Growth and Characterisation of Gel-grown Lead(II)Chloride and Lead(II)Bromide Single Crystals

Single crystals of pure and doped lead(II)chloride and lead(II)bromide were grown by gel technique employing a modified two-stage chemical reaction. Methods to minimise the predomination of needle morphology during the growth of these crystals have been investigated and the results are discussed. The grown crystals were characterised by optical transmission spectrum. Undoped and monovalent cation (K⁺, Na⁺, Cu⁺, Ag⁺ and Hg⁺) doped crystals of PbCl₂ and PbBr₂ were subjected to d.c. electrical conductivity studies. Using the log σT versus T⁻¹ plot, the activation energies for the migration of anion vacancies in lead(II)halides are calculated. They are found to be less for the doped crystals than those of undoped ones.     

Structure of dichloroethanolaminecopper(II) and dibromoethanolaminecopper(II)

CuCl₂(NH₂CH₂CH₂OH) is monoclinic, space group C2/c, witha+11.092(2),b+10.012(2),c+6.401(1) Å, =121.71(1)°, andV=604.8(2)ų withZ+4. The structure was refined to a final value ofR+0.27 for 518 unique observed reflections with |F|>3. The ethanolamine and halide ions coordinate to the copper(II) ion forming a pseudoplanar four-coordinate monomeric CuCl₂L² complex (L²+bidentate ligand). The copper ion also interacts with the halides of neighboring complexes through the formation of semi-coordinate Cu-Cl linkages (2.926(1) Å) between oligomers. The copper thus attains a 4+2 elongated octahedral coordination geometry. In this space group, the ligand is statisticallydisordered The Cu-Cl distance is 2.267(1)Å while the Cu-N/O distances are 2.025(2)Å. The dibromide structure is isomorphous with the dichloride structure, with space group C2/c, anda+11.285(2),b+10.218(2),c+6.715(1) Å, =121.65(1)°, andV=659.2(2)ų.     

Conductivity and Optical Properties of a Polyiodine Canal Complex (Benzophenone)9(KI)2I7, CHCl3

Abstract

(Benzophenone)₉(KI)₂I₇, CHCl₃ single crystals have a golden metallic reflection on the surfaces parallel to the polyiodine chain axis. The compound is a member of a large class of channel-like inclusion compounds in which isolated iodine atom chains are the only possible conducting strands in an otherwise insulating matrix. The (contactless) microwave conductivity is ～ 10 Ω^?1 cm^?1 at room temperature with an activation energy of ～0.03 eV down to 70°K, while the dc conductivity is ～10^?-⁶. Conductivity is strongly frequency dependent and contact problems are severe.     

Spectroscopic and Transport Properties of (NH4)2CuCl4 · 2 H2O Single Crystal

Electron paramagnetic resonance (EPR), Optical absorption and Transport properties of (NH₄)₂CuCl₄ 2 H₂O single crystals have been studied. An anisotropic g tensor was observed with gl = 2.241 and g∥ = 2.081 by EPR method. The spin orbit coupling constant is found to be 540 cm⁻¹. The optical absorption in UV region are characterized by charge transfer band, in the visible and near infrared region at 13,333, 4,480, 4,336, and 3,998 cm⁻¹ attributed to the transitions between the (d-d) stark energy levels of the copper (II) ion in an extended octahedral crystal field. Dc electrical conductivity measurements with temperature reveal an anisotropic characteristic of a two-dimensional layered structure, and exhibits two first order structural phase transitions at about 383 K and 413 K. These transitions are attributed to loss of the two water inolecules of hydration and free rotation of NH⁺₄ ion from a state of torsional oscillation.     

Magnetotransport and Nonlinear Effects In (TMTSF)2PF6

We have measured the magnetoresistance, Hall effect and the nonlinear conductivity characteristics in pure and radiation damaged (TMTSF>₂PF₆. We find that the material below the metal-insulator transition temperature is best described as quasi-two-dimensional with a very high mobility (10⁵ cm²/volt-sec). The nonlinear conductivity is suppressed by the application of a magnetic field and by radiation damage. The magnetoresistance, metal-insulator transition temperature and the superconducting transition temperature are also reduced by radiation damage of order 1000 ppm for the latter and 100 ppm for the former.     

