Crystal structure,ionic conductivity and dielectric relaxation studies in the (C5H10N)2BiBr5 compound

The synthesis and crystal structure of the bis (3-dimethylammonium-1-propyne) pentabromobismuthate(III) salt are given in the present paper. After an X-ray investigation, it has been shown that the title compound crystallizes at 298 K in a centrosymmetric monoclinic system, in the space group C₂/c with the following lattice parameters a=12.9034(3) Å, b=19.4505(6) Å, c=8.5188(2) Å, β=102.449(2). Not only were the impedance spectroscopy measurements of (C₅H₁₀N)₂BiBr₅ carried out from 209 Hz to 5 MHz over the temperature range of 318 K–373 K, but also its ac conductivity evaluated. Besides, the dielectric relaxation was examined using the modulus formalism. Actually, the near values of activation energies obtained from the impedance and modulus spectra confirms that the transport is of an ion hopping mechanism, dominated by the motion of the H⁺ ions in the structure of the investigated material.     

Crystal structure and ferromagnetism of (n-C3H7)4N[CoFe(dto)3] (dto=C2O2S2)

Recently, we have discovered a new type of first order phase transition around 120 K for (n-C₃H₇)₄N[Fe^IIFe^III(dto)₃] (dto=C₂O₂S₂), where the charge transfer transition between Fe^II and Fe^III occurs reversibly. In order to elucidate the origin of this peculiar first order phase transition. Detailed information about the crystal structure is indispensable. We have synthesized the single crystal of (n-C₃H₇)₄N[Co^IIFe^III(dto)₃] whose crystal structure is isomorphous to that of (n-C₃H₇)₄N[Fe^IIFe^III(dto)₃], and determined its detailed crystal structure. Crystal data: space group P6₃, a=b=10.044(2) Å, c=15.960(6) Å, α=β=90°, γ=120°, Z=2 (C₁₈H₂₈NS₆O₆FeCo). In this complex, we found a ferromagnetic transition at T_c=3.5 K. Moreover, on the basis of the crystal data of (n-C₃H₇)₄N[Co^IIFe^III(dto)₃], we determined the crystal structure of (n-C₃H₇)₄N[Fe^IIFe^III(dto)₃] by simulation of powder X-ray diffraction results.     

Rotational spectra of gauche perfluoro-n-butane, C4F10; perfluoro-iso-butane, (CF3)3CF; and tris(trifluoromethyl)methane, (CF3)3CH

The microwave spectra of the gauche conformer of perfluoro-n-butane, n-C₄F₁₀, of perfluoro-iso-butane, (CF₃)₃CF, and of tris(trifluoromethyl)methane, (CF₃)₃CH, have been observed and assigned. The rotational and centrifugal distortion constants for gauche n-C₄F₁₀ are: A = 1058.11750(7) MHz, B = 617.6832(1) MHz, C = 552.18794(1) MHz, Δ_J = 0.0257(5) kHz, δ_J = 0.0052(3) kHz. A C-C-C-C dihedral angle, ω, of ∼55° has been determined. These values agree well with those obtained from a coupled cluster (CCSD/cc-PVTZ) calculation. The rotational and centrifugal distortion constants for iso-C₄F₁₀ and iso-C₄HF₉ are: B_o = 816.4519(4) MHz, D_J = 0.023(2) kHz, and B_o = 903.6985(25) MHz, D_J = 0.043(4) kHz, respectively. The dipole moment of iso-C₄F₁₀ and iso-C₄HF₉ have been measured and found to be 0.0338(8) and 1.69(9) D, respectively.     

