Thermodynamics of (1,4-difluorobenzene + an n-alkane) and of (hexafluorobenzene + an n-alkane)

Excess molar enthalpies H^E and excess molar volumes V^E have been measured, as a function of mole fraction x₁, at 298.15 K and atmospheric pressure for the five liquid mixtures (x₁1,4-C₆H₄F₂ + x₂n-C_lH_2l+2), l = 7, 8, 10, 12 and 16. In addition, H^E and excess molar heat capacities C_P^E at constant pressure have been determined for the two liquid mixtures (x₁C₆F₆ + x₂n-C_lH_2l+2), l = 7 and 14, at the same temperature and pressure. The instruments used were flow microcalorimeters of the Picker design (the H^E version was equipped with separators) and a vibrating-tube densimeter, respectively.

The excess enthalpies of the five difluorobenzene mixtures are all positive and quite large; they increase with increasing chain length l of the n-alkane from H^E(x₁ = 0.5)/(J mol⁻¹) = 1050 for l = 7 to 1359 for l = 16. The corresponding excess volumes V^E are all positive and also increase with increasing l: V^E(x₁ = 0.5)/(cm³ mol⁻¹) = 0.650 for l = 7 and 1.080 for l = 16. Interestingly, the excess enthalphies of the corresponding mixtures with hexafluorobenzene are only about 5% larger, whereas the excess volumes of (x₁C₆F₆ + x₂n-C_lH_2l+2) are roughly twice as large as those of their counterparts in the series containing 1,4-C₆H₄F₂. Specifically, at 298.15 K H^E(x₁ = 0.5)/(J mol⁻¹) = 1119 for (x₁C₆F₆ + x₂n-C₇H₁₆) and 1324 for (x₁C₆F₆ + x₂n-C₁₄H₃₀), and for the same mixtures V^E(x₁ = 0.5)/(cm³ mol⁻¹) = 1.882 and 2.093, respectively. The excess heat capacities for both systems are negative and of about the same magnitude as the excess heat capacities of mixtures of fluorobenzene with the same n-alkanes (Roux et al., 1984): C_P^E(x₁ = 0.5)/(J K⁻¹ mol⁻¹) = −1.18 for (x₁C₆F₆ + x₂n-C₇H₁₆), and −2.25 for (x₁C₆F₆ + x₂n-C₁₄H₃₀). The curve C_P^E vs. (x₁ for x₁C₆F₆ + x₂n-C₁₄H₃₀) shows a sort of “hump” for x₁ 0.5, which is presumed to indicate emerging W-shape composition dependence at lower temperatures.     

Molecular vibrations of complexes with trigonal ligands : VI: Tetrammines with a square-planar-skeleton- the infrared spectrum of [Cu(NH3)4]

A vibrational analysis is performed for [Cu(NH₃)₄]²⁺, which has a square-planar frame work structure. Two versions of symmetry coordinates are produced assuming the C_4V and C_4h structures, respectively. The IR spectrum of [Cu(¹⁵NH₃)₄]²⁺ was recorded, and the observed frequencies used as supplementary data in a normal coordinate analysis along with data available for other isotopic compounds. An approximate force field which reproduces satisfactorily the observed frequencies for all the isotopic compounds is developed. The force constants may be classified as pertaining to the (a) ligand vibrations, (b) ligand-framework couplings and (c) framework vibrations. These calculations for the whole complex are compared with (i) results for free NH₃, (ii) the analysis of the XY₄ (D_4h) point-mass model and (iii) calculations for the pyramidal-axial CuNH₃ (C_3V) fragment. It is concluded that the effects of kinematic coupling are small. The validity of the point-mass model approximation is confirmed.     

Molecular vibrations of complexes with trigonal ligands. Part V. Symmetry coordinates for tetrahedral complexes

Ligands of C_3V symmetry are assumed to be a part of a T_d complex. Suitable combinations of C_3v (a₂ + e) symmetry coordinates, which fit into the T_d model, are studied. The results constitute a useful supplement to the C_3V (a₁ + e) type coordinates studied previously. Torsional coordinates in the Ni(PF₃)₄ type model are treated in particular.     

