Vibrational overtone combination spectroscopy (VOCSY)—a new way of using IR and NIR data

This work explores a novel method for rearranging 1st order (one-way) infra-red (IR) and/or near infra-red (NIR) ordinary spectra into a representation suitable for multi-way modelling and analysis. The method is based on the fact that the fundamental IR absorption and the first, second, and consecutive overtones of NIR absorptions represent identical chemical information. It is therefore possible to rearrange these overtone regions of the vectors comprising an IR and NIR spectrum into a matrix where the fundamental, 1st, 2nd, and consecutive overtones of the spectrum are arranged as either rows or columns in a matrix, resulting in a true three-way tensor of data for several samples. This tensorization facilitates explorative analysis and modelling with multi-way methods, for example parallel factor analysis (PARAFAC), N-way partial least squares (N-PLS), and Tucker models. The vibrational overtone combination spectroscopy (VOCSY) arrangement is shown to benefit from the “order advantage”, producing more robust, stable, and interpretable models than, for example, the traditional PLS modelling method. The proposed method also opens the field of NIR for true peak decomposition—a feature unique to the method because the latent factors acquired using PARAFAC can represent pure spectral components whereas latent factors in principal component analysis (PCA) and PLS usually do not.     

Vibrational spectra,force constants and mean amplitudes of trimethylsilylacetylene (CH3)3SiCCH and (CD3)3SiCCD

The infrared and Raman spectra of (CD₃)₃SiCCD have been obtained. Normal coordinate analysis of trimethylsilylacetylene and its complete     

Structural relationships between dicopper diacetylide (Cu-C≡C-C≡C-Cu) and dicopper acetylide (Cu-C≡C-Cu)

Dicopper diacetylide Cu-C≡C-C≡C-Cu, prepared from butadiyne has been studied by FT-IR spectroscopy in comparison to dicopper acetylide Cu-C≡C-Cu. Upon ageing by exposure to air at room temperature, Cu-C≡C-Cu has been transformed into Cu-C≡C-C≡C-Cu as demonstrated by FT-IR spectroscopy and this compound is further transformed on standing in air. A special kind of solid state oxidative coupling reaction occurs so that polyynes chains are formed in these aged solids. It is shown that the FT-IR spectrum of copper acetylide prepared from ammonia solutions of Cu⁺ and Cu²⁺ ions is comparable to that of air oxidized Cu-C≡C-Cu (and Cu-C≡C-C≡C-Cu) prepared exclusively from Cu⁺ ions in presence of a reducing agent demonstrating that Cu²⁺ ions display the same oxidizing effect as oxygen causing coupling reactions in solution and producing Cu-C≡C-C≡C-Cu.Cu-C≡C-Cu oxidized at 60–70°C with CuCl₂ produces a product which could be formulated as Cu(C≡C)₂₀Cu; FT-IR absorption at 1950 cm⁻¹ could suggest the presence of cumulenic carbon chain although acetylenic carbon chains cannot be excluded completely.     

Synthesis and characterization of stable osmafuran starting from HC≡CCH(OH)C≡CH and OsHCl(CO)(PPh3)3

This paper presents a new convenient route to prepare osmafuran starting from readily accessible HC≡CCH(OH)C≡CH and OsHCl(CO)(PPh₃)₃. Treatment of a solution of OsHCl(CO)(PPh₃)₃ in dichloromethane with HC≡CCH(OH)C≡CH, followed by the addition of acetic acid, produced osmafuran [Os(CHC(PPh₃)CO(CH₂CH₃))Cl(CO)(PPh₃)₂]Cl (2). 2 has been isolated in good yield and fully characterized. ¹H and ¹³C NMR spectra show the characteristic downfield chemical shifts of the ring hydrogen and carbon atoms. NMR and X-ray diffraction data provide strong evidence for the aromatic nature of 2. Probably due to the effect of the phosphonium substituent, 2 exhibits remarkable thermal stability, air stability and lower reactivity.

