Vibrational spectra of cyclooctatetraenyl alkali metal complexes [C8H8M2 (M = Na, K)]: A theoretical study

The cyclooctatetraenyl dianion (C₈H₈²⁻) π-conjugated system forms a stable complex system with alkali and some transition metals. The results of vibrational analysis for C₈H₈M₂ (M = Na, K) complexes were reported here. The geometries of C₈H₈M₂ (M = Na, K) were optimized using ab initio (HF, MP2, CCSD(T)) and DFT (B3LYP) methods with 6-311G** and 6-311++G** basis sets and the harmonic frequencies were obtained. To reproduce and compare with the experimental values the structurally similar molecules C₅H₅M (M = Na, K) and benzene were studied. The scale factors obtained from these systems were applied to predict the experimental frequencies of C₈H₈M₂ (M = Na, K). The force field and vibrational spectra are analyzed and the most probable assignments are proposed for all the fundamentals based on the potential energy distribution.     

异核金属多重键配合物Cp_2MM'(μ-C_8H_8)的理论研究

研究了双核金属多重键配合物Cp2MM'(μ-C8H8)(MM'=ScMn,TiCr,ScCo,TiFe,VMn,VV,CrCr)的结构和成键模式.计算结果表明,对于28价电子体系,Cp2V2(μ-C8H8)基态为含V-V三重键的三态构型,其等电子体Cp2TiCr(μ-C8H8)为Ti-Cr四重键的单态,等电子体Cp2ScMn(μ-C8H8)为Sc-Mn三重键的单态.对于30价电子体系,Cp2Cr2(μ-C8H8)基态为含Cr-Cr三重键的单态,等电子体Cp2VMn(μ-C8H8)为含V-Mn单键的三态,等电子体Cp2ScCo(μ-C8H8)和Cp2TiFe(μ-C8H8)为含Sc-Co和Ti-Fe双键的单态.在三态Cp2MM'(μ-C8H8)中,两个金属原子多为17电子构型,而单态结构中两种金属原子多分别为16和18电子构型.     

Electronic structures of the boron cage molecules B4H4, B4Cl4 and B4F4

Ab initio calculations have been performed on B₄H₄, B₄Cl₄ and B₄F₄ in order to aid our understanding of the bonding in these compounds, which is presumably based on a tetrahedral boron cage. This cage has only 8 electrons and so is less than that expected on the basis of the usual framework electron counting rules. Basis sets with polarisation functions were used at the SCF, CI and CPF levels of theory to confirm that the T _d structures are indeed more stable than the D _4h ones. Davidson-Roby population analyses were able to show that many factors, including 3-centre 2-electron bonding and backbonding from the ligand to the boron cage, are of importance in determining the relative stability of the three compounds, of which B₄Cl₄ is the only one that has yet been observed experimentally.     

Theoretical studies on the structures and isomerization of the LiSiF3 system

Various possible isomers of LiSiF₃ system and isomerization between them have been studied at G2(MP2) level usingab initio calculations. The relative energies of four minimum points on the potential energy surface are-128.6,-194.3,-12.7 and-122.8 kJ/mol (taking the sum of the energies of LiF and SiF₂ as zero). The structural energy of the four-membered ring that contains three F-Si-F-Li four-membered rings with C_3v symmetry is the lowest. The highest potential barrier for the isomerization of the remaining three- or four-membered structure is 12.5 kJ/ mol. Project supported by the National Natural Science Foundation of China (Grant No. 29673026).     

