Showing papers on "Nuclear quadrupole resonance published in 1969"
TL;DR: In this article, CBH et al. reported the 59Co pure nuclear quadrupole resonance spectra of a series of trigonally coordinated cobalt complexes, MX 3 CO(CO)4' where M = Si, Ge, Sn, Pd, and X = Cl, Br, I, and 65.
Abstract: . The 59Co pure nuclear quadrupole resonance spectra of a series of trigonally coordinated cobalt complexes, MX 3 CO(CO)4' where M = Si, Ge, Sn, Pd, and X = Cl, Br, I, and 65 are reported. The 35,37 Cl quadrupo,le resonance in SiCl 3 Co(CO)4 are also reported. The variation in field eradients obtained from the quadrupole coupling constants in these molecules can be interpreted in terms of a and ~ bonding of MX3 to the cobalt. In certain cases explicit a or ~ effects can be separated. 'Finally, strong evidence for the existence of Si-Cl d~-p~ bonding is presented. (1) Paper III in the series Transition Metal Nuclear Quadrupole Resonance by CBH and co-workers. (2) a. Noyes Chemical Laboratory, University of IllinOis, Urbana, 61801. b. Department of Chemistry, University of California, Berkeley •. (3) To whom correspondence and reprint requests should be addressed.
35 citations
TL;DR: In this article, the nuclear quadrupole resonance frequencies have been measured for some of the halogen nuclei in a number of crystalline charge transfer complexes of amines with bromide, iodide, iodine, iodine monobromide and iodine monochloride.
Abstract: Nuclear quadrupole resonance frequencies have been measured for some of the halogen nuclei in a number of crystalline charge-transfer complexes of amines with bromide, iodine, iodine monobromide, and iodine monochloride. From these measurements it has been possible to calculate approximate charge distributions for the bromine, iodine monobromide, and iodine monochloride complexes of 3,5-di-bromopyridine. The results correlate well with a three-centre delocalized LCAO-MO bonding theory. The correlation of this MO description with Mulliken's charge-transfer bonding scheme for n-σ complexes is discussed. This approach indicates the importance of considering an ?ionic? structure (which does not involve transfer of charge from the donor to the acceptor) in the electronic ground state of these complexes.
30 citations
22 citations
17 citations
TL;DR: In this article, the anisotropic spin-lattice relaxation times in pure nuclear quadrupole resonance of 14N in piperazine were investigated in terms of anisotropically molecular rotations with respect to the principal axes of the electric field gradient tensor.
Abstract: The highly anisotropic spin–lattice relaxation times in pure nuclear quadrupole resonance of 14N in piperazine are investigated in terms of anisotropic molecular rotations with respect to the principal axes of the electric‐field‐gradient tensor. A sudden approximation is used to obtain relations between the geometrical parameters of the molecular rotations and the correlation time involved. The double resonance technique is used to determine the relaxation times of the three‐energy‐level system.
17 citations
14 citations
14 citations
TL;DR: In this article, the 35Cl NQR frequencies in trichlorides of Y, Dy, Ho, Tm, Yb, La, and U were analyzed in a "bond switching" scheme.
Abstract: In ErCl3 at 4.2°K the 35Cl NQR frequencies are 4.4566 ± 0.0002 and 4.5157 ± 0.0002 MHz and the asymmetry parameters η are 0.53 ± 0.02 and 0.52 ± 0.03 for the eightfold and fourfold sites, respectively. The electric field gradient xx principal axis at each site is within 4° of the bisector of the Er–Cl–Er angle. The above results are analyzed in a “bond‐switching” scheme. We report also the 35Cl NQR frequencies in the trichlorides of Y, Dy, Ho, Tm, Yb, La, and U. The adequacy of the point‐change model as the primary source of the electric field gradient in these ionic crystals is tested.
13 citations
13 citations
TL;DR: In this article, the effects of pressure on the rotation of PtCl6 groups were investigated in terms of the simple classical model of an activated process, and the activation energy for the rotation was shown to have a value between 12.6 and 18.8
Abstract: The pressure dependences of the 35Cl quadrupolar relaxation rate and nuclear quadrupole resonance frequency in K2PtCl6 are measured for hydrostatic pressures up to 5000 kg cm−2 at six temperatures. The temperatures were selected so that the effects of pressure on the rotation of PtCl6 groups could be investigated. The relaxation resulting from the molecular rotation is discussed in terms of the simple classical model of an activated process. An activation volume ΔV* = 25.6 cm3 mole−1 for the rotation is deduced. The effect of the onset of the rotation on the nuclear quadrupole resonance frequency is noted. The results are shown to be consistent with earlier measurements on the 14N resonance in (CH2)6N4. The activation energy ΔE* for the rotation is shown to have a value between 12.6 and 18.8 kcal mole−1.
TL;DR: The gallium n.q.r. frequencies in donor-acceptor complexes of gallium trichloride are an order of magnitude more sensitive to changes in the ligand than are the chlorine frequencies, but both reflect trends in the available gas-phase heats of formation of the compounds as discussed by the authors.
Abstract: The gallium n.q.r. frequencies in donor–acceptor complexes of gallium trichloride are an order of magnitude more sensitive to changes in the ligand than are the chlorine frequencies, but both reflect trends in the available gas-phase heats of formation of the compounds.
TL;DR: In this article, the temperature dependence of the nuclear quadrupole resonance frequency νQ and spin-lattice relaxation time T1 of the 35Cl nuclei in powdered samples of K2PdCl6 were measured.
Abstract: Measurements of the temperature dependence of the nuclear quadrupole resonance frequency νQ and spin–lattice relaxation time T1 of the 35Cl nuclei in powdered samples of K2PdCl6 are reported. The d...
