Calculations predict rapid tunneling by carbon from the vibrational ground state in the ring opening of cyclopropylcarbinyl radical at cryogenic temperatures

B3LYP/6-31G(d) calculations have been performed on the ring opening of cyclopropylcarbinyl radical 1 to 3-buten-1-yl radical 2. The dynamics of the reaction have been computed with canonical variational transition state theory (CVT), both with and without inclusion of small-curvature tunneling (SCT). The CVT + SCT calculations predict that 1 should undergo rapid and temperature-independent ring opening to 2 at cryogenic temperatures, by tunneling from the lowest vibrational level of 1.     

Measurement of the electric quadrupole moment of N2O

Measurements of the temperature dependence of the Buckingham effect (electric-field-gradient-induced birefringence, EFGIB) for gaseous nitrous oxide are presented. Measurements span the temperature range 298.5-473.9 K, which allows for separation of the temperature-independent hyperpolarizability term from the temperature-dependent quadrupole term, yielding a quadrupole moment of Θ = (-11.03 ± 0.41) × 10(-40) C m(2), and a hyperpolarizability term of b = (-0.638 ± 0.063) × 10(-60) C(3) m(4) J(-2). For dipolar molecules, the quadrupole moment is origin dependent, and the value reported here is referred to an origin called the effective quadrupole center (EQC). Comparison of this value with the center of mass (CM) quadrupole moment obtained from MBER experiments yields information about the dynamic dipole-quadrupole and dipole-magnetic dipole polarizabilities. The temperature-independent term, previously assumed to contribute negligibly to the EFGIB, is found to contribute some (5.2 ± 0.6)% to the effect at room temperature and clearly needs to be accounted for if the quadrupole moment is to be definitively established.     

Thermodynamique des complexes metalliques ternaires des amino-acides. II. Etude des systemes Ni(II)—glycine—valine Ni(II)—alanine—valine

Standard enthalpies and entropies of formation for binary and ternary Ni(II) complexes with pairs of the following amino acids as ligands: glycine, DL--alanine and DL-valine, were calorimetrically determined at 25°C in aqueous solution using 1 M ionic strength (NaClO₄).

The results are discussed according to every possible pathway for mixed ligand complex formation and also using the classical statistical methods. Temperature-dependent and temperature-independent components of the thermodynamic data are calculated. In all cases with these ligands involving identical coordination sites, the temperature-independent component of the enthalpy change is closely constant for binary as well as for ternary complexes. All the data show that the stabilization of mixed ligand complexes with respect to the parent binary complexes arises from the entropy term and is maximum for the Ni(II)—glycine—valine system.     

Measurement of the electric quadrupole moment of CO

Measurements of the temperature dependence of the Buckingham effect (electric-field-gradient-induced birefringence, EFGIB) for gaseous carbon monoxide are presented. The measurements span the temperature range 301.2-473.9 K, which allows for separation of the temperature-independent hyperpolarizability contribution from the temperature-dependent quadrupole contribution. It is demonstrated that in the case of carbon monoxide, quantization of the rotational motion of the molecules needs to be considered, the analysis yielding a quadrupole moment of Θ = (-8.77 ± 0.31) × 10(-40) C m(2) and a hyperpolarizability term of b' = (-0.1243 ± 0.0078) × 10(-60) C(3) m(4) J(-2). For dipolar molecules, the quadrupole moment is origin dependent, and the value reported here is referred to an origin called the effective quadrupole center. Comparison of this value with the center-of-mass quadrupole moment obtained from other experiments yields information about the dynamic dipole-quadrupole and dipole-magnetic dipole polarizabilities. The temperature-independent term, which contributes (7.0 ± 0.6)% to the EFGIB at room temperature, is by no means insignificant, and must necessarily be accounted for if the quadrupole moment is to be definitively established. The measured Θ and b' are compared with the best available ab initio calculated values.     

Vapor-liquid equilibria for alcohol/hydrocarbon systems using the CPA Equation of state

The recently developed Cubic-Plus-Association Equation of State (CPA EoS) is extended in this study to binary systems containing one associating compound (alcohol) and an inert one (hydrocarbon). CPA combines the Soave-Redlich-Kwong (SRK) equation of state for the physical part with an association term based on perturbation theory. The classical van der Waals one-fluid mixing rules are used for the attractive and co-volume parameters, and b, while the extension of the association term to mixtures is rigorous and does not require any mixing rules. Excellent correlation of Vapor-Liquid Equilibria (VLE) is obtained using a small value for the interaction parameter (k_ij) in the attractive term of the physical part of the equation of state even when it is temperature-independent. CPA yileds much better results than SRK and its performance is similar to that of other association models, like the Anderko EoS, and the more complex SAFT and Simplified SAFT EoS.     