Rotational spectra of mono-substituted asymmetric C6H6-H2O dimers

This paper reports the assignment of the rotational spectra of the m = 0 and 1 states of ¹³CC₅H₆-H₂O and C₆H₅D-H₂O dimers. The m = 1 progression was not identified or assigned for both ¹³CC₅H₆-H₂O and C₆H₅D-H₂O in the earlier work, though for the symmetric isotopomers (C₆H₆-H₂O/D₂O/H₂¹⁸O), they were identified [H.S. Gutowsky, T. Emilsson, E. Arunan, J. Chem. Phys. 99 (1993) 4883]. The m = 1 transitions for ¹³CC₅H₆-H₂O and C₆H₅D-H₂O were split into two, unlike that of the parent C₆H₆-H₂O isotopomer. The splitting varied, somewhat randomly, with quantum numbers J and K. The m = 0 lines of ¹³CC₅H₆-H₂O had significant overlap with the m = 1 lines of the parent isotopomer, clouding proper assignment, and leading to an rms deviation of about 200 kHz in the earlier work. The general semi-rigid molecular Hamiltonian coupled to an internal rotor, described recently by Duan et al. [Y.B. Duan, H.M. Zhang, K. Takagi, J. Chem. Phys. 104 (1996) 3914], is used in this work to assign both m = 0 and 1 states of ¹³CC₅H₆-H₂O and C₆H₅D-H₂O dimers. Consequently, the m = 0 fits for ¹³CC₅H₆-H₂O/D₂O have an rms deviation of only 4/7 kHz, comparable to experimental uncertainties. The fits for m = 1 transitions for ¹³CC₅H₆-H₂O and C₆H₅D-H₂O dimers have an rms deviation of about 200 kHz. However, it is of the same order of magnitude as that of the m = 1 state of the parent C₆H₆-H₂O dimer. The A rotational constants determined from the m = 0 fits for both ¹³CC₅H₆-H₂O and ¹³CC₅H₆-D₂O isotopomers are identical and very close to the C rotational constant for ¹³CC₅H₆. This provides a direct experimental determination for the C rotational constant of ¹³CC₅H₆, which has a negligible dipole moment.     

Synthesis and characterization of a new monophosphate [2,5-(CH3)2C6H3NH3]H2PO4

Chemical preparation, calorimetric studies, crystal structure and spectroscopic investigations are given for a new noncentrosymmetric organic cation monophosphate [2,5-(CH₃)₂C₆H₃NH₃]H₂PO₄. This compound is orthorhombic P2₁2₁2₁ with the following unit-cell parameters: a=5.872(4), b=20.984(3), c=8.465(1) Å, Z=4, V=1043.0(5) Å³ and D_x=1.396 g cm⁻³. Crystal structure has been solved and refined to R=0.048 using 2526 independent reflections. Structure can be described as an inorganic layer parallel to (a,b) planes between which organic groups [2,5-(CH₃)₂C₆H₃NH₃]⁺ are located. Multiple hydrogen bonds connecting the different entities of compound thrust upon three-dimensional network a noncentrosymmetric configuration.     

Temperature and pressure effects on formation and decomposition of phenylvinylperoxy radicals in the C6H5C2H2 + O2 reaction

The effects of temperature and pressure on the formation and decomposition of C₆H₅C₂H₂O₂ in the C₆H₅C₂H₂ + O₂ reaction have been investigated at temperatures from 298 to 378 K by directly monitoring the C₆H₅C₂H₂O₂ radical in the visible region by cavity ringdown spectrometry (CRDS). The rate constant for the C₆H₅C₂H₂ + O₂ association and that for fragmentation of C₆H₅C₂H₂O₂ were found to be k₁ (C₆H₅C₂H₂ + O₂ → C₆H₅C₂H₂O₂) = (3.20 ± 1.19) × 10¹¹ exp(+760/T) cm³ mol⁻¹ s⁻¹ and k₂ (C₆H₅C₂H₂ O₂ → C₆H₅CHO + HCO) = (1.68 ± 0.13) × 10⁴ s⁻¹, respectively. Additional kinetic measurements by pulsed laser photolysis/mass spectrometry show that C₆H₅CHO was produced in the C₆H₅C₂H₂ + O₂ reaction as predicted and the formation of C₆H₅CHO from the decomposition of C₆H₅C₂H₂O₂ is temperature-independent, consistent with the CRDS experimental data.     