Big macrocyclic assemblies of carboranes (big MACs): synthesis and crystal structure of a macrocyclic assembly of four carboranes containing alternate ortho- and meta-carborane icosahedra linked by para-phenylene units

The macrocyclic compound, [1,2-C₂B₁₀H₁₀-1,4-C₆H₄-1,7-C₂B₁₀H₁₀-1,4-C₆H₄]₂ (5)—a novel cyclooctaphane, was prepared by condensation of the C,C′-dicopper(I) derivative of meta-carborane with 1,2-bis(4-iodophenyl)-ortho-carborane. The X-ray crystal structure of 5·C₆H₆·6C₆H₁₂ was determined at 150 K, revealing an extremely loose packing mode. Molecule 5 has a crystallographic C_s and local C_2v symmetry; the macrocycle adopts a butterfly (dihedral angle 143°) conformation with the ortho-carborane units at the wingtips and the phenylene ring planes roughly perpendicular to the wing planes. Multinuclear NMR spectra suggest that molecule 5 in solution inverts rapidly via the planar D_2h geometry, which (from ab initio HF/6-31G* calculations) is only 1 kcal mol⁻¹ higher in energy than the C_2v one. An attempt to prepare an even larger macrocycle, comprising three para-carborane and three ortho-carborane units linked by six para-phenylene units, was unsuccessful.     

Raman spectroscopic study of the conformational change of 12-crown-4 due to cation capture

Raman spectra of the Li⁺, Na⁺, K⁺, NH⁺₄, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Pb²⁺ complexes of 12-crown-4 and also 12-crown-4 in various states are observed. The spectra of 12-crown-4 change remarkably by complex formation with cations. Normal vibration calculations of various conformations of 12-crown-4 are carried out. On the basis of the observed spectra and the results of the calculations, the conformation of 12-crown-4 in the Li⁺, Na⁺, K⁺, NH⁺₄, Mg²⁺ complexes is found to have approximate D_2d symmetry, while that in the Ca²⁺, Sr²⁺, Ba²⁺ complexes is found to have approximate C_2V symmetry.     

Characterization of the first mixed-valent liquid-crystalline materials. Synthesis and structural properties of new binuclear ruthenium carboxylates

The syntheses and structural properties of new binuclear ruthenium (II, III) complexes with long chain carboxylates, of general formula Ru₂(RCO₂)₄X (R = C₈H₁₇, C₁₁H₂₃ and X = C1, RCOO), are reported. The thermodynamic behaviour of these compounds is strongly influenced by the nature of the counterion X. The chloro complexes (X = CI) are not mesomorphic whereas the carboxylato species (X = RCOO) are shown to exhibit a thermotropic columnar mesophase, thus providing the first example of a mixed-valent liquid-crystalline material.     

C94 IPR isomeric set: large-scale computations of relative stabilities based on the Gibbs function

At present C₉₄ is one of the highest sets of isomeric fullerenes that has been characterized by ¹³C NMR spectra. This contribution reports quantum-chemical computations on the C₉₄ system. The complete set of 134 isolated-pentagon-rule isomers of C₉₄ is described by four semiempirical quantum-chemical methods (MNDO, AM1, PM3, and SAM1). The C₉₄ energetics is also checked with Hartree–Fock SCF calculations in the standard 4-31G basis set (HF/4-31G). The calculations point out a C₂ structure as the system ground state. As energetics itself cannot produce reliable relative stabilities at high temperatures, entropy terms are also computed and the relative-stability problem is entirely treated in terms of the Gibbs function. The lowest-energy structure remains the most populated isomer at higher temperatures. However, several other structures show significant populations at higher temperatures. The six most populated species at the AM1 computational level read: C₂, C₂, C₁, C₁, C_s, and C₂. This selected six-membered isomeric set indeed contains the four symmetries observed in the available experiment (C₂, C_s, C₂, and C₂). This incidence represents a good agreement with the experiment and can be viewed as another evidence that the supposed inter-isomeric thermodynamic equilibrium does exist in experiments.     

硼化合物研究(Ⅲ)——B10H102-、B12H122-以及B3H8-阴离子的二茂铁季铵盐的合成

本文通过B_nH_n^2-(n=10,12)及B₃H₈^-盐分别与C₅H₅FeC₅H₄CH₂N(R)Me₂Cl和Fe(C₅H₄CH₂N(R)Me₂Cl)₂(R=CH₃-,C₂H₅-,n-C₃H₇-,CH₂=CH-CH₂-和CH≡C-CH₂-)在水溶液中进行反应,合成了相应的三十个新的硼烷阴离子衍生物,这些化合物对水稳定性好,B₁₀H₁₀^2-及B₁₂H₁₂^2-衍生物对热、酸、碱和氧化剂均很稳定。研究了反应物之间的用量比例对反应产物的影响。实验结果表明,不论反应物之间的克分子比如何变化,只能得到相应的一种产物(产率90-98％)。     

