Topological complexity of potential surfaces and application to C2H2 molecule

Summary In this work, we search for the simplest complete surfaces of systems with three and four atoms, i.e. the minimal sets of critical points with their index, which are topologically consistent in the whole configuration space. Then we show the smallest change in the A₂B₂ system by requiring at least one stable acetylene configuration and one stable vinylidene configuration, like on the C₂H₂ surface. Finally, we give complete sets of minima, saddle points and maxima obtained for C₂H₂ with analytical potentials proposed in the literature and with a semi-empirical method at the CAS-CI level.     

Ein neuer Typ quaternärer Oxometallate: K3Na2[InO4]

With K₃Na₂[InO₄] the first example of new kind of oxides of the type A₃A₂[MO₄] with R(A)>R(A) was prepared in form of colourless single crystals by oxidation of the intermetallic compound KNaIn₂. Intimate mixtures of the educts (K₂O₂: K_0.5Na_0.5In=1.2:1) were heated in sealed Ag-tubes (380 °C, 2 d, then 480 °C, 5 d). K₃Na₂[InO₄] crystallizes monoclinic (P2₁/n) witha=1012.6 pm,b=969.9 pm,c=725.4 pm, =91.02°;Z=4. The crystal structure was elucidated by four-circle diffractometer (PW 1100, Ag-K, 6047I _o(hkl),R=7.3%,R _w=4.4%). The new typ forms a very complicated 3-dimensional network ³ {Na₂InO₄} stuffed by 3 K⁺. The Madelung part of lattice energy, MAPLE, is calculated and discussed.

Professor Edwin Hengge zum 60. Geburtstag am 21. Juli 1990 gewidmet     

On the crystal chemistry of three copper(II)-arsenates: Cu3(AsO4)2-III,Na4Cu(AsO4)2, and KCu4(AsO4)3

The three copper(II)-arsenates were synthesized under hydrothermal conditions; their crystal structures were determined by single-crystal X-ray diffraction methods:Cu₃(AsO₄)₂-III:a=5.046(2) Å,b=5.417(2) Å,c=6.354(2) Å, =70.61(2)°, =86.52(2)°, =68.43(2)°,Z=1, space group ,R=0.035 for 1674 reflections with sin / 0.90 Å^–1.Na₄Cu(AsO₄)₂:a=4.882(2) Å,b=5.870(2) Å,c=6.958(3) Å, =98.51(2)°, =90.76(2)°, =105.97(2)°,Z=1, space group ,R=0.028 for 2157 reflections with sin / 0.90 Å^–1.KCu₄(AsO₄)₃:a=12.234(5) Å,b=12.438(5) Å,c=7.307(3) Å, =118.17(2)°,Z=4, space group C2/c,R=0.029 for 1896 reflections with sin / 0.80 Å^–1.Within these three compounds the Cu atoms are square planar [4], tetragonal pyramidal [4+1], and tetragonal bipyramidal [4+2] coordinated by O atoms; an exception is the Cu(2)^[4+1] atom in Cu₃(AsO₄)₂-III: the coordination polyhedron is a representative for the transition from a tetragonal pyramid towards a trigonal bipyramid. In KCu₄(AsO₄)₃ the Cu(1)^[4]O₄ square and the As(1)O₄ tetrahedron share a common O—O edge of 2.428(5) Å, resulting in distortions of both the CuO₄ square and the AsO₄ tetrahedron. The two Na atoms in Na₄Cu(AsO₄)₂ are [6] coordinated, the K atom in KCu₄(AsO₄)₃ is [8] coordinated by O atoms.Die drei Kupfer(II)-Arsenate wurden unter Hydrothermalbedingungen gezüchtet und ihre Kristallstrukturen mittels Einkristall-Röntgenbeugungsmethoden ermittelt:Cu₃(AsO₄)₂-III:a = 5.046(2) Å,b = 5.417(2) Å,c = 6.354(2) Å, = 70.61 (2)°, = 86.52(2)°, = 68.43(2)°,Z = 1, Raumgruppe ,R = 0.035 für 1674 Reflexe mit sin / 0.90 Å^–1.Na₄Cu(AsO₄)₂:a = 4.882(2) Å,b = 5.870(2) Å,c = 6.958(3) Å, = 98.51(2)°, = 90.76(2)°, = 105.97(2)°,Z = 1, Raumgruppe ,R = 0.028 für 2157 Reflexe mit sin / 0.90 Å^–1.KCu₄(AsO₄)₃:a = 12.234(5) Å,b = 12.438(5) Å,c = 7.307(3) Å, = 118.17(2)°,Z = 4, Raumgruppe C2/c,R = 0.029 für 1896 Reflexe mit sin / 0.80 Å^–1.Die Cu-Atome in diesen drei Verbindungen sind durch O-Atome quadratisch planar [4], tetragonal pyramidal [4 + 1] und tetragonal dipyramidal [4 + 2]-koordiniert; eine Ausnahme ist das Cu(2)^{[4 + 1]}-Atom in Cu₃(AsO₄)₂-III: Das Koordinationspolyeder stellt einen Vertreter des Übergangs von einer tetragonalen Pyramide zu einer trigonalen Dipyramide dar. In KCu₄(AsO₄)₃ haben das Cu(1)^[4]O₄-Quadrat und das As(1)O₄-Tetraeder eine gemeinsame O—O-Kante von 2.428(5) Å, was eine Verzerrung der beiden Koordinationsfiguren CuO₄-Quadrat und AsO₄-Tetraeder bedingt. Die zwei Na-Atome in Na₄Cu(AsO₄)₃ sind durch O-Atome [6]-koordiniert, das K-Atom in KCu₄(AsO₄)₃ ist [8]-koordiniert.

