The importance of valencep functions in the bonding of Na2, K2, and Cu2 and their positive and negative ions

Summary The relative importance of the valencep functions for describing the bonding in the valence isoelectronic Na₂, K₂, and Cu₂ molecules and their positive and negative ions is investigated. In absolute magnitude the contribution of thep functions to the dissociation energy follows the trend Cu>Na>K while by percentage of the dissociation energy the importance of thep functions follows the polarizabilities, i.e. K>Na>Cu. The bonding in K₂, K ₂ ⁺ , and K ₂ ^– is analyzed to explain the observed trends.Dedicated to Prof. Klaus Ruedenberg     

球形PVC-MnO2离子筛的制备及锂吸附性能

本实验室前期所制备的Li4Mn5O12超细粉末在卤水体系中对Li+具有较大的吸附容量和良好的选择性。但由于超细粉体的流动性和渗透性差,无法直接应用于固定床,需对粉末吸附材料进行成型造粒,以便于实际应用。本论文采用聚氯乙烯为粘结剂,制备出粒径约为2.0~3.5 mm的球形PVC-Li4Mn5O12,经盐酸处理后得到球形PVC-MnO2离子筛。并通过扫描电镜(SEM)、X射线衍射仪(XRD)、静态和动态连续锂吸附实验研究了球形离子筛形貌和锂离子吸附性能。结果表明,球形离子筛对Li+的吸附容量高达5.28 mmol.g-1,在混合溶液中对Li+具有良好的选择性,这对于在盐湖卤水或海水提锂具有重要的实用意义。     

Application of molecular models to electronic structure calculations of defects in oxide crystals. I. Parametrization of the modified INDO method

A modified calculation scheme of the INDO method is applied for calculating the electronic structure of perfect and imperfect oxide crystals. In order to obtain a flexible scheme permitting reliable calculation of both the electronic structure and the defect conformations, the INDO parameters for H, Li, Mg, Si, O are fitted directly to reproduce one-electron energies as well as the vicinity of the potential energy curve minima for a series of diatomic molecules and the electronic structure of MgO and -crystoballite form of SiO₂. The method is tested on the Li₂SiO₃ crystal calculated within the framework of the large unit cell model.     

HTO/Cellulose Aerogel for Rapid and Highly Selective Li+ Recovery from Seawater

To achieve rapid and highly efficient recovery of Li⁺ from seawater, a series of H₂TiO₃/cellulose aerogels (HTO/CA) with a porous network were prepared by a simple and effective method. The as-prepared HTO/CA were characterized and their Li⁺ adsorption performance was evaluated. The obtained results revealed that the maximum capacity of HTO/CA to adsorb Li⁺ was 28.58 ± 0.71 mg g⁻¹. The dynamic k₂ value indicated that the Li⁺ adsorption rate of HTO/CA was nearly five times that of HTO powder. Furthermore, the aerogel retained extremely high Li⁺ selectivity compared with Mg²⁺, Ca²⁺, K⁺, and Na⁺. After regeneration for five cycles, the HTO/CA retained a Li⁺ adsorption capacity of 22.95 mg g⁻¹. Moreover, the HTO/CA showed an excellent adsorption efficiency of 69.93% ± 0.04% and high selectivity to Li⁺ in actual seawater. These findings confirm its potential as an adsorbent for recovering Li⁺ from seawater.     

The influence of electron correlation on reaction energies. The dimerization energies of BH3 and LiH

Results of rigorous computations employing extended Gaussian-type basis sets are reported for BH₃, B₂H₆, LiH, and Li₂H₂ in their respective equilibrium geometries. The dimerization energy of BH₃ is calculated as −20.7 kcal/mol within the Hartree-Fock approximation and as −36.6 kcal/mol if electron correlation is included. The corresponding results for the dimerization of LiH are −47.3 kcal/mol and −48.3 kcal/mol. Partitioning of the correlation energy contributions allows to attribute the effect of electron correlation to the increase of next neighbour bond interactions on the dimerization of BH₃ and LiH. The difficulties of accurate computations of reaction energies are discussed in detail.     

Peculiarity of the Dickinson H 2 + wave function

According to the zero potential energy criterion proposed recently, the Dickinson wave function for the 2p_u state of the H ₂ ⁺ system is an unexpectedly poor approximation so long as the known parameters are employed. We re-examine the optimum parameters for the Dickinson wave function and find that there exist two sets of optimum parameters with different wave function characteristics. The corresponding energy curves cross at R= 1.91 a.u., though the difference is very small. We suggest that a new set of optimum parameters with slightly higher energy for R>1.91 a.u. is more acceptable physically than the previously reported set.     

