The Helical Coordination Polymer Ag(Nic)2(NO3)

Single crystals of Ag(Nic)₂(NO₃) were obtained from an aqueous solution of silver nitrate and nicotine as plate‐like colourless crystals. The crystal structure (monoclinic, P2₁, Z = 2, a = 933.3(2), b = 1136.8(2), c = 1024.3(2) pm, β = 94.49(2)°) consists of helical chains in which one nicotine molecule bridges with both the pyridine‐N and the pyrrol‐N coordinating and with a second nicotine molecule terminally coordinating with the pyridine‐N. A monodentate nitrate‐O is completing the coordination sphere of Ag⁺ to a distorted tetrahedron. Ag–N distances (229‐240 pm) attest for a rather strong attraction of the nicotine molecules to Ag(I) and thereby constitute essentially a one‐dimensional, helical coordination polymer according to the formulation Ag(Nic1)_2/2(Nic2)_1/1(NO₃)_1/1.     

Structural Changes and Phase Transitions in Whitlockite-Like Phosphates

New compounds with a g -Ca 3 (PO 4 ) 2 structure type were found in three systems: Sr 9+ x M 1.5 m x (PO 4 ) 7 ( M = Mn, Fe, Co, Ni, Cu, and Cd; space group R 3 m ; Z = 3), Sr 9 R (PO 4 ) 7 ( R = Al, Sc, Cr, Fe, Ga, In, and Gd-Lu; space group P 2/ c , Z = 4), and Sr 9+2 x M 1+ x A 1 m 6 x (PO 4 ) 7 ( M = Mn, Ni, Cd; space group R 3 c and Z = 6 for A = Na, K; space group P 2/ m and Z = 4 for A = Li). Crystal structures of these compounds were determined by time-of-flight neutron, synchrotron X-ray, and laboratory X-ray powder diffraction. Reversible polar-to-centrosymmetric phase transitions ( R 3 c {\begin{array}{c}\\[-14pt]\hspace*{.5pt}\to\\[-7pt]\hspace*{-.5pt}\gets \end{array}} R 3 m ) were observed at high temperatures in Ca 3 m x Sr x (PO 4 ) 2 (0 h x h 12/7), Ca 10.5 m 1.5 x Fe x (PO 4 ) 7 (0 h x h 1), and Ca 9 R (PO 4 ) 7 . Solid solutions Ca 3 m x Sr x (PO 4 ) 2 (13/7 h x h 16/7) are centosymmetric with space group R 3 m at room temperature. These phase transitions were studied by high-temperature X-ray diffraction, second-harmonic generation, DSC, electric-conductivity and dielectric measurements.     

Darstellung und Kristallstruktur von Na2Sn2Se5 Ein neues Chalkogenostannat(IV) mit schichtförmigen Komplexanionen

Preparation and Crystal Structure of Na₂Sn₂Se₅ A Novel Chalcogenostannate(IV) with Layered Complex Anions Na₂Sn₂Se₅ was obtained from a stoichiometric mixture of Na₂Se, Sn, and Se powders through a solid state reaction at 450 °C. It crystallizes orthorhombic, space group Pbca with a = 13.952(6) Å, b = 12.602(2) Å, c = 11.524(2) Å; Z = 8 and undergoes peritectic decomposition at 471(2) °C. The crystal structure was determined at ambient temperature from diffractometer data (MoKα‐radiation) and refined to a conventional R of 0.040 (1490 F_o's, 83 variables). Na₂Sn₂Se₅ is characterized by layered complex anions running parallel to (100) which are built up by SnSe₄ tetrahedra sharing common corners. The mean Sn–Se bond length calculates as 2.252(2) Å. The Na⁺ cations are coordinated to 6 or 7 Se in irregular configurations. The crystal structure can be described as a stacking of distorted c. p. 3⁶ chalcogen layers and mixed square 4⁴ alkali‐chalcogen layers.     

