-benzimidazole-2-carboxylic acid

Reaction of rare earth metal ions with 1H-benzimidazole-2-carboxylic acid (H₂BIC) acid yielded two rare earth organic frameworks [Ln(HBIC)₃] _n (Ln?=?Gd 1, Y 2; H₂BIC) under hydrothermal conditions. Both compounds were structurally characterized by single-crystal X-ray diffraction. Their thermal stabilities, luminescent, and magnetic properties were also investigated. Compounds 1 and 2 are isomorphic and present 2-D networks constructed by bridging-chelating HBIC^? linkers and rare earth cation nodes, in which each asymmetric unit consists of one crystallographically unique Ln(III) ion and three HBIC^? with two kinds of coordination modes. The two compounds exhibit high-thermal stability, stable to 320?°C. Antiferromagnetic interactions between Gd(III) centers for 1 were observed from magnetic susceptibility data. 2 exhibits a strong blue emission band in the solid state.     

Sequential Chemistry Toward Core–Shell Structured Metal Sulfides as Stable and Highly Efficient Visible‐Light Photocatalysts

A universal sequential synthesis strategy in aqueous solution is presented for highly uniform core–shell structured photocatalysts, which consist of a metal sulfide light absorber core and a metal sulfide co‐catalyst shell. We show that the sequential chemistry can drive the formation of unique core–shell structures controlled by the constant of solubility product of metal sulfides. A variety of metal sulfide core–shell structures have been demonstrated, including CdS@CoS_x, CdS@MnS_x, CdS@NiS_x, CdS@ZnS_x, CuS@CdS, and more complexed CdS@ZnS_x@CoS_x. The obtained strawberry‐like CdS@CoS_x core–shell structures exhibit a high photocatalytic H₂ production activity of 3.92 mmol h^?1 and an impressive apparent quantum efficiency of 67.3 % at 420 nm, which is much better than that of pure CdS nanoballs (0.28 mmol h^?1), CdS/CoS_x composites (0.57 mmol h^?1), and 5 %wt Pt‐loaded CdS photocatalysts (1.84 mmol h^?1).     

Homometallic Rare‐Earth Metal Phosphinidene Clusters: Synthesis and Reactivity

Two new trinuclear μ₃‐bridged rare‐earth metal phosphinidene complexes, [{L(Ln)(μ‐Me)}₃(μ₃‐Me)(μ₃‐PPh)] (L=[PhC(NC₆H₄iPr₂‐2,6)₂]^?, Ln=Y ( 2 a ), Lu ( 2 b )), were synthesized through methane elimination of the corresponding carbene precursors with phenylphosphine. Heating a toluene solution of 2 at 120 °C leads to an unprecedented ortho C? H bond activation of the PhP ligand to form the bridged phosphinidene/phenyl complexes. Reactions of 2 with ketones, thione, or isothiocyanate show clear phospha‐Wittig chemistry, giving the corresponding organic phosphinidenation products and oxide (sulfide) complexes. Reaction of 2 with CS₂ leads to the formation of novel trinuclear rare‐earth metal thione dianion clusters, for which a possible pathway was determined by DFT calculation.     

La4N2S3: Ein neues Nitridsulfid des Lanthans mit beispielloser Kristallstruktur

La₄N₂S₃: A New Nitride Sulfide of Lanthanum with Unprecedented Crystal Structure The oxidation of lanthanum powder with sulfur and cesium azide (CsN₃) in the presence of lanthanum tribromide (LaBr₃) yields lanthanum nitride sulfide with the composition La₄N₂S₃ when appropriate molar ratios of the reactants are used. Additional cesium bromide (CsBr) as a flux secures fast reactions (7 d) at 900 °C in evacuated silica tubes as well as the formation of almost black single crystals. The orthorhombic crystal structure (Pnnm, Z = 2) was determined from single crystal X‐ray diffraction data (a = 641.98(4), b = 1581.42(9), c = 409.87(3) pm). Two crystallographically different La³⁺ cations are present, La1 resides in sixfold coordination of two N^3? and four S^2? anions forming a trigonal prism and La2 is coordinated by two N^3? and five S^2? in the shape of a monocapped trigonal prism. However, the main feature of the crystal structure comprises N^3?‐centred (La³⁺)₄ tetrahedra which arrange as pairs [N₂La₆]¹²⁺ of edge‐shared [NLa₄]⁹⁺ units and which are further connected via four vertices to form double chains . They get bundled along [001] like a hexagonal rod packing and are held together by two crystallographically different S^2? anions. Further motifs for the connectivity of [NM₄]⁹⁺ tetrahedra in crystal structures of nitride chalcogenides and halides of the rare‐earth elements (M = Sc, Y, La; Ce – Lu) with ratios of N : M = 1 : 2 are presented and discussed for comparison.     