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Zur Kristallchemie dreier Kupfer (II)-Arsenate: Cu₃(AsO₄)₂-III, Na₄Cu(AsO₄)₂ und KCu₄(AsO₄)₃

     

Komplexe des zweiwertigen Molybdäns,Derivate des Oktahalodimolybdat(II)-Ions, 4. Mitt.: Darstellungen und Kristallstrukturen von zwei neutralen Komplexen mit 4-Methylpyridin

Mo₂Cl₄ Pic ₄·CHCl₃ (A) (Pic=4-methylpyridine) and Mo₂Br₄ Pic ₄ (B) crystallize in the monoclinic space group.A inC2/c (No. 15) witha=15.175 (4),b=10.847 (2),c=19.946 (6) and =104.52 (2)°;D _o=1.71 (2),D _c =1.72 gcm^–3 forZ=4.B inP2_l/n (No. 14) witha=9.270 (3),b=16.614 (5),c=9.305 (3) and =91.96 (5)°;D _o=2.03 (3),D _c =2.05 gcm^–3 forZ=2.Two halogens and 4-methylpyridines of the MoX ₂ Pic ₂ group are in the trans position. Mo–Mo bond lengths are 2.153 96) forA and 2.150 92) forB. Both molecules are situated on the inversion center resulting in the eclipsed configuration of the ligands around the molybdenum pair. The structure ofB has been refined to the conventionalR factors of 0.08 and 0.098. Disorder on the part of 4-methylpyridines and chloroform molecules stopped the refinement ofA at the endR value of 0.175.Mean Mo–X and Mo–N bonding distances are 2.40 (2), 2.25 (5) forA and 2.53 (3), 2.25 (1) forB.

     

A structural study of the naringin-β-cyclodextrin complex

The structure of the inclusion complex formed between naringin (naringenin-7-O--neohesperidoside) and-cyclodextrin (BCD) was studied in detail by UV and NMR spectroscopic techniques and potentiometry. A binding constant value of 1016±150M^–1 was arrived at from UV studies. Potentiometric studies showed that pK values of 4-OH and 5-OH were affected by and-cyclodextrins. One-dimensional difference NOE and spin-lattice relaxation time (T ₁) measurements indicated that the aglycone protion was affected more than the neohesperidoside portion. TheT ₁ values analysed for local motions indicated that _c values of complexed naringin was higher than that of free naringin. The internal rotation calculated for different groups showed _i values for the phenolic and dihydrobenzopyran portion decrease by a factor of 2. Also a value of 0.12–0.17 observed for the aglycone portion indicated that the coupling between guest and host is weak. All the studies have shown that the disposition in which the phenol group at 2 is inside the BCD cavity with 4-keto and 5-OH hydrogen bonded to the secondary hydroxyl groups at the rim of the wider end of the BCD cavity is the most probable one.     