[Ag(NH3)2]ClO4: Kristallstrukturen,Phasenumwandlung, Schwingungsspektren

[Ag(NH₃)₂]ClO₄: Crystal Structures, Phase Transition, and Vibrational Spectra [Ag(NH₃)₂](ClO₄) is obtained from a solution of AgClO₄ in conc. ammonia as colourless single crystals (orthorhombic, Pnmn, Z = 4, a = 795.2(1) pm, b = 617.7(1) pm, c = 1298.2(2) pm, R_all = 0.0494). The structure consists of linearly coordinated cations, [Ag(NH₃)₂]⁺, stacked in a staggered conformation and of tetrahedral (ClO₄)^‐ anions. A first order phase transition was observed between 210 and 200 K and the crystal structure of the low‐temperature modification (monoclinic, P2/m, Z = 4, a = 789.9(5) pm, b = 604.1(5) pm, c = 1290.4(5) pm, β = 97.436(5)°, at 170 K, R_all = 0.0636) has also been solved. Spectroscopic investigations (IR/Raman) have been carried out and the assignment of the spectra is discussed.     

Phase formation in the systems Ag2MoO4-MO-MoO3 (M=Ca, Sr, Ba, Pb, Cd, Ni, Co, Mn) and crystal structures of Ag2M2(MoO4)3 (M=Co, Mn)

Phase equilibria in the systems Ag₂MoO₄-MMoO₄ (M=Ca, Sr, Ba, Pb, Ni, Co, Mn) and subsolidus phase relations in the systems Ag₂MoO₄-MO-MoO₃ (M=Ca, Pb, Cd, Mn, Co, Ni) were investigated using XRD and thermal analysis. The systems Ag₂MoO₄-MMoO₄ (M=Ca, Sr, Ba, Pb, Ni) belong to the simple eutectic type whereas in the systems Ag₂MoO₄-MMoO₄ (M=Co, Mn) incongruently melting Ag₂M₂(MoO₄)₃ (M=Co, Mn) were formed. In the ternary oxide systems studied no other compounds were found. Low-temperature LT-Ag₂Mn₂(MoO₄)₃ reversibly converts into the high-temperature form of a similar structure at 450-500°C. The single crystals of Ag₂Co₂(MoO₄)₃ and LT-Ag₂Mn₂(MoO₄)₃ were grown and their structures determined (space group , Z=2; lattice parameters are a=6.989(1) Å, b=8.738(2) Å, c=10.295(2) Å, α=107.67(2)°, β=105.28(2)°, γ=103.87(2)° and a=7.093(1) Å, b=8.878(2) Å, c=10.415(2) Å, α=106.86(2)°, β=105.84(2)°, γ=103.77(2)°, respectively) and refined to R(F)=0.0313 and 0.0368, respectively. The both compounds are isotypical to Ag₂Zn₂(MoO₄)₃ and contain mixed frameworks of MoO₄ tetrahedra and pairs of M²⁺O₆ octahedra sharing common edges. The Ag⁺ ions are disordered and located in the voids forming infinite channels running along the a direction. The peculiarities of the silver disorder in the structures of Ag₂M₂(MoO₄)₃ (M=Zn, Mg, Co, Mn) are discussed as well as their relations with analogous sodium-containing compounds of the structural family of Na₂Mg₅(MoO₄)₆. The phase transitions in Ag₂M₂(MoO₄)₃ (M=Mg, Mn) of distortive or order-disorder type are suggested to have superionic character.     

Synthesis,Crystal Structure,IR Spectra and Thermal Analysis of Na[Ag(sac)2] (sac = saccharinate)