Hierarchical Metal Sulfide/Carbon Spheres: A Generalized Synthesis and High Sodium‐Storage Performance

The development of suitable anode materials is far from satisfactory and is a major scientific challenge for a competitive sodium‐ion battery technology. Metal sulfides have demonstrated encouraging results, but still suffer from sluggish kinetics and severe capacity decay associated with the phase change. Herein we show that rational electrode design, that is, building efficient electron/ion mixed‐conducting networks, can overcome the problems resulting from conversion reactions. A general strategy for the preparation of hierarchical carbon‐coated metal sulfide (MS?C) spheres through thermal sulfurization of metal glycerate has been developed. We demonstrate the concept by synthesizing highly uniform hierarchical carbon coated vanadium sulfide (V₂S₃?C) spheres, which exhibit a highly reversibly sodium storage capacity of 777 mAh g^?1 at 100 mA g^?1, excellent rate capability (410 mAh g^?1 at 4000 mA g^?1), and impressive cycling ability.     

Synthesis and magnetic properties of ALnO2 (A=Cu or Ag; Ln=rare earths) with the delafossite structure

Synthesis, structures, and magnetic properties of ternary rare earth oxides ALnO₂ (A=Cu or Ag; Ln=rare earths) have been investigated. CuLnO₂ (Ln=La, Pr, Nd, Sm, Eu) were synthesized by the direct solid state reaction of Cu₂O and Ln₂O₃, and AgLnO₂ (Ln=Tm, Yb, Lu) were obtained by the cation-exchange reaction of NaLnO₂ and AgNO₃ in a KNO₃ flux. These compounds crystallized in the delafossite-type structure with the rhombohedral 3R type (space group: R-3m). Magnetic susceptibility measurements showed that these compounds are paramagnetic down to 1.8 K. Specific heat measurements down to 0.4 K indicated that CuNdO₂ ordered antiferromagnetically at 0.8 K.     

Crystal and Electronic Structures of the New Carbomolybdates(III), RE2[Mo2C3] with RE = Ce,Sm, Tb,and Dy

Four new ternary carbometalates of the general formula RE₂[Mo₂C₃] with RE = Ce, Sm, Tb and Dy have been prepared by a high temperature synthesis route. The Ce, Tb and Dy compounds crystallize isotypic to Er₂[Mo₂C₃], Sm₂[Mo₂C₃], however, is an isotype of Ho₂[Cr₂C₃]. The crystal structures comprise polyanionic layers [(Mo₂C₃)^6?] with the rare‐earth metal ions in between. The layers are constructed by edge and vertex connected MoC₄ tetrahedra, which display strong covalent Mo–C bonds. The compounds show metallic behaviour close to the classical limit of 100 μΩ cm for metallic conductors. The magnetic properties are quite different, however they are consistent with the presence of trivalent RE³⁺ ions with the exception of Ce₂[Mo₂C₃], which contains nonmagnetic Ce species. Electronic structure calculations reveal that the additional electron mainly populates the Ce partial structure. The title compounds extend the series of known carbomolybdates RE₂[Mo₂C₃]. The late lanthanides Gd, Tb, Dy, Ho, Er, Tm, and Lu with comparatively small RE³⁺ ions and Ce as Ce⁴⁺ adopt the Er₂[Mo₂C₃] structure type, whereas the early lanthanides Sm and Pr with larger RE³⁺ ions crystallize in the structure types of Ho₂[Cr₂C₃] and Pr₂[Mo₂C₃], respectively.     