Role of axial ligation on potentiometric response of Co(III) tetraphenylporphyrin-doped polymeric membranes to nitrite ions

Two types of Co(III) tetraphenylporphyrins, Co(III)TPPX (I) and Co(III)(N)TPPX (II), where X = C1⁻ or NO⁻₂ and N = C₅H₅N or C₆H₅CH₂C₅H₄N, are used as ionophores to prepare nitrite responsive polymeric membrane electrodes. The influence of the initial axial ligand (X⁻ and N) on the operative ionophore mechanism of these metalloporphyrins within the solvent polymeric membranes is examined. Results from potentiometric and electrodialysis experiments suggest that in the presence of nitrite in the test sample and internal solution, both types of Co (III) porphyrins studied (I and II) act as neutral carriers and that the addition of lipophilic cationic sites (e.g., tridodecylmethylammonium ions (TDMA⁺)) to the organic membrane is essential to improve the selectivity and long term stability of sensors prepared with these species. Membranes formulated with (I) or (II) in the nitrite form along with TDMACl in plasticized PVC films exhibit the following selectivity sequence: SCN⁻ > NO⁻₂ ˜ C1O⁻₄ > Sal⁻ > NO⁻₃ > Br⁻ > C1⁻. Membrane electrodes with added lipophilic cationic sites are shown to exhibit rapid, fully reversible and Nernstian response towards nitrite ions in the concentration range of 10⁻¹–10⁻⁵ M, with good long term stability.     

A computational study of adducts between atomic chlorine and carbon dioxide, carbonyl sulfide and carbon disulfide

The geometries and vibrational frequencies of the adducts ClCO₂, ClCOS and ClCS₂ were derived at the Hartree-Fock (HF) 3-21G (^*) level. The C_a, structure of ClCO₂ corresponds to one C-O bond and one C=O bond. Similarly, C_a, ClCS₂ has one C-S and one C=S bond, and ClCOS has one C-S and one C-O bond. Single-point spin-projected fourth-order Møller-Plesset (MP4) 3-21G (^*) calculations at these geometries were used in bond-separation reactions to derive ΔH^o₀ for adduct formation, which is calculated to be about 39 kJ mol⁻¹ exothermic for ClCOS and ClCS₂, but about 39 kJ mol⁻¹ endothermic for ClCO₂. The C_2v structures for ClCO₂ and ClCS₂ were also characterized. The geometry of ClCS₂ has not been determined experimentally; comparison with an available measured entropy for ClCS₂ suggests that the C_2v structure is the one formed by addition of Cl to CS₂, although the energy relative to the C_a form is not reliably calculated because of instability in the HF wavefunction.     

1.54 and 1.75 μm infrared luminescence of Y2O3:Er

A new 1.75 μm infrared emission transition of Y₂O₃:Er³⁺ is assigned to the ⁴S_3/2 → ⁴I_9/2 transition of Er³⁺ ions situated at the C₂ sites of cubic RE₂O₃ (RE = Y, Gd, Lu). The intensities of features in the 1.54 μm ⁴I_15/2–⁴I_13/2 absorption transition due to Er³⁺ at S₆ and C₂ sites are consistent with the site occupation ratio and the relative magnetic dipole–electric dipole intensity contributions of Er³⁺ at the different sites. The 1.54 μm emission lines are predominantly from Er³⁺ ions at C₂ sites. The different behaviours of the emission intensities 1.75 and 1.54 μm groups with change in Er³⁺ dopant ion concentration, preparation technique, Yb³⁺ co-doping, temperature change and different excitation line are rationalized.     

Structures and energetics of C3H6S isomers: a Gaussian-3 ab initio study

Twenty-two isomers/conformers of C₃H₆S^+√ radical cations have been identified and their heats of formation (ΔH_f) at 0 and 298 K have been calculated using the Gaussian-3 (G3) method. Seven of these isomers are known and their ΔH_f data are available in the literature for comparison. The least energy isomer is found to be the thioacetone radical cation (4⁺) with C_2v symmetry. In contrast, the least energy C₃H₆O^+√ isomer is the 1-propen-2-ol radical cation. The G3 ΔH_f298 of 4⁺ is calculated to be 859.4 kJ mol⁻¹, ca. 38 kJ mol⁻¹ higher than the literature value, ≤821 kJ mol⁻¹. For allyl mercaptan radical cation (7⁺), the G3 ΔH_f298 is calculated to be 927.8 kJ mol⁻¹, also not in good agreement with the experimental estimate, 956 kJ mol⁻¹. Upon examining the experimental data and carrying out further calculations, it is shown that the G3 ΔH_f298 values for 4⁺ and 7⁺ should be more reliable than the compiled values. For the five remaining cations with available experimental thermal data, the agreement between the experimental and G3 results ranges from fair to excellent.

