Infrared and Raman Spectra,conformations, ab initio calculations and spectral assignments of 1,3‐disilabutane (SiH3CH2SiH2CH3)

Raman spectra of 1,3‐disilabutane (SiH₃CH₂SiH₂CH₃) as a liquid were recorded at 293 K and as a solid at 78 K. In the Raman cryostat at 78 K an amorphous phase was first formed, giving a spectrum similar to that of the liquid. After annealing to 120 K, the sample crystallized and large changes occurred in the spectra since more than 20 bands present in the amorphous solid phase vanished. These spectral changes made it possible to assign Raman bands to the anti or gauche conformers with confidence. Additional Raman spectra were recorded of the liquid at 14 temperatures between 293 and 137 K. Some Raman bands changed their peak heights with temperature but were countered by changes in linewidths, and from three band pairs assigned to the anti and gauche conformers, the conformational enthalpy difference Δ_confH(gauche–anti) was found to be 0 ± 0.3 kJ mol⁻¹ in the liquid. Infrared spectra were obtained in the vapor and in the liquid phases at ambient temperature and in the solid phases at 78 K in the range 4000–400 cm⁻¹. The sample crystallized immediately when deposited on the CsI window at 78 K, and many bands present in the vapor and liquid disappeared. Additional infrared spectra in argon matrixes at 5 K were recorded before and after annealing to temperatures 20–34 K. Quantum chemical calculations were carried out at the HF, MP2 and B3LYP levels with a variety of basis sets. The HF and DFT calculations suggested the anti conformer as the more stable one by ca 1 kJ mol⁻¹, while the MP2 results favored gauche by up to 0.4 kJ mol⁻¹. The Complete Basis Set method CBS‐QB3 gave an energy difference of 0.1 kJ mol⁻¹, with anti as the more stable one. Scaled force fields from B3LYP/cc‐pVQZ calculations gave vibrational wavenumbers and band intensities for the two conformers. Copyright © 2007 John Wiley & Sons, Ltd.     

Vibrational spectroscopic studies,conformations and ab initio calculations of 1,2‐bis(trifluorosilyl)ethane (SiF3CH2CH2SiF3)

Infrared spectra of 1,2‐bis(trifluorosilyl)ethane (SiF₃CH₂CH₂SiF₃) were obtained in the vapour and liquid phases, in argon matrices and in the solid phase. Raman spectra of the compound as a liquid were recorded at various temperatures between 293 and 270 K and spectra of an apparently crystalline solid were observed. The spectra revealed the existence of two conformers (anti and gauche) in the vapour, liquid and in the matrix. When the vapour was chock‐frozen on a cold finger at 78 K and annealed to 150 K, certain weak Raman bands vanished in the crystal. The vibrational spectra of the crystal demonstrated mutual exclusion between IR and Raman bands in accordance with C_2h symmetry. Intensity variations between 293 and 270 K of pairs of various Raman bands gave ΔH(gauche—anti) = 5.6 ± 0.5 kJ mol⁻¹ in the liquid, suggesting 85% anti and 15% gauche in equilibrium at room temperature. Annealing experiments indicate that the anti conformer also has a lower energy in the argon matrices, is the low‐energy conformer in the liquid and is also present in the crystal. The spectra of both conformers have been interpreted, and 34 anti and 17 gauche bands were tentatively identified. Ab initio and density functional theory (DFT) calculations were performed giving optimized geometries, infrared and Raman intensities and anharmonic vibrational frequencies for both conformers. The conformational energy difference derived in CBS‐QB3 and in G3 calculations was 5 kJ mol⁻¹. Copyright © 2009 John Wiley & Sons, Ltd.     

