Copper and cadmium phosphonates based on 2-quinolinephosphonate

Hydrothermal reactions of 2-quinolinephosphonic acid (1) and CuSO₄ or CdSO₄ result in two new compounds with formula Cu(2-C₉H₆NPO₃) (2) and Cd(2-C₉H₆NPO₃)(H₂O) (3). Compound 2 has a layer structure in which dimers of edge-sharing {CuO₄N} square-pyramids are linked by {CPO₃} tetrahedra through corner sharing. Compound 3 shows a new type of layer structure where chains of corner sharing {CdO₅N} octahedra are connected by {CPO₃} tetrahedra into an inorganic layer. The quinoline groups fill in the inter-layer spaces in both cases. Crystal data for 1: monoclinic, space group P2₁/c, a = 10.270(2) Å, b = 13.566(3) Å, c = 6.9818(16) Å, β = 101.916(4)°, V = 951.8(4) Å³, Z = 4. For 2: monoclinic, space group P2₁/c, a = 13.976(3) Å, b = 7.9398(18) Å, c = 7.8687(18) Å, β = 101.150(5)°, V = 856.7(3) Å³, Z = 4. For 3: monoclinic, space group P2₁/c, a = 17.164(4) Å, b = 5.4870(12) Å, c = 10.850(2) Å, β = 101.557(4)°, V = 1001.1(4) Å³, Z = 4. The magnetic measurement on 2 reveals a dominant antiferromagnetic exchange coupling between the Cu(II) centers. A quasi-reversible electrochemical reaction is observed for complex 2 immobilized on the surface of GC electrode, corresponding to the redox couple Cu²⁺/Cu⁺. The fluorescent properties of 1–3 are also investigated.     

Organic derivatives of tin (II/IV): Investigation of their structure

The structures of tin(II)-oxalate, tin(IV)Na–EDTA and tin(IV)Na₈-inositol hexaphosphate were investigated using XRD analysis. Samples were identified using the Mössbauer study, thermal analysis and FTIR spectrometry. The Mössbauer study determined two different oxidation states of tin atoms, and consequently two different tin surroundings in the end products. The tin oxalate was found to be orthorhombic with space group Pnma, a=9.2066(3) Å, b=9.7590(1) Å, c=13.1848(5) Å, V=1184.62 Å³ and Z=8. SnNa–EDTA was found to be monoclinic with space group P2₁/c₁, a=10.7544(3) Å, b=10.1455(3) Å, c=16.5130(6) Å, β=98.59(2)°, V=1781.50(4) Å³ and Z=4. Sn(C₆H₆Na₈O₂₄P₆) was found to be amorphous.     

Crystal structures of Th(OH)PO4, U(OH)PO4 and Th2O(PO4)2. Condensation mechanism of MIV(OH)PO4 (M = Th,U) into M2O(PO4)2

Three new crystal structures, isotypic with β-Zr₂O(PO₄)₂, have been resolved by the Rietveld method. All crystallize with an orthorhombic cell (S.G.: Cmca) with a = 7.1393(2) Å, b = 9.2641(2) Å, c = 12.5262(4) Å, V = 828.46(4) Å³ and Z = 8 for Th(OH)PO₄; a = 7.0100(2) Å, b = 9.1200(2) Å, c = 12.3665(3) Å, V = 790.60(4) Å³ and Z = 8 for U(OH)PO₄; a = 7.1691(3) Å, b = 9.2388(4) Å, c = 12.8204(7) Å, V = 849.15(7) Å³ and Z = 4 for Th₂O(PO₄)₂. By heating, the M(OH)PO₄ (M = Th, U) compounds condense topotactically into M₂O(PO₄)₂, with a change of the environment of the tetravalent cation that lowers from 8 to 7 oxygen atoms. The lower stability of Th₂O(PO₄)₂ compared to that of U₂O(PO₄)₂ seems to result from this unusual environment for tetravalent thorium.     