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     

CEPA calculations on open-shell molecules. III. Potential curves for the six lowest excited states of He2 in the vicinity of their equilibrium distances

CEPA-PNO and PNO-CI calculations have been performed for the potential energy curves of the He ₂ ⁺ ground state and the six lowest excited states of He₂ in the range of 1.4 a₀ ≤R ≤ 3.5 a₀. The calculated equilibrium distances as well as the spectroscopic constants are in very good agreement with molecular constants as derived experimentally from the rotation-vibration spectrum of He₂ by Ginter, except for thec ³∑ _g ⁺ state. This latter discrepancy is probably due to an “obligatory” hump in thec ³∑ _g ⁺ state occurring at 3.5 a₀ which cannot be properly treated in our calculation. The relative energetic positions of the six lowest states and their ionization energies are reproduced by our calculations with an accuracy of 0–400 cm⁻¹. Extrapolation of our results to infinite basis sets leads to estimates of the dissociation energies of He₂ excited states which cannot be measured spectroscopically because of the humps in all these states.     

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.     

A quantum chemical study of the hydrogen bonding in the CO2⋯HF and N2O⋯HF complexes

Summary Quantum chemical ab initio calculations have been performed for the complex CO₂HF and N₂OHF. The interaction energies were computed through fourth order MBPT and were corrected for basis set superposition errors. Extended polarized basis sets were used which are constructed to give accurate values for electric moments and polarizabilities. The complex NNOHF was found to be bent, while OCOHF is linear, in agreement with experiment. The MBPT calculations give evidence for a second linear isomeric structure FHNNO, a possibility which has also been suggested by recent experimental data. The computed binding energies are: 2.5 kcal/mol for OCOHF, 2.4 kcal/mol for NNOHF, and 3.0 kcal/mol for FHNNO. At the SCF level, the FHNNO complex is less stable than NNOHF, but correlation has a large effect on the geometry and energetics of the latter complex. The NNOHF complex seems to be a system where the positive intramolecular correlation correction prevails over the negative intermolecular component.     

Synthesis and adsorption investigations of zeolites MCM-22 and MCM-49 modified by alkali metal cations

Ion exchange was made on MCM-22 and MCM-49 zeolites with different Si/Al molar ratios, with Li⁺, Na⁺, K⁺, and Cs⁺ ions and the study of the influence of alkali metal cations on CO₂ adsorption properties was performed. The degree of ion-exchange decreased for larger cations (Cs⁺) apparently due to steric hindrances. The exchange with different cations led to a decrease in the surface area and the micropore volume. Our study shows that the adsorption capacity of the tested zeolites depends significantly on the nature and the concentration of the charge-compensating cations. The highest CO₂ adsorption capacity was obtained on the MWW zeolites with the lowest Si/Al molar ratio and the Li⁺ or K⁺ cations.     

The PVT properties of concentrated aqueous electrolytes. IV. Changes in the compressibilities of mixing the major sea salts at 25°C

The speed of sound of mixtures of the six possible combinations of the major sea salt ions (Na⁺, Mg²⁺, Cl^–, and SO ₄ ^2– ) have been determined at I=3.0 and at 25°C. The results have been used to determine the changes in the adiabatic compressibility of mixing K_m the major sea salts. The values of K_m have been fit to the equation K_m=y₂y₃I²[k₀+k₁(1-2y₃)] where y_i is the ionic strength fraction of solute i, k₀ and k₁ are parameters related to the interactions of like-charged ions. The Young cross-square rule is obeyed to within ±0.04×10^–6 cm³-kg^–1-bar^–1. A linear correlation was found between the compressibility k₀ and volume v₀ interaction parameters (10⁴k₀=–0.24+3.999 v₀, s=0.15) in agreement with out earlier findings. Estimates of the sound speeds for the cross square mixtures (NaCl+MgSO₄ and MgCl₂+Na₂SO₄) were made using the equations of Reilly and Wood. The estimated sound speeds were found to agree on the average with the measured values to ±0.36 m-sec^–1.     

