On the structures of X- and Y-type zeolites. Structural changes within the cavities of Na-Y during dehydration and contrasts with Na-X systems

Samples of dehydrated and partially dehydrated Na-Y were examined by X-ray diffraction methods revealing the progressive structural changes which occur as water is removed and the different behaviour compared with Na-X. The differences between Na-Y and Na-X reflect the reduced Al content of Na-Y and the consequential lower average capability of each framework oxygen atom for balancing cation charges. In the small-pore region of Na-Y, the total number of Na atoms remains relatively constant during dehydration (ca. 15 per unit cell compared withca. 18 in Na-X); unlike Na-X, Na-Y, has no site I atoms. Significant dehydration of the small-pore region, and the change from low to high site II occupancy, do not occur until the total water content of the sample is less than that which pertains under atmospheric conditions. In the 12-ring regionn of Na-Y, [Na(H₂O)₂]⁺ units are observed at an intermediate level of dehydration, possibly linked by water molecules astride the site III region to networks in adjacent 12-rings. There is no build-up, as in Na-X, of Na at site III, and site IIB (=III) is (at least partially) occupied by H₂O rather than Na. Further dehydration progressively removes H₂O but there is little rearrangement of Na atom positions, except the build-up in site II which accounts for much of the loss of Na from the mobile phase.     

Thermodynamics of the dissociation of ammonium ion in seawater from 5 to 40°C

The dissociation constant of NH ₄ ⁺ and the associated thermodynamic functions H° and S° in synthetic seawaters of salinity 20.31, 35.00, and 44.55 have been determined by emf measurements of cells without liquid junction over the temperature range 5 to 40°C. Cells with hydrogen electrodes and silver-silver chloride electrodes, whose standard potentials in seawater media were determined in an earlier investigation, were used. At a given temperaturet (in °C), pK _a varies linearly with the formal ionic strengthI _f (uncorrected for ion pairing) according to pK _a=pK _a ^w +(0.1552–0.0003142t)I _f where pK _a ^w is the pK in pure water. The medium effect of seawater on H° amounts to less than 200 cal-mole^–1 for a change inI _f from 0 to 0.72 mole-kg^–1, and S° is less than 1 cal-°K^–1-mole^–1 in all of the media studied, as it is in water. The observed salt effect on pK _a is in close agreement with values predicted from theories of ion-ion interactions.     

IR study of the peculiarities of the stabilization of the NH4Na-Y zeolite structure during its hydrothermal dealumination

The variations in the structure of deep-level calcinated NH₄Na-Y zeolite (68 % NH₄ ⁺, Si/Al = 2.56) at 873 K (stage I of the hydrothermal dealumination) as a result of ammonation and subsequent calcination in water vapor at 973 and 1023 K (stageII) were studied using the IR spectra of zeolite framework vibrations. It was shown that ammonation of the product of stageI promotes the formation of linear disiloxane bonds and extra-framework =Al^VI-OH species identified by absorption at 482, 1196 cm^–1, and 524, 612, 829 cm^–1. The ammonation is also accompanied by an increase in the excessive negative framework charge (ENFC), which is manifested in the high-frequency (HF) shift of the bands that have maxima in thev _as (TO₄) region and equals 10 cm^–1, and also by a decrease in the unit cell parameter (a ₀) by 0.14 Å. The decrease in both the ENFC anda ₀ for the products of stageII, v _as (TO₄) = 10–20 cm^–1 and a ₀ = 0.07–0.14 Å, is due to the formation of nonlinear disiloxane bonds and non-framework aluminum hydroxide species identified by the absorption bands at 478, 1173 cm^–1 and 530, 615, 835 cm^–1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 660–664, April, 1993.     

Adsorption and Desorption of Cr(III) on Natural and Chemically Modified Slovak Zeolites

Natural and chemically modified zeolites from the Slovak Republic and Ukraine have been investigated as the adsorbents for the uptake of Cr(III). Model water solution of low radioactivity was used. The adsorption and desorption kinetics of chromium were established with the gradual radioexchange technique (tracer ⁵¹Cr) and flame AAS. The effect of the factors studied are examined and explained. The sorption coefficient , distribution coefficient K _D , sorption capacity , sorption rate S, and leachability of Cr were calculated in neutral, alkaline and acidic aqueous solutions. The sorption capacity of the modified zeolites was found to be greater by a factor of 2 to 16 than that of the unmodified ones depending on the modifying solution applied. The leachability of chromium from loaded zeolites into the neutral solution was negligible. The leachability into alkaline and acidic solutions increased over 40%.     