Complex polarizability as used to analyze dielectric relaxation measurements

The effect of representing dielectric properties in terms of the complex polarizability ^c = – i is examined. Loss curves ( and tan ) are shifted towards higher frequencies, revealing the existence of new relaxations and allowing the clarifications of ones already known. We have calculated the shift ratios (at maximum or tan )/ (at maximum or tan ) from the more conventional empirical equations representing the dielectric behavior. Some examples are given.     

Effect of sodium oxide doping on solid-solid interactions between V2O5 AND Al2O3

A V₂O₅/Al₂O₃ mixed solids sample was prepared with a molar ratio of 0.41 Na₂O (4 and 10 mol%) was added in the form of sodium nitrate prior to calcination in air in the temperature range 500–1000C. Solid-solid interactions between V₂O₅ and Al₂O₃ were studied using DTA and TG curves and their derivatives together with XRD techniques.The results obtained showed that Na₂O interacted with V₂O₅ at temperatures starting from 500C to yield a sodium/vanadium compound, Na_0.3V₂O₅ which remained stable and decomposed in part by heating at 1000C. V₂O₅ exists in orthorhombic and monoclinic forms in the case of pure mixed solids and those containing 4 mol% of Na₂O and preheated at 500C, and in monoclinic form in the case of the mixed solid doped with 10 mol% of Na₂O.Heating of pure and doped mixed oxide solids at 650C resulted in the conversion of most of the V₂O₅ into AlVO₄. Doping with sodium oxide enhanced the solid-solid interaction between V₂O₅ and Al₂O₃ at 650C to produce AlVO₄. The produced AlVO₄ decomposed completely on heating at 700C to form -Al₂O₃ and V₂O₅, (orthorhombic and monoclinic forms).The presence of Na₂O was found to decrease the relative intensity of the diffraction lines of -Al₂O₃ (corundum) produced at 750C which indicated some kind of hindrance of the crystallization process.Heating of pure and doped mixed solids at 1000C resulted in a further crystallization of acorundum together with V₂O₅ and sodium vanadate, Na_0.3V₂O₅. However, the intensities of diffraction lines relative to those of the sodium vanadium compound were found to decrease markedly by heating at 1000C, indicating partial thermal decomposition into vanadium and aluminium oxides.     

PVT properties of concentrated aqueous electrolytes. II. Compressibilities and apparent molar compressibilities of aqueous NaCl,Na2SO4, MgCl2, and MgSO4 from dilute solution to saturation and from 0 to 50°C

The relative sound velocities (U-U°) of aqueous NaCl, Na₂SO₄, MgCl₂, and MgSO₄ solutions were measured from 0.05m to saturation and from 0 to 45°C. The sound speeds were combined with our earlier work and fitted to a function of molality and temperature to standard deviations within 0.3 m-sec^–1. The adiabatic compressibilities, _s, were determined from the sound speeds and used to calculate adiabatic apparent molar compressibilities, K_,s, isothermal compressibilities, , and apparent molar compressibilities, K, were determined from the adiabatic values using literature data for expansibilities and heat capacities. The values of K have been extrapolated to infinite dilution using an extended limiting law. The resulting K⁰ at various temperatures are in reasonable agreement with literature values. The results of this study have been combined with our earlier results to derive a secant bulk modulus equation of state for NaCl, Na₂SO₄, MgCl₂, and MgSO₄ solutions valid from 0 to 50°C and 0 to 1000 bar.     