Syntheses and crystal structures of new vanadium(IV) oxyphosphates M(VO)2(PO4)2 with M = Co,Ni

We have extended our research interest on titanium oxyphosphates (M^II(TiO)₂(PO₄)₂, with M^II = Mg, Fe, Co, Ni, Cu, Zn) to vanadium oxyphosphates M^II(V^IVO)₂(PO₄)₂ (M^II = Co, Ni). For each compound two phases, named α and β according to synthesis conditions, have been stabilized at room temperature, then characterized. The four crystal structures M(VO)₂(PO₄)₂ (α and β for M = Co, Ni) have been determined in monoclinic P2₁/c space group using X-ray single crystals diffraction data. Structure of the α phase is derived from the Li(TiO)(PO₄) (orthorhombic Pnma) and LiNi_0.50(TiO)₂(PO₄)₂ (monoclinic P2₁/c) types, with cell parameters: a = 6.310(1) Å, b = 7.273(1) Å, c = 7.432(1) Å, β = 90.43(1)° for M = Co, and a = 6.297(2) Å, b = 7.230(2) Å, c = 7.421(2) Å, β = 90.36(2)° for M = Ni. Structure of the β phase is derived from the Ni(TiO)₂(PO₄)₂-type (monoclinic P2₁/c) with cell parameters: a = 7.2742(2) Å, b = 7.2802(2) Å, c = 7.4550(2) Å, β = 120.171(2)° for M = Co, and a = 7.2691(2) Å, b = 7.2366(2) Å, c = 7.4453(2) Å, β = 120.231(2)° for M = Ni. All these structures consist of a three dimensional (3D) framework built up of infinite chains of tilted corner-sharing [VO₆] octahedra, cross-linked by corner-sharing [PO₄] tetrahedra. The M²⁺ ion (M = Co, Ni) is located in a triangular based antiprism which shares faces with two [VO₆] octahedra. Structural filiation is discussed based on a common structural unit, a sheet where divalent cations M²⁺ (M = Co, Ni) are inserted. A thermal study of the α ? β transition is also presented.     

Real structure of SrSi2O2N2

SrSi₂O₂N₂ is an important host lattice for Eu²⁺ doped phosphors. Its crystal structure (space group P1, a = 7.0802(2) Å, b = 7.2306(2) Å, c = 7.2554(2) Å, α = 88.767(3)°, β = 84.733(2)°, γ = 75.905(2)° and V = 358.73(2) Å³, Z = 4) is isotypic with EuSi₂O₂N₂: highly condensed silicate layers are separated by Sr²⁺. The samples are characterized by pronounced real structure effects owing to pseudosymmetry of partial structures. Polysynthetic twinning with domains of various sizes is ubiquitous and oriented intergrowth of domains with different orientations has also been observed and analysed in detail by means of electron diffraction and high-resolution electron microscopy. These effects also affect the X-ray powder pattern and were taken into account in a Rietveld refinement.     

Primary amine catalyzed direct asymmetric aldol reaction assisted by water

l-Valine was found to be an active catalyst in the asymmetric direct aldol reaction. The aldol reaction of a variety of aromatic aldehydes with acetone was catalyzed by 20 mol % of l-valine at 35 °C with the aldol products obtained in moderate to good yields (48–83%) and enantiomeric excesses (42–72%). The reaction was more efficient catalytically with best results observed in the presence of 1 mol equiv of water, with respect to the aldehyde, in either DMSO or DMF as solvent. The effect of water concentration on the reaction rate and enantioselectivity was also investigated. Thus, with increasing water concentration in DMSO there was decreasing enantioselectivity. However, the reaction in the presence of l-phenylalanine showed a lower level of reactivity and enantioselectivity to afford the aldol in 25% with 31% ee. In marked contrast, reaction with l-phenylglycine resulted in the negligible formation of the aldol (<5%). Our results, suggest a new strategy in the design of new bioorganic catalysts for direct asymmetric aldol reactions.     