The reaction of silver nitrate with sodium saccharinate (Na[sac]) in the presence of 2-pyridinepropanol in aqueous solution yields the title complex, Na[Ag(sac)₂]. The compound crystallizes in the triclinic space group [a = 8.0481(6), b = 9.0587(6), c = 11.1642(8) Å; α = 100.064(3), β = 99.917(3) and γ = 92.367(3)°, Z = 2]. The structure consists of Na⁺ and [Ag(sac)₂]^- ions, in which each silver(I) ion is doubly bridged by the sac ligands, exhibiting a distorted 'T' shaped AgN₂O coordination arrangement with one long [Ag-O_sulfonyl = 2.6390(10) Å] and two shorter bonds [Ag-N = 2.1405(11) and 2.1570(11) Å]. The coordination around silver(I) is trigonal planar and the N-Ag-N bond angle is 158.99(5)°. The Na⁺ ion is five-coordinate with two carbonyl and three sulfonyl O atoms of the adjacent sac ligands and acts as a bridge between [Ag(sac)₂]^- units, resulting in a three-dimensional network. The i.r. spectra and thermal decomposition behaviour of Na[Ag(sac)₂] are discussed in detail.     

Syntheses and Crystal Structures of Three Polymeric Silver(I) Terephthalate Complexes with Organic N‐Donor Ligands: [Ag(pren)]2(tp)·2H2O, [Ag(en)][Ag(μ2‐tp)]·H2O,and [Ag2(μ4‐tp)(apy)2]

Three polymeric silver(I) complexes with terephthalate anions as counterions or ligands, [Ag(pren)]₂(tp)·2H₂O ( 1 ), [Ag(en)][Ag(μ₂‐tp)]·H₂O ( 2 ), and [Ag₂(μ₄‐tp)(apy)₂] ( 3 ) (where pren = 1, 2‐propylenediamine, tp =terephthalate dianion, en = ethylenediamine, and apy = 2‐aminopyridine) were synthesized and characterized by X‐ray single crystal analysis and infrared spectroscopy. 1 crystallizes in the monoclinic space group P2₁1/c with a = 11.3221(5), b = 7.1522(3), c = 14.8128(5)Å, V = 1015.77(7)ų, β = 122.132(2), and Z = 2. 2 crystallizes in the orthorhombic space group Pnma with a = 9.6144(6), b = 11.3465(7), c = 11.4810(7)Å, V = 1252.5(1)ų, and Z = 4. 3 crystallizes in the monoclinic space group P2₁/n with a = 8.2003(5), b = 5.8869(4), c = 18.3769(11)Å, β = 92.593(1), V = 886.2(1)ų, and Z = 4. Terephthalate dianions are not coordinated to the metal atoms in 1 , but act as a μ₂‐bridging ligand in 2 and as a μ₄‐bridging ligand in 3 .     

Structural Phase Transition in Li2C2

Pure polycrystalline Li₂C₂ could be obtained by the reaction of lithium and graphite flakes in an arc-melting furnace. X-ray powder investigations on these samples confirm the crystal structure given by Juza, Wehle, and Schuster (Immm, No. 71, Z = 2) which is isotypic to Rb₂O₂ and Cs₂O₂. At about 500 °C a reversible phase transition (1^st order) to a cubic modification (Fm 3 m, No. 225, Z = 4) has been observed. This high temperature modification can be described as an antifluorite-structure with disordered C₂^2– dumbbells.     

Preparation,Crystal Structure,Physical Properties and Electronic Band Structure of TlScQ2 (Q = S,Se and Te)

The title compounds were prepared by reaction of Tl₂Q (Q = S, Se and Te) Sc and Q in the temperature range of 200 to 500 °C. The structures of the selenide and the telluride adopt the α‐NaFeO₂ type, while TlScS₂ crystallizes in the β‐RbScO₂ type structure. The space group is for TlScSe₂ and TlScTe₂ with a = 3.9370(4) Å, c = 23.194(5) Å, and a = 4.2129(4) Å, c = 24.099(3) Å, respectively. The sulphide crystallizes in P6₃/mmc with a = 3.761(3) Å and c = 14.942(4) Å. The crystal chemical relations between the three chalcogenides are discussed. According to the electrical measurements and the band structure calculations, the compounds are semiconductors or poor metals.     

