Cl Nuclear Quadrupole Coupling Research Articles

Interaction of a pseudo-π C-C bond with cuprous and argentous chlorides: Cyclopropane⋯CuCl and cyclopropane⋯AgCl investigated by rotational spectroscopy and ab initio calculations.

Strongly bound complexes (CH2)3⋯MCl (M = Cu or Ag), formed by non-covalent interaction of cyclopropane and either cuprous chloride or argentous chloride, have been generated in the gas phase by means of the laser ablation of either copper or silver metal in the presence of supersonically expanded pulses of a gas mixture containing small amounts of cyclopropane and carbon tetrachloride in a large excess of argon. The rotational spectra of the complexes so formed were detected with a chirped-pulse, Fourier transform microwave spectrometer and analysed to give rotational constants and Cu and Cl nuclear quadrupole coupling constants for eight isotopologues of each of (CH2)3⋯CuCl and (CH2)3⋯AgCl. The geometry of each of these complexes was established unambiguously to have C(2v) symmetry, with the three C atoms coplanar, and with the MCl molecule lying along a median of the cyclopropane C3 triangle. This median coincides with the principal inertia axis a in each of the two complexes (CH2)3⋯MCl. The M atom interacts with the pseudo-π bond linking the pair of equivalent carbon atoms (F)C (F = front) nearest to it, so that M forms a non-covalent bond to one C-C edge of the cyclopropane molecule. The (CH2)3⋯MCl complexes have similar angular geometries to those of the hydrogen- and halogen-bonded analogues (CH2)3⋯HCl and (CH2)3⋯ClF, respectively. Quantitative details of the geometries were determined by interpretation of the observed rotational constants and gave results in good agreement with those from ab initio calculations carried out at the CCSD(T)(F12*)/aug-cc-pVTZ-F12 level of theory. Interesting geometrical features are the lengthening of the (F)C-(F)C bond and the shrinkage of the two equivalent (B)C-(F)C (B = back) bonds relative to the C-C bond in cyclopropane itself. The expansions of the (F)C-(F)C bond are 0.1024(9) Å and 0.0727(17) Å in (CH2)3⋯CuCl and (CH2)3⋯AgCl, respectively, according to the determined r0 geometries. The C-C bond lengthening is in each case about four times that observed by similar methods in the corresponding complexes of MCl with ethyne and ethene, even though the cyclopropane complexes are more weakly bound than their ethyne and ethene analogues. Reasons for the larger increase in r(CC) in the pseudo-π complexes are discussed.

A multinuclear solid-state magnetic resonance and GIPAW DFT study of anhydrous calcium chloride and its hydrates

The group 2 metal halides and corresponding metal halide hydrates serve as useful model systems for understanding the relationship between the electric field gradient (EFG) and chemical shift (CS) tensors at the halogen nuclei and the local molecular and electronic structure. Here, we present a 35/37Cl and 43Ca solid-state nuclear magnetic resonance (SSNMR) study of CaCl2. The 35Cl nuclear quadrupole coupling constant, 8.82(8) MHz, and the isotropic chlorine CS, 105(8) ppm (with respect to dilute NaCl(aq)), are different from the values reported previously for this compound, as well as those reported for CaCl2·2H2O. Chlorine-35 SSNMR spectra are also presented for CaCl2·6H2O, and when taken in concert, the SSNMR observations for CaCl2, CaCl2·2H2O, and CaCl2·6H2O clearly demonstrate the sensitivity of the chlorine EFG and CS tensors to the local symmetry and to changes in the hydration state. For example, the value of δiso decreases with increasing hydration. Gauge-including projector-augmented wave (GIPAW) density functional theory (DFT) calculations are used to substantiate the experimental SSNMR findings, to rule out the presence of other hydrates in our samples, to refine the hydrogen positions in CaCl2·2H2O, and to explore the isostructural relationship between CaCl2 and CaBr2. Finally, the 43Ca CS tensor span is measured to be 31(5) ppm for anhydrous CaCl2, which represents only the fifth CS tensor span measurement for calcium.