An unusual example ofendo-stereoselectivity in the ligand exchange reactions of rhodium(i)diethylene derivatives withpara-semiquinoid ligands

The ligand exchange reactions of [(C₂H₄)₂Rh(acac)] in benzene and [(C₂H₄)₂RhCl]₂ in CH₂Cl₂ with 4-methyl-4-trichloromethyl-2,5-cyclohexadiene-1-one occur with 100%exo-stereoselectivity. The similar process with 4-methyl-4-trichloromethyl-1-(4,4-dimethyl-4,6-dioxocyclohexylidene)-2,5-cyclohexadiene (trienedione) is strictlyexo-stereospecific only if [(C₂H₄)₂Rh(acac)] in benzene is used, while in the case of [(C₂H₄)₂RhCl]₂ in CH₂Cl₂, it proceeds with anendo-stereoselectivity of 43%. An explanation for these facts has been suggested that assumes that the metal atom initially attacks the central double bond in the trienedione, which is removed from the area of main steric hindrance. The subsequent metallotropic rearrangement of the resulting ethylene-triene intermediate gives rise to the final ⁴-coordinated -diene structures.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2320–2323, September, 1996.     

Theoretical studies on structures and reactivities of organocuprate(I) and organocopper(III) species

Systematic evaluation of method and basis set on the structure and energetics of organocuprate(I) and organocopper(III) species has been carried out. Various structures of organocuprate(I) and organocuprate(III) complexes were optimized with the HF, MP2, and B3LYP methods, and compared with the structures determined by X-ray crystallography (i.e., Me(2)Cu(I)(-), (CF(3))(4)Cu(III)(-)). Both the MP2 and B3LYP methods reasonably reproduce the X-ray structures while the HF method does not. Using larger basis set and incorporating the relativistic effects for Cu afford the best results. In the studies on the energetics of a Libond;Cu cluster model (Me(2)CuLi. LiCl) and Me(3)Cu model with the MP2, MP3, MP4DQ, MP4SDQ, CCSD(T), and B3LYP methods, the B3LYP method gives energetics similar to those obtained with the CCSD(T) method with much less cost, and hence, is judged to be the best practical method. The studies have shown that B3LYP method with the basis set incorporating the relativistic effective core potentials for Cu and the 6-31G* basis set for the rest is the theoretical method that is the most cost-effective for the studies of the structure and energetics of organocuprate(I) and organocopper(III) species.     

Crystal structure and characterization of Rb2Ca[B4O5(OH)4]2·8H2O

Dirubidium calcium tetraborate octahydrate, Rb₂Ca[B₄O₅(OH)₄]₂·8H₂O, was prepared by reaction of Rb-borate aqueous solution with CaCl₂ and it's structure has been determined by single-crystal X-ray diffraction data. It crystallizes in the orthorhombic system, space group P2₁2₁2₁ with unit cell parameters, Z=4, The structure contains alternate layers of [B₄O₅(OH)₄]²⁻ polyanions separated by water molecules and Rb, Ca cations. The isolated [B₄O₅(OH)₄]²⁻ is constructed from two BO₃(OH) tetrahedron groups and two BO₂(OH) triangular groups joined at common oxygen atoms. The two BO₃(OH) tetrahedron groups are further linked by means of an oxygen bridge across the ring. The Ca²⁺ ion displays seven coordination, while the two non-equivalent Rb⁺ ions display nine and seven coordination, respectively. Infrared and Raman (4000-400 cm⁻¹) spectra of Rb₂Ca[B₄O₅(OH)₄]₂·8H₂O were recorded at room temperature and analyzed. Fundamental vibrational modes were identified and band assignments were made. The dehydration of this hydrated mixed borate occurs in one step and leads to an amorphous phase which undergoes a crystallization.     

Theoretical studies on the structures and reactivity of stannylenoids I.The structures and isomerization of stannylenoid H_2SnLiF

The structures of singlet stannylenoid H2SnLiF have been examined by ab initio MO theory. Four equilibrium states and three transition states of isomerization reaction are located. The calculation shows that the p-complex 1 is the most stable and experimentally detectable. The other three species, three-membered ring 2, o-complex 3 and tetrahedron 4, are also local minima on the potential energy surface, but are higher in energy.     

