Preparation and phase relationships in systems of the type CdSMIMIIIS2 where MI = Ag,Cu and MIII = Al,Ga, In

Systems of the type M^IM^IIIS₂ (chalcopyrite)-CdS (wurtzite) where M^I = Ag, Cu and M^III = Al, Ga, In were investigated to determine the regions of mutual solid solubility. It was found that the chalcopyrite structure could not tolerate extensive CdS substitution. When M^III was Al or Ga the solubility of M^IM^IIIS₂ in CdS was also very limited. However, when M^III = In (r_In³⁺ ? r_Ga³⁺ > r_Al³⁺), the solubility of M^IInS₂ in CdS was quite extensive (～50%). These results are consistent with a prior study on systems of the type M^IM^IIIS₂ZnS which indicated that in sulfides, larger cations tend to result in the formation of new quaternary, wurtzite phases.     

Cellulose polymorphism study with sum-frequency-generation (SFG) vibration spectroscopy: identification of exocyclic CH2OH conformation and chain orientation

Sum-frequency-generation (SFG) vibration spectroscopy is a technique only sensitive to functional groups arranged without centrosymmetry. For crystalline cellulose, SFG can detect the C6H₂ and intra-chain hydrogen-bonded OH groups in the crystal. The geometries of these groups are sensitive to the hydrogen bonding network that stabilizes each cellulose polymorph. Therefore, SFG can distinguish cellulose polymorphs (I_β, II, III_I and III_II) which have different conformations of the exocyclic hydroxymethylene group or directionalities of glucan chains. The C6H₂ asymmetric stretching peaks at 2,944 cm^?1 for cellulose I_β and 2,960 cm^?1 for cellulose II, III_I and III_II corresponds to the trans-gauche (tg) and gauche-trans (gt) conformation, respectively. The SFG intensity of the stretch peak of intra-chain hydrogen-bonded O–H group implies that the chain arrangement in cellulose crystal is parallel in I_β and III_I, and antiparallel in II and III_II.     

Structural and conductivity studies in LiFeP2O7, LiScP2O7, and NaScP2O7

Structural studies of LiScP₂O₇ by Rietveld refinement confirm that this material is isostructural with LiFeP₂O₇ studied previously. However, NaScP₂O₇ shows a structure different from the structural types of the basic group of Na^IM^IIIP₂O₇ known thus far. Systematic ranges for the six structural types of A^IM^IIIP₂O₇ are presented in terms of ion radii sums and ratios. The framework of LiMP₂O₇ (M=Sc, Fe) has rather wide tunnels running along the crystallographic c-axis. This feature has determined our interest to check the ion conductivity in A^IM^IIIP₂O₇ (A=Li, Na; M=Sc, Fe). The bulk conductivity, however, is low in these compounds, 10⁻⁶–10⁻⁷ S/cm at 300 °C, as determined by impedance spectroscopy. In order to facilitate the conductivity via normal lithium sites, heterovalent substitution is used. Received: 30 April 1999 / Accepted: 15 June 1999     

Syntheses and structures of nine-coordinate K3[DyIII(nta)2(H2O)]·5H2O and eight-coordinate (NH4)3[DyIII(nta)2] complexes

K₃[Dy^III(nta)₂(H₂O)]·5H₂O and (NH₄)₃[Dy^III(nta)₂] have been synthesized in aqueous solution and characterized by IR, elemental analysis and single-crystal X-ray diffraction techniques. In K₃[Dy^III(nta)₂(H₂O)]·5H₂O the Dy^III ion is nine coordinated yielding a tricapped trigonal prismatic conformation, and its crystal belongs to monoclinic system and C2/c space group. The crystal data are as follows: a = 15.373(5) Å, b = 12.896(4) Å, c = 26.202(9) Å; β = 96.122(5)°, V = 5165(3) ų, Z = 8, D _c = 1.965 g·cm^?3, μ = 3.458 mm^?1, F(000) = 3016, R ₁ = 0.0452 and wR ₂ = 0.1025 for 4550 observed reflections with I ≥ 2σ(I). In (NH₄)₃[Dy^III(nta)₂] the Dy^III ion is eight coordinated yielding a usual dicapped trigonal anti-prismatic conformation, and its crystal belongs to monoclinic system and C2/c space group. The crystal data are as follows: a = 13.736(3) Å, b = 7.9389(16) Å, c = 18.781(4) Å; β = 104.099(3)°, V = 1986.3(7) ų, Z = 2, D _c = 1.983 g·cm^?3, μ = 3.834 mm^?1, F(000) = 1172, R ₁ = 0.0208 and wR ₂ = 0.0500 for 2022 observed reflections with I ≥ 2σ(I). The results indicate that the difference in counter ion also influences coordination numbers and structures of rare earth metal complexes with aminopolycarboxylic acid ligands.     

