Dehydration-induced changes in the vibrational states of dioptase Cu6Si6O18·6H2O

This paper reports on the results of temperature studies (20–880°C) of the IR absorption spectra of dioptase crystals in the range 50–4000 cm⁻¹. During the dehydration of dioptase the state of water changes as follows: (1) initial state, (2) intermediate state with damped external vibrations of H₂O, (3) isolated water molecules with new hydrogen bonds, (4) formation of hydroxyls. The bands of the external virations of H₂O (1) vanish in state (2) because of the formation of vacancies in the six-membered water rings. The frequencies of the translation vibrations of 6H₂O in initial dioptase are close to those in liquid water: 169–170 and 277–290 cm⁻¹. A factor-group analysis of the dioptase vibrations in the space group C _3i ² is performed. All IR active vibrations 23A_u+23E_u are described. The thirty five bands observed in the IR spectra are assigned. The dehydration-induced deformations of the silicate rings are determined from the shifts of the vibrational bands of Si₆O₁₈. Institute of Mineralogy and Petrography, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 1, pp. 68–74, January–February, 1996. Translated by I. Izvekova     

An application of near-infrared and mid-infrared spectroscopy to the study of selected tellurite minerals: xocomecatlite,tlapallite and rodalquilarite

Near-infrared and mid-infrared spectra of three tellurite minerals have been investigated. The structures and spectral properties of copper bearing xocomecatlite and tlapallite are compared with an iron bearing rodalquilarite mineral. Two prominent bands observed at 9,855 and 9,015 cm⁻¹ are assigned to ²B_1g → ²B_2g and ²B_1g → ²A_1g transitions of Cu²⁺ ion in xocomecatlite. The cause of spectral distortion is the result of many cations of Ca, Pb, Cu and Zn in the tlapallite mineral structure. Rodalquilarite is characterised by ferric ion absorption in the range 12,300–8,800 cm⁻¹. Three water vibrational overtones are observed in xocomecatlite at 7,140, 7,075 and 6,935 cm⁻¹ whereas in tlapallite bands are shifted to lower wavenumbers at 7,135, 7,080 and 6,830 cm⁻¹. The complexity of rodalquilarite spectrum increases with the number of overlapping bands in the near-infrared. The observation of intense absorption feature near 7,200 cm⁻¹ confirms hydrogen bonding water molecules in xocomecatlite. Weak bands observed near 6,375 and 6,130 cm⁻¹ in tellurites are attributed to the hydrogen bonding between (TeO₃)²⁻ and H₂O. A number of overlapping bands at low wave numbers 4,800–4,000 cm⁻¹ are caused by combinational modes of tellurite ion. (TeO₃)²⁻ stretching vibrations are characterised by three main absorptions at ~1,070, 780 and 665 cm⁻¹. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Characterization of surface thermodynamic properties of p-toluene sulfonate-doped polypyrrole by inverse gas chromatography

Summary p-Toluene sulfonate-doped polypyrrole (PPyTos) powder has been characterized by inverse gas chromatography at various temperatures. We have used apolar n-alkanes and polar probes of differing acidity and basicity to interrogate the London dispersive and Lewis acid-base properties of PPyTos, respectively. We have found that the London component of the surface energy (γs^d) is about 90 mJ · m⁻² at 25°C and the acid-base contribution to the free energy of adsorption (ΔG_a ^AB) for Lewis bases is higher than 8 kJ · mol⁻¹. These results show that PPyTos is a high energy material and is capable of very strong specific acid-base interactions. Lewis acidity is, however, dominant and is shown to increase with temperature. The determination of the heats of adsorption for tetrahydrofuran and ethyl acetate enabled us to determine Drago’s E_A, C_A, E_B and C_B parameters. Whilst E_A and C_A are similar to those published for chloride-doped polypyrrole and rank PPyTos as a hard acidic species, the E_B and C_B values suggest that PPyTos is a very soft Lewis base.     