Computational studies of the halooxyhalocarbenes XOCX (X = F,Cl)

Ab initio calculations at the B3LYP, MP2, MP4 and CCSD(T) levels of theory were performed to predict the stability of the halooxyhalocarbenes, XOCX (X = F, Cl). The calculations indicate that the nonlinear FOCF molecule is stable with an energy 16 kJ mol^?1 below the energy of possible reacting fragments F₂ and CO. However, a nonlinear equilibrium structure for ClOCCl was located, but it was found to be about 192 kJ mol^?1 higher in energy than the energy of Cl₂ and CO. The charge distribution in these molecules was analysed using the atoms in molecules (AIM) method.     

N.M.R. study of internal motion in hexahydrated acid fluorides of cobalt and nickel

A linear relationship between the viscosity B-coefficient of the Jones-Dole equation for aqueous solutions of certain alkali metal salts and the enthalpy of hydration of the gaseous monatomic constituent ions has been established. The assumption that a similar rectilinear law applies to ammonium halides appears justified and the enthalpies of solution of NH₄ ⁺(g)+X^-(g) have been estimated and used to obtain magnitudes for the lattice energies of NH₄X(c) [X=F, Cl, Br, I]. In conjunction with experimental thermochemical data, the latter yield consistent results for the proton affinity of ammonia ΔH ₁ ^?=860·5±2·0 kJ mol^-1 (298·15 K). The lattice energies of the salts are, (in kJ mol^-1) 834 (NH₄F), 708 (NH₄Cl), 682 (NH₄Br) and 637(NH₄I).     

Raman and ab initio study of the conformational isomerism in the 1‐ethyl‐3‐methyl‐imidazolium bis(trifluoromethanesulfonyl)imide ionic liquid

The calculated and experimental Raman spectra of the (EMI⁺)TFSI⁻ ionic liquid, where EMI⁺ is the 1‐ethyl‐3‐methylimidazolium cation and TFSI⁻ the bis(trifluoromethanesulfonyl)imide anion, have been investigated for a better understanding of the EMI⁺ and TFSI⁻ conformational isomerism as a function of temperature. Characteristic Raman lines of the planar (p) and non‐planar (np) EMI⁺ conformers are identified using the reference (EMI⁺)Br⁻ salt. The anion conformer of C₂ symmetry is confirmed to be more stable than the cis (C₁) one by 4.5 ± 0.2 kJ mol⁻¹. At room temperature, the population of trans (C₂) anions and np cations is 75 ± 2% and 87 ± 4%, respectively. Fast cooling quenches a metastable glassy phase composed of mainly C₂ anion conformers and p cation conformers, whereas slow cooling gives a crystalline phase composed of C₁ anion conformers and of np cation conformers. Copyright © 2006 John Wiley & Sons, Ltd.     

Vibrational and reorientational dynamics,crystal structure and solid–solid phase transition studies in [Ca(H2O)6]Cl2 supported by theoretical (DFT) calculations

[Ca(H₂O)₆]Cl₂ between 93 and 300 K possesses two solid phases. One phase transition (PT) of the first‐order type at = 218.0 K (on heating) and = 208.0 K (on cooling) was determined by differential scanning calorimetry. Thermal hysteresis of this PT (10 K), as well as the heat flow anomaly sharpness, suggests that the detected PT is a first‐order one. The entropy change value [ΔS ≈ 8.5 J mol⁻¹ K⁻¹ ≈ Rln(2.8)] associated with the observed PT suggests a moderate degree of molecular dynamical disorder of the high‐temperature phase. The temperature dependencies of the full width at half maximum values of the infrared band are due to ρ(H₂O)A₂ mode (at 205 cm⁻¹), and two Raman bands are arising from τ(H₂O)E and τ(H₂O)A₁ modes (at ca. 410 and 682 cm⁻¹, respectively), suggesting that the observed PT is associated with a sudden change of speed of the H₂O reorientational motions. The estimated mean value of activation energy for the reorientation of the H₂O ligands in the high‐temperature phase is ca. 11.4 kJ mol⁻¹ from Raman spectroscopy and 11.9 kJ mol⁻¹ from infrared spectroscopy. X‐ray single‐crystal diffraction measurement and spectroscopic studies (infrared, Raman and inelastic neutron scattering) also confirm that [Ca(H₂O)₆]Cl₂ includes two sets of differently bonded H₂O molecules. Ab initio calculations of the complete unit cell of one molecule of calcium chloride with a different number of water molecules (2, 4 and 6) have also been carried out. A comparison of Fourier Transform Infrared (FT‐IR), Fourier Transform Raman Scattering (FT‐RS) and inelastic neutron scattering spectroscopies results with periodic density functional theory calculations was used to provide a complete assignment of the vibrational spectra of [Ca(H₂O)₆]Cl₂. Copyright © 2016 John Wiley & Sons, Ltd.     