Thia- und Selena-arachno-undecaboran 6,7-μ-(CH3E)B10H13 Kristallstruktur von arachno-6,7-μ-(CH3Se)B10H13 Theoretische Untersuchungen der Molekülstrukturen und 11B-NMR-Verschiebungen von arachno-6,7-μ-(CH3E)B10H13

Thia- and Selena-arachno-undecaborane 6,7-μ-(CH₃E)B₁₀H₁₃. Crystal Structure of arachno-6,7-μ-(CH₃Se)B₁₀H₁₃. Theoretical Investigations of the Molecular Structures and ¹¹B NMR Shifts of arachno-6,7-μ-(CH₃E)B₁₀H₁₃ The reaction of B₁₀H₁₄ with (CH₃)₂S yields with loss of H₂ the base adduct 6,9-[(CH₃)₂S]₂B₁₀H₁₂. Although an analogous reaction between B₁₀H₁₄ with disulfanes or diselenanes was expected to produce 6,9 bridged dichalcogen derivatives, (CH₃)₂S₂ failed to react even under reflux conditions. Trisulfane (CH₃)₂S₃ does react, but the pathway is different and leads to (CH₃S)B₁₀H₁₃ 2 without loss of H₂. Unlike of (CH₃)₂S₂, (CH₃)₂Se₂ yields (CH₃Se)B₁₀H₁₃, 3 . Both 2 and 3 are formed by substitution of a bridging hydrogen and could be obtained in pure form and characterized ¹¹B NMR spectroscopically. A single crystal X-ray structure analysis also was performed on 3 (space group P2₁/c). The molecular structures of 2 and 3 were optimized at the MP2 level and ¹¹B NMR shifts were computed at the IGLO-SCF, GIAO-SCF and GIAO-B3LYP levels of theory.     

镧石型碳酸镨钕向碱式碳酸镨钕的相转变反应特征及其应用

镧石型碳酸镨钕[(PrNd)2(CO3)3·8H2O,LPN]在95℃的不同起始pH值的溶液中陈化不同时间所得样品的XRD衍射图证明了LPN向碱式碳酸镨钕[(PrNd)(OH)(CO3),BPN]的相态转变。为此,详细研究了这一相态转变的反应条件以及粒子特征变化。结果表明:LPN是由片状或条状结晶连生而成的聚集体,具有大的粒度和小的堆密度。当在热的水溶液中陈化时,由于水解反应而发生由LPN向BPN的相转变。这一相转变可以在95℃下pH=7以上的溶液中发生,其转化率随起始溶液pH值的升高和陈化时间的延长而增大。随着相转变的进行,溶液的pH值开始下降明显,而后趋于平缓。相应地,大的团聚体颗粒解散成小的单个粒子,导致粒度减小,分布变窄,氯根含量降低和堆密度的增大。而且,这些变化直接与溶液pH值和陈化时间相关。据此,发展了一种新的制备具有高堆密度、低氯根含量、细粒度和窄分布的新方法,而且通过改变相转变条件可以方便地调谐颗粒特征。     

镧石型碳酸镨钕向碱式碳酸镨钕的相转变反应特征及其应用

本文研究了镧石型碳酸镨钕[（PrNd）₂（CO₃）₃·8H₂O,LPN]在95℃的不同起始pH值的溶液中陈化不同时间所得样品的XRD衍射图,证明所得样品为碱式碳酸镨钕[（PrNd）（OH）（CO₃）,BPN]。为此,详细研究了这一相态转变的反应条件以及粒子特征变化。结果表明：LPN是由片状或条状结晶连生而成的聚集体,具有大的粒度和小的堆密度。当在热的水溶液中陈化时,由于水解反应而发生由LPN向BPN的相转变。这一相转变可以在95℃下pH=7以上的溶液中发生,其转化率随起始溶液pH值的升高和陈化时间的延长而增大。随着相转变的进行,溶液的pH值开始下降明显,而后趋于平缓。相应地,大的团聚体颗粒解散成小的单个粒子,导致粒度减小,分布变窄,氯根含量降低和堆密度的增大。而且,这些变化直接与溶液pH值和陈化时间相关。据此,发展了一种新的制备具有高堆密度、低氯根含量、细粒度和窄分布的新方法,而且通过改变相转变条件可以方便地调谐颗粒特征。     