Oxonium derivatives of <Emphasis Type="Italic">closo</Emphasis>-decaborate in reactions with sulfur-containing nucleophiles

The reaction of the [B₁₀H₉O₂C₄H₈]⁻, [B₁₀H₉OC₄H₈]⁻, and [B₁₀H₉OC₅H₁₀]⁻ anions with negatively charged S-nucleophiles, such as SH⁻, SCN⁻, and S₂O₃ ²⁻, resulted in the ring opening of the cyclic substituent and the formation of derivatives with the terminal thiol, thiocyanate, and thiosulfate groups. The structures of the products were confirmed by the IR, mass, and ¹H, ¹¹B, and ¹³C NMR spectra.     

HETEROGENEITY OF THE QUINONE ELECTRON ACCEPTOR SYSTEM IN BACTERIAL REACTION CENTERS

Abstract— In reaction centers from Rhodopseudomonas viridis, biphasicity of the charge recombination kinetics between P⁺, the primary electron donor, and Q_A and Q_B^-, the primary and secondary quinone electron acceptors, respectively, have been analyzed by the flash-induced absorption change technique. We have studied the effect of quinone environment modifications on the ratio of the two phases for the P⁺Q_A- ([A_fast/A_slow]^a) and P⁺Q_B^- ([A_fast/A_slow]^b) charge recombination processes. In reaction centers from Rps. viridis reconstituted in phosphatidylcholine liposomes a notable influence of the nature of the Q_B pocket occupancy was observed on (A_fast/A_slow)^a. This ratio is much affected by the presence of o-phenanthroline compared to reaction centers with an empty Q_B pocket or with terbutryn present. Because o-phenanthroline was proposed to hydrogen bind His^L190, whereas terbutryn does not, we suggest that a His^LI90-Fe-His^M217 (the equivalent to His^LI90 in the Q_A pocket) “wire” may be involved in the existence of the two conformational states associated with the two phases of charge recombination. In chromat-ophores from the T₁ (Ser^L223→ Ala; Arg^L217→ His) and T₄ (Tyr^L222→ Phe) mutants no modification of the (A_fast/A_slow)^a ratio is detected, whereas the (A_fast/A_slow)^b ratios are substantially modified compared to the wild type (WT). In the T₃ mutant (Phe^L216→ Ser; Val^M263→ Phe [4.1 Å apart from Q_A]), (A_fast/A_slow)^a is notably changed compared to the WT. Our data show that any modification in the close protein environment of the quinones and/or of the His^L190 and His^M217 affects the equilibrium between the two reaction center states. This is consistent with the existence of two reaction center states from Rps. viridis, associated with two different conformations of the quinones-histidines-iron system. This “wire” allows both quinone protein pockets to interact over quite long distances.     

Synthesis and thermal decomposition kinetics of La(III) complexwith unsymmetrical Schiff base ligand

A new unsymmetrical solid Schiff base (LLi) was synthesized using L-lysine, o-vanillin and 2-hydroxy-l-naphthaldehyde. Solid lanthanum(III) complex of this ligand [LaL(NO₃)]NO₃·2H₂O have been prepared and characterized by elemental analyses, IR, UV and molar conductance. The thermal decomposition kinetics of the complex for the second stage was studied under non-isothermal condition by TG and DTG methods. The kinetic equation may be expressed as: dα/dt=Ae^−E/RT(1−α)². The kinetic parameters (E, A), activation entropy ΔS ^# and activation free-energy ΔG ^# were also gained.     

Infrared spectroscopic study of the structure of the tetrabutyl S-dithiopyrophosphate complex of silver

The structure of the complex Ag·TBDTPP (tetrabutyl S-dithiopyrophosphate) formed in HNO₃ medium was studied by IR and NMR methods. The complex is involved in the isomerization of TBDTPP in the presence of Ag⁺ and NO ₃ ⁻ ions. In the IR spectra, we observe the disappearance of P−O−P band and the occurrence of new absorption bands associated with P−S−P and P=O bonds. The silver ion is coordinated to the thiophosphoryl group of the isomer molecule. The influence of HNO₃ concentration on complex formation is discussed.     

