Anomalous High Pressure Properties in Fullerene Superconductors

Abstract

Correlations among lattice parameter, external pressure, and critical temperature T_c has been surveyed on fullerene superconductors with a wide range of lattice parameters and various valence states. The observed value of dT_c/dP for Na₂Rb_0.5Cs_0.5C₆₀ and Li₃CsC₆₀, having small interfullerene separations, is about a few times lager than that of K₃C₆₀. In contrast, small dT_c/dP values are found in fullerides with expanded unit cells, such as (NH₃)_xNaAA^?C₆₀ (A, A^? = K, Rb and Cs) and A₃Ba₃C₆₀. Interestingly, the chemical and physical pressure effects on T_c are considerably different in these fullerides with large interfullerene spacings. Our results suggest that the pressure dependence is scaled by an interfullerene distance when the interfullerene distances is small, but that this scaling fails when the unit cell is expanded.     

Synthesis and Structure Refinement of Polycrystalline Solid Solution: Na1 + x Zr2 − x Sb x P3O12 (x = 0.1)

Abstract  The solid solution of Na_1 + x Zr_2 − x Sb _x P₃O₁₂ (x = 0.1) was prepared at 1,000 °C by ceramic route. The ceramic material belonging to sodium zirconium phosphate (hereafter NZP) family crystallizes in space group R-3c with unit cell parameters: a = b = 8.77283(16) ?, c = 22.8375(7) ?, α = β = 90.0° γ = 120.0° and Z = 6. The structure of the title phase has been determined by Rietveld refinement of the powder diffraction data on GSAS software. The refinement converges to a satisfactory structure fit with R _p = 0.0764, R _wp = 0.1099 and RF ² = 0.0450. The interatomic distances and bond angles are in good agreement with their standard values. The particle size along prominent reflecting planes ranges between 13 and 50 nm. The polyhedral (ZrO₆ and PO₄ and NaO₈) distortions and valence calculations from bond strength data are also reported. The investigations show that the Sb⁺³ cation occupies the zirconium (A^VI) site of NZP structural framework and resultant charge compensation takes place through partial occupation of M₂ site by Na⁺ ions. Index Abstract  Synthesis and Structure Refinement of Polycrystalline Solid Solution: Na_1 + x Zr _2 −  x Sb _x P ₃ O ₁₂ ( x  = 0.1) O. P. Shrivastava and Rashmi Chourasia Antimony enters crystallochemically in the framework of nano ceramic sodium zirconium phosphate at the Zr site of the ZrO₆ octahedra which are inter linked by PO₄ tetrahedra through corner sharing of the vertical columns. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

NMR Studies of Silicon Clathrate Compounds

Abstract

NMR spectra of ²⁹Si and ¹³⁷Ba in silicon clathrate compounds, Na_xBa_ySi₄₆, Na_xSi₁₃₆ and Ba₈ T _xSi₄₆ (where T = Au, Ag, and Cu) are reported. We found that the local density of states at the Fermi level increases with rising superconducting transition temperature. The silicon Sl site was suggested to hybridize with Ba-orbital in the superconducting clathrate and has a large local density of states.     

Synthesis,X-ray Crystal Structure and Magnetic Study of a μ<Subscript>1,5</Subscript>-dca Bridged Dimeric Copper(II) Complex

Abstract  

The reaction of aqueous solution of copper(II) nitrate trihydrate with methanolic solution of the ligand HL and sodium dicyanamide in aqueous medium results in the formation of a dimeric dicyanamide complex of Cu(II), [Cu₂(L)₂(μ_1,5-dca)₂]·0.5 H₂O (1) [where L = 1-(N-salicylideneamine)-2-(N-ethyl)-aminoethane]. The single crystal X-ray structure reveals that the asymmetric unit of complex 1 consists of two dinuclear units. The complex crystallizes in the monoclinic space group P2₁ with cell parameters, a = 9.8828(19) ?, b = 19.018(4) ?, c = 14.851(3) ?, (°) = 92.979(6) and Z = 4. χ_M T, stays in the 0.94–0.91 cm³ mol⁻¹ K range between 300 and 2 K, which is slightly higher than the spin-only value (χ_M T = 0.75 cm³ mol⁻¹ K) for two uncoupled copper(II) (S = ?) ions assuming g = 2.0, thus indicating that the complex 1 behaves like a simple paramagnet.     