Ionic Mobility in Glasses in the ZrF4-BiF3-MF Systems (M = Li,Na, K) as Probed by 7Li, 19F,and 23Na NMR

The ion mobility in new fluoride glasses (mol %) 45ZrF₄ · 25BiF₃ · 30MF (I) (M = Li, Na, K), (70 - x)ZrF₄ · xBiF₃ · 30LiF (II) (15 ≤ x ≤ 35), and 45ZrF₄ · (55-x)BiF₃ · xMF (III) (M = Li, Na; 10 ≤ x ≤ 30) has been studied by ⁷Li, ¹9F, and ²³Na NMR in the temperature range 250–500 K. The character of ion motion in bismuth fluorozirconate glasses I and III is determined by temperature and the nature and concentration of an alkali-metal cation. Major type of ion mobility in glasses I–III at temperature 400–440 K are local motions of fluorine-containing moieties and diffusion of lithium ions (except for the glass with x = 10). The factors responsible for diffusion in the fluoride sublattice of glasses I have been determined. Sodium ions in glasses I and III are not involved in ion transport.     

IR and Raman spectral and X-ray structural studies of polymorphic forms of sulfamethoxazole

The crystal structure of the polymorphic form III (hemihydrate) of sulfamethoxazole (SMZ) was determined to exist in both the E- and Z-forms by X-ray analysis and was compared with the polymorphic forms I and II which are known to exist in the E-form. IR spectra of I–III and their corresponding forms I_D–III_D which contain the deuterated amino and amido groups and D₂O and Raman spectra of I–III have been measured. For I–III, assignment of the stretching vibration [ν(NH) and ν(CH)] bands of amino and amido groups and the CH bond of the isoxazole ring involved in the inter-molecular hydrogen bonds has been proposed based on consideration of the IR and Raman spectra and the results of X-ray analysis. A relationship was established between the relative intensity and wavenumbers for the ν(CH) band in the inter-molecular C(sp²)H⋯X hydrogen bond of the E-form.     

Partial crystalline transformation of solvated cellulose IIII crystals, reproduced by theoretical calculations

In hot-water molecular dynamics simulation at 370 K, four cellulose III_I crystal models, with different lattice planes and dimensions, exhibited partial crystalline transformations of (1 ?1 0) chain sheets, in which hydroxymethyl groups were irreversibly rotated from gt into tg conformations, accompanied by hydrogen-bond exchange from the original O3–O6 to cellulose-I-like O2–O6 bonds. The final hydrogen-bond exchange ratio was about 95 % for some of the crystal models after 50 ns simulation. The corrugated (1 ?1 0) chain sheet was converted to a cellulose-I-like flat chain sheet with a slightly right-handed twist. The 3D structures of the three types of isolated chain sheet models were optimized using density functional theory calculations to compare their stabilities without crystal packing forces. The cellulose Iβ (1 0 0) models were more stable than the cellulose III_I (1 ?1 0) models. The optimized structure of cellulose III_I (1 0 0) models deviated largely from the initial sheet form. It was proposed to the crystalline transformation from cellulose III_I to Iβ that conversion of the chain sheet structure first take place, followed by sliding of the chain sheet along the fiber axis.     

Mixed ligand complexes of AEE hexafluoroacetylacetonates with diglyme: Synthesis,crystal structure and thermal behavior

The novel mixed ligand complexes [Ca(hfa)₂(diglyme)(H₂O)] (I), [Sr(hfa)₂(diglyme)(H₂O)] (II) and [Ba(hfa)₂(diglyme)₂] (III) (Hhfa = 1,1,1,5,5,5-hexafluoropentane-2,4-dione, diglyme = 2,5,8-trioxanonane) were synthesized by the reactions of the alkaline earth element (AEE) carbonates in n-hexane with a mixture of Hhfa and diglyme, and they were characterized by elemental analysis, ¹H and ¹³C NMR, and FTIR spectroscopy. The crystal structures of I–III, consisting of mononuclear isolated molecules, have been determined. The thermal behavior and composition of the vapor phase have been studied for I–III by thermal analysis at low pressure and mass spectrometry using a Knudsen cell. The stability of the mixed ligand complexes [M(hfa)₂(diglyme)_n] to the removal of diglyme molecules under heating decreases in the row I > II ≈ III, and only I evaporates as the mixed ligand complex after water removal.     