High-precision frequency measurements of the ν1 + ν3 combination band of C2H2 in the 1.5 μm region

A pair of 1.5 μm semiconductor laser frequency standards have been developed for optical telecommunications use, stabilised to transitions of ¹²C₂H₂ and ¹³C₂H₂, using cavity-enhanced Doppler-free saturation absorption spectroscopy. The absolute frequencies of 41 lines of the ν₁ + ν₃ band of ¹²C₂H₂, covering the spectral region 1520-1545 nm, have been measured by use of a passive optical frequency comb generator, referenced to ¹³C₂H₂ transitions of known frequency. The mean experimental uncertainties (coverage factor k = 1) of the frequency values are 3.0 kHz (type A) and 10 kHz (type B). Improved values of the band origin ν₀, rotational constants B′ and B″, and centrifugal distortion coefficients D′, D″, H′, and H″ are presented.     

Infrared crystal spectra of C2H4, C2D4, and as-C2H2D2 and the general harmonic force field of ethylene

Carbon-13 frequency shifts for C₂H₄, C₂D₄, and as-C₂H₂D₂ have been measured in isotopic solid solutions in crystalline films at 60 K. All but two of the shifts (for as-C₂H₂D₂) are compatible with recently determined ζ data for C₂H₄, with ¹³C frequency shifts for C₂H₄ and C₂D₄ in the gas phase and with conventional frequency data. Together, these data completely determine with precision all 18 parameters of the GHFF for ethylene, the previous ambiguity in choice between two sets of A_g species force constants being removed. The force field reproduces closely the observed centrifugal distortion constants for C₂H₄, a ζ constant observed for trans-C₂H₂D₂, and the inertia defects for C₂H₄, C₂D₄, and as-C₂H₂D₂. Vibration and rotation constants for all isotopically deuterated ethylenes are calculated.Possible explanations for the two anomalous crystal shifts in as-C₂H₂D₂ involve the effects of the crystal field, and failure of the use of Dennison's rule for making anharmonic corrections to the shifts. The former explanation is preferred as a result of thorough analysis of the anharmonicity constants for as-C₂H₂D₂ determined from many overtone and combination bands in the gas and crystal spectra.     

Synthesis and characterization of Co7(OH)12(C2H4S2O6)(H2O)2—a single crystal structural study of a ferrimagnetic layered cobalt hydroxide

A novel layered hydrotalcite-like material, Co₇(H₂O)₂(OH)₁₂(C₂H₄S₂O₆), has been prepared hydrothermally and the structure determined using single crystal X-ray diffraction (a=6.2752(19) Å, b=8.361(3) Å, c=9.642(3) Å, α=96.613(5)°, β=98.230(5)°, γ=100.673(5)°, R1=0.0551). The structure consists of brucite-like sheets where 1/6 of the octahedral sites are replaced by two tetrahedrally coordinated Co(II) above and below the plane of the layer. Ethanedisulfonate anions occupy the space between layers and provide charge balance for the positively charged layers. The compound is ferrimagnetic, with a Curie temperature of 33 K, Curie-Weiss θ of −31 K, and a coercive field of 881 Oe at 5 K.     

Theoretical study on the kinetics for OH reactions with CH3OH and C2H5OH

Kinetics and mechanisms for reactions of OH with methanol and ethanol have been investigated at the CCSD(T)/6-311 + G(3df, 2p)//MP2/6-311 + G(3df, 2p) level of theory. The total and individual rate constants, and product branching ratios for the reactions have been computed in the temperature range 200-3000 K with variational transition state theory by including the effects of multiple reflections above the wells of their pre-reaction complexes, quantum-mechanical tunneling and hindered internal rotations. The predicted results can be represented by the expressions k₁ = 4.65 × 10⁻²⁰ × T^2.68 exp(414/T) and k₂ = 9.11 × 10⁻²⁰ × T^2.58 exp(748/T) cm³ molecule⁻¹ s⁻¹ for the CH₃OH and C₂H₅OH reactions, respectively. These results are in reasonable agreements with available experimental data except that of OH + C₂H₅OH in the high temperature range. The former reaction produces 96-89% of the H₂O + CH₂OH products, whereas the latter process produces 98-70% of H₂O + CH₃CHOH and 2-21% of the H₂O + CH₂CH₂OH products in the temperature range computed (200-3000 K).     