Emission spectra of polyatomic radical cations in the gas phase: Ã2Πu → X̃2Πg band systems of Cl(CC)2 Cl+, Br(

Emission spectra of the dihalodiacetylene radical cations, X(CC)₂X⁺ with X = Cl, Br and I, excited in the gaseous phase by low energy e     

A far-infrared investigation of cathodochromic sodalite

Sodalite absorption bands in the 50–350 cm⁻¹ region were studied using Fourier transform spectroscopy. Vibrational modes were identified using chemical substitution, H₂ and vacuum-annealing, and coloration studies. A bromosodalite band at 294 cm⁻¹ was assigned to an Si—O—Al mode based on Ge substitutions for Si. A bromosodalite band at 200 cm⁻¹ is assigned to an Na—cage vibration based on previous H₂annealing studies and chemical substitution of Ge for Si, Ga for Al and Cl and I for Br. A 107 cm⁻¹ band is the Na—Br related vibration, and substitution of 100% Cl for Br moved this band to 111 cm⁻¹, H₂ and vacuum-annealing studies show a correlation between the amount of Br removed from bromosodalite during annealing and the area of the 107 cm⁻¹ band. A band at 68 cm⁻¹ is the Na—Br mode based on 100% substitution of Cl for Br. Coloration studies in the 50–150 cm⁻¹ region show no changes attributable to F-center formation.     

Involvement of weak C?H···X hydrogen bonds in metal‐to‐semiconductor regime change in one‐dimensional organic conductors (o‐DMTTF)2X (X = Cl,Br, and I): combined IR and Raman studies

We report on the infrared (IR) and Raman studies of the three isostructural quasi‐one‐dimensional cation radical salts of 3,4‐dimethyl‐tetrathiafulvalene (o‐DMTTF)₂X (X = Cl, Br, and I), which all exhibit metallic properties at room temperature and undergo transitions to a semiconducting state in two steps: a soft metal‐to‐semiconductor regime change in the temperature region T_ρ = 5–200 K and then a sharp phase transition at about T_MI = 50 K. Polarized IR reflectance spectra (700–16 000 cm⁻¹) and Raman spectra (50–3500 cm⁻¹, excitation λ = 632.8 nm) of single crystals were measured as a function of temperature (T = 5–300 K) to assess the eventual formation of a charge‐ordered state below 50 K. Additionally, the temperature dependence of the IR absorption spectra of powdered crystals in KBr discs was also studied. The Raman spectra and especially the bands related to the CC stretching vibration of o‐DMTTF provide unambiguous evidence of uniform charge distribution on o‐DMTTF down to the lowest temperatures, without any modification below 50 K. However, the temperature dependence of Raman spectra indicates a regime change below about 200 K. Temperature dependence of both electronic dispersion and vibrational features observed in the IR spectra also clearly confirms the regime change below about 200 K and shows the involvement of C H···X hydrogen bonds in the electronic localization; some spectral changes can be also related with the phase transition at 50 K. Additionally, using density functional theory methods, the normal vibrational modes of the neutral o‐DMTTF⁰ and cationic o‐DMTTF⁺ species, as well as their theoretical IR and Raman spectra, were calculated. The theoretical data were compared with the experimental IR and Raman spectra of neutral o‐DMTTF molecule. Copyright © 2011 John Wiley & Sons, Ltd.     