Confusing Quantitative Descriptions of BrønstedLowry AcidBase Equilibria in Chemistry Textbooks – A Critical Review and Clarifications for Chemical Educators

In chemistry textbooks, the pK value of water in the solvent water at 25 °C is sometimes given as 14.0, sometimes as 15.7. This is confusing. The particular chemical reaction considered is the one in which water as Brønsted? Lowry acid reacts with water as Brønsted? Lowry base in water as solvent to yield equal concentrations of hydrated oxonium and hydroxide ions, H₃O⁺(aq) and HO^?(aq), respectively. This reaction is also known as the ‘self‐ionization’ of water for which the equilibrium constant is abbreviated as K_w with its known value of 10^?14.0 at 25 °C, i.e., pK_w(25 °C)=14.0. Identical values for pK and pK_w at a fixed temperature appear reasonable, since K and K_w refer to one and the same reaction. Therefore, reasons for the apparent disagreement between the ‘thermodynamically correct’ pK_a value for water (14.0 at 25 °C) and the value reported in most organic chemistry textbooks (15.7) should be discussed when teaching acid? base chemistry. There are good arguments for introducing, from the very beginning, the concepts of activity and thermodynamic standard states when teaching quantitative aspects of chemical equilibria. This also explains in a straightforward way why all thermodynamic equilibrium constants, including K_w, are dimensionless, and why pK(25 °C)=0.     

Solubility of inert gases and liquid hydrocarbons in water

The thermodynamic statistical model based on the distribution of molecular populations among energy levels has been employed for the analysis of the solubility of hydrocarbons and other inert gases or liquids in water at different temperatures. The statistical distribution is described by a convoluted partition function Z_G·_s. The product of a grand canonical partition function Z_G represents the distribution of the species in the reaction while the canonical partition function Z_G represents the properties of the solvent. The first derivative of the logarithm of the partition function with respect to 1/T is the apparent enthalpy which is the result of the contributions of the separate partition functions, {H_aap}_T=H^o+n_wC_p,wT, where {H_app}_T refers to Z_G, n_wC_p,wT=–H_w to _s, and H^o is the change in enthalpy of hydrocarbon-water reaction. The plot {H_app}_T vs/ T results in a straight line with slope n_w at constant C_p,w. The apparent enthalpy is obtained from the coefficients of the polynomial fitting of the solubility data, as a function of 1/T. Alternatively, the apparent enthalpy can be determined calorimetrically. The enthalpy thus obtained is a linear function of the Kelvin temperature. The values of n_w range from 1.6, 1.9, 5.6 to 5.8 for helium, hydorgen, butane and hexane, respectively. For fluorocompounds the range of n_w is 10.1 to 11.1 indicating that n_w is a function of the number of water molecules expelled from the cage of solvent to form a cavity to host the solute molecule. The analysis of several sets of calorimetric or solubility data with the present molecular thermodynamic model yields values of H^o and n_w consistent with the size of the dissolved molecules.List of Symbols p pressure - H _ij average enthalpy - H _i level enthalpy (=H) - H _i enthalpy difference - H _ij intersublevel energy difference - i index of level - j index of sublevel - Z_G grand canonical partition function - _S canonical partition function - Z_G- convoluted partition function - –G ^o/RT standard Gibbs energy normalized toRT - –H ^o/RT standard enthalpy normalized toRT - S ^o/R standard entropy normalized toR - C _p molar heat capacity - T absolute temperature - H _G- enthalpy of the convoluted ensemble - H _G enthalpy of the solute - H enthalpy of the solvent - H _app apparent enthalpy - H _w enthalpy of water - C_yH_z hydrocarbon - W water - K _s solubility equilibrium constant - x ₂ molar fraction of solute - C_yH_zW_(x-nw) hydrocarbon molecule trapped in a cavity - K _H Henry constant - P _s solubility product - [W] concentration of water - reference temperature - a, b, c, d coefficients of the fitting polynomial - {H _app}_T apparent enthalpy at temperatureT - {H }_T standard enthalpy at temperatureT - {H _w}_T water contribution to enthalpy at temperatureT - C _p,w isobaric molar heat capacity of water - L Ostwald coefficient - C _p isobaric heat capacity difference - Bunsen coefficient - C _p,app apparent isobaric heat capacity difference - n _C number of carbon atoms in the chain - h _w interaction enthalpy of one water molecule - H ₀ intercept for the extrapolated enthalpy     