New Phosphides La5Zn2−xP6 and Ce5Zn2−xP6 – the n = 4 Members of the REZn2P2·n(REP) Series

The new phosphides La₅Zn_2?xP₆ and Ce₅Zn_2?xP₆ were synthesized from the rare earth metals, LaZn and CeZn precursor compounds, Zn, and red phosphorous in NaCl/KCl salt fluxes. They crystallize with a new rhombohedral structure type: , Z = 3, a = 422.11(6), c = 6220(1) pm, wR2 = 0.0369, 356 F² values, 23 variables for La₅Zn_1.69P₆ and a = 417.05(6), c = 6162(1), wR2 = 0.0343, 286 F² values, 23 variables for Ce₅Zn_1.75P₆. The P^3? phosphide anions show an h²c⁴ stacking sequence in which the RE³⁺ and Zn²⁺ cations fill 5/6 and 1/6 of the octahedral and tetrahedral voids in an ordered manner, respectively, leading to a layer of condensed ZnP₄ tetrahedra and quintupled layers of condensed REP₆ octahedra. The structures of La₅Zn_2?xP₆ and Ce₅Zn_2?xP₆ belong to a larger family of phosphides which are intergrowth variants of CaAl₂Si₂ and NaCl related slabs according to REZn₂P₂·n(REP) with n = 4 for the present phosphides.     

Enhancing the Value of Free Metals in the Synthesis of Lanthanoid Formamidinates: Is a Co‐oxidant Needed?

Treatment of N,N′‐bis(aryl)formamidines (ArFormH), N,N′‐bis(2,6‐difluorophenyl)formamidine (DFFormH) or N,N′‐bis(2,6‐diisopropylphenyl)formamidine (DippFormH), with europium metal in CH₃CN is an efficient synthesis of the divalent complexes: [{Eu(DFForm)₂(CH₃CN)₂}₂] ( Eu1 ) or [Eu(DippForm)₂(CH₃CN)₄] ( Eu2 ). The synthetic method was extended to ytterbium, but the metal required activation by addition of Hg⁰. With DFFormH in CH₃CN, [{Yb(DFForm)₂(CH₃CN)}₂] ( Yb1 ) was obtained in good yield, and [Yb(DFForm)₂(thf)₃] ( Yb3 ) was obtained from a synthesis in CH₃CN/THF. Thus, this synthetic method completely circumvents the use of either salt metathesis, or redox transmetallation/protolysis (RTP) protocols to prepare divalent rare‐earth formamidinates. Heating Yb1 in PhMe/C₆D₆ resulted in decomposition to trivalent products, including one from a CH₃CN activation process. For a synthetic comparison, divalent ytterbium DFForm and DippForm complexes were synthesised by RTP reactions between Yb⁰, Hg(R)₂ (R=Ph, C₆F₅), and ArFormH in THF, leading to the isolation of either [Yb(DFForm)₂(thf)₃] ( Yb3 ), or the first five coordinate rare‐earth formamidinate complex [Yb(DippForm)₂(thf)] ( Yb4 b ), and, from adjustment of the stoichiometry, trivalent [Yb(DFForm)₃(thf)] ( Yb6 ). Oxidation of Yb3 with benzophenone (bp), or halogenating agents (TiCl₄(thf)₂, Ph₃CCl, C₂Cl₆) gave [Yb(DFForm)₃(bp)] or [Yb(DFForm)₂Cl(thf)₂], respectively. Furthermore, the structural chemistry of divalent ArForm complexes has been substantially broadened. Not only have the highest and lowest coordination numbers for divalent rare‐earth ArForm complexes been achieved in Eu2 and Yb4 b , respectively, but also dimeric Eu1 and Yb1 have highly unusual ArForm bridging coordination modes, either perpendicular μ‐1κ(N:N′):2κ(N:N′) in Eu1 , or the twisted μ‐1κ(N:N′):2κ(N′:F′) DFForm coordination in Yb1 , both unprecedented in divalent rare‐earth ArForm chemistry and in the wider divalent rare‐earth amidinate field.     