     

B1(1)Π state of KCs: high-resolution spectroscopy and description of low-lying energy levels

The diode laser induced B(1)(1)Π → X(1)Σ(+) fluorescence spectra of the KCs molecule were recorded by Fourier-transform spectrometer with resolution of 0.03 cm(-1). Buffer gas Ar was used to facilitate appearance of rotation relaxation lines in the spectra, thus enlarging the B(1)(1)Π dataset, allowing one to determine the Λ-splitting constants and to reveal numerous local perturbations. A dataset was systematically obtained for B(1)(1)Π vibrational levels ν(') ∈ [0; 5] nonuniformly covering rotational levels with J(') ∈ [7; 233]. For ν(') ∈ [0; 3], the less-perturbed data of f-components were included in the fit. A pointwise potential energy curve (PEC) based on the inverted perturbation approach, as well as the Dunham coefficients, was obtained and compared with ab initio calculations; in particular, the energy of the PEC's minimum T(e) = 14,044.918(6) cm(-1) was determined. Both approaches allowed us to reproduce the vast majority of data used in the fit with accuracy of 0.02 cm(-1). Tentative molecular constants for several vibrational levels of the near lying C(3)(1)Σ(+) state were estimated.     

From dicopper diacetylide (Cu-C≡C-C≡C-Cu) to carbyne

Hydrolysis of dicopper diacetylide Cu-C≡C-C≡C-Cu in HCl solution yields diacetylene as major product together with a mixture of polyynes and minor amounts of carbonaceous matter. After I month ageing the main hydrolysis product from dicopper diacetylide is insoluble carbonaceous matter (23.47% by weight) together with diacetylene and its superior homologues (polyynes formed from solid state oxidative coupling reaction) which have been qualitatively and quantitatively identified by electronic spectroscopy. Similar behaviour and results are observed on dicoppper acetylide Cu-C≡C-Cu. In the carbonaceous insoluble matter recovered after hydrolysis, the presence of carbyne was detected by FT-IR spectroscopy.Dicopper acetylide Cu-C≡C-C≡C-Cu and dicopper acetylide, irrespective for the degree of oxidation reached in air, undergo a controlled thermal decomposition by heating under reduced pressure yielding in few seconds carbyne and copper(I) oxide, both identified by FT-IR spectroscopy.     

Effects of excitation energy on the autodetachment lifetimes of small iodide-doped ROH clusters (R═H-, CH3-, CH3CH(2)-)

The effect of excitation energy on the lifetimes of the charge-transfer-to-solvent (CTTS) states of small (4 ≤ n ≤ 10) iodide-doped water and alcohol clusters was explored using femtosecond time-resolved photoelectron imaging. Excitation of the CTTS state at wavelengths ranging from 272 to 238 nm leads to the formation of the I···(ROH)(n)(-) (R═H-, CH(3)-, and CH(3)CH(2)-) species, which can be thought of as a vibrationally excited bare solvent cluster anion perturbed by an iodine atom. Autodetachment lifetimes for alcohol-containing clusters range from 1 to 71 ps, while water clusters survive for hundreds of ps in this size range. Autodetachment lifetimes were observed to decrease significantly with increasing excitation energy for a particular number and type of solvent molecules. The application of Klots' model for thermionic emission from clusters to I(-)(H(2)O)(5) and I(-)(CH(3)OH)(7) qualitatively reproduces experimental trends and reveals a high sensitivity to energy parametrization while remaining relatively insensitive to the number of vibrational modes. Experimental and computational results therefore suggest that the rate of electron emission is primarily determined by the energetics of the cluster system rather than by details of molecular structure.     