Optimation of PGNAA instrument design for cement raw materials using the MCNP code

A simulation study of a PGNAA measuring arrangement with a²⁵²Cf neutron source for the characterization of cement raw materials was carried out using the MCNP code to investigate the effect on the system response of varying the bulk density and the water contentv _w of samples of fixed dry composition. The source is placed at the centre of a lead cylinder of extemal radiusR _Pb. This cylinder is enclosed in a coaxial cylinder of polyethylene moderator of extermal radiusR _in. The sample material is confined to the space between an outer cylindrical surface of radiusR _out and the moderator cylinder. The first series of simulation runs was carried out for different sets of values ofR _in,R _out and , and constantv _w. The system specific responseS (count rate per wt%) shows a broad maximum aroundT _M=R _in-R _Pb=4 cm andT _S=R _out-R _in=8.5 cm and a dependence on that is almost linear in the region of the maximum. In a second series of runs the dependence ofS onv _w was studied for a geometry corresponding to a real experiment described elsewhere and for a geometry for which the density saturation effect is already apparent. It is shown that when the sensitivity of the system is optimized both andv _w must be used as calibration parameters while in the low-sensitivity design regionv _w can be used as the only calibration parameter.     

CPS K 843 Radiation-induced crosslinking: Effect on structure of polyethylene

Branched polyethylene irradiated (0–400 Mrad) with a Co⁶⁰ source at room temperature under vacuum was studied by density, wide- and small-angle X-ray scattering (WAXS and SAXS) measurements. The radiation effects on the structure of bulk, branched polyethylene are quite similar to those observed by others on single crystals or oriented preparations. These effects include changes in bulk density, crystallinity(w _c orv _c) and¯d ₁₀₀ and¯d ₂₀₀ spacings as a function of irradiation. A decrease in crystallinity is seen to begin at radiation dose 100 Mrad whereas lattice expansion indicating onset of an orthorhombic-hexagonal transition can begin as low as 10 Mrads. The decrease in crystallinity can be attributed to additional lattice distortions primarily introduced by the crosslinks occurring at the lateral grain boundaries, while lattice expansion can be associated with the same crosslinking mechanism which begins at the defects both within the crystals as well as those outside the crystals at the lateral grain boundaries. Strong evidence for a primary crosslinking-at-the-defects mechanism has also come from _c and _a data obtained in this study as a function of radiation dose. The same data have also led to an excellent correspondence between the measured density crystallinityv _c and the measured WAXS crystallinityw _c. Without consideration of the effects of crosslinks on _c and _a one would have obtained a divergence of the two crystallinities, especially at radiation doses greater than 100 Mrads.Dedicated Prof. Dr. R. Bonart on the occasion of his 60^th birthday     

Characterisation of Siliceous Extra‐Framework Species in DAY Zeolites by 29Si MAS NMR and IR Spectroscopic Measurements

Dealuminated Y zeolites (DAY) were obtained by steaming of NH₄NaY at temperatures between 450 °C and 700 °C. They were characterised by means of ²⁷Al and ²⁹Si MAS NMR, IR spectroscopic and XRD measurements. The Si/Al framework ratios of samples were calculated using the ²⁹Si MAS NMR signal intensities, the wave numbers of the double‐ring vibration band w_DR and the asymmetrical TOT valence vibration w_TOT of IR spectra as well as the XRD lattice constant a₀. In contrast to actual Si/Al ratio obtained from w_DR and a₀, the NMR spectroscopic and w_TOT values were determined to be too high because of the superposition of the signals coming from dealuminated zeolite framework and silica gel which forms in the zeolite as a result of steaming. The differently determined Si/Al ratios characterise the siliceous extra‐framework species.     