Double beryllium iodate dihydrates,M2Be(IO3)4·2H2O (M = K,NH4+, Rb): Preparation,X-ray powder diffraction and vibrational spectra

The solubilities in the three-component systems MIO₃–Be(IO₃)₂–H₂O (M = K, NH₄⁺, Rb, Cs) were studied at 25 °C by the method of isothermal decrease of supersaturation. It has been established that double salts, K₂Be(IO₃)₄·2H₂O, (NH₄)₂Be(IO₃)₄·2H₂O, and Rb₂Be(IO₃)₄·2H₂O, crystallize from the ternary solutions within wide concentration ranges. Both the X-ray powder diffraction and the spectroscopic studies (infrared and Raman) reveal that the title compounds are isostructural. They crystallize in the monoclinic space group P2/m with lattice parameters: K₂Be(IO₃)₄·2H₂O – a = 14.218(5) Å, b = 6.747(2) Å, c = 5.765(2) Å, β = 98.74(4)°, V = 546.6(2) Å³; (NH₄)₂Be(IO₃)₄·2H₂O – a = 14.414(4) Å, b = 6.838(2) Å, c = 5.947(2) Å, β = 99.52(4)°, V = 578.0(2) Å³; Rb₂Be(IO₃)₄·2H₂O – a = 14.423(4) Å, b = 6.867(2) Å, c = 5.743(3) Å, β = 98.15(3)°, V = 562.9(3) Å³.Infrared spectroscopic experiments show that comparatively strong hydrogen bonds are formed in the potassium and rubidium salts as deduced from the wavenumbers of ν_OD of matrix-isolated HDO molecules (isotopically dilute samples) owing to the strong Be–OH₂ interactions (synergetic effect). However, the IO₃⁻ ions in the ammonium compound are involved in hydrogen bonds with NH₄⁺ ions additionally to those with water molecules and as a result of these intermolecular interactions the proton acceptor strength of the iodate ions decreases (anti-cooperative effect), thus leading to the formation of weaker hydrogen bonds in this compound (bonds of moderate strength) as compared to those formed in the potassium and rubidium ones. The normal vibrations of other entities (IO₃⁻ ions and BeO₄ tetrahedra (skeleton vibrations)) are also discussed.     

Inhibitors for magnesium corrosion: Metal organic frameworks

Electrochemical measurements demonstrate that magnesium surfaces can be protected by alkyl carboxylate. In a nearly neutral pH solution of sodium decanoate, the reduced corrosion rate and a passivation behaviour are attributed to the formation of Mg(C₁₀H₁₉O₂)₂(H₂O)₃ (Mg(C10)₂) at the magnesium surface whereas heptanoate Mg(C₇H₁₃O₂)₂(H₂O)₃ (Mg(C7)₂) is not efficient in such media. The crystal structures of the two metal carboxylates Mg(C7)₂ and Mg(C10)₂ are determined by X-ray diffraction. Single crystal data: Mg(C7)₂, P2₁/a, a = 9.130(5) Å, b = 8.152(5) Å, c = 24.195(5) Å, β = 91.476(5)°, V = 1800.3(15) Å³, D_x = 1.242 g cm⁻³, Z = 4. Synchrotron powder data: Mg(C10)₂, P2₁/a, a = 9.070(3) Å, b = 8.165(1) Å, c = 32.124(1) Å, β = 98.39(1)°, V = 2353.85(8) Å³, D_x = 1.188 g cm⁻³, Z = 4. Their layered structures are quite similar and differ mainly by the length of the hydrophobic chains. They consist of two planes of O-octahedra centred by Mg atoms, parallel to (001). The distorted octahedra are constituted by three oxygen atoms from carboxylate groups and by three oxygen atoms coming from water molecules. The layers are connected by hydrogen bonds. The carboxylate chains are located perpendicularly and on both sides of these planes. One carboxylate chain is bridging the Mg atom along [010] while the other is monodendate. The presence of structural water is confirmed by thermal analyses.     