Synthesis and Structure of Acetonitrile Solvates of Copper(II) Monofluoroacetate and Silver(I) Trifluoroacetate, [Cu2(CH2FCOO)4· 2CH3CN](CH3CN) and Ag3(CF3COO)3(CH3CN)2

Compounds [Cu₂(CH₂FCOO)₄· 2CH₃CN](CH₃CN) (I) and Ag₃(CF₃COO)₃(CH₃CN)₂(II) were synthesized and studied by X-ray structural analysis. Crystals Iare monoclinic, space group C2/c, a= 27.854(6), b= 8.286(2), c= 19.428(4) Å, = 106.82(3)°, V= 4292(2) ų, Z= 8, R ₁= 0.0426; crystals IIare triclinic, space group , a= 8.676(2), b= 9.819(2), c= 11.961(2) Å, = 95.27(3), = 109.59(3)°, = 104.60(3)°, V= 911.4(3) ų, Z= 2, R ₁= 0.0252. Structure Iis composed of the structural units (lanterns) typical of copper(II) carboxylates. The presence of an additional acetonitrile molecule noncoordinated by the copper atoms makes it possible to consider compound Ias a lattice clathrate. Structure IIhas no analogs among the silver carboxylates. It simultaneously contains silver atoms with coordination numbers varying from 2 to 4.     

Accurate ab initio potential energy surface, thermochemistry, and dynamics of the Cl(2P, 2P(3/2) + CH4 → HCl + CH3 and H + CH3Cl reactions

We report a high-quality, ab initio, full-dimensional global potential energy surface (PES) for the Cl((2)P, (2)P(3/2)) + CH(4) reaction, which describes both the abstraction (HCl + CH(3)) and substitution (H + CH(3)Cl) channels. The analytical PES is a least-squares fit, using a basis of permutationally invariant polynomials, to roughly 16,000 ab initio energy points, obtained by an efficient composite method, including counterpoise and spin-orbit corrections for the entrance channel. This composite method is shown to provide accuracy almost equal to all-electron CCSD(T)/aug-cc-pCVQZ results, but at much lower computational cost. Details of the PES, as well as additional high-level benchmark characterization of structures and energetics are reported. The PES has classical barrier heights of 2650 and 15,060 cm(-1) (relative to Cl((2)P(3/2)) + CH(4)(eq)), respectively, for the abstraction and substitution reactions, in good agreement with the corresponding new computed benchmark values, 2670 and 14,720 cm(-1). The PES also accurately describes the potential wells in the entrance and exit channels for the abstraction reaction. Quasiclassical trajectory calculations using the PES show that (a) the inclusion of the spin-orbit corrections in the PES decreases the cross sections by a factor of 1.5-2.5 at low collision energies (E(coll)); (b) at E(coll) ≈ 13,000 cm(-1) the substitution channel opens and the H/HCl ratio increases rapidly with E(coll); (c) the maximum impact parameter (b(max)) for the abstraction reaction is ~6 bohr; whereas b(max) is only ~2 bohr for the substitution; (d) the HCl and CH(3) products are mainly in the vibrational ground state even at very high E(coll); and (e) the HCl rotational distributions are cold, in excellent agreement with experiment at E(coll) = 1280 cm(-1).     

A photoionization study of the ion-neutral complexes CH3CH +CH 3 · CH2CH3] and CH3CH2CH+CH 3 · CH3 in the gas phase: Formation,H-transfer and C—C bond formation between partners,and channeling of energy into dissociation