Nitrocellulose Membrane,Modified by RC(S)NHP(X)(OiPr)2 (X = S,R = PhNH; X = O,R = PhNH,Ph), for Sorption Extraction of Cobalt Cations

The complexation and extraction properties of RC(S)NHP(X)(OiPr)₂ [X = S, R = PhNH (HL^I); X = O, R = PhNH (HL^II), Ph (HL^III)] towards cobalt cations were studied. The nitrocellulose membrane was used as a carrier for HL^I?III. The maximal degree of extraction of cobalt cations from an aqueous solution is observed at pH = 7.8–8.4. It was established that complexes formed are kept in a water solution on a surface of the carrier and washed away in 96% aqueous ethanol. The membrane modified by HL^I allows extraction and concentration of Co(II) selectively, while the modification by HL^III leads to the selective extraction of Co(III).     

Study of substituent effects on rotational isomers and monomer–dimer equilibria of the 3-carboxy group in 4-substituted (R)-2-(3,4-methylenedioxyphenyl)-6-isopropyloxy-2H-chromen-3-carboxylic acids in dilute CCl4 and CHCl3 solutions by FTIR spectroscopy

FTIR spectra of the title carboxylic acids (I–III) with 4-substituents (H, CH₃ or C₆H₅) and their related compounds IV–VI with 4-(substituted phenyl) groups were measured in dilute CCl₄ and CHCl₃ solutions. The concentration dependence of FTIR spectra of I–IV was also measured in these solutions. These spectra were subjected to curve analysis in order to quantitatively identify the rotational isomers of 3-carboxy group attributable to steric hindrance of the 4-substituents. For I, II and III–VI, two, four and five ν(CO) bands were observed for their carboxy groups, respectively, indicative of monomer–dimer equilibrium and two and three kinds of rotational isomers for II and III–VI, respectively. Compounds III–VI were found to form intra-molecular hydrogen bonds between the trans-type of the 3-carboxy group and the π-electrons in the 4-benzene ring. We have worked out a method to estimate the association constant (K) of complicated monomer–dimer equilibria such as II–VI. The K values of I–IV decrease remarkably in the order of H (I), C₆H₅ (III), CH₃ (II) and C₆H₄-p-OCH₃ (IV) in CCl₄ and I, II, III and IV in CHCl₃; these orders are discussed.     

Heterometallic complexes of macrocyclic oxamide with polycarboxylates: Syntheses,crystal structures,and magnetic properties

Three complexes with the formula [Co(Ip)(CuL)(H₂O)₂] · H₂O (I), [Co(Ip)(NiL)(H₂O)₂] · H₂O (II), [Co(CuL)₂(Hbtc)(H₂O)] (III), (H₂Ip = m-isophthalic acid; H₂L = 2,3-dioxo-5,6,14,15-dibenzo-1,4,8,12-tetraazacyclo-pentadeca-7,13-dien; H₃Btc = 1,3,5-benzenetricarboxylic acid) were synthesized and structurally characterized by elemental analysis, IR and UV spectroscopy. Single-crystal X-ray analyses reveal that the complexes I and II contain neutral heterometallic binuclear CoM (for I and II, M = Cu, Ni, respectively) moieties, and complex III contains discrete neutral trinuclear CoCu₂ moieties. The structures of I–III consist of two-dimensional supramolecular architecture formed by strong O-H…O intermolecular hydrogen bonds. Furthermore, the magnetic properties of complex I were investigated and discussed in detail.     