Synthesis and crystal structure of the first chain-type nitridosilicates RE5Si3N9 (RE = La,Ce)

The novel branched chain-type nitridosilicates Ce₅Si₃N₉ and La₅Si₃N₉ have been synthesized in a radio-frequency furnace starting from the respective metals and silicon diimide Si(NH)₂ at 1625 °C for La₅Si₃N₉ and 1650 °C for Ce₅Si₃N₉, respectively. The structure of Ce₅Si₃N₉ has been determined by single-crystal X-ray diffraction (Ce₅Si₃N₉, Cmca (no. 64), a = 10.567(2) Å, b = 11.329(2) Å, c = 15.865(3) Å, V = 1899.3 Å³, Z = 8, R₁ = 0.0391, 1480 independent reflections, 90 refined parameters). The structure of isotypic La₅Si₃N₉ has been refined by the Rietveld method, starting from single-crystal data of Ce₅Si₃N₉ (La₅Si₃N₉, Cmca (no. 64), a = 10.647(4) Å, b = 11.414(4) Å, c = 16.030(5) Å, V = 1948.1 Å³, Z = 8, R_P = 0.0348, R_F² = 0.0533). Both compounds are built up of alternating Q²- and Q³-type corner sharing SiN₄ tetrahedra with additional corner sharing Q¹-units attached to the Q³-tetrahedra pointing alternately in opposing directions. These zipper-like chains are intertwined in both directions perpendicular to the chain itself to form a three-dimensionally interlocked structure with the rare-earth ions situated between the chains. Magnetic measurements resulted in a ferromagnetic ground state with a magnetic moment in agreement with Ce³⁺.     

Two metal-organic frameworks with infinite indium hydroxide chains connected through tetradentate carboxylate linkers

Two indium-based metal-organic framework have been hydrothermally synthesized by using 1,2,4,5-benzenetetracarboxylate (pyromellitate) or 3,3′,4,4′-benzophenonetetracarboxylate as linkers. Their structures have been characterized by means of single-crystal X-ray diffraction analysis and reveal closely related networks consisting of identical infinite chains of indium-centered trans-connected octahedra, linked to each other through the tetradentate carboxylate linkers. The structure of the indium pyromellitate (MIL-60) delimits a 3D frameworks with one-dimensional 4.0 × 2.7 Å² channels running along [001] encapsulating water. The second compound (MIL-119) is built up from the compact stacking of the 3,3′,4,4′-benzophenonetetracarboxylate molecules connected to four distinct inorganic chains. In the latter, water species are found to be trapped between two indium hydroxide chains or in terminal positions, bonded to the indium cations. Strong hydrogen interactions are observed between these types of water molecules. Both compounds do not exhibit any significant porosity.Crystal data: In₂(OH)₂[C₁₀O₈H₂]·2H₂O (MIL-60): monoclinic, C2/m, a = 7.1854(7) Å, b = 17.1940(17) Å, c = 6.5167(7) Å, β = 100.639(2)°, V = 791.27(14) Å³, Z = 2. In₂(OH)₂(H₂O)[C₁₇O₉H₆]·H₂O (MIL-119), monoclinic, P2₁/c, a = 14.2530(11) Å, b = 14.4024(10) Å, c = 11.7027(9) Å, β = 93.018(2)°, V = 2399.0(3) Å³, Z = 4.     

Pressure–temperature phase diagram of SeO2. Characterization of new phases

We have investigated SeO₂ at high pressures and high temperatures. Two new phases (β-SeO₂ and γ-SeO₂) and the boundary separating them have been found, following experimental runs performed at pressures up to 15 GPa and temperatures up to 820°C. The two phases crystallize in the orthorhombic system in space group Pmc2₁ (no. 26) with a=5.0722(1) Å, b=4.4704(1) Å, c=7.5309(2) Å, V=170.760(9) Å³ and Z=4 for the β-phase, and with a=5.0710(2) Å, b=4.4832(2) Å, c=14.9672(6) Å, V=340.27(3) Å³ and Z=8 for the γ-phase. Both phases are stable at ambient pressure and temperature below −30°C. At ambient temperature the phases return to the starting phase (α-SeO₂) in a few days. We discuss our findings in relation to a previous report of in-situ measurements at high pressures and ambient temperature.     