New (TMTSF)2X Derivatives: A Change in the Selenium Network Dimensionality Derived From the Molecular and Crystal Structures of (TMTSF)2(Fso3) [T=298K, 123K] and (TMTSF)2(Bro4) T=298K

Abstract

We report the first crystallographic analysis, as a function of temperature, of a TMTSF derivative. Both (TMTSF)₂(FSO₃) and (TMTSF)₂(BrO₄) are isostructural (triclinic, with space group PI) with superconducting (TMTSF)₂(ClO₄). (TMTSF)₂(FSO₃) undergoes a metal-to-insulator transition at 86-90K as observed by microwave conductivity, D.C. conductivity, and magnetic susceptibility. The crystal structure contains 2-dimensional sheets of short Se-Se contacts in the molecular stacking direction and perpendicular to the stacking direction. The temperature dependent variations in these contact distances appear to be of special importance in determining the conduction properties of these materials, and are observed to change in a surprising manner when (TMTSF)₂(FSO₃) is cooled (298 → 123K). The homoatomic Se separations within each TMTSF molecule appear to increase slightly, but not significantly. At the same time the entire 2-dimensional sheet of intermolecular (intra- and interstack) Se-Se contacts between TMTSF molecules contract quite anisotropically, which results in an increase in “dimensionality” of the Se-Se network. Hence, an increase in electrical conduction, in the absence of insulating phenomena, over the temperature range 298 → 123K is not surprising. The intermolecular Se-Se contact distances in (TMTSF)₂(BrO₄) are significantly longer than in (TMTSF)₂(FSO₃) which suggests that the room temperature electrical conductivity of the (BrO₄)^? salt may be diminished compared to the (FSO₃)^? analogue.     

Change in the crystal structure of zink(II) sulphate heptahydrate and magnesium(II) sulphate heptahydrate due to isodimorphous substitution by copper(II), iron(II), and cobalt(II) ions

The physico-chemical analytical data on the systems ZnSO₄(MgSO₄)–CuSO₄(FeSO₄, CoSO₄ resp.)–H₂O at 25.0°C have shown that due to isodimorphous substitution of Zn²⁺, Mg²⁺ resp., in the orthorhombic crystals of ZnSO₄ · 7 H₂O MgSO₄ · 7 H₂O, resp. for Cu²⁺, Fe²⁺ or Co²⁺ above a specific degree of ionic substitution, the orthorhombic crystals are converted into monoclinic mixed crystals. The crystal phases are characterized by X-ray diffraction, microscopic and optical studies. The dominant effect of the admixed Cu²⁺, Fe²⁺, Co²⁺ ions is explained in terms of their electronic configurations, for which, owing to the operation of the Jahn-Teller effect, a deformation of the regular octahedral arrangement of the water ligands about the metal ion is found to occur. The strongest deforming effect is that of Cu²⁺ ions followed by the Fe²⁺ ions, the weakest deforming effect being that of Co²⁺ ions.     

Crystal and molecular structures of several tetrakis (nitrile)copper(I) complexes

The crystal structures of several [Cu(RCN)₄]X salts (R = Me, X = SO₃CF₃ ^–; R = Ph, X = BF₄ ^–, ClO₄ ^–, and PF₆ ^–) were determined using single crystal X-ray diffraction. All of the compounds contain distorted tetrahedral Cu(I) centers and noncoordinating anions, with the acetonitrile and benzonitrile structures containing three and one unique CuL₄ ⁺ complex in their respective asymmetric units. One important distortion is observed in the benzonitrile-Cu bonds, which are bent up to 23° away from linearity. The result is a flattened complex that maximizes the – tacking of the aromatic rings and is the dominant packing interactions between the complexes.     

Phenylamido and Diphenylamido Complexes of Chromium(II)