On the formation and decomposition of C7H8

The kinetics of reactions on the C₇H₈ surface were studied with state-of-the-art ab initio transition state theory (TST) and master equation methodologies. A priori predictions of the capture rate for C₆H₅ + CH₃ and for C₇H₇ + H are obtained from direct variable reaction coordinate TST simulations. These simulations employ small basis set CASPT2 interaction energies coupled with one-dimensional reaction path corrections based on higher level simulations for related reactions. For the C₇H₇ + H reaction, predictions are obtained for both the total rate and for the branching between toluene, o-isotoluene and p-isotoluene. A mapping of the low energy pathways for isomerization from these three C₇H₈ isomers identifies a number of processes with barriers at or below the dissociation threshold. Nevertheless, at combustion temperatures the dissociation rates are predicted to exceed the isomerization rates, and it is reasonable to treat the kinetics of each isomer as a simple single well association/dissociation equilibrium. Master equation simulations yield predictions for the temperature and pressure dependence of each of the recombination and dissociation processes, as well as for the C₇H₇ + H → C₆H₅ + CH₃ bimolecular reaction. These simulations implement collisional energy transfer probabilities based on the work of Luther and co-workers. The theoretical predictions are found to be in satisfactory agreement with the available experimental data for the photodissociation of toluene, the temperature and pressure dependent dissociation of toluene, and the reaction of benzyl radical with H. For the C₆H₅ + CH₃ recombination, the theoretical predictions exceed the experimental measurements of Lin and coworkers by a factor of 2 or more for all temperatures.     

Accurate rest frequencies of submillimeter-wave lines of H2D and D2H

We re-examined the submillimeter-wave transition frequencies of H₂D⁺ (J = 1₁₀ − 1₁₁ at 372.4 GHz) and D₂H⁺ (J = 1₁₀ − 1₀₁ at 691.7 GHz) to resolve suggested slight difference in velocity (v_LSR) of these species detected in the cold pre-stellar core 16293E recently. Both H₂D⁺ and D₂H⁺ were generated in a magnetically confined extended-negative glow discharge of a gaseous mixture of H₂/D₂/Ar. A combination of small improvements in various aspects of the measurements such as double modulation technique combined with a conventional frequency modulation and magnetic field modulation and more efficient signal accumulation method allowed us to improve signal-to-noise ratio, and thus to determine the transition frequencies more accurately. Both transition frequencies for the H₂D⁺ and D₂H⁺ lines have been thus determined to be 372421.385(10) and 691660.483(20) MHz, respectively. These precise rest frequencies suggest that the v_LSR of H₂D⁺ and D₂H⁺ in the pre-stellar core 16293E are indeed different as indicated in a recent astronomical observation. In addition, in this investigation, another transition of H₂D⁺ which falls in this frequency region, J = 3₂₁ − 3₂₂ transition, has been observed at 646430.293(50) MHz. As H₂D⁺ is a lightest asymmetric-top molecule and it is difficult to predict the rotational transition frequencies by using the effective asymmetric rotor Hamiltonian, any new observation of the rotational lines will be useful to improve the molecular parameters. The molecular constants for the ground state have been obtained for H₂D⁺ and D₂H⁺ by fitting these new measured frequencies together with the combination differences.     

Submillimeter-wave spectroscopy of HN2 and DN2 in the excited vibrational states

The pure rotational transitions of HN₂⁺ and DN₂⁺ in the first excited vibrational states for all the fundamental vibrational modes have been observed in the range of 300-750 GHz. The molecular constants determined are much more accurate compared with those obtained from the infrared spectroscopy. The equilibrium rotational constants, B_e = 46832.45 (71) MHz for HN₂⁺ and B_e = 38708.38 (58) MHz for DN₂⁺, have been determined by correcting for the higher-order vibration-rotation interaction effects, γ_ij, obtained by an infrared investigation. The equilibrium bond lengths are derived from these equilibrium rotational constants: r_e(H-N) = 1.03460 (14) Å and r_e (N-N) = 1.092698 (26) Å.     