Raman spectroscopy of M3B7O13X boracites (M = Cr,Co,Ni,Cu,Zn,Cd; X = Cl,Br,I)

We report results of a Raman study on single crystals of 16 boracites M₃B₇O₁₃X (M = Cr,Co,Ni,Cu,Zn,Cd; X = Cl,Br,I) over a broad temperature range. The Raman modes for all boracites in their high‐temperature prototype cubic (F3c) phase are compared. With decreasing temperature, most (but not all) compounds present a transition to the low‐temperature orthorhombic phase (Pca2₁) or to a sequence of orthorhombic, monoclinic (Pa), and trigonal (R3c) phases. The variations of the Raman spectra through different phases are studied in detail. Special attention is paid to the temperature hysteresis near the transitions and the dependence of transition temperature on the direction of crystal growth for the same material. Copyright © 2014 John Wiley & Sons, Ltd.     

The vapor phase Raman spectra,Raman band contour analyses,Coriolis constants,force constants,and values for thermodynamic functions of the trihalides of group V

The vapor phase Raman spectra have been recorded of the molecules PX₃ (X = F, Cl, or Br), AsX₃ (X = F, Cl, Br, or I), and SbX₃ (X = Cl, Br, or I) in sealed tubes at 22–365°C as appropriate. Attempts to record the vapor phase Raman spectra of the molecules PI₃, SbF₃, and BiX₃ (X = F, Cl, Br, or I) were unsuccessful. The infrared and Raman rotational branch separations of the a₁ species fundamentals for these molecules are in agreement with the theoretically calculated values. The Raman band contours of the e-species fundamentals have been analyzed to yield, in favorable cases, values for the corresponding Coriolis constants which have been compared with those obtained from infrared band contour analyses, and which have been employed to constrain the e-species force constants. It is concluded that the Raman contour method for defining Coriolis and thus force constants should be regarded as further, but not necessarily the best, experimental method with which to help to constrain the field. Values for various thermodynamic functions of the molecules have been calculated from the new values for the fundamental frequencies and from the most recent structural data.     

Photoelectron spectra of bis-cyclopentadienyl metal dihalides

He(I) and HE(II) photoelectron spectra are reported for (η-C₅H₅)₂MX₂ (M = Ti; X = F, Cl, Br, I: M = Zr, Hf; X = Cl, Br: M = Ta; X = Cl, Br) and (η-MeC₅H₄)₂MX₂ (M = Nb, X = Cl: M = Mo; X = Cl, Br, I). A substantial variation is found in the ordering of the halogen and cyclopentadienyl ionizations, the order being dependent on the metal as well as on the halogen. The compounds may be divided into three classes, namely, those in which the electrons in cyclopentadienyl e₁ orbitals ionize at a lower energy than those occupying halogen pπ orbitals, those in which halogen pπ electrons have lower ionization energy than cyclopentadienyl e₁ electrons and those in which the corresponding electrons arise from extensively delocalized molecular orbitals with significant contributions from both these categories of fragment orbital.     

The nature of the electronic factor governing diastereofacial selectivity in remotely substituted (X) 2‐adamantyl cations: 5‐X versus 4‐X substitution

A limited series of 4^eq‐substituted (X) 2‐methyleneadamantanes ( 6 , Y?CH₂, X?F, Cl, Br, I, and SnMe₃) has been synthesized and diastereoselectivities for their hydrochlorination (HCl/CH₂Cl₂) have been determined. Diastereoselectivities for the fluorination (DAST/CH₂Cl₂) of secondary alcohol mixtures, obtained from the hydride reduction of the precursor ketones ( 6 ,Y?O) to the alkenes, have also been measured. A comparison of this selectivity data for nucleophilic trapping of 4^eq‐substituted (X) 2‐adamantyl cations ( 4 , R?H and Me) with the corresponding information for 5‐substituted (X) 2‐adamantyl cations ( 1 , R?H and Me) has revealed important distinctions between the two series. In particular, whereas extended hyperconjugative effects appear to be the predominant electronic effect governing facial selectivity in the 5,2‐series, electrostatic influences prevail in the 4,2‐disposition. Copyright © 2007 John Wiley & Sons, Ltd.     