Asymmetric oxidation of sulfides with H2O2 catalyzed by titanium complexes of Schiff bases bearing a dicumenyl salicylidenyl unit

The sterically hindered Schiff bases (L³–L⁵), prepared from 3,5‐dicumenyl salicylaldehyde and chiral amino alcohols, were used in combination with Ti(OiPr)₄ for asymmetric oxidation of aryl methyl sulfides with H₂O₂ as terminal oxidant. Among the ligands L³–L⁵, L⁴ with a tert‐butyl group in the chiral carbon of the amino alcohol moiety gave the best result with 89% yield and 73% ee for the sulfoxidation of thioanisole under optimal conditions [with 1 mol% of Ti(OiPr)₄ in a molar ratio of 100:1:1.2:120 for sulfide:Ti(OiPr)₄:ligand:H₂O₂ in CH₂Cl₂ at 0 °C for 3 h]. The reaction afforded good yield (84%) with a moderate enantioselectivity (62% ee) even with a lower catalyst loading from 1.0 to 0.5 mol%. The oxidations of methyl 4‐bromophenyl sulfide and methyl 4‐methoxyphenyl sulfide with H₂O₂ catalyzed by the Ti(OiPr)₄–L⁴ system gave 79–84% yields and 54–59% ee of the corresponding sulfoxides in CH₂Cl₂ at 20 °C. The chiral induction capability of the cumenyl‐modified sterically hindered Schiff bases for sulfoxidation was compared with the conventional Schiff bases bearing tert‐butyl groups at the 3,5‐positions of the salicylidenyl unit. Copyright © 2011 John Wiley & Sons, Ltd.     

Synthesis of porous biocarbon supported Ni3S4/CeO2 nanocomposite as high-efficient electrode materials for asymmetric supercapacitors

Biocarbon-supported polymetallic composites (CAS@Ni₃S₄/CeO₂) were fabricated by a facile hydrothermal process. The as-prepared CAS@Ni₃S₄/CeO₂ materials integrated the advantages of transition metal sulfides (good conductivity), rare-earth metal oxides (excellent stability), as well as porous carbon with high surface area, thus exhibiting promising electrochemical performance in supercapacitor applications. Indeed, the optimal CAS@Ni₃S₄/CeO₂-150 composite displayed a high specific capacitance of 1364 F g^?1 and impressive cycle performance with capacitance retention of 93.81 % after 10,000 cycles. The calculation of capacitance contribution showed that the satisfying behavior of the electrode was a combination of the diffusion process and the surface capacitance characteristics. Furthermore, the assembled asymmetric supercapacitor (CAS@Ni₃S₄/CeO₂-150//CAS) delivered an ultrahigh energy density of 102.76 Wh kg^?1, which was better than that of the commercial activated carbon-based ASC device. This novel strategy might provide a new perspective for transition metal sulfide/rare earth metal oxide composite in the electrochemical energy storage field.     

Three Ternary Rare Earth(III) Complexes Based on 3‐[(4,6‐Dimethyl‐2‐pyrimidinyl)thio]‐propanoic Acid and 1,10‐Phenanthroline: Synthesis,Crystal Structure and Antioxidant Activity

Three ternary rare earth [Nd^III ( 1 ), Sm^III ( 2 ) and Y^III ( 3 )] complexes based on 3‐[(4,6‐dimethyl‐2‐pyrimidinyl)thio]‐propanoic acid (HL) and 1,10‐phenanthroline (Phen) were synthesized and characterized by IR and UV/Vis spectroscopy, TGA, and single‐crystal X‐ray diffraction. The crystal structures showed that complexes 1 – 3 contain dinuclear rare earth units bridged by four propionate groups and are of general formula [REL₃(Phen)]₂ · nH₂O (for 1 and 2 : n = 2; for 3 : n = 0). All rare earth ions are nine‐coordinate with distorted mono‐capped square antiprismatic coordination polyhedra. Complex 1 crystallizes in the monoclinic system, space group P2₁/c with a = 16.241(7) Å, b = 16.095(7) Å, c = 19.169(6) Å, β = 121.48(2)°. Complex 2 crystallizes in the monoclinic system, space group P2₁/c with a = 16.187(5) Å, b = 16.045(4) Å, c = 19.001(4) Å, β = 120.956(18)°. Complex 3 crystallizes in the triclinic system, space group P1 with a = 11.390(6) Å, b = 13.636(6) Å, c = 15.958(7) Å, α = 72.310(17)°, β = 77.548(15)°, γ = 78.288(16)°. The antioxidant activity test shows that all complexes own higher antioxidant activity than free ligands.     