Equilibrium in Saturated Ca(OH)2 Solutions: Parameters and Dissociation Constants

A new computer program has been developed for the calculation of pH, pOH, hydroxide ion concentration m _OH, species distribution coefficients _i, ionic activity coefficients _i ionic strength I, buffer capacity , solubility product K _s0, and the two dissociation constants, K _b1 and K _b2, corresponding, respectively, to first and second dissociation steps of Ca(OH)₂ in aqueous solution. Previously developed methodology, for the calculation of pH, _i, _i I, and parameters of pH buffer solutions, starting from the corresponding acidity constants, has been adapted for the case of aqueous Ca(OH)₂ solutions, for which the pertinent stoichiometric relationships are different from those applicable to mixtures of acids and their salts. The results show that, contrary to what is currently assumed, the first dissociation is far from complete. Values are given for the concentrations and activities of species Ca(OH)₂(aq), Ca(OH)⁺(aq), and Ca²⁺ (aq) in saturated calcium hydroxide solutions at 25°C.     

Apparent molar heat capacity and relative enthalpy of aqueous NaOH between 323 and 523K

The apparent molar heat capacity, C _p,, of aqueous NaOH has been measured at temperatures between 50 and 250°C and molalities from 0.05 to 1.5 mol-kg^–1. Enthalpies of dilution L were also determined at 99°C and apparent molar relative enthalpies L were calculated up to 1.9 m. Measurements were performed by means of a flow calorimetric apparatus constructed in our laboratory and standardized for C _p, and L with aqueous Na₂SO₄ and with the formation of water from its ions, respectively. Characteristics and performance of this calorimeter are described in detail. Pitzer's semiempirical equations are used for the representation of the results and a general fitting of C _p, data is reported using also recent literature values measured between 4 and 55°C. The fitted parameters are finally utilized, through an integration procedure, to derive a general equation to calculate L at any temperature between 4 and 250°C.     

Preparation of Al2TiO5-ZrO2 mixed powders via sol-gel process

Sol-gel routes in the ternary system Al₂O₃-TiO₅-ZrO₂ were investigated to prepare Al₂TiO₅-ZrO₂ mixed powders. The preparation of ZrTiO₄ and Al₂TiO₅ was studied before going on with the ternary system. Zirconium titanate precursor gels were prepared from Ti(OPrⁱ)₄ and Zr(OPrⁿ)₄ mixtures. The crystallization of ZrTiO₄ develops at T<700°C. Al₂TiO₅ was prepared by different ways, using mixtures of Al(OBu^s)₂(C₆H₉O₃) with Ti(OPr ⁱ )₄ (i), or with acetic acid addition (ii). Route (i) leads to a separate crystallization of TiO₂ and -Al₂O₃, with subsequent formation of -Al₂TiO₅ at T1360°C. Although the pseudobrookite -Al₂TiO₅ is thermodynamically unstable below 1280°C, route (ii) leads to the crystallization of metastable -Al₂TiO₅ at T800°C. At increasing temperature, -Al₂TiO₅ decomposes into TiO₂ and -Al₂O₃, then the two compounds react to form stable -Al₂TiO₅. For the ternary system, all the preparation routes which were studied lead to ZrTiO₄ and -Al₂O₃ with subsequent reaction (at T1500°C) to give -Al₂TiO₅ and ZrO₂.     

Adsorption behavior of polymers having phosphoric acid group on γ-Fe2O3 and magnetic characteristics in magnetic coatings

Polymers having phosphoric acid groups were prepared as a model binder for magnetic coatings, and the correlation among the adsorption behavior of the polymers onto-Fe₂O₃ particles and the dispersibility, the orientation, and the packing density of-Fe₂O₃ particles in the magnetic coatings was investigated.PMMA homopolymer molecules hardly adsorbed on-Fe₂O₃, and the interfacial tension at a water/polymer solution (toluene) interface ( _W/T) was scarcely changed compared with a water/toluene interface. Increasing with the content of polymeric phosphoric acid group, the adsorbance of polymer increased and the interfacial tension ( _W/T) decreased. When the content of polymeric phosphoric acid groups was over 0.4 mol%, the adsorbance of polymer and interfacial tension ( _W/T ) remained constant. When these polymers were used as a binder for magnetic tapes, the dispersibility of-Fe₂O₃ in the magnetic coatings was improved, increasing with the content of polymeric phosphoric acid group; however, when the content of phosphoric acid group was over 0.2 mol%, its dispersibility decreased abruptly.Studies on Recording Magnetic Materials and Magnetic Composite. XVIII.     