Single crystal X-ray diffraction study of a mixed-valence gold compound, Cs2AuAuCl6 under high pressures up to 18 GPa: Pressure-induced phase transition coupled with gold valence transition

We performed the single-crystal X-ray diffraction study of a perovskite-type gold mixed-valence compound, Cs₂Au^IAu^IIICl₆, under high pressures up to 18 GPa by using a diamond-anvil-cell with helium gas as an ideal hydrostatic pressure-transmitting medium. The lattice parameters and the variable atomic positional parameters were obtained with reasonable accuracy at various pressures. A structural phase transition at ca. 12.5 GPa from I4/mmm to Pm3m was found. The lattice parameters a₀ and c₀, denoted in the tetragonal cell setting, result in the relationship 2^1/2a₀=c₀, and the superstructure reflections h k l (l is odd), caused by the shift of the Cl ions from the midpoint of the Au ions, disappeared at pressures above the phase transition. Both elongated [Au^IIICl₆] and compressed [Au^ICl₆] octahedra in the low-pressure phase smoothly approach regular octahedra with increasing pressure. Above the structural phase transition at 12.5 GPa, all the [AuCl₆] octahedra are crystallographically equivalent, which shows that the tetragonal-to-cubic phase transition accompanies the valence transition from the Au^I/Au^III mixed-valence state to the Au^II single-valence state.     

Trialkylantimony(V) o-amidophenolates: Electrochemical transformations and antiradical activity

The electrochemical transformations and antiradical activity of trialkylantimony(V) o-amidophenolate derivatives, (AP)SbR₃ (AP = 4,6-di-tert-butyl-N-(2,6-diisopropylphenyl)-o-amidophenolate); R = CH₃ (I), C₂H₅ (II), and C₆H₁₁ (III), are studied. The electrochemical oxidation of compounds I–III proceeds successively to form mono- and dicationic forms of the complexes. The presence of the donor hydrocarbon groups at the antimony(V) atom shifts the oxidation potentials to the cathodic range and decreases the stability of the monocationic complexes formed in electrochemical oxidation. The second anodic process is irreversible and accompanied by o-iminoquinone decoordination. The antiradical activity of compounds I–III is studied in the reaction with the diphenylpicrylhydrazyl radical and oleic acid autooxidation. The values obtained for indices EC₅₀ and IC₅₀ indicate the antiradical activity of the studied compounds. Complexes I–III were found to be the efficient inhibitors of oleic acid oxidation and act as efficient destructors of hydroperoxides.     

Synthesis,structure and optical properties of new lanthanide-based derivatives Ln2SbS5Br (Ln=La,Ce)

The first bromothioantimonates of cerium and lanthanum, Ce₂SbS₅Br (I), CeLaSbS₅Br (II) and La₂SbS₅Br (III), have been synthesized and characterized. I and III crystallize in the Pnma (n°62) space group while the structure of II was refined in the P2₁2₁2₁ (n°19) space group probably due to an ordering between Ce and La. The cell parameters are: a=8.847(2) Å, b=5.492(1) Å, c=17.697(6) Å, V=859.9(6) ų for I; a=8.9023(9) Å, b=5.5113(6) Å, c=17.809(2) Å, V=873.8(3) ų for II and a=8.905(2) Å, b=5.526(1) Å, c=17.883(3) Å, V=880.0(5) ų for III. These three materials exhibit the same novel structural arrangement with lanthanides surrounded by sulfur and bromine anions in two different LnS₇Br₃ and LnS₈Br units. Some sulfur atoms are engaged in SS bonding dimers while antimony exhibits a SbS₄E coordination (E=lone pair), the characteristics of which hint at a stereo-active 5s² electron pair. The charge balance in the materials is written as Ln^III₂Sb^III(S₂)^–IIS^–II₃Br. The same red color of the three materials rules out the occurrence of the Ce-4f¹→Ce-5d¹ electronic transition usually observed in Ce containing sulfides. In contrast, band structure calculations (TB-LMTO-ASA) assigned the observed absorption threshold around 2.08 eV for the three phases to the existence of a VB→CB electronic transition, i.e. an unpaired S or Br→Sb or paired S charge transfer.     

Thermal degradation of copolymers of 2-hydroxyethyl methacrylate and alkyl methacrylates

Thermal degradation of homopolymers of ethyl methacrylate (I), n-butyl methacrylate (II), 2-hydroxyethyl methacrylate (III), and copolymers of III with I and II were carried out by thermal volatilization analysis (TVA) up to 440°C with subsequent subambient thermal volatilization analysis (SATVA). An on-line mass spectrometry coupled with TVA and SATVA was employed to identify the products of thermal degradations. Isothermal pyrolyses of the polymers were carried out separately at 400°C in vacuum for 30 min and the liquid products of decomposition were collected and analysed by gas chromatography. The relationship between the amounts of I and II obtained from pyrolysis and the amounts of these components actually present in the copolymer samples was determined. Also the amount of III and ethyleneglycol dimethacrylate obtained from pyrolysis increases with the amount of III in the copolymer. The polymers were also characterized by differential thermal analysis.     