Li17Ag3Sn6: a polar intermetallic pi-system with carbonate-like [AgSn3]11- anions and trefoil aromatic [Ag2Sn3]6- layers

A new lithium silver stannide, Li17Ag3Sn6, was synthesized from high-temperature reactions of the pure elements in tantalum containers. Its crystal structure, in the space group, P31m, with a = 8.063(3) A, c = 8.509(4) A, Z = 1, features two distinct AgSn-based anionic layers. Defect graphitic layers of Ag2Sn3, with ordered vacancies at one-third of the Ag sites, are alternately stacked with Kagome-like nets of isolated trigonal planar AgSn3 units. Double layers of Li ions are sandwiched between the stacked AgSn-based layers. Theoretical calculations show unusual pi-interactions within both anionic layers, with the trigonal planar [AgSn3]11- units being isoelectronic with CO(3)2-. In addition, the chemical bonding of the layered [Ag2Sn3]6- pi-network features incompletely filled lone-pair Sn states involved in in-plane trefoil aromatic interactions. Transport and magnetic susceptibility measurements on Li17Ag3Sn6 indicate excellent metallic behavior and temperature-independent paramagnetism consistent with results from band structure calculations. The "trefoil" aromaticity, previously postulated for aromatic molecular systems, is finally observed, albeit in a polar intermetallic solid-state structure that lies at the border between metals and nonmetals.     

Dielectric anisotropy of a homochiral rare-earth metal complex

A homochiral rare-earth metal Tb complex that exhibited a very large dielectric anisotropic property with a temperature-independent feature is obtained. Our findings on high-dielectric anisotropy will provide a new impetus in this field of materials science.     

Molecular-dynamics analysis of the diffusion of molecular hydrogen in all-silica sodalite

In order to investigate the technical feasibility of crystalline porous silicates as hydrogen storage materials, the self-diffusion of molecular hydrogen in all-silica sodalite is modeled using large-scale classical molecular-dynamics simulations employing full lattice flexibility. In the temperature range of 700-1200 K, the diffusion coefficient is found to range from 1.610(-10) to 1.810(-9) m(2)/s. The energy barrier for hydrogen diffusion is determined from the simulations allowing the application of transition state theory, which, together with the finding that the pre-exponential factor in the Arrhenius-type equation for the hopping rate is temperature-independent, enables extrapolation of our results to lower temperatures. Estimates based on mass penetration theory calculations indicate a promising hydrogen uptake rate at 573 K.     

Relativistic four-component calculations of Buckingham birefringence using London atomic orbitals

We present the first relativistic study of the electric-field-gradient induced birefringence (Buckingham birefringence), with application to the series of molecules CX₂ (X?=?O, S, Se, Te). A recently developed atomic-orbital-driven scheme for the calculation of time-dependent molecular properties using one-, two- and four-component relativistic wave functions (Bast et?al. in Chem Phys 356:177, 2009) is extended to first-order frequency-dependent magnetic-field perturbations, using London atomic orbitals to ensure gauge-origin independent results and to improve basis-set convergence. Calculations are presented at the Hartree?CFock and Kohn?CSham levels of theory and results for CO₂ and CS₂ are compared with previous high-level coupled-cluster calculations. Except for the heaviest member of the series, relativistic effects are small??in particular for the temperature-independent contribution to the birefringence. By contrast, the effects of electron correlation are significant. However, the reliability of standard exchange-correlation functionals in describing Buckingham birefringence remains unclear based on the comparison with high-level coupled-cluster singles-and-doubles calculations.     

Modelling of high-pressure phase equilibria using the Sako–Wu–Prausnitz equation of state: II. Vapour–liquid equilibria and liquid–liquid equilibria in polyolefin systems

Phase equilibria in binary and ternary polyolefin systems are calculated using the cubic equation of state proposed by Sako–Wu–Prausnitz (SWP). Calculations were done for high-pressure phase equilibria in ethylene/polyethylene (LDPE) systems and for liquid–liquid equilibria (LLE) in systems containing either high-density polyethylene or poly(ethylene-co-propylene). The calculations for the copolymer/solvent systems are compared with those using the SAFT EOS. The two equations of state can describe UCST, LCST as well as U-LCST behaviour with similar accuracy. Whereas, the binary interaction parameter is temperature-independent for SAFT, it is found to be a function of temperature for the SWP model. Moreover, the influence of an inert gas on the LCST of the polyethylene/hexane system is investigated using the SWP EOS. The polydispersity of the different polyethylenes is considered in the phase equilibrium calculations using pseudocomponents chosen by the moments of the experimental molecular weight distributions.     