Photoionization mass spectrometry was used to investigate the dynamics of ion-neutral complex-mediated dissociations of the n-pentane ion (1). Reinterpretation of previous data demonstrates that a fraction of ions 1 isomerizes to the 2-methylbutane ion (2) through the complex CH₃CH⁺CH ₃ ^· CH₂CH₃ (3), but not through CH₃CH⁺CH₂CH ₃ ^· CH₃ (4). The appearance energy for C₃Hin ₇ ⁺ formation from 1 is 66 kJ mol^?1 below that expected for the formation of n-C₃H ₇ ⁺ and just above that expected for formation of i-C₃H ₇ ⁺ . This demonstrates that the H shift that isomerizes C₃H ₇ ⁺ is synchronized with bond cleavage at the threshold for dissociation to that product. It is suggested that ions that contain n-alkyl chains generally dissociate directly to more stable rearranged carbenium ions. Ethane elimination from 3 is estimated to be about seven times more frequent than is C-C bond formation between the partners in that complex to form 2, which demonstrates a substantial preference in 3 for H abstraction over C-C bond formation. In 1 → CH₃CH⁺CH₂CH₃ + CH₃ by direct cleavage of the C1–C2 bond, the fragments part rapidly enough to prevent any reaction between them. However, 1 → 2 → 4 → C4H ₈ ⁺ + CH₄ occurs in this same energy range. Thus some of the potential energy made available by the isomerization of n-C₄H₉ in 1 is specifically channeled into the coordinate for dissociation. In contrast, analogous formation of 3 by 1 → 3 is predominantly followed by reaction between the electrostatically bound partners.     

Properties and structure of new volatile phenyl-containing β-diketonates of trimethylplatinum(IV): (CH3)3Pt(btfa)H2O, (CH3)3Pt(bac)Py, and initial complex [(CH3)3PtI]4

By interaction of trimethylplatinum(IV) iodide with phenyl-containing β-diketonates, the volatile monomeric complexes of trimethylplatinum(IV) based on benzoyltrifluoroacetone (Hbtfa) and benzoylacetone (Hbac) of the composition (CH₃)₃Pt(btfa)H₂O (I) and (CH₃)₃Pt(bac)Py (II) are obtained. Synthesis of the complexes is described; data of elemental analysis and IR spectra are reported; thermal characteristics are studied by thermogravimetry. For the first time, a single crystal X-ray diffraction study of complexes (I), (II), and the initial tetrameric complex [(CH₃)₃PtI]₄ (III) is performed.     

Vibrational spectra,force fields and NMR-data for triorganyl-tetrelomethanes CH4−n(TtR3)n (Tt = Sn and Pb)

Based on vibrational spectra normal coordinate calculations have been carried out for trimethyltetrelomethanes CH_4−n(TtMe₃)_n (Tt = Sn and Pb, n = 2 and 4). The resulting comparable force constants of the two distinguishable types of carbon-metal bonds for Tt = Sn (range K(C-Sn) 220 - 180 Nm⁻¹) are 10 – 15% higher than for Tt = Pb (K(C-Pb) 190 - 170 Nm⁻¹). These force constants K(C-Tt) are similar to the K(C-Hg) values of corresponding methylmercuriomethanes CH_4−n(HgMe)_n. The force constants K (C-Tt), and also the coupling constants ¹J(Tt,C) from NMR spectra, indicate weakening of the carbon-metal bonds in the central CTt_n groups with growing n, whereas the peripheral TtMe bonds are almost unaffected by variations of n.     

Spectra and structure of phosphorus-boron compounds—XIV. Vibrational study of P-hexamethylcyclotriborophosphane, [(CH3)2PBH2]3.

The i.r. spectra of solid (3500-30 cm⁻¹) and gaseous (3500-200 cm⁻¹) P-hexamethylcyclotriborophosphane have been recorded along with the Raman spectra (3500-10 cm⁻¹) of the solid, liquid, and gas. The vibrational data have been interpreted in detail on the basis of C_3υ molecular symmetry. The observed intermolecular vibrations in the solid state indicate only slight factor group effects. The molecular structure of P-hexamethylcyclotriborophosphane is discussed in relation to X-ray diffraction and recent NMR data.     

Orbital imaging of the “lone pair” electrons in N(CH3)3, NH3and NF3 by electron momentum spectroscopy

The electron density in each of the outermost MOs of N(CH₃)₃and NF₃, as measured by electron momentum spectroscopy, is found to exhibit a very much higher degree of s character than the corresponding orbital in NH₃. This behaviour is clearly predicted by MO calculations which indicate appreciable delocalization of electron density away from the nitrogen in N(CH₃)₃ and NF₃. The observed results for N(CH₃)₃ are contrary to predictions based on commonly used intuitive arguments involving lone pairs, molecular geometry and hybridized orbitals. The present work is supportive of the view that CH₃ groups are intrinsically more electron attracting than H when bonded to N.     