Experimental Detection and Properties of H2O⋅⋅⋅AgCl and H2S⋅⋅⋅AgCl by Rotational Spectroscopy

We report the first generation and characterization of two simple compounds formed by the interaction of either H2O or H2S with AgCl, namely H2O···Ag Cl and H2S···Ag Cl. They were observed in the gas phase by rotational spectroscopy. The AgCl is produced by laser ablation of metallic silver in the presence of CCl4 and then picks up an H2O or H2S molecule. AgCl is known, from interpretation of its Cl nuclear quadrupole coupling constant, to have a fractional ionic character of approximately 0.7, so that it has significant ionpair character. The interaction of AgCl with H2Omolecules, and in particular one H2O molecule, is of fundamental chemical interest because the H2O molecules have the opportunity to interact with an incipient Ag ion. How does this interaction differ from those of H2O with the less polar, covalent Lewis acids HCl and ClF (fractional ionic characters of 0.25 and 0.35)? The hydrogenand halogen-bonded complexes H2O···H Cl and H2O···Cl F have each been investigated in the gas phase by rotational spectroscopy as part of an extensive systematic program. H2O···H Cl and H2O···Cl F have equilibrium geometries of Cs symmetry, [2,3] with a pyramidal configuration at O when HCl or ClF forms either a hydrogen or halogen bond to that atom (see Figure 1). In each case, however, there is a low potential-energy barrier to the planar, C2v geometry so that even in the zero-point state the molecule is inverting and is effectively planar. On the other hand, in the analogous pair of complexes H2S···H Cl and H2S···Cl F the potential energy barrier is high enough to ensure that each has a permanently pyramidal configuration at S, with HCl or ClF forming a weak bond to S at approximately 908 to the H2S subunit, as shown in Figure 1. These angular geometries, and those of many other hydrogenand halogen-bonded complexes, can be rationalized by means of some simple empirical rules. For both H2O and H2S acting as Lewis bases, the electrophilic ends H and Cl of the weakly polar molecules HCl and ClF, respectively, are assumed to seek the axis of a nonbonding electron pair carried by the base. A further question is: Are the angular geometries of the resulting molecules H2Y···Ag Cl isomorphic with those of H2Y···H Cl and H2Y···Cl F (Y=O or S), indicating that the empirical rules are also obeyed when AgCl is the Lewis acid? All B···M X (B=CO, M=Cu, Ag, Au) have a linear arrangement similar to those in OC···H Cl and OC···Cl F. Thus, in all these systems, the Lewis acid attaches along the axis of the n-pair on C. A linear geometry was also found in N2···Cu F. Observed rotational transitions of both H2O···Ag Cl and H2S···Ag Cl were characteristic of a nearly prolate asymmetric rotor of large A value having only a-type transitions, which exhibit Cl nuclear quadrupole hyperfine structure. For H2O···Ag Cl, R-branch K 1= 1 transitions of the type (J+ 1)1,J+1 !J1,J and (J+ 1)1,J !J1,J 1 were observed in addition to the (J+ 1)0,J+1 !J0,J series and for a given J were more intense than those having K 1= 0. This observation confirms that the molecule has a pair of equivalent H nuclei exchanged by a rotationC2 about the a axis and therefore that the equilibrium geometry of H2O···Ag Cl is either C2V planar at equilibrium or Cs pyramidal but with a potential-energy barrier to planarity low enough that the v= 0 and 1 states associated with the motion that inverts the configuration at the O atom are well separated. For H2S···Ag Cl only the (J+ 1)0,J+1 !J0,J series could be detected despite a careful search, an observation consistent with a pyramidal configuration at the S atom and no inversion on the microwave timescale. The reason for the different behavior with respect to inversion is presumably that H2S···Ag Cl is more strongly bound than H2O···Ag Cl (see below) and that there is a much larger angle between the n-electron pairs on S than on O. The result is a higher and wider barrier to inversion in H2S···Ag Cl. The usual arguments show that for H2O···Ag Cl in the ground state the K 1= 1 levels occur in combination with the three symmetric proton spin functions while theK 1= 0 levels combine with the single antisymmetric function. Moreover, population transfer from K 1= 1 levels into K 1= 0 levels during the supersonic expansion is hindered by a collisional propensity rule which forbids triplet state (K 1= 1) to Figure 1. Angular geometries of several H2Y M X compounds; d indicates the local C2 axis of the H2O or H2S subunit.