A small angle neutron scattering study of the interface between solids and oil-continuous emulsions and oil-based microemulsions

We have measured the small angle neutron scattering (SANS) from slurries of powder in contact with surfactant solutions and emulsions to determine the fluid/solid interfacial structure. The slurry solids consisted either of graphite or pyrites particles; and the fluids were hexadecane containing the robust commercial polyisobutylenesuccinamide (PIBSA) surfactant, or a high internal phase emulsion of aqueous ammonium nitrate in hexadecane stabilised by PIBSA. To resolve the interfacial structure for both systems, combinations of deuterated and protonated materials were used.At low concentration in hexadecane, PIBSA forms a complete monolayer on graphite with a footprint per molecule of 103 Å² and a layer thickness of 19 Å. At higher concentrations, the complete monolayer of footprint is 61 Å² and 30 Å thick indicating compression of the PIBSA chain coil structure. Geometric exclusion effects caused by the stacking of the graphite particles also results in an excess of oil for ca. 160 Å above the surfactant monolayer.For pyrites in contact with surfactant in hexadecane, the oxidised surface layer, while smooth at the oil interface, is diffuse and/or rough at the interface with the bulk sulphide below. There is again a complete monolayer of surfactant adsorbed at the oxide surface, in a relatively compressed state with a footprint of 70 Å², more tightly bound than on graphite. The excess of oil phase above the adsorbed surfactant monolayer is observed for samples with larger pyrites particle sizes but not for a sample with smaller particles. This suggests that the oil excess does arise from purely geometric solid particle packing, but that the local particle surface curvatures are significantly higher than the overall particle size would suggest.The scattering from the pyrites/emulsion interface was modelled by a 30 Å thick monolayer of surfactant coating an oxide surface with a molecular footprint of 123 Å². For the larger particle size samples, there is a 30 Å thick layer of oil above the pyrites particle surface before a bulk emulsion/pyrites mixture is reached.These results extend previous reflectometry experiments on the silicon/emulsion interface, indicating that for stable emulsions the structures are qualitatively similar for three dissimilar solid surfaces. They show that useful results on surfactant structure and emulsion layering at the solid/emulsion and other solid/fluid interfaces can be simply obtained by SANS on powder samples variously contrasted by deuteration. SANS can be applied to a much greater range of solid interfaces than reflectometry since large neutron-transparent single crystals are not required, although the variety of faces in a powdered material degrades the quality of the information.     

Jahn–Teller phase transition in Cu0.50TiO(PO4): Powder structural characterization of the β-variety and thermal study

The thermal study of Cu_0.50TiO(PO₄), by X-ray diffraction and DSC, shows a phase transition α → β with a hysteresis (∼600 °C during heating; ∼300 °C during cooling). Single crystals have been obtained for the α-phase but the β-phase can only be stabilised at room temperature as a powder mixture with α. Structural characterization of the β-variety has been done with diffraction data (X-ray Cu Kα₁ and neutrons) using a powder rich in β-phase (α(20%) + β(80%)). A monoclinic cell (a = 7.1134(7) Å; b = 7.7282(7) Å; c = 7.3028(7) Å; β=119.30(1)°; V = 350.1(1) Å³) has been found for β-phase, space group P2₁/c. An “ab initio” structure determination has been done, and the Rietveld refinement leads to cR_wp = 0.150 and R_B = 0.041. The results from the X-ray data were confirmed by refinements from neutron data.Similarly to the α-phase, the structure of β-Cu_0.50TiO(PO₄) can be described as a TiOPO₄ framework constituted of chains of tilted corner-sharing [TiO₆] octahedra running parallel to the c axis and cross linked by [PO₄] tetrahedra. Ti atoms are displaced from the centres of the octahedral units, leading to long (2.27 Å) and short (1.73 Å) Ti–O(1) bonds. The [CuO₆] octahedra exhibit a typical Jahn–Teller distorted coordination with four short equatorial Cu–O bonds (2 × 1.93 Å and 2 × 2.06 Å), and two longer apical Cu–O bonds (2 × 2.33 Å). The two longer Cu–O bonds are almost parallel to the b axis.The transition from the α to the β-phase is characterized by a “rocking” of the Jahn–Teller elongation from the (a,c) plane to the b direction accompanied by a relatively strong expansion of the cell volume.     