Vibrational spectrum of BiH3: Six-dimensional variational calculations on high-level ab initio potential energy surfaces

We report a theoretical study of the ground electronic state of BiH₃. The potential energy surface (PES) is obtained from coupled cluster CCSD(T) calculations with a large basis set (289 contracted Gaussian functions). The previously available quartic force field (P4) is extended by adding the dominant quintic and sextic stretching terms to yield improved potential functions in symmetry coordinates (P6) and Morse-type coordinates (M4). Second-order rovibrational perturbation calculations on the P4-PES and full variational calculations on the P6-PES and M4-PES yield almost identical vibrational term values which is rationalized by considering the local mode behavior of BiH₃ and the Morse-type character of the M4-PES. The remaining deviations between the computed and observed vibrational term values must thus be caused by imperfections in the CCSD(T) surface. A refinement of this ab initio surface by a restrained fit to experimental data allows an essentially perfect reproduction of the observed vibrational term values. Variational calculations on this refined surface provide predictions for several overtone and combination bands that have not yet been observed. Dedicated to Hermann Stoll on the occasion of his 60th birthday     

Hybrid organic-inorganic conductor with a magnetic chain anion: kappa-BETS2[Fe(III)(C2O4)Cl2] [BETS = bis(ethylenedithio)tetraselenafulvalene

The synthesis, crystal structure, and electrical, optical, and magnetic properties of kappa-BETS2[Fe(III)(C2O4)Cl2], where BETS is bis(ethylenedithio)tetraselenafulvalene, are reported. The black plate crystals consist of parallel donor layers, two per unit cell, displaying a kappa-type packing of BETS(0.5+) within the bc plane and anionic magnetic chains, [Fe(C2O4)Cl2-]n, running along the c axis. It displays metallic behavior down to 4.2 K, and analysis of the optical reflectivity data gives unscreened plasma energies of 0.69 eV (E parallel c) and 0.40 eV (E perpendicular c). The optical anisotropy is larger than that seen for other kappa phases and is described well by transfer integrals obtained from extended Hückel calculations. However, the transfer integrals need to be scaled down uniformly by a factor of 1.21 to reproduce the absolute experimental plasma frequencies. The band structure consists of a one-dimensional (1D) band and a hole pocket, characteristics of kappa phases. The magnetic properties were modeled by the sum of a 1D antiferromagnetic chain contribution from the d spins of Fe3+, a temperature-independent paramagnetic contribution, and a Curie impurity term. At 4.5 K, there is a signature of long-range magnetic ordering to a canted-antiferromagnetic state in the zero-field-cooled-field-cooled magnetizations, and at 2 K, a small hysteresis loop is observed.     

Time-Resolved Diffusion NMR Measurements for Transient Processes

A general procedure for measurement of time-resolved diffusion coefficients of molecular species by NMR is described, including the use of methanol for fast temperature-independent gradient calibration.     

Atomic Charges in the Quadrupole Solvation Energy Calculations

A procedure is described and tested for the use of atomic charges instead of bond dipole moments in the calculations, based on the reaction field theory, of quadrupole term of the solvation energy.     

Magnetic circular dichroism study of directly fused porphyrins.

The magnetic circular dichroism (MCD) spectra of doubly and triply linked fused bisporphyrins (2MD and 2MT, M = Ni, Zn, Cu, Pd, and H2) and triply linked higher oligomers (3ZnT and 4ZnT) have been measured, and their Q-bands assigned based on the results of INDO/s calculations. In contrast to the Faraday A term observed for the Q(0,0) band of Ni(II) tetraphenylporphyrin, a single positive Faraday B term was observed for the lowest energy transition of the fused systems. The calculations indicated that the molecular orbitals (MOs) of the directly fused porphyrins consist of linear combinations of the constituent monomeric MOs, and that the effect of lowering the symmetry is always larger on the lowest unoccupied molecular orbital (LUMO) than on the highest occupied molecular orbital (HOMO). On the basis of Michl's perimeter model, these features can be correlated with the observed positive MCD signs in the near infrared region. A weak absorption band at 600-700 nm for the fused dimers can be assigned to a short-axis polarized Q transition.     