The microwave spectrum and structure of the argon trifluoroacetonitrile complex

The rotational spectrum of argon trifluoroacetonitrile complex has been studied by pulsed-nozzle, Fourier transform microwave spectroscopy. Both a-type and b-type transitions have been observed. The rotational constants are A = 3053.0903(2) MHz, B = 1039.9570(2) MHz, and C = 895.5788(1) MHz. The ¹⁴N nuclear quadrupole hyperfine components of the rotational transitions have been resolved, the ¹⁴N nuclear quadrupole coupling constants are χ_aa = 1.746(1) MHz, and χ_bb − χ_cc = −6.426(2) MHz. The complex is T-shaped, with the argon atom located 3.73 Å from the center of mass of the trifluoroacetonitrile molecule.     

Crystal structure and thermal behavior of two new organic monosulfates NH3(CH2)5NH3SO4 1.5H2O and NH3(CH2)9NH3SO4 H2O

The chemical preparation, the calorimetric studies and the crystal structure are given for two new organic sulfates NH₃(CH₂)₅NH₃SO₄ 1.5H₂O (DAP-S) and NH₃(CH₂)₉NH₃SO₄·H₂O (DAN-S). DAP-S is monoclinic P2₁/n with unit cell dimensions: a=11.9330(2) Å; b=10.9290(2) Å; c=17.5260(2) Å; β=101.873(1)°; V=2236.77(6) Å³; and Z=8. Its atomic arrangement is described as inorganic layers of units and water molecules separated by organic chains. DAN-S is monoclinic P2₁/c with unit cell parameters: a=5.768(2) Å; b=25.890(10) Å; c=11.177(5) Å; β=115.70(4)°; V=1504.0(11) Å³ and Z=4. Its structure exhibits infinite chains, parallel to the [100] direction where the organic cations are interconnected. In both structures a network of strong and weak hydrogen bonds connects the different components in the building of the crystal.     

High-resolution FTIR spectrum of the ν12 band of ethylene-d (C2H3D)

The infrared absorption spectrum of the ν₁₂ fundamental band of ethylene-d (C₂H₃D) has been recorded with an unapodized resolution of 0.004 cm⁻¹ in the wavenumber range of 1340-1460 cm⁻¹ using the Fourier transform technique. By assigning and fitting a total of 870 infrared transitions using a Watson’s A-reduced Hamiltonian in the I^r representation, three rotational and five quartic centrifugal distortion constants for the upper state (v₁₂ = 1) were determined for the first time. The rms deviation of the fit was 0.00044 cm⁻¹ which is close to the experimental precision of the absorption lines. The A-type ν₁₂ band centred at 1400.762811 ± 0.000041 cm⁻¹was found to be relatively free from local frequency perturbations. The inertial defect Δ₁₂ was found to be 0.20928 ±  0.00002 μŲ.     

Crystal chemistry of layered carbide, Ti3(Si0.43Ge0.57)C2

 The crystal structure of a layered ternary carbide, Ti₃(Si_0.43Ge_0.57)C₂, was studied with single-crystal X-ray diffraction. The compound has a hexagonal symmetry with space group P6₃/mmc and unit-cell parameters a=3.0823(1) Å, c=17.7702(6) Å, and V=146.21(1) Å³. The Si and Ge atoms in the structure occupy the same crystallographic site surrounded by six Ti atoms at an average distance of 2.7219 Å, and the C atoms are octahedrally coordinated by two types of symmetrically distinct Ti atoms, with an average C-Ti distance of 2.1429 Å. The atomic displacement parameters for C and Ti are relatively isotropic, whereas those for A (=0.43Si+0.57Ge) are appreciably anisotropic, with U₁₁ (=U₂₂) being about three times greater than U₃₃. Compared to Ti₃SiC₂, the substitution of Ge for Si results in an increase in both A-Ti and C-Ti bond distances. An electron density analysis based on the refined structure shows that each A atom is bonded to 6Ti atoms as well as to its 6 nearest neighbor A site atoms, whether the site is occupied by Si or Ge, suggesting that these bond paths may be significantly involved with electron transport properties.     