The experimental and DFT studies of 1,3-dimethyl-2-[4-chloro-styryl]-benzimidazolium iodide

1,3-Dimethyl-2-[4-chloro-styryl]-benzimidazolium iodide (1) was synthesized and characterized by X-ray diffraction, ¹H NMR, MS, IR, UV–vis spectra and elemental analysis. The crystals are monoclinic, space group P2₁/c, with a = 12.507(3) Å, b = 7.3259(19) Å, c = 36.705(9) Å, V = 3358.9(15) Å³, and Z = 4 (at 296(2) K). Crystal stacking scheme indicates the face-to-face π?π aromatic stacking interactions. Molecular geometries, frequencies, IR, ¹H NMR and UV–vis were calculated at DFT/TD-DFT level using two hybrid exchange–correlation functionals, B3LYP and PBE1PBE. The stability of the molecule arising from hyperconjugative interaction and charge delocalization had been analyzed using natural bond orbital (NBO) analysis. These calculations on (1) provide deep insight into its electronic structure and properties.     

Synthesis,spectroscopic studies and structures of square-planar nickel(II) and copper(II) complexes derived from 2-{(Z)-[furan-2-ylmethyl]imino]methyl}-6-methoxyphenol

Two new nickel(II) [Ni(L)₂] and copper(II) [Cu(L)₂] complexes have been synthesized with bidentate NO donor Schiff base ligand (2-{(Z)-[furan-2-ylmethyl]imino]methyl}-6-methoxyphenol) (HL) and both complexes Ni(L)₂ and Cu(L)₂ have been characterized by elemental analyses, IR, UV–vis, ¹H, ¹³C NMR, mass spectroscopy and room temperature magnetic susceptibility measurement. The tautomeric equilibria (phenol-imine, O–H?N and keto-amine, O?H–N forms) have been systemetically studied by using UV–vis absorption spectra for the ligand HL. The UV–vis spectra of this ligand HL were recorded and commented in polar, non-polar, acidic and basic media. The crystal structures of these complexes have also been determined by using X-ray crystallographic techniques. The complexes Ni(L)₂ and Cu(L)₂ crystallize in the monoclinic space group P2₁/n and P2₁/c with unit cell parameters: a = 10.4552(3) Å and 12.1667(4) Å, b = 8.0121(3) Å and 10.4792(3) Å, c = 13.9625(4) Å and 129.6616(3)Å, V = 1155.22(6) Å³ and 1155.22(6) Å³, D_x = 1.493 and 1.476 g cm^?3 and Z = 2 and 2, respectively. The crystal structures were solved by direct methods and refined by full-matrix least squares to a find R = 0.0377 and 0.0336 of for 2340 and 2402 observed reflections, respectively.     

Modulations in the onoratoite system

The iodide form of the mineral onoratoite was synthesized, and like the Cl and Br based analogues, it displays super structure ordering, but for the iodide, the super structure is clearly incommensurate. Due to the poor quality of crystals attainable, the structure was solved by converting the solution of the Cl analogue to a super space formalism, and then using the structural elements from this solution to model the iodide. The structure is triclinic, crystallizing in the 3+1d super space group P-1(αβγ) with the (pseudomonoclinic) cell parameters a = 19.066(8) Å, b = 4.102(2) Å, c = 10.82(6) Å, β = 108.9(2)° and the modulation wave vector q = (0.4716a¹ + 0.25b¹ + 0.1679c¹) been changed accordingly.     