Effective central potentials for molecular fluids

A recent suggestion by Lebowitz and Percus that the median intermolecular potential may serve as a simple temperature-independent effective central potential is tested against virial inversion data for the site-site Lennard-Jones potential obtained by Smith and Tindell. Excellent agreement is found even when the anisotropy in the potential is large. Second virial coefficients computed from the effective potential reproduce the true values to a high degree of accuracy.     

Calcium tetraboride-does it exist? Synthesis and properties of a carbon-doped calcium tetraboride that is isotypic with the known rare earth tetraborides

Crystalline samples of carbon-doped CaB4 were synthesized by solid-state reactions in sealed niobium ampules from the elements Ca, B, and C. The structure was determined by single-crystal X-ray diffraction (P4/mbm, Z = 4, a = 7.0989(7) A, c = 4.1353(5) A, R1 = 0.026, and wR2 = 0.058) revealing an atom arrangement containing a three-dimensional boron network built up from B6 octahedra and B2 dumbbells which is well-known from the structures of rare earth tetraborides. Crystals of CaB(4-x)Cx are black with a metallic luster and behave stable against mineral acids. Band structure calculations indicate that CaB4 is a stable semiconducting compound with a narrow band gap and that carbon should not necessarily be required for the stability of this compound. The presence of carbon in the crystalline samples of CaB(4-x)Cx was indicated by electron energy loss spectroscopy, but the carbon content in the samples was estimated to be less than 5% according to inductively coupled plasma-atomic emission spectrometry measurements. The distribution of boron and carbon atoms in the structure was investigated by means of 11B and 13C solid-state magic angle spinning NMR. Measurements of the magnetic susceptibility indicate a temperature-independent paramagnetism down to 20 K.     

High-pressure phase equilibria in the carbon dioxide + pyrrole system

Liquid–vapor (LV) and liquid–liquid (LL) phase equilibria in the carbon dioxide + pyrrole system were measured at temperatures between 313 K and 333 K, and pressures between 8.4 MPa and 15.1 MPa. The data were used to predict the overall phase behavior of the system using the Patel–Teja equation of state and the Mathias–Klotz–Prausnitz mixing rules with two temperature-independent parameters. The calculations suggest that the carbon dioxide + pyrrole system may exhibit type IV phase behavior according to the classification of Scott and van Konynenburg.     

Calculating energy levels of isomerizing tetra-atomic molecules. II. The vibrational states of acetylene and vinylidene

A general, full-dimensional computational method for the accurate calculation of rotationally and vibrationally excited states of tetra-atomic molecules is further developed. The resulting computer program may be run in serial and parallel modes and is particularly appropriate for molecules executing wide-amplitude motions and isomerizations. An application to the isomerizing acetylene/vinylidene system is presented. Large-scale calculations using a coordinate system based on orthogonal satellite vectors have been performed in six dimensions and vibrational term values and wave functions for acetylene and vinylidene states up to approximately 23 000 cm(-1) above the potential minimum have been determined. This has permitted the characterization of acetylene and vinylidene states at and above the isomerization barrier. These calculations employ more extensive vibrational basis sets and hence consider a much higher density of states than in any variational calculations reported hitherto for this system. Comparison of the calculated density of states with that determined empirically suggests that our calculations are the most realistic achieved for this system to date. Indeed more states have been converged than in any previous study of this system. Calculations on lower lying excited states of acetylene based on HC-CH diatom-diatom coordinates give nearly identical results to those based on orthogonal satellite vectors. Comparisons are also made with calculations based on HH-CC diatom-diatom coordinates.     

Equation of state for square-well chain molecules with variable range II. Extension to mixtures

An equation of state (EOS) developed in our previous work for square-well chain molecules with variable range is further extended to the mixtures of non-associating fluids. The volumetric properties of binary mixtures for small molecules as well as polymer blends can well be predicted without using adjustable parameter. With one temperature-independent binary interaction parameter, satisfactory correlations for experimental vapor–liquid equilibria (VLE) data of binary normal fluid mixtures at low and elevated pressures are obtained. In addition, VLE of n-alkane mixtures and nitrogen + n-alkane mixtures at high pressures are well predicted using this EOS. The phase behavior calculations on polymer mixture solutions are also investigated using one-fluid mixing rule. The equilibrium pressure and solubility of gas in polymer are evaluated with a single adjustable parameter and good results are obtained. The calculated results for gas + polymer systems are compared with those from other equations of state.