A conformational study of butyryl chloride using chirped pulse Fourier transform microwave spectroscopy and quantum chemical calculations

Abstract The pure rotational spectrum of butyryl chloride has been recorded between 8 and 16 GHz using a chirped pulse, Fourier transform microwave spectrometer. The transitions recorded were assigned to two different conformers which have previously been designated syn-gauche and syn-anti. Quantum chemical calculations have produced rotational constants in good agreement with those obtained from the observed spectra. For the syn-gauche conformer the τ 1 (CCCO) dihedral angle is calculated to be 10° and the τ 2 (CCCC) dihedral angle is calculated to be 70°. For the syn-anti conformer τ 1 (CCCO) is calculated to be 0° and τ 2 (CCCC) is calculated to be 180°. For both MP2 and M06-2X methods with 6-311G∗∗ basis sets the syn-gauche conformer is calculated to be marginally lower in energy than the syn-anti conformer. The resolution of the experiments was sufficient to resolve hyperfine structure from the 35 Cl and 37 Cl nuclei in both conformers, and in all cases the full Cl nuclear quadrupole coupling tensors have been determined for the first time.

XeCu Covalent Bonding in XeCuF and XeCuCl, Characterized by Fourier Transform Microwave Spectroscopy Supported by Quantum Chemical Calculations

XeCu covalent bonding has been found in the complexes XeCuF and XeCuCl. The molecules were characterized by Fourier transform microwave spectroscopy, supported by MP2 ab initio calculations. The complexes were prepared by laser ablation of Cu in the presence of Xe and SF(6) or Cl(2) and stabilized in supersonic jets of Ar. The rotational constants and centrifugal distortion constants show the XeCu bonds to be short and rigid. The (131)Xe, Cu, and Cl nuclear quadrupole coupling constants indicate major redistributions of the electron densities of Xe and CuF or CuCl on complex formation which cannot be accounted for by simple electrostatic effects. The MP2 calculations corroborate the XeCu bond lengths and predict XeCu dissociation energies approximately 50-60 kJ mol(-)(1). The latter cannot be accounted for in terms of induction energies. The MP2 calculations also predict valence molecular orbitals with significant shared electron density between Xe and Cu and negative local energy densities at the XeCu bond critical points. All evidence is consistent with XeCu covalent bonding.

Microwave spectra of the 35Cl and 37Cl isotopomers of dichloromethylene: Nuclear quadrupole-, spin–rotation-, and nuclear shielding constants from the hyperfine structures of rotational lines

The rotational spectra of the isotopomers C 35Cl 37Cl and C 37Cl 2 of dichloromethylene in the ground vibronic state were recorded in the range 10–33 GHz using a molecular beam Fourier transform microwave spectrometer. CCl 2 was generated by flash pyrolysis using different precursors. The observed spectra were analyzed to yield rotational and centrifugal distortion constants, as well as the complete Cl nuclear quadrupole coupling tensors and the spin–rotation interaction constants from the hyperfine structure of the rotational lines. With inclusion of data from previous work on the most abundant species C 35Cl 2 [N. Hansen, H. Mäder, F. Temps, Phys. Chem. Chem. Phys. (3) (2001) 50–55.] a refined r 0 structure was determined. The spin–rotation interaction constants of all three isotopomers were used to derive 35Cl and 37Cl principal inertial axis nuclear magnetic shielding components which have not yet been determined by NMR spectroscopy.

Rotational Spectra, Structures, Hyperfine Constants, and the Nature of the Bonding of KrCuF and KrCuCl.

Rotational spectra of KrCuF and KrCuCl have been measured in the frequency range 8-18 GHz, using a pulsed jet cavity Fourier transform microwave spectrometer. The molecules were prepared by ablating Cu metal with a pulsed Nd:YAG laser (1064 nm) and allowing the plasma to react with appropriate precursors (Kr plus SF(6) or Cl(2)) contained in the backing gas of the jet (Ar or Kr). Rotational constants, internuclear distances, vibration frequencies, and (83)Kr, Cu, and Cl nuclear quadrupole coupling constants have all been evaluated. The Kr-Cu bonds are short and the complexes are rigid. The (83)Kr coupling constant of KrCuF is large (128.8 MHz). The Cu nuclear quadrupole coupling constants differ radically from those of uncomplexed CuF and CuCl molecules. The results are supported by those of ab initio calculations, which have also yielded Mulliken populations, MOLDEN plots of valence molecular orbitals and Laplace concentrations, and electron localization functions. The results are consistent with those reported earlier for other noble gas-noble metal halide complexes. The results have been used to assess the nature of the bonding in the complexes and have produced good evidence for weak noble gas-noble metal chemical bonding.