NQR, NMR and Crystal Structure Studies of [C(NH2)3]2HgX4 (X = Br, I)

The crystal structure of [C(NH₂)₃]₂HgBr₄ has been determined at room temperature: monoclinic, space group C2/c, with a = 10.035(2), b = 11.164(2), c = 13.358(3) Å, β = 111.67(3)°, and Z = 4. The crystal consists of planar [C(NH₂)₃]⁺ and distorted tetrahedral [HgBr₄]^2? ions. The Hg atom is located on a two-fold axis such that two sets of inequivalent Br atoms exist in an [HgBr₄]^2? ion. In accordance with the crystal structure, two ⁸¹Br NQR lines widely separated in frequency were observed between 77 and ca. 380 K. [C(NH₂)₃]₂HgI₄ yielded four ¹²⁷I NQR lines ascribable to m = ±1/2 ? ±3/2 transitions, indicating that its crystal structure is different from the bromide complex. The ¹H NMR T ₁ measurements showed a single minimum for the bromide but two minima for the iodide. The analyses based on the C₃ reorientations of the planar [C(NH₂)₃]⁺ ions gave the activation energies of 29.8 kJ mol^?1 for the bromide, and 30.2 and 40.0 kJ mol^?1 for the iodide.     

Concentration‐ and temperature‐dependent conformation change of cyclohexyl isocyanide on gold nanoparticle surfaces

The conformational changes of cyclohexyl isocyanide (CHNC) on gold nanoparticle surfaces were investigated by means of concentration‐ and temperature‐dependent surface‐enhanced Raman scattering (SERS). The equatorial chair conformer appeared to be dominant at high‐bulk concentrations or low temperatures, whereas both the equatorial and axial chair conformers of CHNC were found to exist at low‐bulk concentrations or high temperatures as in the previous reports of cyclohexanethiol (CHT). Depending on concentrations and temperatures, the spectral changes of the NC stretching vibration on gold nanoparticles appeared to be more conspicuous than those of the cyclohexyl ring modes. A density functional theory (DFT) calculation was performed at the level of B3LYP/6‐31G + + (d,p) to compare the energetic stability of the various conformers of CHT and CHNC. The energy differences between the equatorial and axial chair conformers were predicted to be smaller for CHNC than for CHT by ∼3 kJ mol⁻¹ from the DFT calculation. Copyright © 2008 John Wiley & Sons, Ltd.     

Rotational isomers of methyl trans-cinnamate: A Raman study

The Raman and infrared spectra of methyl trans-cinnamate were measured as a function of temperature in the liquid and solid phases. The temperature dependence of the band intensities established the presence of two conformers in the liquid phase (the s-cis and s-trans forms, with CC CO dihedral angles equal to 0° and 180°, respectively; ΔH_{(s-trans)-(s-cis)} = 3.43 ± 0.84 kJ mol⁻¹) and led to the conclusion that the thermodynamically most stable s-cis form is the only form present in the solid.     

IR/Raman spectroscopy and DFT calculations of cyclic di‐amino acid peptides. Part III: comparison of solid state and solution structures of cyclo(L‐Ser‐L‐Ser)