Gaussian basis sets for CO2 molecule generated with the molecular improved generator coordinate Hartree–Fock method

The molecular improved generator coordinate Hartree–Fock (MIGCHF) method is used to generate increasing size atom-centered Gaussian basis sets for the CO₂ molecule. From these basis sets total HF energies and second-order correlation energies were calculated and compared with results obtained with other approaches. Considering our largest basis set, the HF energy is in error by 98 hartree and the second-order correlation energy corresponds to 95.6% of an estimate of the limiting value. The relevance of the present calculations is to show the accuracy that can be achieved in studies of small polyatomic molecules with the MIGCHF method.Acknowledgement We acknowledge the financial support of CNPq (Brazilian Agency). We employed computational facilities at Universidade Federal do Espírito Santo and Universidade Estadual Paulista (IQ Araraquara).     

The crystal structure determinations and refinements of K2S2O7, KNaS2O7 and Na2S2O7 from X-ray powder and single crystal diffraction data

The crystal structures of K₂S₂O₇, KNaS₂O₇ and Na₂S₂O₇ have been solved and/or refined from X-ray synchrotron powder diffraction data and conventional single-crystal data. K₂S₂O₇: From powder diffraction data, monoclinic C2/c, Z=4, a=12.3653(2), b=7.3122(1), , β=93.0792(7)°, R_Bragg=0.096. KNaS₂O₇: From powder diffraction data; triclinic , Z=2, a=5.90476(9), b=7.2008(1), , α=101.7074(9), β=90.6960(7), γ=94.2403(9)°, R_Bragg=0.075. Na₂S₂O₇: From single-crystal data; triclinic , Z=2, a=6.7702(9), b=6.7975(10), , α=116.779(2), β=96.089(3), γ=84.000(3)°, R_F=0.033. The disulphate anions are essentially eclipsed. All three structures can be described as dichromate-like, where the alkali cations coordinate oxygens of the isolated disulphate groups in three-dimensional networks. The K-O and Na-O coordinations were determined from electron density topology and coordination geometry. The three structures have a cation-disulphate chain in common. In K₂S₂O₇ and Na₂S₂O₇ the neighbouring chains are antiparallel, while in KNaS₂O₇ the chains are parallel. The differences between the K₂S₂O₇ and Na₂S₂O₇ structures, with double-, respectively single-sided chain connections and straight, respectively, corrugated structural layers can be understood in terms of the differences in size and coordinating ability of the cations.     

The synthetic microporous tellurites Na2[Me 2(TeO3)3]·3H2O (Me=Zn,Co): Crystal structure,De- and rehydration,and ion exchange properties

Summary The crystal structure investigations of hydrothermally synthesized Na₂[Zn₂(TeO₃)₃]·3H₂O (NZT) and Na₂[Co₂(TeO₃)₃]·3H₂O (NCT) using single-crystal X-ray diffraction methods revealed a microporous framework structure of hexagonal symmetry with tubular channels running parallel to the c-axis (zemannite type). The statistically occupied sites of the Na⁺ ions and H₂O molecules within the channels as well as the channel dimensions indicate a possible zeolitic behaviour of the compounds. Thermoanalytical investigations ofNZT show an irreversible breakdown of the framework already atT=533 K caused by complete dehydration. A reversible rehydration was solely observed for partially dehydratedNZT (T493 K); a remarkable ion exchange rate from alkali-chloride solutions was observed only for Li⁺. Both the rehydration and the ion exchange properties are characterized by relatively long reaction times. The relatively poor zeolitic properties compared to typical zeolitic compounds could be related to the stereochemical activity of the lone-pair electrons of the Te⁴⁺ atoms which claim a certain volume within the channels and constrict the effective channel dimension to a free diameter of approximately 2.5 Å.

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Die synthetischen zeolithartigen Tellurite Na₂[Me ₂(TeO₃)₃]·3H₂O (Me=Zn, Co): Kristallstruktur, De- und Rehydratisierung und Ionenaustauschvermögen

Zusammenfassung Die Kristallstrukturuntersuchungen mittels Röntgen-Einkristalldiffraktionsmethoden von hydrothermal dargestelltem Na₂[Zn₂(TeO₃)₃]·3H₂O (NZT) und Na₂[Co₂(TeO₃)₃]·3H₂O (NCT) ergaben eine zeolithartige Gerüststruktur hexagonaler Symmetrie mit parallel zur c-Achse angeordneten röhrenartigen Kanälen (Zemannittyp). Die statistisch besetzten Punktlagen der Na⁺-Atome und H₂O Moleküle innerhalb der Kanäle wie auch die Kanaldimensionen selbst weisen auf mögliche zeolithische Eigenschaften der Verbindungen hin. Thermoanalytische Untersuchungen anNZT ergaben einen irreversiblen Zusammenbruch der Gerüststruktur bereits beiT=533 K durch vollständige Entwässerung. Eine reversible Rehydratisierung wurde nur für partiell entwässertesNZT (T493 K) beobachtet; ein nennenswerter Ionenaustausch aus Alkalichlorid-Lösungen konnte nur für Li⁺ bestimmt werden. Sowohl die Rehydratisierung als auch das Ionenaustauschvermögen sind durch relativ lange Reaktionszeiten charakterisiert. Die im Vergleich zu typisch zeolithischen Verbindungen relativ schlechten zeolithischen Eigenschaften konnten auf die stereochemische Aktivität der einsamen Elektronenpaare der Te⁴⁺ Atome zurüchgefürt werden, die einen gewissen Platz innerhalb der Kanäle beanspruchen und den effektiven freien Durchmesser der Kanäle auf etwa 2.5 Å einengen.