Kristallstruktur von Sulfamid,SO2(NH2)2

X-ray crystal structure analyses of sulfamide were carried out at 293 K and at 100 K:M=96.10, orthorhombic, Fdd2,Z=8,F(000)=400, Mo K, =0.71069 Å (graphite monochromator). A) 293 K:a=9.127 (1) Å,b=16.857 (5) Å,c=4.579 (1) Å,V=704.50 ų,d _x =1.812 Mgm^–3, =0.648 mm^–1,R=1.77%,R _w =1.94% (384 reflections, 33 parameters). B) 100K:a=9.059 (1) Å,b=16.780 (8) Å,c=4.517 (1) Å,V=686.63 ų,d _x =1.859 Mgm^–3, =0.665 mm^–1,R=1.78%,R _w =1.95% (404 reflections, 33 parameters). The sulfamide molecule shows at 293 K S-O and S-N distances of 1.429 (1) Å and 1.620 (1) Å, respectively, which are in agreement with IR data. Hydrogen positions could be determined from differenceFourier syntheses. Strong weakening of some intense low order reflections by extinction was observed, their anisotropy depends on the crystal and on temperature.

     

Effects of pressure and solvent on the diffusion of aromatic compounds through polymers

The diffusion of six azo and five anthraquinone derivatives through nylon 6, poly(ethylene terephthalate) and secondary cellulose acetate films were studied under high hydrostatic pressures of up to 3000 bar and at temperatures 80–130 °C, by analyzing the diffusion profiles yielded in a stacked multiple film, placed in the solution of the diffusant. It was found that the diffusion coefficient,D, of the diffusant decreased with increasing pressure, giving a linear relationship between InD and the pressure, the slope of which gave the activation volume for the diffusion,V . It was revealedV increased linearly with increasing intrinsic molecular volume of the diffusant,V _w , the slopes being different between the azo and the anthraquinone derivatives. The ratio ofV toV _w (V /V _w ) ranged from 0.13 to 0.93, depending in a sensitive manner on the degree of swelling of the polymer matrix which in turn was varied by the solvent. The overall results could be explained in accordance with the formulation,V _{f, local} +V =V _w , whereV _{f, local} represents the free volume contribution. It was proposed thatV _w is increased by solvation when the solvent is good for the diffusant.     

Charge Transfer Salt with Substituted Lindquist Polyoxometalate: Synthesis, Crystal Structure, and Physical Properties of α-(BEDT-TTF)6(VW5O19)⋅DMF⋅2H2O

A new charge transfer salt based on bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) and the vanadium substituted Lindquist anion [VW₅O₁₉]^3– was synthesized and characterized by X-ray and spectroscopic analysis. Monoclinic, C2, F _w =3789.2, a=41.5019(5), b=11.2600(2), c=12.7514(2) Å, =101.877(5)°, Z=2, R=0.060, based on 12095 reflections with I>2(I). The structure consists of alternating organic and inorganic layers. The inorganic layer is generated by [VW₅O₁₉]^3– anions, dimethylformamide (DMF) and water molecules. The organic layer, which is generated by three different BEDT-TTF units, belongs to the -type of packing and consists of trimerized chains parallel to the c direction. The compound is a semi-conductor with _{300 K} =1.1 Scm^–1 and E _a =0.1 eV. Polarized reflectance spectra of single crystals were measured over the spectral range from 650 to 25000 cm^–1. FT-NIR Raman spectra of powdered crystals dispersed in KBr pellets were also recorded. Vibrational and electronic features are discussed.     

Volumetric study on the inclusion complex formation of α- and β-cyclodextrin with 1-alkanols at different temperatures

The partial molar volumes (V_a) of 1-alkanols (carbon number, m=5, 6, 7) in - and -cyclodextrin (CD) solutions at 5.00 mmol kg^–1 have been determined as a function of alkanol concentration (C_a) between 293.2 and 308.2 K by using a dilatometer. It has been observed that with an increase in C_a, V_a increased in -CD solution but decreased in -CD solution, asymptotically to a value of V_a in CD-free water. The dependence of V_a on C_a provided the binding constant (K) of 1:1 complex, the volume change in complex formation, and the partial molar volume of complex itself. The complex formation mechanism has been discussed on the basis of these values and their carbon number dependences in the respect of geometric behavior, hydrophobic interaction, and van der Waals interaction. It is concluded that the CD cavity in water is not rigid but flexible for fitting in nicely with guest molecule.     