Rotational spectra, structures, hyperfine constants, and the nature of the bonding of KrCuF and KrCuCl.

Rotational spectra of KrCuF and KrCuCl have been measured in the frequency range 8-18 GHz, using a pulsed jet cavity Fourier transform microwave spectrometer. The molecules were prepared by ablating Cu metal with a pulsed Nd:YAG laser (1064 nm) and allowing the plasma to react with appropriate precursors (Kr plus SF(6) or Cl(2)) contained in the backing gas of the jet (Ar or Kr). Rotational constants, internuclear distances, vibration frequencies, and (83)Kr, Cu, and Cl nuclear quadrupole coupling constants have all been evaluated. The Kr-Cu bonds are short and the complexes are rigid. The (83)Kr coupling constant of KrCuF is large (128.8 MHz). The Cu nuclear quadrupole coupling constants differ radically from those of uncomplexed CuF and CuCl molecules. The results are supported by those of ab initio calculations, which have also yielded Mulliken populations, MOLDEN plots of valence molecular orbitals and Laplace concentrations, and electron localization functions. The results are consistent with those reported earlier for other noble gas-noble metal halide complexes. The results have been used to assess the nature of the bonding in the complexes and have produced good evidence for weak noble gas-noble metal chemical bonding.

Microwave spectra, geometries, and hyperfine constants of OCCuX (X = F, Cl, Br).

A pulsed jet cavity Fourier transform microwave spectrometer has been used to measure the rotational spectra of OCCuX (X = F, Cl, Br) in the frequency range 5-21 GHz. Metal atoms were generated via laser ablation and were allowed to react with CO and a halide precursor, prior to stabilization of the products within a supersonic jet. These are the first experimental observations of OCCuF and OCCuBr and the first high-resolution spectroscopic study of gas-phase OCCuCl. All three molecules were found to be linear. Rotational constants, centrifugal distortion constants, nuclear quadrupole coupling constants, and nuclear spin-rotation coupling constants have been precisely determined. The rotational constants have been used to evaluate the various bond lengths, and the results are in good agreement with the trend established for OCAuX species. The C-O distance is found to be comparatively short and close to that of free CO. The M-C distance is longer than that predicted by ab initio calculations, and the Cu-X distances are very similar to those observed in the corresponding metal halides. Vibrational wavenumbers have been estimated from the distortion constants and are compared with the results of various ab initio studies. Changes in the Cu, Cl, and Br nuclear quadrupole coupling constants indicate that substantial charge rearrangement takes place on coordination with CO, consistent with the formation of strong Cu-C bonds. Mulliken orbital population analyses have been performed and provide evidence of pi-back-donation from Cu in all of the species studied. The evaluated nuclear spin-rotation coupling constants have been used to estimate the (63)Cu nuclear shielding constants, sigma, and their spans (Omega) in OC(63)CuF, OC(63)Cu(35)Cl, and OC(63)Cu(79)Br.

Pure rotational spectra, structures, and hyperfine constants of OC-AuX (X = F, Cl, Br).

Rotational spectra of OC-AuX (X = F, Cl, Br) have been measured in the frequency range 5-21 GHz, using a pulsed jet cavity Fourier transform microwave spectrometer. The molecules were prepared by ablating Au metal with a Nd:YAG laser and allowing the vapor to react with CO plus a halide precursor contained in the Ar backing gas of the jets. For OC-AuCl and OC-AuBr these are the first high-resolution spectroscopic measurements; for OC-AuF these are the first observations of any kind. All three molecules are linear. Rotational constants, centrifugal distortion constants, and nuclear quadrupole coupling constants have been precisely evaluated. The geometries determined for all three molecules show CO bond lengths close to that of free CO, plus relatively long Au-C bonds. These results are corroborated by ab initio calculations, which have also produced Mulliken populations showing significant sigma-donation from CO to Au, plus some pi-back-donation from Au to CO. There are major changes in the Au, Cl, and Br nuclear quadrupole coupling constants when CO bonds to AuX, consistent with the formation of strong Au-C bonds. The structural properties of OC-AuF are somewhat different from those of OC-AuCl and OC-AuBr.