     

Structure and magnetism of NaRu2O4 and Na2.7Ru4O9

The structures of NaRu₂O₄ and Na_2.7Ru₄O₉ are refined using neutron diffraction. NaRu₂O₄ is a stoichiometric compound consisting of double chains of edge sharing RuO₆ octahedra. Na_2.7Ru₄O₉ is a non-stoichiometric compound with partial occupancy of the Na sublattice. The structure is a mixture of single, double and triple chains of edge-shared RuO₆ octahedra. NaRu₂O₄ displays temperature independent paramagnetism with . Na_2.7Ru₄O₉ is paramagnetic, χ₀= with and a Curie constant of 0.0119 emu/mol Oe K. Specific heat measurements reveal a small upturn at low temperatures, similar to the upturn observed in La₄Ru₆O₁₉. The electronic contribution to the specific heat (γ) for Na_2.7Ru₄O₉ was determined to be15 mJ/mole_Ru K².     

Ion-exchange chromatography using vanadyl and vandate salts as mobile phases with indirect detection

Summary Vanadyl sulfate, VOSO₄, was characterized as the mobile phase for the ion exchange separation of Li⁺, Na⁺, NH ₄ ⁺ , and K⁺ using indirect photometric detection at 254 nm. Detection limits ranged from 0.2 ppm for Li⁺ to 1 ppm for K⁺. Indirect electrochemical detection of these separated cations by reduction of VO (II) to V³⁺ was compared to spectrophotometric detection. The potential of the vanadate species, HVO ₄ ^2– , for the separation of F^–, Cl^–, and SO ₄ ^2– , with indirect photometric detection was also demonstrated.     

Thermodynamic properties of aqueous mixtures of LiCl and Li2SO4 at different temperatures

Emf measurements were made on the cell without liquid junction: Li?ISE LiCl(m₁), Li₂SO₄(m₂) Ag/AgCl. The performances of the electrode pairs constructed in our laboratory were tested and exhibited near-Nernstian behavior. The mean activity coefficients of LiCl for the system Li⁺?Cl^??SO ₄ ^2? ?H₂O have been investigated by the emf values at temperatures of 0, 15, 35°C and constant total ionic strengths of 0.05, 0.1, 0.5, 1.0, 2.0, 3.0 and 5.0 mol·kg^?1. The activity coefficients decrease with increasing temperature and the ionic strength fraction of Li₂SO₄ in the mixtures. The thermodynamic properties are interpreted by use of Harned's empirical equations and Pitzer's ion interaction approach including the contribution of higher order electrostatic terms. The experimental results obey Harned's rule and are described by using Pitzer equations satisfactorily. The activity coefficients of Li₂SO₄, the osmotic coefficients and the excess free energies of mixing for the system in the experimental temperature range were reported.     

Ab initio potential energy surface and excited vibrational states for the electronic ground state of Li2H

A 285-point multi-reference configuration-interaction involving single and double excitations (MRS-DCI) potential energy surface for the electronic ground state of Li₂H is determined by using 6-311G (2df, 2pd) basis set. A Simons-Parr-Finlan polynomial expansion is used to fit the discrete surface with a X² of 4.64 × 10^-6. The equilibrium geometry occurs at R_e =0.172 nm and <LiHLi =94.10. The dissociation energy for reaction Li₂H(²A)⇑ Li₂(¹⌆_g)+H(²S) is 243.910 kJ/mol. and that for reaction Li₂H(²A)⇑HLi(¹be)+Li(²S) is 106.445 kJ/mol. The inversion barrier height is 50.388 kJ/mol. The vibrational energy levels are calculated using the discrete variable representation (DVR) method. Project supported by the National Natural Science Foundation of China (grant No. 29673029) and by the Special Doctoral Research Foundation of the State Education Commission of China.