Macromolecular conformations at the water-air interface: Interactions between alpha and beta conformations of polypeptides

Bidimensional miscibility between alpha and beta conformations of polypeptides was investigated at the water-air interface in the 15°–30°C temperature range. The polypeptides were poly--methyl-L-glutamate (PGMG), poly--benzyl-L-glutamate (PGBG) and poly--benzyl-L-aspartate (PBBA). The polypeptide conformations, alpha or beta, were checked by IR spectroscopy using the MIR technique.The spreading isotherms for mixed monolayers alpha-PGMG/alpha-PGBG and beta-PGMG/beta-PBBA showed bidimensional miscibility both for alpha-alpha and beta-beta mixtures.For the alpha-alpha system, attractive interactions among the polypeptide alphahelices were found (G_mix<0) and the driving factor appeared to be the entropic one (packing). Compressibility moduli and surface potential measurements showed a fluidification effect of alpha-PGBG on mixed monolayers. In the case of beta-beta mixed monolayers, ideal behaviour was observed and no fluidification effect detected.Scanning electron micrographs made on collapsed monolayers showed hexagonal structures for alpha-alpha mixtures and no well-defined or characterized features for the beta-beta system.     

Effect of Thermal Activation of Supported Catalysts Pt/MeOx,Where MOx = Al2O3, CeO2, La2O3, and ZrO2, for Complete Oxidation

A sharp increase in the atomic catalytic activity (ACA) of supported platinum catalysts in the model reaction of n-pentane complete oxidation is found on going from the preliminary calcination temperature of 500–600°C to a temperature of 700°C. ACA increases by an order of magnitude for the Pt/-Al₂O₃ system, 3 times for Pt/ZrO₂, and 1.5 times for Pt/CeO₂. The per-gram activities of all catalysts decrease because of a decrease in the dispersion of supported platinum with an increase in the temperature of preliminary calcination.     

An aqueous thermodynamic model for Ca2+−SO 3 2− ion interactions and the solubility product of crystalline CaSO3·1/2H2O

The solubility of CaSO₃·1/2H₂O(c) was studied under alkaline conditions (pH>8.2), in deaerated and deoxygenated Na₂SO₃ solutions ranging in concentration from 0.0002 to 0.4M and in CaCl₂ solutions ranging in concentration from 0.0002 to 0.01M, for equilibration periods ranging from 1 to 7 days. Equilibrium was approached from both the over- and the under-saturation directions. In all cases, equilibrium was reached in <1 days. The aqueous Ca²⁺–SO ₃ ^2– ion interactions can be satisfactorily modeled using either ion-association or ion-interaction aqueous thermodynamic models. In the ion-association model, the log K°=2.62±0.07 for Ca²⁺+SO ₃ ^2– CaSO ₃ ⁰ . In the Pitzer ion-interaction model, the binary parameters (⁰) and (¹) for Ca²⁺–SO ₄ ^2– were used, and the value of (²) was determined from the experimental data. As expected given the strong association constant, the value of (⁰) was quite small (about –134). We feel a combination of the two models is most useful. The logarithm of the thermodynamic equilibrium constant (K°) of the CaSO₃·1/2H₂O(c) solubility reaction (CaSO₃·1/2H₂O(c)Ca²⁺+SO ₃ ²⁺ +0.5H₂O) was found to be –6.64±0.07.     

Synthese und Strukturanalyse von Na3SbSe3·3Sb2O3·0,5Sb(OH)3

Investigations in the system Sb-Se-NaOH-H₂O, hydrothermal conditions, yielded crystals of the compound Na₃SbSe₃·3Sb₂O₃·0,5Sb(OH)₃. The structure of this compound (a=14.40 Å,c=5.568 Å; space group P 6₃-C ₆ ⁶ ;Z=2) was determined from 985 independent X-ray intensities — collected on an automaticWeissenberg type diffractometer — by thePatterson method and refined by the least squares method toR=8.3% (with -weighting 5.9%). The structure consists of SbO₃ pyramids which are connected via common oxygen corners to tubes parallel [001]. These tubes and SbSe₃ pyramids are combined by Na atoms to a framework. The Sb(OH)₃ groups are statistically located within the channels of the tubes.