Theoretical study of XCN− (XF,Cl) anions

Geometrical parameters, vibrational frequencies, zero‐point energy, dipole moment, NBO atomic charges of FCN^?, ClCN^? and their isomers, and the isomerization energy of FCN^? and ClCN^? are studied in detail using the ab initio MP2, CCSD, CCSD(T), and density functional B3LYP methods. The results are compared with the existing data reported using various theoretical methods in conjunction with different basis sets. The effect of electron correlation on the structural properties of these molecular anions is discussed. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Structure of a C26H28 alkene formed via titanium-promoted reductive dimerization of 4-(spirocyclopropyl)-pentacyclo[5.4.0.02,6.03,10.05,9]undecan-8-one

A spiro-fused C₂₆H₂₈ cage≓ dimer hydrocarbon contains two three-membered rings, two four-membered rings, eight five-membered rings, and two six-membered rings. The molecule is calculated by molecular mechanics to have 902 kJ/mol of strain energy distributed primarily between angle strain (457 kJ/mol) and torsional interactions (368 kJ/mol). Molecular mechanics calculations and a geometry-optimized ab initio calculation are used to analyze the bond lengths and bond angles in the molecule. There is one major discrepancy between observed and calculated distances.     

Theoretical studies of the reactions of O(3P) with halogenated methyl (I)

The reaction of o(³P) with CH₂C1 radical has been studied usingab initio molecular orbital theory. G2 (MP.2) method is used to calculate the geometrical parameters, vibrational frequencies and energies of various stationary points on the potential energy surface. The reaction mechanism is revealed. The addition of o(³P) with CH₂Cl leads to the formation of an energy rich intermediate OCH₂Cl^* which can subsequently undergo decomposition or isomerization to the final products. The calculated heat of reaction for each channel is in agreement with the experimental value. The production of H+CHClO and C1+CH₂O are predicted to be the major channels. The overall rate constants are calculated using transition state theory on the basis ofab initio data. The rate constant is pressure independent and exhibits negative temperature dependence at lower temperatures, in accordance with the experimental results.     

Thermochemistry of europium and dithiocarbamate complex Eu(C5H8NS2)3(C12H8N2)

A solid complex Eu(C₅H₈NS₂)₃(C₁₂H₈N₂) has been obtained from reaction of hydrous europium chloride with ammonium pyrrolidinedithiocarbamate (APDC) and 1,10-phenanthroline (o-phen⋅H₂O) in absolute ethanol. IR spectrum of the complex indicated that Eu³⁺ in the complex coordinated with sulfur atoms from the APDC and nitrogen atoms from the o-phen. TG-DTG investigation provided the evidence that the title complex was decomposed into EuS. The enthalpy change of the reaction of formation of the complex in ethanol, Δ_r H _m ^θ(l), as –22.214±0.081 kJ mol^–1, and the molar heat capacity of the complex, c _m, as 61.676±0.651 J mol^–1 K^–1, at 298.15 K were determined by an RD-496 III type microcalorimeter. The enthalpy change of the reaction of formation of the complex in solid, Δ_r H _m ^θ(s), was calculated as 54.527±0.314 kJ mol^–1 through a thermochemistry cycle. Based on the thermodynamics and kinetics on the reaction of formation of the complex in ethanol at different temperatures, fundamental parameters, including the activation enthalpy (ΔH _≠ ^θ), the activation entropy (ΔS _≠ ^θ), the activation free energy (ΔG _≠ ^θ), the apparent reaction rate constant (k), the apparent activation energy (E), the pre-exponential constant (A) and the reaction order (n), were obtained. The constant-volume combustion energy of the complex, Δ_c U, was determined as –16937.88±9.79 kJ mol^–1 by an RBC-II type rotating-bomb calorimeter at 298.15 K. Its standard enthalpy of combustion, Δ_c H _m ^θ, and standard enthalpy of formation, Δ_f H _m ^θ, were calculated to be –16953.37±9.79 and –1708.23±10.69 kJ mol^–1, respectively.     