Crystal structure of cesium sodium hexathiocyanatobismuthate Cs2Na[Bi(SCN)6] and characterization of Cs2Na[Bi(SCN)6−x Cl x ] and Cs2Na[Bi2(SCN)9−x Cl x ] complexes by X-ray powder diffraction

Cs₂Na[Bi(SCN)₆] crystallizes in the trigonal space group with one formal molecule per unit cell.M=846.25,a=7.189(1),c=10.580(2) ,V=473.5(1) ,D _x =2.967 g cm^–3, (MoK)=13.70 mm^–1,F(000)=378. FinalR=0.029 for 917 absorption-corrected reflections. The structure consists of infinite[Bi(SCN)₆Na] ^2– anionic chains along thec axis with slightly distorted octahedral Bi–6S and Na–6N coordination and Cs⁺ ions surrounded by three anionic chains with irregular coordination by six N and three S atoms. X-ray powder diffractograms of three complexes, Cs₂Na[Bi(SCN)_6–x Cl _x ] withx=2, 3 and 4, indicate that the mixed complexes are not isostructural and can be indexed in different orthorombic unit cells witha=14.617(8),b=12.32(1),c=10.769(6) forx=2;a=15.37(1),b=10.81(1),c=10.287(6) forx=3 anda=14.662(7),b=14.366(7),c=7.932(4) forx=4. The two dinuclear complexes Cs₂Na[Bi₂(SCN)_9–x Cl _x ] withx=2 and 3, despite the large similarity of their diffractograms, are not isostructural and can be indexed in different orthorombic unit cells witha=14.79(1),b=13.72(1),c=10.591(5) forx=2 anda=18.423(8),b=15.657(7),c=7.410(7) forx=3.     

Synthesis,structure and IR characterization of disodium tetra(9,10-dihydro-9-oxo-10-acridineacetato)zincate(II) bis(ethanol) heptahydrate

The synthesis, crystal structure and IR data are reported for Na₂[Zn(CMA)₄]·2EtOH·7H₂O, where CMA^– is the 9,10-dihydro-9-oxo-10-acridinacetate ion. The complex crystallizes in the monoclinic space group P2/n, with cell dimensionsa=17.335(9),b=8.440(5),c=21.875(12) Å, =91.94(5)°,Z=2. The structure was solved by direct methods and refined to a finalR value of 0.0363 for 3022 non-zero reflections. The Zn²⁺ ion occupies twofold axis and is coordinated to four carboxylate ligands, the ZnO₄ tetrahedron is considerably distorted with Zn–O distances of 1.978(3) and 1.961(3)Å. Each Na⁺ cation interacts with two water, one ethanol, and three carboxylate O atoms comprising distorted octahedron. The Zn²⁺ and Na⁺ cations are linked through monooxygen and syn-syn carboxylate bridges forming a trinuclear, mixed-metal cluster. The Zn...Na separation is 3.267(2)Å and Na...Na distance equals 3.520(2)Å. All oxygen bonded H-atoms are utilized in hydrogen bonds. The acridone rings overlap in the crystal with the 3.5 Å interlayer separations. The compound has been characterized by IR spectroscopy.     

Structural and Magnetic Characterisation of Ce@C82

Abstract

We report the structural and magnetic properties of the endohedral metallofullerene Ce@C₈₂. A hexagonal close packing phase [P6₃/mmc [a=11.1544Å, c=18.2256Å] is formed exclusively after vacuum annealing of the solvent precipitated compound. In contrast, sublimed Ce@C₈₂ was found to be dominantly face-centred cubic close packed [Fm-3m; a=15.766Å]. X-ray powder profile calculations revealed that the endohedral cerium atom lies close to 1.8Å from the C₈₂ cage centre in both phases. Hexagonal Ce@C₈₂ has been investigated by magnetic susceptibility measurements. Paramagnetic behaviour is maintained down to 2K attributable to Ce³⁺ ions. Towards lower temperatures, the observed paramagnetic moment falls from the free ion Ce³⁺(μ_eff =2.54μB) value, monotonically approaching 1μB at 2K.     

