Cl Nuclear Quadrupole Coupling Research Articles

Microwave rotational spectrum of a weakly bound complex formed by hydrogen sulphide and hydrogen chloride

A weakly bound dimer formed by hydrogen sulphide and hydrogen chloride has been identified in the gas phase by means of its rotational spectrum which has been detected with the aid of the sensitive technique of pulsed-nozzle, Fourier-transform microwave spectroscopy. The spectra of eight isotopic species have been analysed to give rotational constants (B0+C0), centrifugal distortion constants DJ and Cl nuclear quadrupole coupling constants Xaa as follows: [graphic omitted]The listed spectroscopic constants allow us to establish that the weak intermolecular linkage occurs through a hydrogen bond, with HCl acting as the proton donor and the S atom acting as the proton acceptor. The S⋯H—Cl nuclei are collinear (or nearly so) with r(S⋯Cl)= 3.8092 A, and the plane of the H2S molecule is almost perpendicular (ϕ= 93.8°) to the line of the hydrogen bond. Conclusions about the relative strength of the hydrogen bond are drawn from analyses of the constants DJ and Xaa.

Comparison of molecular structure and 35Cl nuclear quadrupole coupling tensors in 2,3,6-trichlorophenyl acetate

The crystal structure of 2,3,6-Cl 3C 6H 2OCOCH 3 was determined at room temperature; C 5 2h-P2 1/c; Z=4. 35Cl Zeeman split NQR at 294K shows, that the EFG tensors are mainly determined by the CCl bonds. φ zz for the three Cl atoms is nearly parallel to the directions CCl. The asymmetry parameter of the EFG's are 0.1423 for Cl(2), 0.1037 for Cl(3) and 0.1015 for Cl(6). φ xx of Cl(2), Cl(3) and Cl(6) is almost perpendicular to the ring plane. The NQR results are discussed with respect to the molecular structure. Temperature dependences of 35Cl NQR resonances are reported for the range 77≦ T/K≦ 300.

Identification and molecular geometry of a weakly bound dimer (H 2O, HC1 in the gas phase by rotational spectroscopy

Rotational transitions of (H 2O,H 35Cl) and (H 2O,H 37Cl) have been observed and assigned in the frequency range 7–18 GHz. Values of the rotational constants B o + C o and B o − C o, the centrifugal distortion constants D J and D JK and the Cl nuclear quadrupole coupling constants χ aa and χ bb are reported for the vibrational ground state of both species. Arguments based on small spin-spin splittings resolved in some Cl nuclear quadrupole components lead to the conclusion that (H 2O, HCl) has a pair of equivalent protons and is effectively planar in the zero-point state. Values of r o (O…Cl) have been determined for the planar model in which the HCl molecule forms a hydrogen bond to the oxygen atom of H 2O.

The C–Cl bonds in trichloroethylidene trichlorolactic ester, Cl3CCHOCOCHOCCl3. A 35Cl–NQR single crystal study

By single crystal 35Cl–NQR with a 4π Zeeman spectrometer, the six independent 35Cl-nuclear quadrupole coupling tensors in trichloroethylidene trichlorolactic ester (chloralide) Cl3CCHOCOCHOCC13 have been studied at T=21 °C. The directions of the electric field gradient (EFG) tensor components have been determined. The main axes φzz are within ±0.5° parallel to the C–Cl bound directions. Very small asymmetry parameters in the range 0.005≤η≤0.053 are characteristic for the EFG tensors of Cl bond to carbon in aliphatic systems, and the six nuclear quadrupole coupling constants are found in the range 76.053≤e2qQh−1/MHz≤78.790. The orientations of the principal axes φxx and φyy is explained as due to intramolecular interactions likely of through space origin.

Rotational spectrum, structure, and intramolecular force field of the ArClCN van der Waals complex

The rotational spectrum of the ArClCN van der Waals complex has been assigned using pulsed Fourier transform microwave spectroscopy in a Fabry-Perot cavity with a pulsed supersonic nozzle as the molecular source. ArClCN is T-shaped and the data were fit to the Watson rotational parameters and an exact expression for the Cl and N nuclear quadrupole coupling. The spectroscopic constants for Ar35ClCN are A′′ = 6152.5411(21) MHz, B′′ = 1577.0362(8) MHz, C′′ = 1246.7514(6) MHz, τ1 = −576.0(2) kHz, τ2 = −97.28(8) kHz, τaaaa = −234.8(17) kHz, τbbbb = −55.97(10) kHz, τcccc = −21.60(7) kHz, χClaa = 37.9468(23) MHz, χClbb = −79.5239(20) MHz, χNaa = 1.6403(22) MHz, and χNbb = −3.4571(20) MHz. The centrifugal distortion constants are used to derive the intramolecular force field and a normal coordinate analysis is performed. The Cl nuclear quadrupole coupling tensor indicates that the field gradients in ClCN are slightly perturbed upon complex formation but not enough to proscribe their use in structural determinations of weakly bound complexes.