Structural investigation of cellulose Iα and Iβ by 2D RFDR NMR spectroscopy: determination of sequence of magnetically inequivalent d-glucose units along cellulose chain

In our previous studies of the crystal structure of native cellulose (cellulose I) by solid-state two-dimensional (2D) ¹³C–¹³C INADEQUATE, it was revealed that cellulose I_α contains two kinds of β-d-glucose residues (A and A′) in the unit cell and that cellulose I_β contains another two kinds of residues (B and B′). In the present study, the sequence of residues A and A′ along the same chains in cellulose I_α and that of residues B and B′ in I_β were investigated by 2D ¹³C–¹³C rotor-synchronized radiofrequency-driven recoupling (RFDR) experiments using, respectively, uniformly ¹³C₆-labeled (U−¹³C₆) bacterial cellulose and the same [U−¹³C₆] cellulose sample after thermal treatment at 260 °C. The RFDR spectra recorded with a short mixing time (1.0 ms) showed dipolar-coupled ¹³C spin pairs of only the neighboring carbon of the both phases, while those recorded with a longer mixing time (3.0–15 ms) provided correlations between weakly coupled ¹³C spin pairs as well as strongly coupled ¹³C spin pairs such as neighboring carbon nuclei. In the RFDR spectrum of the [U−¹³C₆] cellulose recorded with a mixing time of 15 ms, the inter-residue ¹³C–¹³C correlation between C4 of residue A and C2 of residue A′ and that between C3 of residue A and C4 of residue A′ were clearly observed. In the case of cellulose I_β, however, inter-residue ¹³C–¹³C correlations between residues B and B′ could not be detected in the series of RFDR spectra recorded with different mixing times of annealed [U−¹³C₆] cellulose. From these findings, that cellulose I_α was revealed to have the –A–A′– repeating units along the cellulose chain. For cellulose I_β, it was revealed that the respective residues B and B′ are composed of independent chains (–B–B– and –B′–B′– repeating units) and that there are no –B–B′– repeating units in the chain.     

A kinetic analysis of thermal decomposition of polyaniline/ZrO<Subscript>2</Subscript> composite

Synthesis, characterization and thermal analysis of polyaniline (PANI)/ZrO₂ composite and PANI was reported in our early work. In this present, the kinetic analysis of decomposition process for these two materials was performed under non-isothermal conditions. The activation energies were calculated through Friedman and Ozawa-Flynn-Wall methods, and the possible kinetic model functions have been estimated through the multiple linear regression method. The results show that the kinetic models for the decomposition process of PANI/ZrO₂ composite and PANI are all D₃, and the corresponding function is ƒ(α)=1.5(1−α)^2/3[1−(1-α)^1/3]−1. The correlated kinetic parameters are E _a=112.7±9.2 kJ mol⁻¹, lnA=13.9 and E _a=81.8±5.6 kJ mol⁻¹, lnA=8.8 for PANI/ZrO₂ composite and PANI, respectively.     

Acylation of [B12H12]2− dianion by carboxylic acid halides

The sodium salt of [B₁₂H₁₂]²⁻ dianion reacts with carboxylic acid halides to give a mixture of B-acylated product [B₁₂H₁₁COR]²⁻ and an unstable intermediate, the latter undergoing hydrolysis to form [B₁₂H₁₁OH]²⁻. The ratio of the products formed depends on the nature of the radical R. The reaction mechanism was studied by NMR spectroscopy. A number of novel [B₁₂H₁₁COR]²⁻ compounds were synthesized; their structures were confirmed by NMR and IR spectral data. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 980–985, May, 1998.     