Electric charge redistribution in BrCl resulting from interaction with Ar: the rotational spectrum of the linear complex Ar⋯BrCl

Ground-state rotational spectra of four isotopomers Ar⋯79Br35Cl, Ar⋯81Br35Cl, Ar⋯79Br37Cl and Ar⋯81Br37Cl of a complex involving argon and bromine monochloride were observed. Spectroscopic constants were interpreted on the basis of a linear species Ar⋯BrCl, with atoms in the indicated order and r(Ar⋯Br)=3.466Å. When intermolecular electron transfer was assumed negligible, the Br and Cl nuclear quadrupole coupling constants were interpreted to show that a fraction δ(Br→Cl)=3.5(5)×10−3 of an electron is transferred from Br to Cl on complex formation. The values kσ=2.79(1)Nm−1 and kββ=4.7(2)×10−20Jrad−2 were established for the intermolecular stretching and bending quadratic force constants, respectively.

HF–DFT calculations of 14N and 35Cl quadrupole coupling constants on optimized molecular structures of pyridine and the monochloropyridines

14N and 35Cl nuclear quadrupole coupling constants in the monochloropyridines and 14N in pyridine have been determined in the principal axes of both the inertia and coupling constant tensors by HF–DFT calculations of the molecular electric field gradients on B3P86/6-31G(3d,3p) optimized molecular structures.In the case of 4-chloropyridine, the calculated 14N coupling constants are probably more accurate than the experimental values.Investigation of the substitution effect shows that the differences in nitrogen nqccs between 2-chloropyridine and pyridine are largely due to the presence of the chlorine substituent (as opposed to distortion of the ring). The small differences found in 3-chloropyridine can be understood as due to near cancellation of effects due to the substituent and ring distortion. In 4-chloropyridine, on the other hand, these effects are additive, accounting for the differences for this molecule.

Interaction of water and dichlorine in the gas phase: An investigation of H2O⋯Cl2 by rotational spectroscopy and ab initio calculations

Ground-state rotational spectra of the seven isotopomers H2O⋯35Cl2, H2O⋯37Cl35Cl, H2O⋯35Cl37Cl, D2O⋯35Cl2, D2O⋯37Cl35Cl, HDO⋯35Cl2, and HDO⋯37Cl35Cl of the complex formed between water and dichlorine were observed by pulsed-jet, Fourier-transform microwave spectroscopy. Rotational constants B0 and C0, centrifugal distortion constants ΔJ and ΔJK, and Cl nuclear quadrupole coupling constants χaa(Clx) and {χbb(Clx)−χcc(Clx)}, where x=i (inner) or o (outer), were obtained via spectral analyses. The spectroscopic constants were interpreted, on the basis of models for the complex, to give the geometry, the binding strength, and the extent of inter- and intramolecular electron transfer on complex formation. The zero-point geometry is defined in terms of the effective values r(O⋯Cli)=2.8479(3) Å and φ=43.4(3)°, where φ is the angle made by the bisector of the HÔH angle with the O⋯Cl internuclear line. The intermolecular stretching force constant kσ=8.0(1) N m−1. Fractions δi=0.005(5) and δp=0.034(3) of an electron were estimated to be transferred from O to Cl and from Cli to Clo, respectively. The geometrical conclusions are supported by ab initio calculations at the aug-cc-pVDZ/MP2 level of theory, with good agreement for φ and r(O⋯Cli). A comparison of the properties of H2O⋯Cl2 with those of H2O⋯HCl provides evidence in support of a recent proposal of a halogen bond B⋯XY that is the analog of the hydrogen bond B⋯HX, where X and Y are halogen atoms.

The rotational spectrum of dichlorocarbene, C35Cl2, observed by molecular beam-Fourier transform microwave spectroscopy

The rotational spectrum of the most abundant isotopomer of dichlorocarbene, C35Cl2, in its 1A1 ground electronic state has been recorded using a molecular beam—Fourier transform microwave spectrometer. The CCl2 was generated by flash pyrolysis in a pulsed free jet expansion using CBr2Cl2 or CHCl2COCl as precursors. 43 hyperfine structure lines of 6 rotational transitions were recorded in the frequency range 8–40 GHz. The analysis of the observed spectrum yielded the rotational constants, the complete 35Cl nuclear quadrupole coupling tensor, and the nuclear spin-rotation interaction constants. In addition, a refined r0 structure of CCl2 was derived.