B3‐LYP/cc‐pVDZ calculations of the gas‐phase structure and vibrational spectra of the isolated molecule cyclo(L ‐Ser‐L ‐Ser), a cyclic di‐amino acid peptide (CDAP), were carried out by assuming C₂ symmetry. It is predicted that the minimum‐energy structure is a boat conformation for the diketopiperazine (DKP) ring with both L ‐seryl side chains being folded slightly above the ring. An additional structure of higher energy (15.16 kJ mol⁻¹) has been calculated for a DKP ring with a planar geometry, although in this case two fundamental vibrations have been calculated with imaginary wavenumbers. The reported X‐ray crystallographic structure of cyclo(L ‐Ser‐L ‐Ser), shows that the DKP ring displays a near‐planar conformation, with both the two L ‐seryl side chains being folded above the ring. It is hypothesized that the crystal packing forces constrain the DKP ring in a planar conformation and it is probable that the lower energy boat conformation may prevail in the aqueous environment. Raman scattering and Fourier‐transform infrared (FT‐IR) spectra of solid state and aqueous solution samples of cyclo(L ‐Ser‐L ‐Ser) are reported and discussed. Vibrational band assignments have been made on the basis of comparisons with the calculated vibrational spectra and band wavenumber shifts upon deuteration of labile protons. The experimental Raman and IR results for solid‐state samples show characteristic amide I vibrations which are split (Raman: 1661 and 1687 cm⁻¹, IR: 1666 and 1680 cm⁻¹), possibly due to interactions between molecules in a crystallographic unit cell. The cis amide I band is differentiated by its deuterium shift of ∼30 cm⁻¹, which is larger than that previously reported for trans amide I deuterium shifts. A cis amide II mode has been assigned to a Raman band located at 1520 cm⁻¹. The occurrence of this cis amide II mode at a wavenumber above 1500 cm⁻¹ concurs with results of previously examined CDAP molecules with low molecular weight substituents on the C^α atoms, and is also indicative of a relatively unstrained DKP ring. Copyright © 2009 John Wiley & Sons, Ltd.     

Spectroscopic and ab initio characterization of the conformational states of the bis(perfluoro‐ ethanesulfonyl)imide anion (BETI−)

Ab initio calculations were combined with infrared and Raman studies to spectroscopically distinguish the two conformers of the BETI⁻ or bis(perfluoroethanesulfonyl)imide anion, [N(SO₂C₂F₅)₂]⁻, as was previously done for [N(SO₂CF₃)₂]⁻, the TFSI⁻ anion. BETI⁻ is predicted to exist, as does TFSI⁻, in two conformational states of C₂ and C₁ symmetries, the former being more stable by about 6 kJ mol⁻¹. This conformational isomerism produces weak Raman splittings that can be resolved only at low temperatures. Thus, solutions of LiBETI with glymes cooled down to 113 K exhibit a very intense Raman doublet at ∼745–740 cm⁻¹ characteristic of a quenched conformational equilibrium between the C₂ and C₁ conformers. Annealing of the (G3)₂:LiBETI solvate, where G3 is triglyme, leads to an ordered crystalline phase with all the anions in the C₂ conformation, as in the reference salt Me₄NBETI. This conclusion cannot be extended to all the systems in which the BETI⁻ anion interacts weakly with the cation, however, since the diglyme solvate, (G2)₂:LiBETI, contains both C₁ and C₂ anion conformers (in 2:1 ratio) at low temperatures independent of the sample's thermal history. The conformational splittings are larger in infrared, as illustrated by two absorption bands at 601 and 615 cm⁻¹ associated with the C₂ and C₁ anion conformers, respectively. It is possible to follow the relative intensities of these bands in a LiBETI solution with diglyme above room temperature up to 387 K. The C₂ conformer is found to be more stable than C₁ by 4.7 ± 0.7 kJ mol⁻¹. Copyright © 2006 John Wiley & Sons, Ltd.     

Ultraviolet photoelectron spectra of gas phase and condensed tin and lead dihalides (MX2 ; M = Sn,Pb; X = Cl,Br, I)

The photoelectron spectra and electronic structures of the methylene dihalides, CH₂X₂ (X = F, Cl, Br and I), have been calculated by the overtapping-spheres SCF-Xα-MS method. The results are in good agreement with experimental data. Calculated assignments of the spectra are also presented and interpreted by assuming interaction between lone-pair and bonding orbitals.