Abstract  Addition LiNHPh to a [(NacNac)Cr(μ-I)]₂ [NacNac = 2,4 pentane-N-N′-bis(2,6-diisopropylphenyl) ketiminato] in THF yields a dimeric anilido complex, 1, that crystallizes in P2₁/n with unit cell parameters a = 13.390(2) ?, b = 26.298(5) ?, c = 21.326(4) ?, β = 93.905(4)°, V = 7492(2) ?³ and Z = 4. The same reaction in the presence of aniline yields a monomeric anilido complex, 2, with a coordinated aniline molecule. Complex 2 crystallizes in P2 ₁ /c with unit cell parameters a = 28.530(5) ?, b = 10.8116(18) ?, c = 26.492(5) ?, β = 115.685(3)°, V = 7364(2) ?³ and Z = 8. Addition of aniline to isolated 1 yields 2. Addition of LiNPh₂ to [(NacNac)Cr(μ-I)]₂ in THF yields a monomeric complex that crystallizes in P2₁/n with the unit cell parameters a = 11.152(6) ?, b = 23.820(12) ?, c = 17.915(9) ?, β = 106.223(9)°, V = 4569(4) ?³ and Z = 4. All complexes have been spectroscopically and structurally characterized. Graphical Abstract  Addition of LiNHPh or LiNPh₂ to [(NacNac)Cr(μ-I)]₂ yields a dimeric or a monomeric complex whereas addition of LiNHPh in the presence of aniline yields the monomeric anilido complex.      

Synthesis, Crystal Structures and Properties of Two Copper (II) Complexes with Pyridazine Derivative Ligand

Abstract  Two new complexes, [Cu(L)₂(CH₃OH)] · (ClO₄)₂ (1) and [Cu(L)₂(H₂O)] · (NO₃)₂ (2), have been synthesized and their crystal structures have been determined by X-ray analysis, where L = 3-(3,5-bimethylpyrazole-yl)-6-chloro-pyridazine]. The complex 1 crystallizes in the monoclinic, space group C2/c, and the coordination configuration of copper (II) is better described as trigonal pyramidal geometry with four N atoms from L and one O_methanol^. The coordination configuration of 2 is quite similar to that of 1 except O_water instead of O_methanol^. The intermolecular hydrogen bonds link the repeat units and extend the molecules to multinuclear structures in both compounds. The spectral properties of the title compounds have been studied and discussed. Furthermore, the antibacterial activities of the title compounds have been detected, the results indicate that the ligands and two copper(II) complexes exhibit certain fungicidal activities again several bacteria. Index Abstract  Two new complexes, [Cu(L)2(CH3OH)]·(ClO4)2 (1) and [Cu(L)2(H2O)]·(NO3)2 (2), have been synthesized and their crystal structures have been determined by X-ray analysis, where L= 3-(3,5-bimethylpyrazole-yl)-6-chloro-pyridazine. The intermolecular hydrogen bonds extend the molecules to multinuclear structures in both compounds.      

Crystal structure of bis(benzimidazolium) tetrabromocuprate(II)

Stable, dark-violet crystals of (C₇H₇N₂)₂CuBr₄ were obtained from an aqueous solution of CuBr₂, HBr, and benzimidazole. The crystal structure was determined by three-dimensional X-ray analysis. The crystals are monoclinic:C2/c, a=15.651(4),b=7.945(1),c=15.775(4) Å,=91.44(2)°,Z=4,V _c=1960.96 ų,D _x=2.105 g cm^–3. The structure was refined by full-matrix least squares to giveR=0.042 andR _w=0.048 for 1254 intensities above 3(I). The copper(II) ions are four-coordinated in the form of a distorted tetrahedron CuBr₄ ofC ₂ symmetry. Two different Cu-Br bond lengths are observed: Cu-Br(1)=2.426(2), Cu-Br(2)=2.330(2) Å. Only one flattened angle [Br(2)-Cu-Br(2)=132.71(9)°] in the CuBr₄ tetrahedron is noted. The angles Br(1)-Cu-Br(1)=108.83(7), Br(2)-Cu-Br(1)=99.92(5) and Br(2)-Cu-Br(1)=107.13(5)° have been found. Hydrogen bonds explain the deformation of the CuBr ₄ ^2– coordination polyhedron. The structure is compared with other CuX ₄ ^2– complexes.     

On the Structural and Electronic Characteristics of Titanium Sulphide (Tis1.7) Crystals

TiS_1.7 crystals have been grown by vapour transport technique employing a two-zone furnace with the temperatures of reaction and growth zone maintained at 1073 K and 973 K, respectively. We have measured the variation of electrical conductivity (s̀) with temperature (T) of TiS_1.7 single crystals. It has been found that the conductivity increases at temperatures T > 433 K, which provides convincing evidence that the TiS_1.7 crystal is a semiconductor. Another electronic characteristic of TiS_1.7 crystals observed in the present investigation is the occurrence of voltage controlled negative resistance (VCNR) at a field of 32.1 V cm^-1 to 35.7 V cm^-1. All the polytypes of TiS_1.7 were found to exhibit VCNR nearly at the same field which indicates that the VCNR is polytype independent property. The occurrence of VCNR has been explained on the intervally transfer of electrons in the conduction band.     