Chain mechanism of the reactions of <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>′-diphenyl-1,4-benzoquinone diimine with thiophenol and 1-decanethiol

The kinetics of the reactions of N,N′-diphenyl-1,4-benzoquinone diimine with thiophenol and 1-decanethiol in chlorobenzene at 343 K has been investigated spectrophotometrically in an argon atmosphere with monitoring of the disappearance of quinone diimine as its absorbance in the visible range. The acceleration of the reactions in the presence of initiators—tetraphenylhydrazine and azobisisobutyronitrile—indicates that the reactions proceed via a chain mechanism under the chosen experimental conditions. The chain length of the reactions in the absence of an initiator is estimated: ν ≈ 10 units in the reaction of quinone diimine with thiophenol and ν ≈ 100 units in the reaction with 1-decanethiol at a quinone diimine concentration of about 10⁻⁴ mol/L and thiol concentrations of about 10⁻³ mol/L. The dependence of the kinetic parameters of the initiated reaction on the thiophenol concentration suggests that the reaction of the thiyl radical with quinone diimine is the rate-determining step of chain propagation. The rate constant of this reaction is estimated at k _pr = 3.2 × 10⁵ L mol⁻¹ s⁻¹. The rates of chain initiation due to the direct interaction of the initial reactants are estimated. In these reactions, the homolytic cleavage of the S-H bond occurs in the thiol, due to which, other conditions being equal, the radical formation rate in the quinone diiminethiophenol system is at least two orders of magnitude higher than that in the quinone diimine-1-decanethiol, in which the strength of S-H bond is higher. A radical chain mechanism is proposed for the reaction of quinone diimine with the thiols on the basis of the data obtained.     

DFT calculation of α-cyclodextrin dimers. contribution of hydrogen bonds to the energy of formation

The structures and energies of formation of α-cyclodextrin (α-CD) dimers formed according to the “head-to-head” (HH), “head-to-tail” (HT), and “tail-to-tail” (TT) modes, harmonic vibrational frequencies, and intensities of IR bands of the IR transitions were calculated by the DFT/PBE density functional method with full geometry optimization without symmetry restrictions. The spectral data were transformed into spectral patterns. An α-CD molecule can exist in two isomeric forms close in energy, namely, α-CD⁻ and α-CD⁺, with different directions of the ring intramolecular hydrogen bonds. Among the three α-CD⁻ dimers, the highest dimerization energy (E _d/kcal mol⁻¹) belongs to the HH⁻ (68.9), TT⁻ (43.4), and HT⁻ (24.8) dimers. The strength of the α-CD⁺ dimers decreases in the series: TT⁺ (56.7), HT⁺ (49.4), and HH⁺ (42.4). The energies E _H of hydrogen bonds were calculated from the low-frequency shifts of bands of stretching vibrations of the OH groups involved in the formation of these hydrogen bonds. The E _H value for each dimer correlates with E _d. A possibility of formation of intermolecular hydrogen bonds is a driving force of association of α-CD molecules in aqueous solutions. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1289–1296, August, 2006.     

The Dissolution Properties of 2-(1,1-Dinitromethylene)-1,3-diazepentane in N-methyl Pyrrolidone

The dissolution properties of 2-(1,1-dinitromethylene)-1,3-diazepentane in N-methyl pyrrolidone(NMP) were studied with a RD496-2000 Calvet microcalorimeter at three different temperatures. The measured molar enthalpies (Δ_sol H) for 2-(1,1-dinitromethylene)-1,3-diazepentane in NMP at T=(298.15,306.15,311.15) K are (5.02, 5.59, 6.67) kJ⋅mol⁻¹, respectively. The differential molar enthalpies (Δ_dif H), the specific enthalpies (Δ_sol h), and the standard heat effect (Q ^Θ) for 2-(1,1-dinitromethylene)-1,3-diazepentane in NMP were obtained at the same time. The kinetic parameters of activation energy E and pre-exponential factor A are 2.26×10⁴ J⋅mol⁻¹ and 10^2.06 s⁻¹, which indicate that NMP is a good solvent for the title compound.     