TL;DR: In this paper, the Zeeman effect of the 81Br and 35Cl nuclear quadrupole resonance on single crystals of para-bromophenol and para-chlorophenol was studied with high precision.
Abstract: The Zeeman effect of the 81Br and 35Cl nuclear quadrupole resonance has been studied with high precision on single crystals of para‐bromophenol and para‐chlorophenol, respectively. The results substantially agree with previous x‐ray and NQR studies of para‐chlorophenol (x‐ray studies are known only for this substance). In p‐bromophenol, four physically inequivalent sites were found, instead of two, as reported by other authors. Values of the asymmetry parameter are, respectively, ηBr = 0.0534 ± 0.001, ηCl = 0.071 ± 0.001 (34.12 MHz), and ηCl = 0.096 ± 0.001 (34.35 MHz).
TL;DR: In this article, the nuclear quadrupole resonance of 14N in sodium nitrite was observed in a temperature range of 77-400°K. The mean square amplitude of torsional vibration of nitrite ions and its temperature coefficient were evaluated at 300°K about the principal axes of rotation.
TL;DR: In this article, the authors used the bond electronegativity equalization method, BEEM, to examine the Townes and Dailey interpretation of 35Cl nuclear quadrupole resonance frequencies; the quadrupoles coupling constants from gaseous microwave spectroscopy, and from solid state N.R.
Abstract: The bond electronegativity equalization method, BEEM, is used to examine the Townes and Dailey interpretation of 35Cl nuclear quadrupole resonance frequencies; the quadrupole coupling constants from gaseous microwave spectroscopy, and from solid state N.Q.R. are considered. There is a distinct change in the s character of the chlorine σ orbital between the gaseous and solid state, and the s character depends upon the atom to which the chlorine bonds. It is independent of the rest of the molecule, changes in which affect the ionic character of the chlorine bond. A consistent interpretation of the N.Q.R. data for chlorine bonded to silicon, phosphorus and sulphur is achieved without postulating dπ−pπ bonding.
TL;DR: In this article, the nuclear quadrupole resonance (NQR) due to 35Cl and the Mossbauer effect due to 119Sn were investigated by means of the NQR.
Abstract: Several hydrates of tin(IV) chloride, e.g., SnCl4·xH2O (x=2, 3, 4 and 5) and SnCl4·yD2O (y=3, 4 and 5), were investigated by means of the nuclear quadrupole resonance (NQR) due to 35Cl and the Mossbauer effect due to 119Sn. The NQR-frequencies were observed at the temperature of liquid nitrogen and room temperature; they were found to range from 17.656 to 21.439 MHz. The Mossbauer effect was investigated only at the temperature of liquid nitrogen; it resulted in isomer shifts ranging from 0.275 to 0.350 mm/sec. The NQR-frequency and the isomer shift decreased with an increase in the number of water molecules in the hydrates, and the relationship between the NQR-frequency and the isomer shift was nearly linear. This relation was interpreted in terms of the transfer of the s-electrons of the tin atom to the chlorine atoms. Furthermore, it was revealed that there was a significant difference between the Sn-Cl bond of the hydrates and that of ammonium chlorostannate.
TL;DR: In this paper, a method for calculating the lattice contribution to the field gradient at a point in a crystal is outlined and is applied to the calculation of the chlorine N.R. frequencies.
Abstract: A method for calculating the lattice contribution to the field gradient at a point in a crystal is outlined and is applied to the calculation of the chlorine N.Q.R. frequency difference between K2PtCl6 and Cs2PtCl6. Closer agreement with the experimental value is obtained as compared with a previous calculation but complete agreement is not obtained using any reasonable value for the quadrupole antishielding factor. The importance of the lattice contribution to the individual N.Q.R. frequencies is also discussed.
TL;DR: In this article, the pure nuclear quadrupole resonance spectrum of 59Co in dicobaltoctacarbonyl was studied in the temperature range of − 196 to −µ30°C.
Abstract: The pure nuclear quadrupole resonance spectrum of 59Co in dicobaltoctacarbonyl was studied in the temperature range of − 196 to − 30°C. At liquid‐nitrogen temperature, the quadrupole coupling parameters for the two independent crystallographic sites are (A)e2qQ / h = 90.18 ± 0.15 MHz, η = 0.3149 ± 0.001 and (B)e2qQ / h = 89.30 ± 0.15 MHz, η = 0.4837 ± 0.001. The asymmetry parameters for the two sites approach each other with increasing temperature. To understand the observed parameters, the environment of the cobalt atom in Co2(CO)8 is described in terms of an octahedron with distortions along its three and fourfold axes. Defining two corresponding axially symmetric field gradient tensors with z components qa and qb, a quadratic equation relating the ratio qa / qb to the observed asymmetry parameter η is derived. The calculated field gradient with the z axis along the Co–Co direction is in reasonable agreement with the observed quadrupole splitting in Fe2(CO)9. The difference in the η values for the two s...
TL;DR: The 35Cl n.q.r. frequencies of Cl3PNPOCl2, Cl3PNSO2Cl, (SNOCl)3, S2PN3O2CL4, and C6H5PCl4 were reported in this article.
Abstract: The 35Cl n.q.r. frequencies of Cl3PNPOCl2, Cl3PNSO2Cl, (SNOCl)3, S2PN3O2Cl4, and C6H5PCl4, are reported. The frequencies are related to the chemical bonding of the 35Cl, by qualitative comparison with previously reported 35Cl frequencies in similar molecules. Where possible, the frequencies are related to the crystal structure of the molecule.
TL;DR: In this article, the nitrogen-14 nuclear quadrupole resonance spectrum of several ferroelectric guanidines has been observed and the onset of rotational motion of the guanidium ion at low temperature can be deduced.