Infrared matrix isolation studies of complexes formed between dimethylsulfide, dimethyldisulfide and nitrous acid

The complexes formed by dimethylsulphide (DMS) and dimethyldisulphide (DMDS) with two isomers of nitrous acid have been observed, and characterised in argon and nitrogen matrices. The ν₁ OH stretching vibration of the perturbed trans-HONO monomer is 425 and 294 cm⁻¹ red shifted, respectively, for the DMS and DMDS complex in solid argon, and 441 and 301 cm⁻¹ in solid nitrogen. A large blue shift is also observed for the ν₃ NOH in-plane deformation mode: 101 and 80 cm⁻¹ for DMS–HONO-trans in argon and nitrogen matrices and 46 cm⁻¹ for DMDS–HONO-trans in nitrogen matrix. The results indicate formation of strong hydrogen bonds in the studied DMS–HONO and DMDS–HONO systems. The origin of the complicated shape of the ν₁ OH absorption is discussed. Similarities and differences between argon and nitrogen matrices are considered.     

The conformations of 1,2-acenaphthene derivatives and steric interaction of contiguous nitroxy groups

Inter-oxygen distances and conformational flexibility were estimated for cis- and trans-1,2-acenaphthenediol from X-ray data, intramolecular hydrogen bonding, the kinetics of glycol cleavage, and cyclization experiments. The optical and NMR spectra of the isomeric dinitrate esters and related compounds in solution showed significant differences. The symmetric and anti-symmetric stretching bands of the nitroxy group occurred at 1276 ± 2 cm⁻¹ and 1639 ± 7 cm⁻¹ respectively in the trans-dinitrate and in ethyl and benzyl nitrates and were shifted to higher frequencies by 9 cm⁻¹ and 16 cm⁻¹ respectively in the cis-dinitrate. The analogy to similar effects observed in cyclic 1,2-diketones, -haloketones, and o-halonitrobenzenes suggested intramolecular interaction of the contiguous nitroxy groups.

The reaction of the dinitrates with pyridine at 25° was pseudo first-order and the ratio k_trans/k_cis of 6·5 was consistent with an E_CO mechanism involving nitroxy group interaction in the cis isomer.     

A comparative ab initio study of the geometry and force field of thionformic acid with formic and thiolformic acids

The energy and force field for the planar cis and trans conformers of thionformic acid have been calculated using the 4–31 G basis set, augmented by a complete set of d-functions on the sulfur atom, with full geometry optimization. Extensive comparisons are made between the changes in geometry and selected force constants in going from cis- (chain) to the trans- (ring) structures of thionformic, thiolformic and formic acid. These changes are discussed in terms of a hydrogen bonding type of interaction in the O---HS, S---HO and O---HO structural units respectively. Of the thioacid conformers, the trans-thiol is found to be the most stable; the trans-thion and cis-thiol both about 10 kJ mol⁻¹ less stable; and the cis-thion the least stable by about 38 kJ mol⁻¹.     

The active catalytic species and its isomerisation in the catalytic carbonylation of methanol — a density functional study

The Monsanto acetic acid process is one of the most effective ways to produce acetic acid industrially. This process has been studied experimentally but theoretical investigations are so far sparse. In the current work the active catalytic species [Rh(CO)₂I₂]⁻ (1) and its isomerisation has been studied theoretically using the hybrid B3LYP exchange and correlation functional. Similar calculations has been performed for the iridium complex [Ir(CO)₂I₂]⁻ (2) that also is catalytically active in the methanol carbonylation. Experimental work has confirmed the existence of the cis forms of the active catalytic species, but they do not rule out the possibility of the trans isomers. Our gas phase results show that cis-1 has 4.95 kcal/mol lower free energy than trans-1, and cis-2 has 10.39 kcal/mol lower free energy than trans-2. In the case of rhodium, trans-1 can take part to the catalytic cycle but in case of iridium this is not very likely. We have also investigated the possible mechanisms of the cis to trans conversions. The ligand association mechanism gave free energy barrier of 13.7 kcal/mol for the rhodium complex and 19.8 kcal/mol for iridium. Thus the conversion for the rhodium complex is feasible whereas for iridium it is unlikely.     