Coordination Chemistry of [Nb2(S2)2]4+ Clusters: Preparation and Crystal Structures of K4[Nb2(S2)2(C2O4)4] · 6 H2O and (NH4)6[Nb2(S2)2(C2O4)4](C2O4)

Bis(disulfido)bridged Nb^IV cluster oxalate complexes [Nb₂(S₂)₂(C₂O₄)₄]^4– were prepared by ligand substitution reaction from the aqua ion [Nb₂(μ‐S₂)₂(H₂O)₈]⁴⁺ and isolated as K₄[Nb₂(S₂)₂(C₂O₄)₄] · 6 H₂O ( 1 ), (NH₄)₆[Nb₂(S₂)₂(C₂O₄)₄](C₂O₄) ( 2 ) and Cs₄[Nb₂(S₂)₂(C₂O₄)₄] · 4 H₂O ( 3 ). The crystal structures of 1 and 2 were determined. The crystals of 1 belong to the space group P1, a = 720.94(7) pm, b = 983.64(10) pm, c = 1071.45(10) pm, α = 109.812(1)°, β = 91.586(2)°, γ = 105.257(2)°. The crystals of 2 are monoclinic, space group C2/c, a = 1567.9(2) pm, b = 1906.6(3) pm, c = 3000.9(4) pm, β = 95.502(2)°. The packing in 2 shows alternating layers of cluster anions and of ammonium/uncoordinated oxalates perpendicular to the [1 0 1] direction. Vibration spectra, electrochemistry and thermogravimetric properties of the complexes are also discussed.     

Crystal Structure,Phase Transition and Ferroelastic Properties of [N(CH3)4]3[As2Cl9]

The crystal structure of [N(CH₃)₄]₃[As₂Cl₉] is determined at 293 K. It crystallizes in trigonal space group P31c: a = 9.2199(8), c = 21.065(3)Å, Z = 2, R₁ = 0.0505, wR₂ = 0.1283. The crystal is built of the discrete bioctahedral [As₂Cl₉]^3— anions and the deformed tetramethylammonium cations. A structural phase transition in [N(CH₃)₄]₃[As₂Cl₉] is detected by the DSC and dilatometric techniques at 146/151 K (on cooling/heating). Dielectric relaxation studies in the frequency range 75 kHz — 5 MHz indicate reorientations of the tetramethylammonium cations within the high temperature phase. Optical observations show the existence of the ferroelastic domain structure below 146 K. The possible mechanism of phase transition is discussed on the basis of the presented results.     

[Ag(NH3)2]Ag(OsO3N)2: a new nitridoosmate(VIII)

Dark brown single crystals of [Ag(NH₃)₂]Ag(OsO₃N)₂ were obtained from the reaction of Ag₂CO₃, OsO₄, and NH₃ in aqueous solution. The crystal structure was solved in the monoclinic space group C2/m, with the following unit-cell dimensions: a=1962.5(3), b=633.1(1), c=812.6(1) pm, β=96.71(1)°. The final reliability factor was R=0.0256 for 1034 reflections with I>2σ(I). Linear [Ag(NH₃)₂]⁺ ions are present oriented perpendicular to the [010] direction, leading to short Ag⁺-Ag⁺ distances of 316 pm. A second type of Ag⁺ ions in the crystal structure present coordination number “6+1” and are surrounded by oxygen and nitrogen atoms of the nitridoosmate groups. Within the first of the two crystallographically distinguishable anions one can clearly differentiate between oxygen and nitrogen atoms while the second one exhibits a N/O disorder over two positions. The infrared spectrum of [Ag(NH₃)₂]Ag(OsO₃N)₂ shows the typical absorptions which can be attributed to the complex anions and the NH₃ ligands.     