Jet-cooled rotational spectra and structure of the cyclobutanone⋯hydrogen chloride complex

The rotational spectra of three isotopic species C 4H 6O⋯H 35 Cl, C 4H 6O⋯H 37 Cl and C 4H 6O⋯D 35 Cl of the hydrogen-bonded dimer formed by cyclobutanone and hydrogen chloride have been studied by means of microwave spectroscopy in a supersonic jet. Rotational constants, centrifugal distortion constants and Cl-nuclear quadrupole coupling parameters have been determined for the ground state and for a vibrationally excited state attributable to the ring-puckering motion of the cyclobutanone subunit. The spectroscopic constants have been interpreted in terms of a C s symmetry in which the monomers are coplanar with: r(O⋯H)=1.88(3) Å, ∠(CO⋯H)=112.3(7)° and a deviation θ of the O⋯H–Cl nuclei from collinearity of 13.1(6)°.

The hydrogen-bonded complex H3P···HCl investigated by a combination of rotational spectroscopy and ab initio SCF calculations

Ground-state rotational spectra were observed for the four symmetric-top isotopomers H3P···H35Cl, H3P···H37Cl, H3P···D35Cl and D3P···H35Cl and the four asymmetric-rotor isotopomers H2DP···H35Cl, H2DP···H37Cl, HD2P···D35Cl and H2DP···D35Cl of a complex formed in mixtures of phosphine and hydrogen chloride. Rotational constants, centrifugal distortion constants, Cl nuclear quadrupole coupling constants and spin–rotation coupling constants were determined through spectral analyses. Interpretation of various of the spectroscopic constants with the aid of models of the complex provided information about its symmetry and geometry, about the strength of the intermolecular binding and about the subunit dynamics. The complex has C3v symmetry and the order of the nuclei is unambiguously established as H3P···HCl. Ab initio calculations carried out with three different basis sets [6-311++G(d,p), aug-cc-pVDZ, and aug-cc-pVTZ] and with electron correlation taken into account at the MP2 level were used to optimise the geometry under the assumption of C3v symmetry and indicated that only small geometrical distortions of the PH3 and HCl subunits accompany formation of the complex. By assuming that similar distortions are also appropriate to experimental geometries of the subunits, the rotational constants of the symmetric-top isotopomers of the complex were used to establish the distances r(P···H) and r(P···Cl). Although r(P···H) was constant at 2.5802(2) A for the three species based on PH3, this distance shortened to 2.5736(5) A in D3P···H35Cl. An alternative analysis indicated that r(P···Cl) shortened by 0.0014 A per D atom substituted for phosphine H atoms in H3P···H35Cl, an effect attributed to an increased magnitude of the electric dipole moment of PH3 as it is deuteriated. The centrifugal distortion constants DJ and D = 2DJ+DJK were used to determine values of the quadratic intermolecular stretching and bending force constants kσ and kθθ, respectively. The latter also yielded an average value 〈θ2〉1/2 of the PH3 oscillation angle θ, which decreased significantly for D3P···H35Cl relative to the (constant) value for species based on PH3. After correction of the Cl nuclear quadrupole coupling constant of H3P···H35Cl for the effects of the electric field gradient due to PH3 by using estimates from the MP2/aug-cc-pVTZ calculation, the corrected value was used to give the average βav = cos−1〈cos2β〉1/2 = 15° for the oscillation angle of the HCl subunit.

The rotational spectra and structure of the jet-cooled heterodimer 7-oxabicyclo[2.2.1]heptane···HCl

The hydrogen-bonded heterodimer 7-oxabicyclo[2.2.1]heptane···HCl (OBH···HCl) has been investigated using a molecular beam Fourier-transform microwave spectrometer. The ground state rotational spectra of the OBH···H35Cl, OBH···H37Cl and OBH···D35Cl isotopomers have been studied in the frequency range 6–18.5 GHz. Spectral analysis gave rotational, quartic centrifugal distortion constants and the complete Cl-nuclear quadrupole coupling tensor for all isotopomers. A Cs symmetry has been established for the complex where the hydrogen chloride lies on the plane bisector to the COC angle of OBH. The distance r(O···H) and the angle φ between the OBH C2 axis and the O···H bond direction were found to be 1.764(29) A and 129.7(37)°, respectively. A small deviation of the linearity of the atoms O···H–Cl involved in the hydrogen bond, θ = 7(4)°, was observed. Ab initio calculations were also performed to complement the experimental work.