Matrix isolation infrared studies of complexes formed between substituted phenols and trimethylamine

Infrared spectroscopy and matrix isolation technique have been used to study the 1 : 1 complexes formed between 2,4,5-trichlorophenol (TCP), pentachlorophenol (PCP) or 2-chloro-4,6-dinitrophenol (CNP) and trimethylamine (TMA) isolated in solid argon. The results were analyzed in relation to the type of complex formed. Depending on the proton-donor ability of the phenol three different types of hydrogen bonded complexes have been identified in argon matrices. The weakest phenol in the series, TCP (pK_a = 6.72), forms a strong molecular hydrogen bonded complex with TMA as indicated by the broad ν(OHN) absorption with a maximum at 2490 cm⁻¹ and a band at 811 cm⁻¹ due to the ν_s(C₃N) mode of the perturbed amine. The strongest phenol, CNP (pK_a = 2.01), interacts with TMA in an argon matrix to form ionic complex with the proton transferred to the base molecule. This is evidenced by the presence of the ν(NH⁺---O⁻) absorption between 3000−1800 cm⁻¹, by the ν_as(C₃N⁺) and ν_s(C₃N⁺) absorptions due to the protonated amine and by numerous product bands due to the relatively strongly perturbed modes of the phenol ring. The interaction between TMA and a phenol of intermediate strength, PCP (pK_a = 4.74), in solid argon probably leads to the formation of two types of hydrogen bonded complexes: an ionic complex with the proton transferred to the amine molecule and a pseudosymmetric one with the proton more or less equally shared between the phenol and amine molecules. In this case the protonic absorption consists of two broad features situated in the 3000–1600 cm⁻¹ and 950–400 cm⁻¹ regions due to the ν(NH⁺O⁻) and ν(OHN) modes, respectively.     

Syntheses, crystal structures and electronic properties of a series of copper(II) complexes with 3,5-halogen-substituted Schiff base ligands and their solutions

We have systematically investigated the structural features, electronic properties, thermally-induced structural phase transitions and absorption spectra depending on the solvent for ten Cu(II) complexes with 3,5-halogen-substituted Schiff base ligands. Structural characterization of two new complexes, bis(N-R-1-phenylethyl- and N-R,S-2-butyl-5-bromosalicydenaminato-κ²N,O)copper(II), reveals that they afford a compressed tetrahedral trans-[CuN₂O₂] coordination geometry with trans-N–Cu–N = 159.4(2)° and trans-O–Cu–O = 151.7(3)° for the 1-phenylethyl complex and trans-N–Cu–N = 157.9(3)° and trans-O–Cu–O = 151.0(3)° for the 2-butyl one. All the complexes exhibit a structural phase transition by heating in the solid state regardless of their structures at room temperature. The absorption spectra of a series of ten complexes exhibit a slight shift of the d–d band at 16 000–20 000 cm⁻¹ and remarkable shift of the π–π* band at 24 000–28 000 cm⁻¹, which suggests that the dipole moment of the solvents presumably affects the conformation of the π-conjugated moieties of the ligands rather than the coordination environment. We have also attempted ‘photochromic solute-induced solvatochromism’ by a system of bis(N-R-1-phenylethyl-3,5-dichlorosalicydenaminato-κ²N,O)copper(II) and photochromic 4-hydroxyazobenzene in chloroform solution. We successfully observed a change of the d–d and π–π* bands of the complex in the absorption spectra caused by cis–trans photoisomerization of 4-hydroxyazobenzene.     

Multidimensional anharmonic calculation of the vibrational frequencies and intensities for the trans and cis isomers of HONO with the use of normal coordinates

The equilibrium geometry and the potential energy and dipole moment surfaces have been determined for the cis and trans isomers of the HONO molecule by an ab initio Moller–Plesset (MP2) calculation with a wide set of atomic orbitals. The multidimensional anharmonic vibrational Schrodinger equations are solved using the variational method with the Hamiltonian and wave functions written in the normal coordinates of cis and trans isomers. All one- and two-dimensional and a number of three-dimensional vibrational problems are solved to obtain the energy levels and vibrational eigenfunctions. The frequencies and intensities for the fundamental, overtone and some combination bands are determined in good agreement with the available experimental results. The calculation shows the strength of coupling between different vibrational modes and reveals the presence of strong resonances between the (v₁, v₃, v₆) and (v₁, v₃−1, v₆+2) states of cis-HONO. This fact may be important for understanding the energy redistribution between the intermolecular degrees of freedom. The magnitude and direction of vibrationally averaged ground-state dipole moment of both isomers, as well as the direction of transition dipole moments, are in good agreement with the experimental findings. The changes in the values of dipole moment and some geometrical parameters of cis- and trans-HONO on vibrational excitation are also computed.     