Cation CH₃CHSCH₂^+√ (10⁺) has the least energy among the eleven distonic radical cations identified. Their ΔH_f298 values range from 918 to 1151 kJ mol⁻¹. Nevertheless, only one of them, CH₂=SCH₂CH₂^+√ (12⁺), has been observed. Its G3 ΔH_f298 value is 980.9 kJ mol⁻¹, in fair agreement with the experimental result, 990 kJ mol⁻¹.

A couple of reactions involving C₃H₆S^+√ isomers CH₂=SCH₂CH₂^+√ (12⁺) and trimethylene sulfide radical cation (13⁺) have also been studied with the G3 method and the results are consistent with experimental findings.     

Density functional theory analysis of CaRgn complexes: (Rg=He, Ne, Ar; n=1–4)

CaRg_n⁺ (Rg=He, Ne, Ar) complexes with n=1–4, are investigated by performing using the B3LYP/6-311+G (3df) density functional theory calculations. The CaHe_n⁺ (n=1–4) complexes are found to be stable. In the case of CaNe_n⁺ and CaAr_n⁺, stable structures and stationary point were found only for n=1 and 2. For n=3 in the C_3V and the D_3h point group as well as for n=4 in the T_d (tetrahedral) point group a saddle point (imaginary frequency) is observed and global minimum could be obtained along the potential energy surface.     

Dipole polarizability pseudospectra and C6 dispersion coefficients for H2–H2

Pseudostate decomposition of static dipole polarizabilities for ground state H₂⁺ from a Givens-Householder diagonalization of the excitation operator (

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H" height="17" width="20">₀−E₀) over an N-term basis of appropriate symmetry allows for a rapidly convergent evaluation of C₆ dispersion coefficients for H₂⁺–H₂⁺. 27-term pseudospectra of hypergeneralized James functions with a 30-term GGJ⁺ unperturbed wavefunction with an optimized scale factor δ=0.918 at R=2₀ give C₆ and γ₆ values that are accurate to no less than nine significant figures.     

AQUEOUS PHASE SYNTHESIS OF(RC_5H_4)_2Ti(O_2CC_6H_4X)_2

Nine complexes(RC_5H_4)_2Ti(O_2CC_6H_4X)_2(R=H,CH_3;X=H,o-Cl,o-OH,o-NH_2,o-NHPh)have been conveniently prepared by the reaction of(RC_5H_4)_2TiCl_2 with 2 equiv.sodium salts of corresponding carboxylic acidin aqueous solution containing acetylacetone.The carboxylate ligands inthe complexes coordinate to titanium atom in monodentate mode.     

Five-membered OsC3N heterocycles from osmium azavinylidenes as precursors

The azavinylidene osmium complex [(mes)Os(=N=CPh₂(PⁱPr₃)]PF₆ (3; MES = 1.3.5-C₆H₃Me₃), which was prepared in two steps from [(mes)OsCl₂(PⁱPr₃], CH₃CO₂Na/KPF₆ and HN=CPh₂, has been shown to react with trifluoracetic acid to give the isomeric heterocycle [(mes) ₆H₄)(Pⁱ Pr₃)]PF₆ (4) in almost quantitative yield. With CF₃CO₂D, the monodeuterated compound 4-d₄,containing a N---D unit in the five-membered ring, is obtained. An analogue of 4 with the composition [(mes) ₆H₄)(PMe₃)]X(X = PF₆ 14a, SbF₆ 14b) has been made both from [(mes)Os(=N=CPh₂)(PMe₃)]PF₆ 12 and CF₃CO₂H and from [(mes)OsCl(NH= CPh₂(PMe3)]SbF6 (13) and CF₃CO₂Ag. The reaction of 4 with NaH or KO^tBu gives the uncharged heterocycle [(mes) ₆ H₄)(PⁱPr₃)] (15), while treatment of [(mes)OsCl ₂(NH=CPh2)] (19) with NaS^tBu gives the related complex [(mes) ₆H₄)(S^t Bu)] (20). The crystal structure of 4 has been determined. kw]Osmium; Azavinylidene; Cyclometallation; Crystal structure; Arene complexes     