Die Kristallstruktur der Tieftemperaturmodifikation von Ag5Te2Cl

The Crystal Structure of the Low‐Temperature Form of Ag₅Te₂Cl Crystals of trimorphic Ag₅Te₂Cl were obtained by solid state reaction from a stoichiometric mixture of silver, tellurium, and tellurium(IV)chloride (480 °C, 4–10 days). The crystals were cooled down to –80 °C without decomposition and data collection was carried out at this temperature. The low temperature form of the title compound crystallizes in space group P2₁/c with lattice constants of a = 19.359(1) Å, b = 7.713(1) Å, c = 19.533(1) Å, β = 90.6°(1), V = 2916.4(1), and Z = 16. The refinement converged to residual values of R₁ = 0.0381 and wR₂ = 0.0847, respectively. Te and Cl atoms form empty, distorted octahedra interconnected by common vertices to give a 3D‐network. Ag atoms form clusters with Ag–Ag distances between 2.83 Å and 3.10 Å.     

Silver Complexes with Cyanoguanidine: Preparation and Crystal Structures of [Ag(cgn)2]F and [Ag(cgn)2][BF4]

The silver cyanoguanidine complexes [Ag(cgn)₂]F ( 1 ), [Ag(cgn)₂][BF₄] ( 2 ), [Ag(cgn)₂][ClO₄] ( 3 ) and [Ag(cgn)][NO₃] ( 4 ) were obtained from aqueous solutions of the corresponding silver salts and cyanoguanidine. The crystal structures of 1 and 2 have been determined by single crystal X‐ray diffraction. 1 : Space group P1¯, Z = 2, cell constants at —65 °C: a =618.18(3), b = 761.49(8), c = 971.2(1) pm; α = 93.56(1), β = 97.439(8), γ = 97.376(9)β; R₁ = 0.0218 2 : Space group P1¯, Z = 2, cell constants at —65 °C: a = 549.79(9), b = 958.17(17), c = 1121.04(12) pm; α = 90.026(13), β = 102.520(11), γ = 95.937(14)°; R₁ = 0.0283.     

Synthese und Kristallstrukturen von α‐ und β‐Ba3(PS4)2 sowie von Ba3(PSe4)2

Synthesis and Crystal Structures of α‐, β‐Ba₃(PS₄)₂ and Ba₃(PSe₄)₂ Ba₃(PS₄)₂ and Ba₃(PSe₄)₂ were prepared by heating mixtures of the elements at 800 °C for 25 h. Both compounds were investigated by single crystal X‐ray methods. The thiophosphate is dimorphic and undergoes a displacive phase transition at about 75 °C. Both modifications crystallize in new structure types. In the room temperature phase (α‐Ba₃(PS₄)₂: P2₁/a; a = 11.649(3), b = 6.610(1), c = 17.299(2) Å, β = 90.26(3)°; Z = 4) three crystallographically independent Ba atoms are surrounded by ten sulfur atoms forming distorted polyhedra. The arrangement of the PS₄ tetrahedra, isolated from each other, is comparable with the formation of the SO₄^2? ions of β‐K₂SO₄. In β‐Ba₃(PS₄)₂ (C2/m; a = 11.597(2), b = 6.727(1), c = 8.704(2) Å; β = 90.00(3)°; Z = 2) the PS₄ tetrahedra are no more tilted along [001], but oriented parallel to each other inducing less distorted tetrahedra and polyhedra around the Ba atoms, respectively. Ba₃(PSe₄)₂ (P2₁/a; a = 12.282(2), b = 6.906(1), c = 18.061(4) Å; β = 90.23(3)°; Z = 4) is isotypic to α‐Ba₃(PS₄)₂ and no phase transition could be detected up to about 550 °C.     

Synthese,Struktur und Eigenschaften der tantalreichen Silicidchalkogenide Ta15Si2QxTe10–x (Q = S,Se)