Organometallic complexes for nonlinear optics: Part 32: Synthesis, optical spectroscopy and theoretical studies of some osmium alkynyl complexes

The complexes trans-[Os(CCPh)Cl(dppe)₂] (1), trans-[Os(4-CCC₆H₄CCPh)Cl(dppe)₂] (2), and 1,3,5-{trans-[OsCl(dppe)₂(4-CCC₆H₄CC)]}₃C₆H₃ (3) have been prepared. Cyclic voltammetric studies reveal a quasi-reversible oxidation process for each complex at 0.36–0.39 V (with respect to the ferrocene/ferrocenium couple at 0.56 V), assigned to the Os^II/III couple. In situ oxidation of 1–3 using an optically transparent thin-layer electrochemical (OTTLE) cell affords the UV–Vis–NIR spectra of the corresponding cationic complexes 1⁺–3⁺; a low-energy band is observed in the near-IR region (11 000–14 000 cm⁻¹) in each case, in contrast to the neutral complexes 1–3 which are optically transparent below 20 000 cm⁻¹. Density functional theory calculations on the model compounds trans-[Os(CCPh)Cl(PH₃)₄] and trans-[Os(4-CCC₆H₄CCPh)Cl(PH₃)₄] have been used to rationalize the observed optical spectra and suggest that the low-energy bands in the spectra of the cationic complexes can be assigned to transitions involving orbitals delocalized over the metal, chloro and alkynyl ligands. These intense bands have potential utility in switching nonlinear optical response, of interest in optical technology.     

Cis- and trans-3-hexene: infrared spectrum in liquid argon solution, ab initio calculations of equilibrium geometry, normal coordinate analysis, and vibrational assignments

The infrared spectra of cis-3-hexene and trans-3-hexene dissolved in liquid argon have been obtained at temperatures from 93 to 120 K. The absorptions were observed with a low-temperature cell and a Fourier transform infrared spectrophotometer. Ab initio molecular orbital calculations were performed to obtain the equilibrium geometry, vibrational frequencies, force fields, and infrared intensities. The calculations were done at the Hartree-Fock level using 6-31G basis set. The Cartesian force fields from ab initio calculations have been converted to the force field in symmetry coordinates. The scale factors of ab initio calculated force fields were determined. Normal coordinate calculations were performed using a scaled quantum mechanical (SQM) force field. Vibrational normal modes calculated for the lowest energy rotamers of cis- and trans-3-hexene have been assigned to infrared absorption bands observed in liquid argon solution. The assignments were based on calculated frequencies and potential energy distributions. The equilibrium geometries of the two lowest energy rotamers (symmetry C₂ and C_s) of cis-3-hexene and of the three lowest energy rotamers (symmetry C_i, C₂, and C₁) of trans-3-hexene were calculated. Variable temperature studies of the infrared spectrum of cis- and trans-3-hexenes dissolved in liquid argon were done to obtain the ΔH of conversion between the rotamers C₂ and C_s of cis-3-hexene and between the rotamers C_i, C₂, and C₁ of trans-3-hexene.     

An ab initio potential energy surface for the υ4 vibrational mode of hydrogen peroxide

In this paper, the levels and the torsional microstates of hydrogen peroxide are determined from fully optimized ab initio calculations using a nuclear model in one dimension. Calculations have been performed at the MP2 level with the 6-311 G(2df,2pd), 6-31 1+G(2df,2pd), cc-pVTZ and AUG-cc-pVTZ basis sets including polarization orbitals and diffuse functions. The most stable conformation, calculated with the MP2/AUG-cc-pVTZ approach, is a trans–gauche conformer lying at 67.5° from the trans structure. By using the same level of calculations, the heights of the trans and cis barriers have been determined to be 386.5 and 2643.8 cm⁻¹ in a good agreement with the experimental data. The variational torsional levels split into four components by the tunnelling effect of the barriers. The splitting of the fundamental level caused by the trans barrier has been found to be 11.8683 cm⁻¹, whereas the splitting caused by the cis barrier is insignificant under n=2. Current ab initio energies confirm the experimental assignments and verify the separability of the torsion from the rest of the vibrations. However, the experimental relation of dependence on the torsion of the rotational constants cannot be reproduced in one-dimension and depends on several additional vibrational effects.     

A two-dimensional potential function for bent hydrogen bonded systems. II-6-hydroxy-2-formylfulvene

A simple and practical method for treating the non-adiabatic proton tunneling in 6-hydroxy-2-formylfulvene was used. A two dimensional potential energy surface function, which couples OH stretching and in-plane bending modes, has been constructed for motion of hydrogen by the aid of quantum mechanical calculations at MP2/6-31G** level for a fixed skeleton geometry. This potential was used for calculation of energy levels from which a tunneling splitting of 181±14 cm⁻¹ was obtained in an excellent agreement with the experimental value of at least 150 cm⁻¹. The calculated barrier height for these results was about 26–27 kJ/mol. This method also assigns a broad band at about 1740 cm⁻¹ to the OH in-plane bending mode. The calculated hydrogen bond strength was estimated to be about 80 kJ/mol.     