Heat Capacity and Thermodynamic Properties of p'-Substituted p-n-Hexyloxybenzylideneaniline. I. p-n-Hexyloxybenzylideneamno-p'-Benzonitrile (HBAB)

Abstract

The heat capacity of the nematogenic liquid crystal, HBAB, has been measured between 15 K and 385 K by using an adiabatic calorimeter. The crystal-crystal phase transition has been discovered at 27 K below the crystal-nematic phase transition temperature. The transition temperatures, the enthalpies and the entropies of the three phase transitions have been determined: T ₁ = 306.98 K, ΔH _t = 5.11 kJ mol^?1, ΔS _t = 16.7 JK^?l; T _m = 334.05 K, ΔH _m = 23.77 kJ mol^?1, ΔS_m = 71.2 J K^?l mol^?1; and T _c = 375.10 K, ΔH _c = 1.75 kJ mol^?1, ΔS _c = 3.2 J K^?1 mol^?1, respectively. The thermodynamic functions of HBAB from 0 K to 385 K have been determined from the heat capacity data and the enthalpies of the transitions. Two crystal modifications, one yellow and granular form and the other white and needle-like form, have been obtained during the course of the preparation of the sample. It turned out that the yellow form was the stable crystal and the white the metastable modification. The crystal-crystal phase transition has been discussed as an onset of partial melting from the entropy consideration. In this connection the total entropies of the transitions, 91.1 J K^?1 mol^?1 has been proposed to be an important measure of melting.     

A Novel Keggin-Type Aluminotungstate Dimeric Compound: H3.5[Ni(2,2′-bipy)3]3{[AlW 10VI W 2V O40Ni(2,2′-bipy)2(H2O)]2Na0.5}

Abstract  A novel dimeric compound H_3.5[Ni(2,2′-bipy)₃]₃{[AlW₁₂O₄₀Ni(2,2′-bipy)₂(H₂O)]₂Na_0.5} prepared by the hydrothermal method consists of a {[AlW₁₂O₄₀Ni(2,2′-bipy)₂(H₂O)]₂Na_0.5}^9.5− heteropolyanion, and in the anion, two reduced Keggin heteropolyanions [AlW^VI ₁₀W₂^VO₄₀]⁷⁻ are bridged via Na coordination ion by means of an O–Na1–O linkage (O atoms from the surface bridging oxygen atoms of [AlW^VI ₁₀W₂^VO₄₀]⁷⁻) and two Ni coordination ions are linked to the Na1 square planar moiety by making use of Ni–Ow–Na1–Ow–Ni bridges. The crystal belongs to the monoclinic-space group C2/c, a = 46.592(9), b = 14.306(3), c = 25.967(5) ?, β = 90.14(3)°, V = 17308(6) ?³, Z = 4, D _c  = 3.116 Mg/m³. Index Abstract  A novel dimeric compound H_3.5[Ni(2,2′-bipy)₃]₃{[AlW₁₂O₄₀Ni(2,2′-bipy)₂(H₂O)]₂Na_0.5} prepared by the hydrothermal method consists of a {[AlW₁₂O₄₀Ni(2,2′-bipy)₂(H₂O)]₂Na_0.5}^9.5− heteropolyanion, and in the anion, two reduced Keggin heterpolyanions [AlW^VI ₁₀W^V ₂O₄₀]⁷⁻ are bridged via Na coordination ion by means of an O–Na1–O linkage (O atoms from the surface bridging oxygen atoms of [AlW^VI ₁₀W^V ₂O₄₀]⁷⁻) and two Ni coordination ions are linked to the Na1 square planar moiety by making use of Ni7–Ow7–Na17–Ow7–Ni bridges.      

Insulator-like electrical transport in structurally ordered Al65Cu20+xRu15−x (x = 1.5, 1.0, 0.5, 0.0 and −0.5) icosahedral quasicrystals

Low-temperature resistivities, in zero-field and 8 T field, and magnetoresistance have been measured down to 1.4-300 K for stable icosahedral quasicrystals Al₆₅Cu_20+xRu_15−x (x = 1.5, 1.0, 0.5, 0.0 and −0.5). The analysis of the magnetoresistance data shows an overwhelming presence of anti weak-localization effect (τ_so ∼ 10⁻¹² s). But the sample with x = −0.5 shows anomalous magnetoresistance and the anti weak-localization effect breaks down (τ_so to be 10⁻¹⁵ s). The in-field σ-T between 5 K and 20 K, for x = 1.0, 0.5, 0.0 and −0.5 samples, and between 1.4 K and 40 K for x = 1.5 sample, follow a power-law behavior with an exponent of 0.5 and above ∼30 K the exponent ranges from 1.17 to 1.58. The observed power-laws basically characterize the presence of critical regime of the metal-insulator (MI) transition, dominated by electron-electron and electron-phonon inelastic scattering events respectively. In samples with x = 1.0, 0.5, 0.0 and −0.5 the in field σ-T has been found to follow ln σ-vs-T^1/4 below 5 K, which indicates the presence of variable range hopping. The observed transport features indicate the occurrence of proximity of metal-insulator transition in these Al-Cu-Ru quasicrystal samples.     