The tetrahydrofuran⋯hydrogen chloride complex: Rotational spectrum and theoretical analysis

The hydrogen bonded heterodimer tetrahydrofuran⋯HCl has been investigated using molecular beam Fourier transform microwave spectroscopy in combination with ab initio calculations. The rotational spectrum, observed in the range 6–18 GHz, shows a complex pattern originated by the existence of small tunneling splittings in addition to the Cl-nuclear quadrupole coupling hyperfine structure. The vibrational energy difference between the members of the doublet, ΔE=3.550(25) MHz, has been determined from the analysis of the a-type Coriolis coupling interaction between them. Doublets of the same magnitude are also present in the spectra of the different HCl isotopomers analyzed. These tunneling splittings were not observed for the species C4D8O⋯H35Cl. The analysis of all the available data has allowed us to conclude that these splittings are due to pseudorotation within the tetrahydrofuran subunit. The spectroscopic constants have been interpreted in terms of a geometry in which tetrahydrofuran has a conformation close to the twisted ring-form with HCl lying on the plane bisector to the COC ring angle. The potential energy surface for the interaction between tetrahydrofuran and hydrogen chloride has been explored by using ab initio methodologies at the correlated level [MP2, MP4(SDTQ)] with Pople’s 6-31G** and Dunning’s aug-cc-pVDZ basis sets. One minimum and three transition structures were located and characterized at the MP2/6-31G** level. The geometry parameters and rotational constants of the minimum agree quite well with those determined from the spectroscopic data. The transition structures correspond to interconversions between equivalent conformations, the first one via an inversion motion and the remaining two via pseudorotation movements. One of these latter two is responsible for the splittings detected in the microwave spectroscopy study. The tetrahydrofuran⋯hydrogen chloride interaction can be seen as a combination of electrostatic and charge transfer contributions both consistent with the angular geometry exhibited by the complex.

Angular geometry, binding strength and charge transfer for the complex H 2S⋯ICl determined by rotational spectroscopy

Ground-state rotational spectra of the isotopomers H 2 S⋯ I 35 Cl , H 2 S⋯ I 37 Cl , HDS⋯ I 35 Cl and D 2 S⋯ I 35 Cl of a complex of hydrogen sulphide and iodine monochloride were measured. Rotational constants, centrifugal distortion constants, halogen nuclear quadrupole coupling constants, and I spin–rotation coupling constants were determined. Interpretation of various spectroscopic constants showed that the complex has a geometry in which the S⋯I–Cl nuclei are collinear, with r(S⋯I)=3.154(3) Å and the ICl subunit almost perpendicular to the plane of the H 2S nuclei [ φ=91.9(12)°]. Observed I and Cl nuclear quadrupole coupling constants are used with a simple model to deduce that intramolecular charge transfer from S to I is ∼0.05 e −. The intermolecular stretching force constant k σ =16.6(3) N m −1.

The Cl-nuclear quadrupole coupling tensors and the internal rotation barrier of 1,1-dichloroethane by Fourier transform microwave spectroscopy

The rotational spectra of 1,1-dichloroethane in the ground state of the CH 3CH 35 Cl 2 , CH 3CH 35 Cl 37 Cl and CH 3CH 37 Cl 2 isotopomers and in four low frequency excited states of the main species have been investigated in the range 6–250 GHz. Measurements have been carried out using molecular beam and waveguide Fourier transform microwave spectrometers as well as Stark and source modulation spectrometers. Accurate rotational and centrifugal distortion constants have been obtained. The complete Cl-nuclear quadrupole coupling tensors have been determined from the analysis of the resolved hyperfine structure for the three observed isotopomers. From the small A–E splittings observed in the first torsional excited state, the barrier to internal rotation of the methyl group has been determined to be 4.260(9) kcal mol −1.