     

Predissociation lifetime of the 1σ g 2 2σ g diabatic state of He 2 + : a one-channel approach

Summary This work is concerned with the application of a one-channel model to obtaining predissociation lifetimes and transition rates in a system of crossing diabatic states. The calculation focuses on the first shape resonance of the 1 _g ² 2 _g diabatic state of He ₂ ⁺ , which is relatively stable with respect to tunneling. This resonance predissociates as a result of the 1 _g ² 2 _g state being crossed by the 1 _g 1 _u ² dissociative diabatic state near the resonance level. We have estimated its predissociation lifetime to be of the order of 10^–11 s.     

Die Phase La2U2N5

In the system U–La–N a new phase of composition La₂U₂N₅ was observed. The differaction pattern of this phase can be indexed with a tetragonal unit cell:a=8.43 Å,c=8.50 Å andc/a=1.008. The pseudocubic sub-cell withaca/2 is closely related to the CsCl-type.

Auszug aus der von der Technisch-Naturwissenschaftlichen Fakuktät der TU Wien approbierten Diplomarbait des Herrn Dipl.-Ing.J. Waldhart.     

Additive telluromolybdates. Structure and catalysis in oxidation

Additive telluromolybdates, MoO₃·2TeO₂ and M^IIO·TeO₂·MoO₃ (M^IITeMoO₆; M^II = Co, Mn, Zn), converted ethyl lactate selectively to pyruvate in a vaporphase fixedbed flow system at 250–300 °C. A synergy in activity was observed for binary TeO₂–MoO₃, and crystalline Te₂MoO₇ was suggested as the active species. The Rietveld analysis of powder XRD patterns of ternary CoTeMoO₆ revealed the layer structure quite different from that of the reference Te₂MoO₇, but tellurium was again located adjacent to molybdenum linked through lattice oxygen.     

Crystal structure of Li2Cu3(SeO3)2(SeO4)2

Summary Single crystal X-ray data of the hydrothermally grown new phase Li₂Cu₃(SeO₃)₂(SeO₄)₂ were measured with a four-circle diffractometer up to sin /=0.81 Å^–1 [I2/a,Z=4,V=1175.5 ų,a=16.293(6),b=5.007(2),c=14.448(6) Å, = 94.21(1)°]. The structure was determined by direct and Fourier methods and refined toR=0.034,R _w =0.027 for 2 086 independent reflections.Cu(1)^[4+1]O₅ forms a tetragonal pyramid, Cu(2)^{[4 + 2]}O₆ is a strongly elongated octahedron. The Li atom is surrounded by four O atoms forming a distorted tetrahedron. Se(IV)O₃ and Se(VI)O₄ groups are in accordance to literature, mean Se-O bond lengths are 1.714 and 1.644 Å.

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Die Kristallstruktur von Li₂Cu₃(SeO₃)₂(SeO₄)₂

Zusammenfassung Einkristall-Röntgendaten der hydrothermal gezüchteten neuen Phase Li₂Cu₃(SeO₃)₂(SeO₄)₂ wurden mit einem Vierkreisdiffraktometer im Bereich bis zu sin /=0.81 Å^–1 gemessen [I2/a,Z=4,V=1175.5 ų,a=16.293(6),b=5.007(2),c=14.448(6) Å, =94.21(1)°]. Die Kristallstruktur wurde mittels direkter und Fourier-Methoden bestimmt und für 2 086 unabhängige Reflexe zuR=0.034,R _w =0.027 verfeinert.Cu(1)^[4+1]O₅ bildet eine tetragonale Pyramide, Cu(2)^[4+2]O₆ ist ein stark verlängertes Oktaeder. Das Li-Atom ist von vier O-Atomen in Gestalt eines verzerrten Tetraeders umgeben. Die Se(IV)O₃-und Se(VI)O₄-Gruppen entsprechen der Literatur, die mittleren Se-O-Abstände betragen 1.714 und 1.644 Å.