Synthesis, Structure, and Properties of the Tantalum‐rich Silicide Chalcogenides Ta₁₅Si₂Q_xTe_10–x (Q = S, Se) The quaternary tantalum silicide chalcogenides Ta₁₅Si₂Q_xTe_10–x (Q = S, Se) are accessible from proper, compacted mixtures of the respective dichalcogenides, silicon and elemental tantalum at 1770 K in sealed molybdenum tubes. The structures were determined from the strongest X‐ray intensities of fibrous crystals with cross sections of about 3 μm and confirmed by fitting the profile of single phase X‐ray diffractograms. The phases Ta₁₅Si₂S_3.5Te_6.5 and Ta₁₅Si₂Se_3.5Te_6.5 crystallize in the monoclinic space group C2/m with two formula units per unit cell, a = 2393.7(1) pm, b = 350.08(2) pm, c = 1601.2(1) pm, β = 124.700(4)°, and a = 2461.3(2) pm, b = 351.70(2) pm, c = 1601.7(1) pm, β = 124.363(5)°, respectively. Tri‐capped trigonal prismatic Ta₉Si clusters stabilized by encapsulated Si atoms can be seen as the characteristic unit of the structure. The clusters are fused into twin columns which are connected by additional Ta atoms, thus forming corrugated layers. The remaining valences at the surfaces of the layered Ta–Si substructure are saturated by those of chalcogen atoms which are coordinated only from one side by three, four or five Ta atoms. Few bridging covalent Ta–S–Ta and Ta–Se–Ta bonds and, otherwise, dispersive interactions between the Q atoms hold these nearly one nanometer wide slabs together. The phases are moderate metallic conductors. There is no evidence for any electronic instability within 10–310 K in spite of the high anisotropy of the structures.     

Phase Instability in van der Waals In2Se3 Determined by Surface Coordination

van der Waals In₂Se₃ has attracted significant attention for its room-temperature 2D ferroelectricity/antiferroelectricity down to monolayer thickness. However, instability and potential degradation pathway in 2D In₂Se₃ have not yet been adequately addressed. Using a combination of experimental and theoretical approaches, we here unravel the phase instability in both α- and β′-In₂Se₃ originating from the relatively unstable octahedral coordination. Together with the broken bonds at the edge steps, it leads to moisture-facilitated oxidation of In₂Se₃ in air to form amorphous In₂Se_3−3xO_3x layers and Se hemisphere particles. Both O₂ and H₂O are required for such surface oxidation, which can be further promoted by light illumination. In addition, the self-passivation effect from the In₂Se_3−3xO_3x layer can effectively limit such oxidation to only a few nanometer thickness. The achieved insight paves way for better understanding and optimizing 2D In₂Se₃ performance for device applications.     

X‐Ray Crystal Structures of Hexa‐oxotellurate Complexes of Ruthenium(VI) and Silver(III): Na6[RuO2{TeO4(OH)2}2]·16H2O and Na5[Ag{TeO4(OH)2}2]·16H2O

X‐ray crystal structures are reported for Na₆[RuO₂{TeO₄(OH)₂}₂]·16H₂O and Na₅[Ag{TeO₄(OH)₂}₂]·16H₂O which contain respectively Ru^VI and Ag^III coordinated to chelating bidentate tellurate ([TeO₄(OH)₂]⁴⁻) groups. Na₆[RuO₂{TeO₄(OH)₂}₂]·16H₂O: Space group P1¯, Z = 2, lattice dimensions at 120 K; a = 6.9865(1), b = 8.7196(2), c = 11.7395(2)Å, α = 74.008(1), β = 79.954(1), γ = 88.514(1)°; R1 = 0.025. Na₅[Ag{TeO₄(OH)₂}₂]·16H₂O: Space group P1¯, Z = 2, lattice dimensions at 120 K; a = 5.888(1), b = 8.932(1), c = 12.561(2)Å, α = 98.219(6), β = 97.964(9), γ = 93.238(14)°; R1 = 0.047.     

Phase Transitions and Structures of Poly(ethylene-co-chlorotrifluoroethylene)

Poly( ethylene-co-chlorotrifluoroethylene) having 1∶ 1 molar ratio of ethylene andchlorotrifluoroethylene components( PECTFE) is widely used in cable coating industryand lining for dry boxes and chemical tanks[1 ,2 ] .This polymer has been commonlycharacterized as a semicrystalline polymer,and its structures and properties have beenwidely reported.It was originally described as a two-phase( crystalline-amorphous)material consisting of distinct amorphous and hexagonal crystal domains at room…