Synthesis and structure of 1-benzyl-5-amino-1H-tetrazole in the solid state and in solution: Combining X-ray diffraction, 1H NMR,FT–IR,and UV–Vis spectra and DFT calculations

Compound 1-benzyl-5-amino-1H-tetrazole (BAT) was synthesized and characterized by ¹H NMR, FT–IR, and UV–Vis spectroscopies and elemental (CHNS) analysis. The crystal structure was further elucidated by single-crystal X-ray diffraction. Density functional theory (DFT) calculations with B3LYP and PBE1PBE functionals of the BAT were performed to provide structural and spectroscopic information and guide spectral assignments. The compound crystallizes in monoclinic primitive system space group P2(1)/c with a = 14.91 Å, b = 5.12 Å, c = 11.19 Å, V = 852 Å³, Z = 4, R₁ = 0.0428 at 298 K. The structure exhibits intermolecular hydrogen bonds of the type N–H(amino)···N(tetrazole). Simultaneous hydrogen bonds between amino···tetrazole and tetrazole···amino establish a dimeric intermolecular structure, whereas another hydrogen bond between the remaining H atom of the amino group and the other N atoms of the tetrazole ring extends the structure into another dimension. The crystal structure of BAT is properly reproduced by DFT calculations only when a dimeric or tetrameric model is employed in the modeling. Comparisons between experimental and calculated spectral properties suggest that the monomeric form of BAT is dominant in aprotic, polar, hydrogen-bonding solvents, such as DMSO and DMF.     

A new intersecting tunnel structure in the AIMIII[PO3(OH)]2 series for AI = Ag,MIII = In: Analysis of structural relationships

A new indium hydroxyphosphate containing silver, AgIn[PO₃(OH)]₂, has been synthesized using hydrothermal method. It crystallizes in the P2₁/c space group with the cell parameters a = 6.6400(2) Å, b = 14.6269(6) Å, c = 6.6616(4) Å, β = 95.681(5)°, V = 643.82(6) Å³, Z = 4. Its three-dimensional framework, built up of corner-sharing PO₃(OH) tetrahedra and InO₆ octahedra, presents intersecting tunnels running along <111> and [100] directions, in which the Ag⁺ cations are located. The presence of hydroxyl groups has been confirmed from IR spectroscopy studies and hydrogen atoms were located from the single crystal X-ray diffraction study. The structural relationships with the other compounds of general formula A^IM^III[PO₃(OH)]₂ are analyzed.     

Phase transition and thermal decomposition of silver isocyanate (AgNCO)

The thermal behavior of AgNCO (silver isocyanate) has been studied via thermal analysis, optical spectroscopy, X-ray powder diffraction and transmission electron microscopy. Upon quenching the high temperature polymorph (HT-AgNCO) to room temperature, a new modification has been obtained (q-AgNCO). Its crystal structure was solved from X-ray powder diffraction data and refined by the Rietveld method (Pmmn (no. 59), a = 3.579(3) Å, b = 5.777(4) Å, c = 5.807(2) Å, V = 120.08(3) Å³, Z = 2, T = 295 K). The structure consists of chains of Ag⁺ ions bridged by isocyanate units. HT-AgNCO exists between T = 135 °C and the melting/decomposition point and exhibits virtually free rotation of the complex anions. According to preliminary single-crystal studies, HT-AgNCO (C2/m, a = 5.87 Å, b = 3.51 Å, c = 5.81 Å, ß = 105.953°, Z = 2, T = 373 K) is structurally related to α-NaN₃. The crystal structures of both, HT-AgNCO and q-AgNCO have been compared with that of the room temperature modification (RT-AgNCO). The thermal behavior and the ionic conductivity of AgNCO are discussed with respect to the related compounds AgN₃ and KSCN. Decomposition of AgNCO proceeds in distinct steps, as seen from TGA, and results in the formation of nanoparticles of elemental silver and an amorphous polymer consisting of C, N and O, only.