The x-ray crystal structure,resolution and absolute configuration of thecis-α-dichloro(1, 8-diamino-3, 6-diazaoctane)-ruthenium(III) cation

Summary Acis- configuration for the [RuCl₂(trien)]Cl·2H₂O (trien=1, 8-diamino-3, 6-diazaoctane) complex has been confirmed by an x-ray crystal structure determination. Crystals are monoclinic, space group P2₁/c witha=7.336 (1),b=8.477 (2),c=23.181 (4) Å, =103.3 (1)°, U=1403 (1) Å.³ Z=4 and M=389.7, D_c=1.84 g cm^–3. The structure was refined by full matrix least squares methods to final residual values of R=0.025 and R_w=0.033 on the basis of 3882 unique reflections. The complex has been resolved into its optical isomers using the (+)1, 2-diaminoethanebis(oxalato)cobaltate(III) anion and the absolute configuration assigned.     

The solubility and isotopic fractionation of gases in dilute aqueous solution. IIa. solubilities of the noble gases

A method for the analysis of precise gas solubility data is presented and applied to new determinations of the Henry constant, k₂, for He, Ne, Ar, Kr, and Xe. The values of k₂ are fitted to the same sets of temperature functions which we have tried for oxygen. Our previously proposed power series in 1/T, ln(k_2/P )=a₀+a₁/T+a₂/T² (Mark I), gives the best 3-term fit within the temperature range 0–60°C. For use over the full range to the critical temperature of water, we have discovered a new function given by (T^*)²ln(k_2/P )=A₀(T^*)²+A₁(1-T^*)^1/3+A₂(1-T^*)^2/3(Mark II), where T^*T/T _c1 . It fits our data from 0–60°C nearly as well as Mark I; it fits high temperature data from other sources; and at the critical temperature of water it satisfies theoretical requirements. Expansion of Mark II reveals the relationship between Mark II and Mark I and leads to a 4-term smoothing function, ln(k_2/P )=a_–2(T^*)^–2+a_–1(T^*)^–1+a₀+a₁T^* (Mark III), which we believe gives the best values only for the 0–60°C range. Mark III is used to calculate values for , and , 0–60°C, and a procedure is empolyed to estimate the errors. Agreement is excellent between these results and those obtained from precise microcalorimetric measurements made by others. With the inclusion of pressure correction terms, Mark II yields the four thermodynamic function changes for use at high temperatures. With increasing temperature, these changes suddenly turn upward toward plus infinity as T _c1 is approached. Essentially direct determinations of for argon by other workers are in excellent agreement with our results. The symmetrical activity coefficient at infinite dilution, ₂ ^° is examined and the hypothetical properties of k₂ are explored below 0°C. Mark II can be expressed in the reduced form (T^*)²ln(k ₂ ^* )=A₁(1-T^*)^1/3+A₂(1-T^*)^2/3, where k ₂ ^* k ₂/(p _c12c1). A₂ is a very good linear fit to A₁, which suggests a characteristic temperature for water at 287.3 K.     

Di- and tri-nuclear osmium carbonyl chloride complexes: x-ray structures of Os2(CO)8Cl2 and Os3(CO)12Cl2

Summary Os₂(CO)₈Cl₂ (1) is orthorhombic P2₁2₁2₁ witha=9.3599(9),b=9.879(2),c=16.014(3), V=1480³, D_c=3.03 Mgm^–3 for Z=4. Structure solved by Patterson methods. Final R=0.038, R_w=0.038 [w=(²F)] for 1270 observed reflections and 141 parameters. Os₃(CO)₁₂Cl₂ (2) is monoclinic C2/m witha=12.105(3), b=10.612(3),c=8.798(1) , =117.02(2)°, V=1006³, D_c=3.22 Mgm^–3 for Z=2. Structure solved by Patterson methods. Final R=0.036, R_w=0.037 (w=(²F)^–) for 821 observed reflections and 75 parameters.Complex(1) has an osmium-osmium single bond 2.897(1), with the chloride ligands in equatorial positions,(2) has a linear triosmium chain with osmium-osmium single bonds 2.893(1) and the chloride ligands occupy equatorial sites on the terminal osmium atoms. Both(1) and(2) are isostructural with their osmium carbonyl iodide analogues.     