131Xe nuclear quadrupole coupling and the rotational spectra of XeHCl

Rotational spectra have been assigned for the 129XeH35Cl, 129XeH37Cl, 129XeD35Cl, 131XeH35Cl and 132XeH35Cl van der Waals molecules by employing pulsed microwave Fourier transform spectroscopy in a Fabry–Perot cavity with a pulsed supersonic nozzle as the molecular source. The rotational constants, centrifugal distortion constants, and Cl nuclear quadrupole coupling constants obtained from the spectra are used to determine the structure of XeHCl and to gain information on the intermolecular potential binding of Xe to HCl. From the spectrum of 131XeH35Cl and an analysis of the centrifugal distortion in 129XeH35Cl, 131XeH35Cl, and 132XeH35Cl the 131Xe nuclear quadrupole coupling constant in XeHCl is found to be −4.9±0.2 MHz. Using the known nuclear quadrupole moment of 131Xe, the electric field gradient at the Xe nucleus is calculated. The observed field gradient is discussed in terms of Sternheimer shielding and formation of the weak Xe–HCl van der Waals bond.

A new method for observing the rotational spectra of weak molecular complexes: KrHCl

A new method of observing the rotational transitions of weak molecular complexes by combining the techniques of microwave Fourier transform spectroscopy, a Fabry–Perot cavity, and a pulsed nozzle source of molecules is described. High resolution and good sensitivity are achieved. Twelve isotopic species of the KrHCl molecule involving all combinations of the 86Kr, 84Kr, 82Kr, H, D, 35Cl, and 37Cl isotopes are assigned and the rotational constants, Cl nuclear quadrupole coupling constants, and centrifugal distortion constants are all given. The molecular structure indicates a linear equilibrium structure with the H(D) atom between the Kr and Cl atoms. However, the inverse moments of inertia measured here indicate large amplitude vibrations of the H(D) atom relative to the Kr–Cl internuclear line. Estimates of the Kr–Cl stretching frequency and force constants, which show considerable dependence on the isotopic species, are also given. Bending frequencies and force constants are also given.

The effect of conformation on nuclear quadrupole coupling constants of α-chloro-ethers

The difference in the bond length between axial and equatorial carbon–chlorine bonds in chlorodioxans is paralleled by a large change in the 35Cl nuclear quadrupole coupling constant and both these effects are compatible with an orientation-dependent conjugative interaction between the oxygen atom and the carbon–chlorine bond.

The microwave spectrum and 35Cl nuclear quadrupole coupling in chlorotrifluoroethylene

The microwave spectrum of F 2CCF 35Cl was observed in the 8–26 GHz frequency range. The rotational constants are (MHz): A = 4506.05 ± 0.02; B = 2268.66 ± 0.02; and C = 1508.09 ± 0.01. The 35Cl quadrupole coupling constants along the appropriate inertial axes are (MHz): χ aa = −50.10 ± 0.10; χ bb = +11.36 ± 0.10; and χ cc = +38.74 ± 0.20. The 35Cl quadrupole coupling constants in H 2CCF 35Cl were remeasured and a structure was proposed for this molecule. The coupling constants are (MHz): χ aa = −73.04 ± 0.10; χ bb = +38.60 ± 0.10; and χ cc = +34.44 ± 0.20. The coupling constants in both molecules were transformed into the principal field gradient axis systems and compared with quadrupole coupling constants in similar molecules.

On the Correlation of 35Cl Nuclear Quadrupole Coupling Constants with π→γ3 and π→γ5 Optical Electron Transfer Bands of Transition Metal Complexes and its Significance in Pi-Bonding

From a consideration of odd-even intramolecular electron transfer processes in octahedrally co-ordinated transition metal complexes, two relationships have been derived. The first correlation describes π → γ3 optical electron transfer bands of the complexes K2OsCl6, K2IrCl6, K2PtCl6, K2PtCl4 as a function of the respective 35Cl nuclear quadrupole coupling constants. The second relationship correlates π → γ5 optical charge transfer transitions of the substances K2ReCl6, K2OsCl6, K2IrCl6 with the 35Cl nuclear quadrupole coupling constants of these compounds. By using this charge transfer model, a linear relationship has been verified between the optical electronegativity values of the quadrivalent transition metal ions W4⨁, Re4⊖, Os4⨁, Ir4⨁, Pt4⨁ and the 35Cl nuclear quadrupole coupling constants of their hexachloro complexes. The empirically established equation χMen+ = 0.537 which describes the 35Cl n.q.r. frequencies of the hexachloro complexes of Re4⨁, Os4⨁, Ir4⨁, Pt4⨁ and Pd4⨁ as a function of the optical electronegativity values χ of these metal ions, has been used to estimate 35Cl nuclear quadrupole resonance frequencies of chloro complexes as yet not probed by nuclear quadrupole resonance spectroscopy, e.g. Zeise's salt (KPtCl3C2H4), K3IrCl6, K2RuCl6, K3RhCl6 and K3MoCl6. Conversely, by the same procedure the optical electronegativity χ of W4⨁ and Au3⨁ has been estimated from the 35Cl quadrupole resonance frequency of K2WCl6 and KAuCl4 (χ W4⨁= 1.71 and χ Au3⨁=2.80). In the case of analogous bromo complexes, the equation χ Men+ = 0.19 mol accounts for the dependence of the 79Br nuclear quadrupole resonance frequencies upon the optical electronegativity of the metal ions. The assignment of electron transfer bands in other chloro complexes is discussed in the light of this “nuclear quadrupole resonance criterion“ of optical charge transfer bands.