Structure of 9-oxa-2,3-(4′-methoxy)-benzo bicyclo[4,3,0]non-1(6)-ene-7,8-dione: C13H10O4

The crystal and molecular structure of the title compound: C₁₃H₁₀O₄,M _r=230.22, determined by single crystal X-ray diffraction is reported. Crystals are monoclinic, space groupP2_l/c,a=3.991(3),b=21.381(4),c=12.289(4)Å,b=91.15(1)°,V=1048(1)Å₃,z=4,D _x=1.46Mg m^–3, (MoK)=0.7107 Å,m=0.87 mm^–1,F(000)=480,T=298 K. The structure was solved by direct methods and the finalR value is 0.071 (wR=0.055) for 795 independent observed reflections. The cyclohexadienic moiety of the molecule adopt a twist conformation.     

Growth and morphology of the single crystals of thermoelectric oxide material NaxCoO2

We have grown single crystals of recently discovered thermoelectric oxide material Na_xCoO₂ using NaCl flux. Crystals of sizes upto 1.5 x 1.5 x 1.5 mm³ having different morphological habits were reproducibly grown. The atomic force microscopic studies show that along c‐axis crystals grow via 2D layer‐by‐layer mechanism. The X‐ray diffraction analyses show that grown crystals are rich in Na content as compared to the starting charge indicating that NaCl flux also acts as a source of Na. The resistivity of the crystals exhibited a linear temperature dependence in the region between 30 and 300 K. © 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim     

Crystal structure of a nucleoside analog: 9-(R)-[6-(R)-hydroxymethyl-1-oxa-4-thiacyclohexan-2-yl] adenine

The title compound (C₁₀H₁₃N₅O₂S,M _r=267.3) crystallizes in the orthorhombic space groupP2₁2₁2₁ witha=7.579(8),b=7.686(2) andc=20.941(4)Å,V=1220(1)ų,D _x=1.456 gm cm^–3,Z=4,=23.6 cm^–1,F(000)=560 andT=293 K. The structure was solved by direct methods and refined to aR value of 0.068 for 776 unique observed reflections. The oxathiane ring adopts a chair conformation. In the crystal structure the molecules are held together by hydrogen bonds and C-HO close contacts.     

Crystal structure of a nucleoside analog: 1-(R)-[6-(R)-hydroxymethyl-1,4-dioxan-2-yl] uracil

The title compound (C₉H₁₂N₂O₅,M _r =228.2) crystallizes in the trigonal space groupP3₁,21 witha=b=9.438(3) andc=19.775(3) Å,V=1525.5 ų,D _x =1.490 gm cm^–3,Z=6,=0.12 mm^–1,F(000)=720.0,T=293 K. The structure was solved by direct methods and refined by full-matrix least-squares calculations to anR value of 0.044 on 843 unique observed reflections. The dioxane ring adopts a chair conformation. The crystal structure is stabilized by N-HO hydrogen bonds and C-HO close contacts.     

Spin-Spin Relaxation Process of 23Na-NMR in Na-Loaded NaY

Abstract

Spin-spin relaxation of ²³Na-NMR is observed by the spin echo method at room temperature for Y-type zeolite loaded with Na metal without hydration. For saturated and no levels of loading, the echo decay is well fitted by single exponential function. T ₂ decreases to be 0.25 times smaller by loading. This decrease of T ₂ is explained semiquantitatively with assuming nuclear dipole-dipole interaction between neighboring Na.     

Crystal structures of two allotropic forms of Na2CoP2O7

Na₂CoP₂O₇ may be prepared in two allotropie forms:I, rose,M _r =278.85, triclinic, P1,a=9.735(2),b=10.940(3),c=12.289(4) Å,=148.78,=121.76(1), =68.38(2)°,V=566.8(2) ų,Z=4,D _meas=3.28(5) g cm^–3,D _calc=3.267 g cm^–3, (MoK)=0.71069 Å,=37.12 cm^–1, F(000)=540,T=298 K,R=5.4% for 2911 observed reflections; andII, blue,M _r =278.85, orthorhombic, P2₁cn,a=7.713(2) Å,b=10.271(4),c=15.378(6)°,V=1218.2(8) ų,Z=8,D _meas=3.06(5) g cm^–3,D _calc=3.040 g cm^–1, (MoK ) Å,=34.55 cm^–1, F(000)=1080,T=298 K,R=9.9% for 1450 observed reflections. Cobalt displays octahedral coordination to six oxygen atoms in the rose form whereas the metal coordination is tetrahedral in the blue form.     