Vibrational spectra and structure of chlorine substituted cyclopropanes : Part I. cis-1,2,3-Trichlorocyclopropane

The synthesis of cis-1,2,3-trichlorocyclopropane is reported. The infrared spectra have been recorded between 4000 and 400 cm⁻¹ in the polycrystalline solid phase, and between 4000 and 200 cm⁻¹ in the gas phase. The spectrum of a solution in carbon disulphide was measured from 1400 to 400 cm⁻¹. The Raman spectrum has been obtained between 4000 and 100 cm⁻¹ in the solid phase. An assignment of the fundamentals of the title compound is proposed and compared with similar molecules. The spectrum unequivocally proves the C_JV structure of the molecule.     

Carbon—hydrogen stretching vibrations in fluorocyclohexanes

For perfluorocyclohexane derivatives in which not more than one fluorine at each carbon atom is replaced by a hydrogen atom, it is established that C---H groups with an axial hydrogen show infra-red absorption at 2980 cm⁻¹ and with equatorial hydrogen at 2974 cm⁻¹. With 1H/2H-, 1H:2H/- and 1H:3H/-decafluorocyclohexane the frequencies are reduced somewhat. When the C---H groups are adjacent to a double bond the absorption is at 2961 cm⁻¹, while olefinic C---H groups absorb near 3095 cm⁻¹ in the fluorocarbon series. The C---H absorption is at 3102 cm⁻¹ in pentafluorobenzene.     

High resolution electronic spectroscopy of p-vinylphenol in the gas phase

A recent controversy regarding the proper assignment of two closely spaced bands in the S₁ ← S₀ electronic transition of trans-p-coumaric acid (pCA) has been addressed by recording their spectra at full rotational resolution. The results show unambiguously that the carrier of these two bands is p-vinylphenol (pVP), a thermal decomposition product of pCA. The two bands belong to two conformers of pVP; trans-pVP at 33,207.3 cm⁻¹ and cis-pVP at 33,211.8 cm⁻¹.     

Reactivity of ruthenium complexes with uninegative (X,S)-donor ligands (X = S,P)—II. Phosphine substitution in [Ru(S,S)2(PR3)2] derivatives. Crystal structure of trans-bis(O-ethyldithiocarbonate)bis(dimethylphenylphosphine)-ruthenium(II)

The complexes [Ru(S,S)₂(PPh₃)₂] [S,S = EtCOCS₂⁻, (CH₂)₄NCS₂⁻] react with a variety of tertiary phosphines with the substitution of triphenylphosphine and the formation of [Ru(S,S)₂(PR₃)₂]. The reaction occurs with the formation ofthe cis isomer, except for the complex with PMe₂Ph that gives rise to the trans isomer as the crystal structure shows. The effect of the different phosphines on the ruthenium complex is analysed in terms of the spectroscopic and electrochemical properties of the isolated compounds. The cyclic voltammetric studies of the cis complexes show that isomerization to the trans isomer occurs on oxidation. This isomerization is not observed in the trans-[Ru(S,S)₂(PMe₂Ph)₂] complexes that give rise to stable trans-ruthenium(II)/ruthenium(III) couples. In a similar way the diphosphine complexes afford a quasi-reversible cis-ruthenium(II)/ruthenium(III) process.     

Binuclear methyplatinum and phenylplatinum complexes with bis(dimethylphosphino)methane ligands

Reaction of cis-[Ptph₂(SMe₂)₂] with Me₂PCH₂PMe₂ (dmpm) gave cis-[PtPh₂(dmpm-P)₂] (1) or cis,cis-[Pt₂Ph₄(μ-dmpm)₂] (2) and reaction of 1 with [Pt₂Me₄(μ-SMe₂)₂] gave cis,cis-[Ph₂Pt(μ-dmpm)₂PtMe₂] (3). Reaction of 1 with trans-[PtClR(SMe₂)₂] gave cis,trans-[Ph₂Pt(μ-dmpm)₂PtClR], R = Me (5) or Ph (6), and in polar solvents, these isomerized to give [Ph₂Pt(μ-dmpm)₂PtR]⁺Cl⁻. When R = Me, further isomerization via the phenyl group transfer gave [PhMePt(μ-dmpm)₂PtPh]⁺Cl⁻. Oxidative addition of methyl iodide occurred reversibly at the cis-[PtMe₂P₂ unit of 3 to give cis,fac-[Ph₂Pt(μ-dmpm)₂PtIMe₃] but complex 2 failed to react with MeI. A comparison with similar known complexes of Ph₂PCH₂PPh₂ (dppm) is made and differences are attributed primarily to the lower steric hindrance of dmpm.     