自由基照相体系的ESR波谱研究

本文用自旋捕获剂t-BuNO(2-甲基2-亚硝基丙烷)与ESR技术结合的方法研究了CBr₄-φ₂NH、CBr₄-LCV及CBr₄-LMG体系的光化学过程。从ESR谱的超精细结构及其随组分浓度的变化,证实了上述体系中除有Br^·外,还分别形成了 自由基。由这些体系在避光条件下的UV谱,证明溶液中存在(HX…CBr₄)型的部分电荷转移络合物。因此,上述自由基照相体系的光引发反应既包括CBr₄的光解,又包括(HX…CBr₄)^*的光解。     

Formation of [C60C5H5] adduct cations and theoretical study of the isomers

We study here the reactions between C₆₀ and planar C₅H₅⁺ cations that lead to the formation of [C₆₀C₅H₅]⁺ adduct cations in the chemical ionization source of the mass spectrometer. The structures, stabilities and charge locations of some possible isomers of [C₆₀C₅H₅]⁺: σ-adduct, π-complex, [1,4]- and [l,2]-addition cations, are studied by AM1 semiempirical molecular orbital calculations. We find that the most stable is the σ-addition cation. Another interesting and stable structure is the π-complex cation which is bonded by the electrostatic interaction at the inter-ring distance of 1.589 Å with the C_5v symmetry. The C₅H₅⁺ cyclopentadienium cation seems to be an “inverted umbrella” sitting on a five-membered ring of the C₆₀ cage.     

Metallorganische lewissäuren : XX. Reaktionen von (π-C5H5)(CO)2LM-X (L = CO, PR3; M = Mo, W; X = BF4, PF6, AsF6, SbF6) mit Schwefel-haltigen liganden

The compounds (π-C₅H₅)(CO)₂LM-X (L = CO, PR₃; M = Mo, W; X = BF₄, PF₆, AsF₆, SbF₆) react with H₂S, p-MeC₆H₄SH, Ph₂S and Ph₂SO(L′) to give ionic complexes [(π-C₅H₅)(CO)₂LML′]⁺ X⁻. Also sulfur-bridged complexes, [(π-C₅H₅)(CO)₃W---SH---W(CO)₃(π-C₅H₅)]⁺ AsF₆⁻ and [(π-C₅H₅)(CO)₃M-μ-S₂C=NCH₂Ph-M(CO)₃(π-C₅H₅)], have been obtained. Reactions with SO₂ and CS₂ have been examined.     

2,4-二硫代尿嘧啶的紫外吸收光谱和共振拉曼光谱

硫代嘧啶碱基是光动力疗法潜在的重要光敏剂,其最低单重激发态的光物理研究已有广泛报道。然而,其较高激发态的跃迁性质和反应动力学研究较为稀少。因此,本文采用共振拉曼光谱和密度泛函理论计算方法研究2,4-二硫代尿嘧啶的紫外光谱和几个较高单重激发态的短时结构动力学。首先,基于共振拉曼光谱强度与电子吸收带振子强度f的关系,将紫外光谱去卷积成四个吸收带,分别为358 nm(f=0.0336)中等强度吸收带(A带),338 nm(f=0.1491)、301 nm(f=0.1795)和278 nm(f=0.3532)强而宽的吸收带(B、C和D带)。这一结果既吻合密度泛函理论计算结果,又符合共振拉曼光谱强度模式对紫外光谱带的预期。据此,去卷积得到的四个吸收带被分别指认为S0→S2跃迁、S0→S6跃迁、S0→S7跃迁和S_0→S_8跃迁。同时,分别对B,C和D带共振拉曼光谱进行了详细的指认,获得了短时动力学信息。结果表明,S_8态短时动力学的显著特征是在Franck-Condon区域或附近发生了S8(ππ~*)/S(nπ~*)势能面交叉引发的、伴随超快结构扭转的非绝热过程。S7和S6态短时动力学的主要特征是反应坐标的多维性,它们分别沿C_5C_6/C_2S_8/C_4S_(10)/N_2C_3+C_4N_3H_9/N_1C_2N_3/C_2N_1C_6/C_6N_1H_7/C_5C_6H_(12)和C_5C_6/N_3C_2/C_4S_(10)/C_2S_8+C_6N_1H_7/C_5C_6H_(12)/C_5C_6N_1/C_5C_6H_(12)/C_2N_1C_6/N_1C_2N_3/C_4N_3H_9/N_1C_2N_3等内坐标演化。