Assembly of Dipicolinic Acid by Alkali-Metal Cations

Abstract  

Different types of structures of hydrogen-bond assemblies derived from partially deprotonated dipicolinic acid (LH2) molecules having alkali metal cation such as sodium, potassium and cesium are structurally characterised. These self assembled complexes have general formula [M(LH)(LH2)(H₂O) _m ] _n xH₂O {m = 2, 3, n = 1, 2, n, and x = 0, 0.5 M = Na (1); K (2) and Cs(3)}. Sodium complex is a hepta-coordinate mononuclear complex; potassium complex is octa-coordinate complex with dinuclear K₂O₂ type of carboxylate core; whereas the cesium complex is nona-coordinate polymeric complex. All these complexes crystallises in Triclinic, P-1 space group. Sodium complex has a = 6.9003(4) ?; b = 11.1440(6)?; c = 11.2059(5)?; α = 85.695(4)o; β = 82.103(3)o; γ = 87.432(4)o and volume = 850.60(8) ?³ Z = 2; Potassium complex has a = 7.0937(4)?; b = 11.0034(5)?; c = 11.2732(6)?; α = 91.603(3)o; β = 96.088(3)o; γ = 97.207(4)o; volume = 867.29(8) ?³; Z = 1 and cesium complex has a = 7.1410(6)?; b = 11.0625(8)?; c = 12.0667(9)?; α = 96.849(4)o; β = 93.850(4)o; γ = 105.495(4)o; volume = 907.14(12) ?³; Z = 2.     

Crystal and molecular structures of trans-bis(acetonitrile)bis(bipyridine)ruthenium(II) perchlorate and trans-diamminebis(bipyridine)ruthenium(II) perchlorate

The structures of trans-[(MeCN)₂(bpy)₂Ru](ClO₄)₂(I) andtrans-[(NH₃)₂(bpy)₂Ru](ClO₄)₂(II) have been determined by single crystal X-ray diffraction methods. (I) forms monoclinic crystals in the space groupP2₁/c witha=8.399(2),b=10.406(2),c=15.590(3) Å,=93.78(2)° andZ=2 atT=293 K. The final refinement gaveR=0.040 for 2448 reflections withF _o ² >3(F _o ² ). (II) crystallizes in the triclinic space groupP¯1 witha=1.702(1),b=8.439(2),c=10.525(2) Å,=107.56(2),=104.63(1), =100.89(2)° andZ=1 atT=293 K. Refinement using 1878 reflections withF _o ² >3(F _o ² ) produced a finalR value of 0.036. Both of these structures have the ruthenium atom located on a crystallographic inversion center. The bipyridine ligands in both structures are in the bowed conformation as a means of circumventing the steric problems associated with the trans arrangement of the bipyridine ligands. The Ru-N(monodentate) distance is longer for the ammonia complex (2.106(3) Å) than for the acetonitrile complex (2.008(4) Å); there are no significant differences in the distances and angles of the two Ru(bpy)₂ frameworks.     

Structural Analysis of the Layered Compounds Cu x TiS2

Abstract

A structural analysis of single crystals of the layered compounds Cu _x TiS₂ (x=0. 0.21 and 0.38), which were prepared by the iodine transport and the electrochemical methods, has been performed by X-ray diffraction. The displacement parameters of Ti and S atoms along the c axis are larger than those along the a axis. It is understood that the intra-layer bonding between Ti-Ti and S-S atoms is stronger than the inter-layer bonding between Ti-and S-layers. Both distances between Ti-and S-layers and between Cu-and S-layers are enlarged without changing the structure of the mother phase after intercalating Cu atoms.     

Magnetic Susceptibility of Deintercalated Tunnel Compound of KxCr5Se8 and Mössbauer Spectra of Kx(Cr0.95 57Fe0.05)5Se8

Abstract

KCr₅Se₈ has a TIV₅S₈-type structure, containing K ions in one-dimensional tunnels. Deintercalated samples of K_xCr₅Se₈ (0.32 ≤ x ≤ 0.93) were prepared by leaching method using Alc₃/FeCl₃ aqueous solution. These samples showed a broad peak of magnetic susceptibility at ca. 130 K. ⁵⁷Fe-Mössbauer spectra of K_x(Cr_0.95 ⁵⁷Fe_0.05)₅Se₈ (x = 1.0, 0.49) showed a quadrupole doublet at 300 K. Magnetic sextets appeared at 4.2 K in both samples, indicative of magnetic ordering. The observed isomer shift indicated that the charge of Fe is +3 in both samples. It was proposed that Se^2- was partially oxidized by the deintercalation.