Synthesis and crystal structures of heterobimetallic Fe-Cd,Fe-Zn,and Fe-In complexes containing hemilabile phosphorus/oxygen and silicon/oxygen bridging ligands

The reactions of K[Fe{Si(OMe)₃}(CO)₃(PY)][PY=Ph₂PCH₂C(O)Ph, Ph₂PCH₂C(O)[(-C₅H₄)FeCp] (Cp=⁵-C₅H₅), Ph₂P(CH₂)₂CN] with CdCl₂·2.5H₂O, ZnX ₂ (X=Cl, I) or InCl₃ afforded Fe-Cd-Fe or Fe-M(-X)₂ M-Fe (M=Cd, Zn, In;X=Cl, I) and Fe-InCl₂ complexes. Some of them contain an unusual and labile -²-SiO alkoxysilyl bridge which may be associated with a bridging mode for the ketophosphine ligand (first such example structurally established), thus providing original results in bimetallic chemistry on the intramolecular coordination of oxygendonor functions ofchemically different hemilabile ligands firmly attached to a neighboring metal center. The structures of the trinuclear complex (3), of the chlorobenzene solvate of the tetranuclear complex (4a·C₆H₅Cl) and of [mer-(OC)₃{(EtO)₃Si} (4e) have been determined by X-ray diffraction. Crystals of 3 are orthorhombic, space groupPbcn, witha=19.010(4),b=11.766(5),c=26.998(7)Å, andZ=4. Crystals of4a·C₆H₅Cl are monoclinic, space groupC2/c witha=22.455(3),b=17.680(2),c=16.627(4)Å, =90.80(4)°, andZ=4. Crystals of4e are monoclinic, space groupC2/c witha=25.392(5),b=18.554(6),c=16.28(1)Å, =120.73(3)°, andZ=4. The structures were solved using direct methods and Fourier difference techniques and refined by blocked full-matrix least squares toR=0.035 (R _w =0.049) for 2719 observed reflections, toR=0.042 (R _w =0.056) for 3082 observed reflections, and toR=0.057 (R _w =0.075) for 1850 observed reflections for3, 4a·C₆H₅Cl and4e, respectively. The Fe-Zn complexes (9a), (9b) and (9c) were prepared and characterized by spectroscopic methods.Part 21 in the Series: Complexes with Functional Phosphines. Part 20: P. Braunstein, S. Coco Cea, A. DeCian, and J. Fischer (1992).Inorg. Chem. 31, 4203.     

Synthesis and Crystal Structure of Diaqua(2,2"-Dipyridyl)isothiocyanatoneptunoyl Monohydrate [NpO2(C10H8N2)(NCS)(H2O)2] · H2O

The crystal structure of the complex [NpO₂(C₁₀H₈N₂)(NCS)(H₂O)₂] · H₂O is determined. The unit cell parameters are a= 7.406, b= 9.517, c= 11.518 Å, = 103.65°, = 92.68°, = 96.53°, V= 781.6 ų, space group , Z= 2, (calcd) = 2.257 g/cm³, R= 0.046, R _w= 0.122. The coordination polyhedron of the Np atom is a pentagonal bipyramid with two nitrogen atoms of dipyridyl, a nitrogen atom of isothiocyanate ion, two oxygen atoms of water molecules lying in the equatorial plane, and oxygen atoms of the neptunoyl group lying in the axial positions.     

Light-scattering studies on solutions of potassium-polyphosphate

Summary Light scattering measurements on a number of samples of potassium polyphosphate dissolved in 0.1 M NaBr solution in water were made. With fair approximation, the second virial coefficient was found to be inversely proportional toM _w ^0.5 (M _w = Weight-average Molecular Weight). In conjunction with intrinsic viscosities, the values ofM _w were used in calculating the radius of gyration, . The ratio was found to be constant indicating that potassium Kurrol Salt exists as random coils in solutions. The average value of Flory constant calculated with the help of the available data was found to be 1.96 × 10²¹ which is quite close to that predicted by Flory.Post Doctoral fellow.