Simulation and interpretation of the vibrational spectra of heterofullerenes

This paper reports on a computer simulation of the vibrational spectra of C₅₉B, C₅₉N, C₅₉BN, and C₅₉HN. The modes whose frequencies are most sensitive to carbon substitution by heteroatoms are revealed. It is shown that the new bands at 818, 839, and 845 cm⁻¹ in the experimental IR spectrum of C₅₉HN arise from changes in selection rules and by removal of degeneracies due to a reduction in the symmetry of the molecule and force field perturbation. In the Raman spectrum of C₅₉HN, the shifts of the 1460 and 491 cm⁻¹ bands to the low-frequency region by 7 and 3 cm⁻¹, respectively, relative to two A_g modes of C₆₀ are explained by the perturbation induced by the N and C(H) atoms in the force field of adjacent CC bonds not containing these atoms. Institute of Spectroscopy, Russian Academy of Sciences (Troitsk, Moscow Region). Scientific and Production Association “Complex.” Scientific and Production Association “Tekhon.” Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 3, pp. 401–411, May–June, 1998.     

Protonation of Chloro-, Bromo- and Iodo-pentacyanocobaltate(III) Complexes

The reactions between Fe(Phen)₃²⁺[phen = tris-(1,10) phenanthroline] and Co(CN)₅X³⁻ (X = Cl, Br or I) have been studied in aqueous acidic solutions at 25 °C and ionic strength in the range I = 0.001–0.02 mol dm⁻³ (NaCl/HCl). Plots of k₂ versus √I, applying Debye–Huckel Theory, gave the values −1.79 ± 0.18, −1.65 ± 0.18 and 1.81 ± 0.10 as the product of charges (Z_AZ_B) for the reactions of Fe(Phen)₃²⁺ with the chloro-, bromo- and iodo- complexes respectively. Z_AZ_B of ≈ −2 suggests that the charge on these Co^III complexes cannot be −3 but is −1. This suggests the possibility of protonation of these Co^III complexes. Protonation was investigated over the range [H⁺] = 0.0001 −0.06 mol dm⁻³ and the protonation constants K_a obtained are 1.22 × 10³, 7.31 × 10³ and 9.90 × 10² dm⁶ mol⁻³ for X = Cl, Br and I, respectively.     

Synthesis,crystal structure,and thermal decomposition kinetics of complex [Nd(BA)<Subscript>3</Subscript>bipy]<Subscript>2</Subscript>

The complex of [Nd(BA)₃bipy]₂ (BA = benzoic acid; bipy = 2,2′-bipyridine) has been synthesized and characterized by elemental analysis, IR spectra, single crystal X-ray diffraction, and TG/DTG techniques. The crystal is monoclinic with space group P2(1)/n. The two–eight coordinated Nd³⁺ ions are linked together by four bridged BA ligands and each Nd³⁺ ion is further bonded to one chelated bidentate BA ligand and one 2,2′-bipyridine molecule. The thermal decomposition process of the title complex was discussed by TG/DTG and IR techniques. The non-isothermal kinetics was investigated by using double equal-double step method. The kinetic equation for the first stage can be expressed as dα/dt = A exp(−E/RT)(1 − α). The thermodynamic parameters (ΔH ^≠, ΔG ^≠, and ΔS ^≠) and kinetic parameters (activation energy E and pre-exponential factor A) were also calculated.     

Spectroscopy of selected copper group minerals: ktenasite,orthoserpierite and kipushite

Near-infrared (NIR) and IR spectroscopy have been applied for the characterisation of three complex Cu–Zn sulphate/phosphate minerals, namely ktenasite, orthoserpierite and kipushite. The spectral signatures of the three minerals are quite distinct in relation to their composition and structure. The effect of structural cation substitution (Zn²⁺ and Cu²⁺) on band shifts is significant both in the electronic and in the vibrational spectra of these Cu–Zn minerals. The variable Cu:Zn ratio between Zn-rich and Cu-rich compositions shows a strong effect on Cu(II) bands in the electronic spectra. The Cu(II) spectrum is most significant in kipushite (Cu-rich) with bands displayed at high wavenumbers, 11,390 and 7,545 cm⁻¹. The isomorphic substitution of Cu²⁺ for Zn²⁺ is reflected in the NIR and IR spectroscopic signatures. The multiple bands for ν₃ and ν₄ (SO₄)²⁻ stretching vibrations in ktenasite and orthoserpierite are attributed to the reduction in symmetry of the sulphate ion from T_d to C_2V. The IR spectrum of kipushite is characterised by strong (PO₄)³⁻ vibrational modes at 1,090 and 990 cm⁻¹. The range of IR absorption is higher in ktenasite than in kipushite, while it is intermediate in orthoserpierite.     