A mixed valence Cu(I)/Cu(II) chain compound: crystal structure of 1,4,8,11-tetraazacyclotetradecanecopper(II) tribromocuprate(I)

The essentially anaerobic reaction of CuBr₂ and 14ane-N₄ in water/acetone solvent (14ane-N₄ = 1,4,8,11-tetraazacyclotetradecane) yields a mixed valence Cu(I)/Cu(II) compound. The compound is orthorhombic, space group Pcnn, with a = 23.6310(1) Å, b = 23.6429(2) Å, c = 12.4537(1) Å and V = 6957.95(9) ų with Z = 16, for _calc = 2.349 g/cc. Refinement of a twinned crystal with 8,504 unique reflections yielded final values of R₁ = 0.0725 (|F| > 2) and w R₂ = 0.114 and a goodness of fit of 1.448. The compound contains chains of Cu(14ane-N₄)²⁺ cations and CuBr₃ ^2– anions, which are linked together by long semicoordinate Cu(II)···Br bonds. The chains run perpendicular to the c axis and are arranged in layers in which the chains alternately run parallel to the (1 1 0) and to the (1 –1 0) crystal directions. The Cu(II) ion is coordinated by the tetradentate macrocycle to yield an approximate square planar coordination. The CuBr₃ ^2– anions have a nearly trigonal planar with Cu–;Br(ave) = 2.38(1) Å.     

Correlations between nuclear magnetic resonance spectra and crystal structure. III. A13C nuclear magnetic resonance study in the solid state of bis(xanthato) complexes of mercury(II); The crystal and molecular structure of bis(n-propyl-dithiocarbonato)mercury(II)

The cross-polarization magic angle carbon-13 nmr spectra of a series of bis(xanthato) complexes of mercury(II) are reported; [Hg(S₂COR)₂] _n R=Me, Et, ⁿ Pr and ⁱ Pr. The spectra correlate well with the known crystal structures of theR=Me, Et, and ⁱ Pr compounds and with that of theR= ⁿ Pr derivative for which a single-crystal X-ray diffraction study is also reported. The X-ray analysis of [Hg(S₂CO ⁿ Pr)₂] _n shows that this compound adopts a two-dimensional structure comprised of connected 16-membered rings which arise as a result of bridgingn-propylxanthate ligands. The mercury atom lies on a crystallographic twofold axis of symmetry and exists in a distorted tetrahedral geometry with two unique Hg-S bond distances of 2.418(3) and 2.835(4) Å. Unit-cell dimensions for [Hg(S₂CO ⁿ Pr)₂] _n are:a=7.371(3),b=8.534(4),c=11.618(4) A andZ=2 for the orthorhombic space groupP2₁2₁2. The structure was refined by a full-matrix least-squares procedure to finalR=0.047 andR _w =0.044 for 899 reflections withI2.5(I). While the solid state nmr spectra provide information on molecular (and crystallographic) symmetry they do not provide sufficient detail to enable structure determination for the [Hg(S₂COR)₂] compounds.     

Synthesis and crystal structure of bis(2-methylbenzimidazolium) tetrahalocuprate(II)

The crystal structures of 2-methylbenzimidazolium tetrahalocuprates (H2-mebz)₂[CuX₄] (X = Cl and Br) have been detemined. The chloride salt is monoclinic, P2₁/c, with a = 8.540(2) Å, b = 16.591(2) Å, c = 14.303(3) Å, and = 98.69(2)°. The bromide salt is also monoclinic, P2₁/c, with a = 8.316(3) Å, b = 17.436(3) Å, c = 14.747(3) Å, and = 98.82(3)°. Both the compounds contain discrete distorted tetrahedral CuX₄ ^2– anions and almost planar 2-methylbenzimidazolium cations. In the chloride salt, three chloride ions are involved in hydrogen bonding instead of two bromide ions in the bromide salt.     