FT-Raman and FTIR spectra, normal coordinate analysis and ab initio computations of (2-methylphenoxy)acetic acid dimer

The Fourier Transform Raman and infrared spectra of the crystallized herbicide (2-methylphenoxy)acetic acid (MPA) have been recorded in the region 4000–400 cm⁻¹. The geometry, intermolecular hydrogen bond, and harmonic vibrational frequencies of MPA have been investigated with the help of B3LYP density functional theory (DFT) methods. The calculated molecular geometry has been compared with the experimental data obtained from XRD data. The assignments of the vibrational spectra have been carried out with the aid of normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology (SQMFF). The strong doubly hydrogen bonded interface of the dimerized system is well demonstrated by the red shift in OH stretching frequency concomitant with the elongation of bond length. The most stable structure of the dimer possesses center of symmetry and interaction energy of −83.642 kJ mol⁻¹ after the basis set superposition error (BSSE) correction by the counterpoise (CP) method. The natural bond orbital analysis (NBO) ascertains that the delocalization of unpaired electron of oxygen atom onto the CO bond causes double bond character.     

Vibrational spectrum of I(H2O)

The infrared spectrum of the ionic cluster I⁻(H₂O) was recorded from 3170 to 3800 cm⁻¹ by vibrational predissociation spectroscopy. A strong multiplet observed at 3415 cm⁻¹ and a narrow band at 3710 cm⁻¹ were assigned as a hydrogen-bonded OH stretch and free OH stretch respectively, indicating that H₂O forms a single hydrogen bond with the iodide anion. Ab initio vibrational frequencies and intensities were computed at the second-order Møller-Plesset (MP2) level for the minimum energy configuration, a nearly linear hydrogen-bonded isomer, and for a low-lying saddlepoint, a symmetric C_2v bridged isomer. The spectrum predicted for the hydrogen-bonded isomer agreed well with experiment.     

Kinetische und mechanistische untersuchungen von übergangsmetallkomplex-reaktionen : IX. Substitution von CO durch PPh3 in aminocarbinkomplexen: Präparative und kinetische untersuchungen

Pentacarbonyl(diethylaminocarbyne)chromium tetrafluoroborate, [(CO)₅₋ CrCNEt₂]BF₄ (I), reacts with PPh₃ with substitution of CO and formation of trans-tetracarbonyl(diethylaminocarbyne)triphenylphosphanechromium tetra-fluoroborate, trans-[PPh₃(CO)₄CrCNEt₂]BF₄ (III). Substitution of CO by PPh₃ in neutral trans-tetracarbonyl(halo)(diethylaminocarbyne)chromium complexes, trans-X(CO)₄CrCNEt₂ (IVa: X = Br, IVb: X = I), leads in a reversible reaction to the corresponding tricarbonyl complexes, mer-X(PPh₃)(CO)₃₋ CrNEt₂ (V), PPh₃ occupying the cis-position to the carbyne ligand. With PPh₃ in large excess both reactions follow a first-order rate law. This as well as the activation parameters (ΔH≠ = 104–113 kJ mol⁻¹, ΔS≠ = 64–71 J mol⁻¹ K⁻¹) indicate a dissociative mechanism.     

Vibrational (FT-IR and FT-Raman) and NMR studies on selected metal (Ca, Mn, Zn) complexes with ortho-, meta-, and para-iodobenzoic acids

The vibrational (FT-IR and FT-Raman) and NMR (¹H and ¹³C) spectra of Ca, Mn, and Zn complexes with ortho-, meta-, and para-iodobenzoic acids have been studied. The solid state samples of all complexes have been measured within the range 4000–400 cm⁻¹, while water solutions of ortho-iodobenzoates within the range 4000–800 cm⁻¹. Based on previous experimental data and normal mode calculations for simpler complexes the assignment of bands observed in vibrational spectra of studied compounds has been done. Some significant differences in vibrational structure (frequency and intensity of selected bands) have been observed and discussed. The effect of metal on ring vibrations and carboxylic anion stretching and deformation has been investigated. Also, influence of iodine substitution on the aromatic ring and carboxylic anion, depending on iodine ring position, has been discussed. In case of soluble compounds, wavenumbers of characteristic bands of water solution samples have been compared with wavenumbers of corresponding bands of solid state samples.