The X˜1A1, a˜3B1, a˜1B˜1, and B˜1A1 electronic states of SiH2

Four electronically low-lying states of silylene (SiH₂) have been studied systematically using high level ab initio electronic structure theory. Self-consistent field (SCF), two-configuration (TC) SCF, complete active space (CAS) SCF, configuration interaction with single and double excitations (CISD), and CASSCF second-order (SO) CI levels of theory were employed with eight distinct basis sets. The zeroth-order wave functions of the ground (X˜ ¹A₁ or 1 ¹A₁) and B˜ ¹A₁ (or 2 ¹A₁) excited states are appropriately described by the first and second eigenvectors of the TCSCF secular equations. The TCSCF-CISD, CASSCF, and CASSCF-SOCI wave functions for the B˜ ¹A₁ (or 2 ¹A₁) state were obtained by following the second root of the CISD, CASSCF, and SOCI Hamiltonian matrices. At the highest level of theory, the CASSCF-SOCI method with the triple zeta plus triple polarization augmented with two sets of higher angular momentum functions and two sets of diffuse functions basis set [TZ3P(2f,2d)+2diff], the energy separation (T₀) between the ground (X˜ ¹A₁) and first excited (a˜ ³B₁) states is determined to be 20.5 kcal/mol (0.890eV,7180cm⁻¹), which is in excellent agreement with the experimental T₀ value of 21.0 kcal/mol (0.910eV,7340cm⁻¹). With the same method the T₀ value for the a˜ ¹B₁−X˜ ¹A₁ separation is predicted to be 45.1 kcal/mol (1.957 eV,15780 cm⁻¹), which is also in fine agreement with the experimental value of 44.4 kcal/mol (1.925 eV,15530 cm⁻¹). The T₀ value for the B˜ ¹A₁−X˜ ¹A₁ separation is determined to be 79.6 kcal/mol (3.452 eV,27 840 cm⁻¹). After comparison of theoretical and experimental T₀ values for the a˜ ³B₁ and a˜ ¹B₁ states and previous studies, error bars for the B˜ ¹A₁ state are estimated to be ±1.5 kcal/mol (±525 cm⁻¹). The predicted geometry of the B˜ ¹A₁ state is r_e(SiH)=1.458 and θ_e=162.3^∘. The physical properties including harmonic vibrational frequencies of the B˜ ¹A₁ state are newly determined. Received: 10 March 1997 / Accepted: 2 April 1997     

On the analog of benzene B6H 6 n ? , 2 ≤ n ≤ 6: Geometry of B6H 6 n ? anions

The possibility of existence of the B₆H ₆ ⁶⁻ anion as the analog of the benzene molecule with a planar structure was considered. It was shown that on addition of two electrons to the [B₆H ₆ ⁴⁻ (O _h )] anion, the change from the octahedral to the planar geometry and the formation of B₆H ₆ ⁶⁻ (C _6v ) is thermodynamically unfavorable. The lithium ions in Li₆B₆H₆ can be used as the stabilizing coordination factor in the anion. The occurrence in the B₆H ₆ ⁿ⁻ ions (n = 2−6) of the shared π-electrons responsible for the formation of the highly aromatic systems with the planar geometry was shown to be impracticable. Original Russian Text ? N.T. Kuznetsov, S.P. Ionov, 2007, published in Koordinatsionnaya Khimiya, 2007, Vol. 33, No. 10, pp. 738–741.