Crystal structures of copper(II) nitrate,copper(II) chloride,and copper(II) perchlorate complexes with 2-formylpyridine semicarbazone

Compounds dinitrato(2-formylpyridinesemicarbazone)copper (I), dichloro(2-formylpyridinesemicarbazone) copper hemihydrate (II), and bis(2-formylpyridinesemicarbazone)copper(2+) perchlorate hydrate (III) are synthesized and their crystal structures are determined. In compounds I–III, the neutral 2-formylpyridine semicarbazone molecule (L) is tridentately attached to the copper atom via the N,N,O set of donor atoms. In compounds I and II, the Cu: L ratio is equal to 1: 1, whereas, in III, it is 1: 2. In complex I, the coordination sphere of the copper atom includes two nitrate ions with different structural functions in addition to the L ligand. The structure is built as a one-dimensional polymer in which the NO₃ bidentate group fulfills a bridging function. The coordination polyhedron of the copper(2+) atom can be considered a distorted tetragonal bipyramid (4 + 1 + 1). Compound II has an ionic structure in which the main element is the [CuLCl₂ · Cu(H₂O)LCl]⁺ dimer. In the dimer, the copper atoms are linked via one of the μ₂-bridging chlorine atoms. The coordination polyhedra of the central atoms of the Cu(H₂)LCl and CuLCl₂ complex fragments are tetragonal bipyramid and tetragonal pyramid, respectively. In compound III, the copper atom is octahedrally surrounded by two L ligands in the mer configuration.     

Lattice Vibrations and Interatomic Forces in AIIB2IIIC4VI Defect-Chalcopyrite Compounds (II). Analysis of Nonpolar Optical Modes

A simplified version of the Keating model originally derived for defect-chalcopyrite compounds is extended to include all A^IIB₂^IIIC₄^VI compounds with ordered arrays of vacancies. It is shown that the trends and frequencies of the nonpolar optical modes of these compounds can be described within this model. Simple scaling laws for the interatomic force constants are proposed and compared with corresponding relations for other binary and ternary compounds with tetrahedral coordination.     

Electrical Conductivity and Thermoelectric Power of Silver Iododichromate Fast Ion Conducting Electrolytes

Fast ion conducting solid electrolytes are becoming increasingly important owing to their application in solid state ionic devices. The present work deals with the silver ion conducting x AgI – (1–x)Ag₂Cr₂O₇ electrolyte system. These electrolytes have been characterised by X-ray diffraction, electrical conductivity, electronic conductivity and thermoelectric power techniques. A high ionic conductivity of the order of 10⁻³ S/cm has been observed for the composition mol% 80 AgI–20 Ag₂Cr₂O₇, at room temperature. The electronic conductivity of this electrolyte is three orders of magnitude lower than the ionic conductivity.     

Electrical properties of copper phosphate glasses II. Dielectric properties

The ac and dc electrical properties of the P₂O₅BaOCuO glass system have been measured.TSPC and TSDC experiments and dc conductivity as a function of time indicate the predominantly electronic character of these glasses. The conduction process can be basically explained by a polaron hopping model in an adiabatic regime. Conductivity values which depend on the glass microstructure and switching phenomena are observed. The filamentary-feature of this process suggests a Poole-Frenkel mechanism.A Debye dielectric relaxation non-simple process is deduced from the frequency and temperature dependence of loss tangent and dielectric constant. The activation energies agree with those determinated from dc measurements, suggesting a unique electronic hopping conduction mechanism in both regimes.The ac and dc electrical properties are strongly affected by the glass composition and essentially by the redox Cu⁺/Cu_t ratio.A conduction model accounting for ac and dc behaviour is finally proposed.     

Preparation and Electrical Resistivity of Intercalation Compounds of Graphitized Cokes with Antimony Halides

Preparation of intercalation compounds of a graphitized electrode coke and a synthetic graphite with SbCl₅, SbCl₄F, SbCl₂F₃ and SbF₆ have been described and stages have been characterized by X-ray diffraction technique. On applying pressure a de-intercalation of antimon pentahalides have been found. The stability of intercalation compounds of graphitized cokes to pressure, temperature, organic solvents and aqueous HCI is lower than that of natural graphite compounds. Electrical resistivity of compacted intercalation compounds of different stages parallel and perpendicular to pressure direction decreases with increasing pressure, intercalant concentration and particle size. Intercalation increases anisotropy of electrical conductivity in graphitized coke and decreases it in synthetic graphite.