稀土与华法灵、水杨酸三元配合物的合成和抗凝血作用研究

用氯化稀土与华法灵钠、水杨酸钠在不同介质中制备了稀土三元配合物, 所试验各种制备方法均可获得恒定组成的配合物REL₂L'•2H₂O (HL＝华法灵离子; HL'＝水杨酸离子). 通过元素分析、红外光谱、核磁共振氢谱、X射线衍射、摩尔电导、电子吸收光谱和溶解性试验对配合物进行了表征. 抗凝血试验表明稀土三元配合物具有优良的抗凝血性质.     

Syntheses and Crystal Structures of the Novel Ternary Thioborates Na3BS3, K3BS3, and Rb3BS3

The orthothioborates Na₃BS₃, K₃BS₃ and Rb₃BS₃ were prepared from the metal sulfides, amorphous boron and sulfur in solid state reactions at temperatures between 923 and 973 K. In a systematic study on the structural cation influence on this type of ternary compounds, the crystal structures were determined by single crystal X‐ray diffraction experiments. Na₃BS₃ crystallizes in the monoclinic space group C2/c (No. 15) with a = 11.853(14) Å, b = 6.664(10) Å, c = 8.406(10) Å, β = 118.18(2)° and Z = 4. K₃BS₃ and Rb₃BS₃ are monoclinic, space group P2₁/c (No. 14) with a = 10.061(3) Å, b = 6.210(2) Å, c = 12.538(3) Å, β = 112.97(2) and a = 10.215(3) Å, b = 6.407(1) Å, c = 13.069(6) Å, β = 103.64(5)°, Z = 4. The potassium and rubidium compounds are not isotypic. All three compounds contain isolated [BS₃]^3– anions with boron in a trigonal‐planar coordination. The sodium cations in Na₃BS₃ are located between layers of orthothioborate anions, in the case of K₃BS₃ and Rb₃BS₃ stacks of [BS₃]^3– entities are connected via the corresponding cations. X‐ray powder patterns were measured and compared to calculated ones obtained from single crystal X‐ray structure determinations.     

Insights into photoluminescence property and photocatalytic activity of cubic and rhombohedral ZnIn2S4

Cubic and rhombohedral ZnIn₂S₄ were synthesized by thermal sulfidation of Zn-In mixed oxide precursor in H₂S atmosphere at different temperatures. Cubic ZnIn₂S₄ was obtained when Zn-In mixed oxide precursor was sulfurized at 400 °C. With sulfidation temperature increasing from 400 to 800 °C, the crystal phase of ZnIn₂S₄ gradually turned from cubic to rhombohedral, which was demonstrated by different analysis techniques such as XRD, Raman, SEM, etc. UV-vis absorption spectra indicated that cubic ZnIn₂S₄ displayed better light absorption property than rhombohedral ZnIn₂S₄, with band gaps calculated to be 2.0 and 2.5 eV, respectively. However, under visible light irradiation, rhombohedral ZnIn₂S₄ photocatalyzed H₂ evolution from aqueous sodium sulfite/sulfide solution efficiently, whereas cubic ZnIn₂S₄ was not active for this reaction. The photoluminescence property revealed the different dynamics of photogenerated carriers, which made a predominant contribution to the increasing photocatalytic performances of ZnIn₂S₄ with crystal phase turning from cubic to rhombohedral.     

Na2C2 und K2C2: Synthese,Kristallstruktur und spektroskopische Eigenschaften

Na₂C₂ and K₂C₂: Synthesis, Crystal Structure, and Spectroscopic Properties By the reaction of sodium or potassium solved in liquid ammonia with acetylene and subsequent heating in high vacuum Na₂C₂ and K₂C₂ could be synthesised as single phase products. The crystal structures described by Föppl could be confirmed by X-ray and neutron diffraction experiments (K₂C₂) on powdered samples. Both compounds crystallise in a tetragonal structure (I4₁/acd, no. 142, Z = 8) which can be described as a distorted variant of the antifluorite-structure type. At temperatures above room temperature (Na₂C₂: 580 K, K₂C₂: 420 K) a reversible phase transition (1^st order transition) to a cubic modification (Fm 3 m, no. 225, Z = 4) has been observed, analogous to the alkaline earth metal acetylides. This high temperature modification represents an undistorted antifluorite structure with disordered C₂^2– dumbbells. The results of raman- and ¹³C-MAS-NMR-spectroscopic investigations are in agreement with acetylide dumbbells in the title compounds and allow a comparison to the respective monoalkalimetal and alkaline earth metal acetylides.