Structural changes with oxygen content and ordering of defects in the high-Tc oxide YBa2Cu3O6+x

From the study of the composition evolution of the atomic positions in the high-T_c superconducting system YBa₂Cu₃O_6+x, we suggest that for intermediate values of x the oxygen atom vacancies interact quite strongly so as to produce regions of separated Cu^III and Cu^I atoms. This result is both in accord with recent experimental work and consideration of stable geometries for the various oxidation states of copper.     

Hydrolysis behavior of various crystalline celluloses treated by cellulase of Tricoderma viride

Cellobiose and glucose are valuable products that can be obtained from enzymatic hydrolysis of cellulose. This study discusses changes in the crystalline form of celluloses to enhance the production of sugars and examines the effect on structural properties during enzymatic hydrolysis. Various crystalline celluloses consisting of group I (cell I, cell III_I, cell IV_I) and group II (cell II, cell III_II, cell IV_II) of similar DPs were prepared as starting materials. The similar DP values allowed a more direct comparison of the hydrolysis yields. The outcomes were analyzed and evaluated based on the residues and supernatants obtained from the treatment. As a result: (1) action of the cellulase of Trichoderma viride decreased both DP and crystallinity, with greater changes in group II celluloses, (2) the polymorphic interconversion process that occurred for cell III_I, cell IV_I, cell III_II and cell IV_II during the treatment was independent of the enzymatic hydrolysis, thus, the hydrolysis behaviors depended on the starting material of the celluloses, and (3) higher sugar production was obtained from cell III_I and group II. Therefore, the hydrolysis behavior of the various crystalline celluloses depended on the particular polymorph of the starting material.     

Three metal complexes based on tetrazolyl ligands: Hydrothermal syntheses,crystal structures,and fluorescence properties

Three new complexes based on 1-tetrazole-4-imidazole-benzene (Tibz), namely, [Cd(Tibz)₂(H₂O)₂] _n (I), [Mn(Tibz)₂(H₂O)₄] · 2H₂O (II) and [Co(Tibz)₂(H₂O)₄] · 2H₂O (III) have been synthesized through hydrothermal method and structurally characterized by element analyses, IR spectroscopy and single-crystal X-ray diffraction analyses (CIF files CCDC nos. 1443867 (I), 1443868 (II), 1443869 (III)). Single-crystal X-ray diffraction reveals that complex I is a 1D double-chain architecture, II and III are both mononuclear complexes. The results of single-crystal X-ray diffraction analyses indicate that the hydrogen bond and π··· π stacking exist in the complexes, which make great contribution to the stabilities of complexes I–III. The fluorescent properties of these complexes have also been studied in the solid state at room temperature.     

Crystal structures and luminescence of a series of cadmium(II) complexes based on isophorone derivative containing imidazolyl

Three new complexes, [CdL₂(CH₃COO)₂(H₂O)₂] (I), CdL₂Br₂ (II), CdL₂I₂ (III), have been successfully synthesized by self-assembly of corresponding metal salts with (E)-2-(3-(4-(1H-imidazole-1-yl)styryl)-5,5-dimethylcyclohex-2-enylidene)malononitrile (L). The structures of the complexes were determined by single crystal X-ray diffraction analysis (CIF file CCDC nos. 957831 (I), 957792 (II), 957832 (III)). In complex I, central metal is six-coordinated and the crystal packing shows a 3D supramolecular framework. Complexes II and III display the similar 2D supramolecular structures in which the central metals are four-coordination. The luminescent properties were investigated.     

The influence of the electron wave function on the PtL I andL III ionization probabilities by 3.6 MeV he impact

For 3.6 MeV He impact theL _I andL _III subshell ionization probabilities of Pt have been measured. Due to relativistic effects in the electron wave functions, theL _I subshell ionization probabilityI _LI (b) is strongly enhanced at small impact parameters exceeding evenI _LIII (b) in nice agreement with the SCA theory.