The complete closed coexistence curves for 2H,3H,6H,7H,8H-5,8-(Dimethylmethano)-5(R)-methylquinoxaline with water and with deuterium oxide

The complete closed solubility curves for 2H, 3H, 6H, 7H, 8H-5,8-(dimethylmethano)-5(R)-methylquinoxaline with water and with deuterium oxide have been determined. With water the lower critical solution temperature (LCST) was found to be 51.4°C and the critical solution temperature (CST) was found to be 215.0°C. With deuterium oxide the values were 40.4°C for the LSCT and 221.7°C for the CST. The deuterium oxide curve completely encompassed the water curve. Solution compositions at the critical temperatures were also determined.     

An exact expression for the wiener index of a TUC<Subscript>4</Subscript>C<Subscript>8</Subscript>(R) nanotorus

The Wiener index of a graph G is defined as , where V(G) is the set of all vertices of G and for denotes the length of a minimal path between x and y. A C ₄ C ₈ net is a trivalent decoration made by alternating squares C ₄ and octagons C ₈. It can cover either a cylinder or a torus. In this paper, an algorithm for computing the distance matrix of a C ₄ C ₈(R) nanotorus T = T[p,q] is given. Using this matrix, the Wiener index of T is computed.     

Simultaneous thermoanalytical investigations of (C6H5)4AsCl and (C6H5)4PCl under air and argon atmospheres

The thermoanalytical curves of (C₆H₅)₄AsCl (I) and (C₆H₅)₄PCl (II) were generated simultaneously by using a Netzsch simultaneous thermal analyser 409 under static air and dynamic argon atmospheres. The ranges of thermal stability of I and II were found to be 145–310°C and 137–365°C, respectively, and their melting points to be 261 and 278°C. The DTA profiles of I and II differ and can be used for their distinction.     

La3Ru8B6 and Y3Os8B6, new members of a homologous series R(A)nM3n−1B2n

Two new compounds, La₃Ru₈B₆ and Y₃Os₈B₆, were synthesized by arc melting the elements. Their structural characterization was carried out at room temperature on as-cast samples by using X-ray diffractometry. According to X-ray single-crystal diffraction results these borides crystallize in Fmmm space group (no. 69), Z=4, a=5.5607(1) Å, b=9.8035(3) Å, c=17.5524(4) Å, ρ=8.956 Mg/m³, μ=25.23 mm⁻¹ for La₃Ru₈B₆ and a=5.4792(2) Å, b=9.5139(4) Å, c=17.6972(8) Å, ρ=13.343 Mg/m³, μ=128.23 mm⁻¹ for Y₃Os₈B₆. The crystal structure of La₃Ru₈B₆ was confirmed from Rietveld refinement of X-ray powder diffraction data. Both La₃Ru₈B₆ and Y₃Os₈B₆ compounds are isotypic with the Ca₃Rh₈B₆ compound and their structures are built up from CeCo₃B₂-type and CeAl₂Ga₂-type structural fragments taken in ratio 2:1. They are the members of structural series R(A)_nM_3n−1B_2n with n=3 (R is the rare earth metal, A the alkaline earth metal, and M the transition metal). Structural and atomic parameters were also obtained for La_0.94Ru₃B₂ compound from Rietveld refinement (CeCo₃B₂-type structure, P6/mmm space group (no. 191), a=5.5835(9) Å, c=3.0278(6) Å).