Vibrational spectra of bis(halomercurio)methanes CH2(HgX)2 (X  Cl,Br and I) in poly- and monocrystalline states

Vibrational spectra of polycrystalline bis(chloromercurio)methane CH₂(HgCl)₂ (space group Pnma, Z = 4), and of the deuterated analogue, as representatives of the bis(halomercurio)methanes, are preliminarily assigned. Low-temperature Raman and IR spectra of CH₂(HgCl)₂ reveal correlation splittings between g and u species, and partly within the sets of g and u modes, as predicted by unit-cell group analysis. Single-crystal Raman studies not only confirm the suggested assignments but are also the only method to unequivocally assign some bands. The limitations of the applicability of unit-cell group analysis in the present case are discussed.     

Aliphatic C-H to C-C conversion: synthesis of (-)-cameroonan-7α-ol

In the course of a synthesis of the tricyclic sesquiterpene (-)-cameroonan-7α-ol from the acyclic (+)-citronellal, seven aliphatic C-H bonds were converted to C-C bonds, and three rings and four new stereogenic centers were established.     

Vibrational solvatochromism and electrochromism of infrared probe molecules containing C≡O, C≡N, C=O, or C-F vibrational chromophore

Solvatochromic vibrational frequency shifts of a few different infrared (IR) probe molecules have been studied by carrying out quantum chemistry calculations for a number of their water clusters. We are particularly focused on the vibrational solvatochromic and electrochromic effects on the CO, CN, and CF stretch modes in carbon monoxide, acetone, 4-cyanopyridine, p-tolunitrile, fluorobenzene, and 3-fluoropyridine. Using multiple interaction site antenna model, we show that their solvatochromic vibrational frequency shifts can be successfully described by considering spatially nonuniform electrostatic potential generated by the surrounding water molecules. It turns out that the CO and CF stretch mode frequencies are approximately proportional to the solvent electric field projected onto the bond axes, whereas the vibrational frequencies of the nitrile stretch mode in 4-cyanopyridine and p-tolunitrile are not. Consequently, it is confirmed that the vibrational Stark tuning rates of the CO and CF stretching modes can be directly used to describe their solvatochromic frequency shifts in condensed phases. However, the nitrile stretch mode frequency shift induced by solvent electrostatic potential appears to be more complicated than its electrochromic phenomenon. To examine the validity of the distributed interaction site model for solvatochromic frequency shifts of these vibrational chromophores, we thus calculated the vibrational Stark tuning rates of the CO, CN, and CF stretch modes and found that they are in good agreement with the experimental results found in literatures. This confirms that a collection of properly chosen distributed interaction sites can be an excellent electric antenna sensing local electrostatics that affects on vibrational frequencies of IR probe modes.     

Synthesis and structures of silicon-, germanium-, and tin-containing tungsten carbyne complexes (ButO)3W≡C—EPh3 and [(ButO)3W≡C]2EPh2 (E = Si,Ge, Sn)

New tungsten carbyne complexes (Bu^tO)₃WC—SiPh₃, [(Bu^tO)₃WC]₂SiPh₂, [(Bu^tO)₃WC]₂GePh₂, and [(Bu^tO)₃WC]₂SnPh₂ were prepared by the reactions of (Bu^t)₆W₂ with Ph₃SiCC—Pr or Ph₂E(CC—Pr)₂ (E = Si, Ge, Sn) in individual crystalline form in 48—80% yields. The structures of both the (Bu^tO)₃WC—GePh₃ and (Bu^tO)₃WC—SnPh₃ compounds synthesized earlier and the new complexes were established by X-ray diffraction analysis.