Pressure broadening and collisional shift of the Rb D2 absorption line by CH4, C2H6, C3H8, n-C4H10, and He

The pressure broadening and shift rates of the rubidium D2 absorption line 5²S_1/2→5²P_3/2 (780.24 nm) with CH₄, C₂H₆, C₃H₈, n-C₄H₁₀, and He were measured for pressures ≤80 Torr using high-resolution laser spectroscopy. The broadening rates γ_B for CH₄, C₂H₆, C₃H₈, n-C₄H₁₀, and He are 28.0, 28.1, 30.5, 31.3, and 20.3 (MHz/Torr), respectively. The corresponding shift rates γ_S are −8.4, −8.8, −9.7, −10.0, and 0.39 (MHz/Torr), respectively. The measured rates of Rb for the hydrocarbon buffer gas series of this study are also compared to the theoretically calculated rates of a purely attractive van der Waals difference potential. Good agreement is found to exist between measured and theoretical rates.     

Microwave spectra, inversion splittings and quadrupole coupling constants of NHDCl and ND2Cl

The microwave spectra of monochloroamine (NH₂Cl) and its isotopic species have been observed by Cazzoli et al. [G. Cazzoli, D.G. Lister, P.G. Favero, J. Mol. Spectrosc. 42 (1972) 286-295; G. Cazzoli, D.G. Lister, J. Mol. Spectrosc. 45 (1973) 467-474]. We observed microwave spectra of four isotopic species of ¹⁴NHD³⁵Cl, ¹⁴NHD³⁷Cl, ¹⁴ND₂³⁵Cl, and ¹⁴ND₂³⁷Cl produced by the direct reaction of ammonia gas-d₃ or ammonium hydroxide-d₅ with N-chlorosuccinimide. The microwave spectra of NHDCl (d₁-species) and ND₂Cl (d₂-species) were observed in the frequency range from 8.0 to 60 GHz. The inversion splitting (ΔE_o) of ¹⁴NHD³⁵Cl and ¹⁴NHD³⁷Cl in the ground vibrational state are shown to be 11.46(15) and 11.44(15) MHz for K_a = 0 ← 1, and 10.49(15) and 10.26(15) MHz for K_a = 1 ← 2, respectively. However, the inversion splitting of the d₂-species could not be observed in our spectrometer. Only small J and K-dependence of the inversion splitting of d₁-species was observed. The rotational constants of ¹⁴NHD³⁵Cl were determined to be A = 187895.44(18), B = 13353.343(15) and C = 12859.794(15) MHz for the 0⁺ ← 0⁻ state, which means the transition from the lower inversion level to the upper one, and A = 187918.52(18), B = 13353.345(15) and C = 12859.798(14) MHz for the 0⁻ ← 0⁺ state. The rotational and centrifugal distortion constants of ¹⁴ND₂³⁵Cl were determined to be A = 141030.885(72), B = 12594.481(6) and C = 12055.356(6) MHz, and Δ_J = 18.342(23), Δ_JK = 318.15(56), Δ_K = 2219.3 (fixed), δ_J = 0.8717(17) and δ_K = 157.78(61) kHz. The values of the planar moments P_bb = (I_b − I_a − I_c)/2, of ¹⁴ND₂³⁵Cl and ¹⁴ND₂³⁷Cl were found to be 2.68898(2) and 2.68890(2) u Å², respectively, which are about twice as large as those of normal species (P_bb = 1.3548(6) and 1.3544(16) u Å², respectively). It was found that the bond length of r(N-Cl) of NH₂Cl was longer than that of Cl-NCO by 0.045(12) Å, and was almost the same as that of CH₂N-Cl, while it was much shorter than those of Cl-NO₂ and Cl-NO, by 0.092(6) and 0.227(6) Å, respectively.     

The pressure influence on the incommensurate-commensurate ferroelectric phase transition in [4-NH2C5H4NH][SbCl4]

The dielectric properties of the [4-NH₂C₅H₄NH] SbCl₄ (abbreviated as 4-APCA) crystal were investigated under hydrostatic pressure up to 300 Mpa. The pressure-temperature phase diagram was given. The paraelectric-ferroelectric phase transition (II→III) temperature (T_c) increases linearly with increasing pressure with a slope dT_c/dp=21×10⁻² K/MPa. The pressure dependence of Curie-Weiss constants has been evaluated also. In the paraelectric phase (II) the Curie constant (C₊) was pressure dependent whereas the C₋ constant over the ferroelectric phase (III) was almost constant. The results are interpreted in terms of improper and displacive type phase transition model with a soft phonon at a zone boundary.