Showing papers on "Nuclear quadrupole resonance published in 1971"

Nuclear quadrupole resonance spectroscopy. General principles

Abstract: In order to understand the origin of nuclear quadruple resonance, we need to consider in some detail the electrical interactions between the nuclei and electrons which form part of an atom or molec...

Chlorine nuclear quadrupole resonance in mercury chlorides and complex chlorides

Abstract: Chlorine nuclear quadrupole resonance frequencies are reported for solid compounds of known structure containing linear molecules HgCl2 and Hg2Cl2, approximately trigonal HgCl3-, and a variety of distorted octahedral forms including NH4HgCl3, CsHgCl3, and K2HgCl4,H2O. Compounds of unknown structure of the type (cation+)HgCl3, (cation+)2HgCl4, (cation+)Hg2Cl5, (cation+)2Hg9Cl20, and (cation+)4HgCl6 have also been studied. There are clear correlations between observed n.q.r. frequencies and Hg-Cl infrared stretching frequencies and bond distances. These correlations show the dependence of the degree of covalent bonding in the Hg-Cl bond with distance. The n.q.r. data confirm that many of the complex chlorides of mercury are built up by the joining of octahedral HgCl6 units, distorted in such a way as to preserve to varying extents the identity of the HgCl2 molecule. Predictions of the structures are made for some complex chlorides of unknown structure, and the role of bridging in building up the compounds is discussed in terms of observed n.q.r. data for bridging chlorines.

Halogan nuclear quadrupole resonance in tetrahedral halo complexes of zinc

Abstract: Halogen nuclear quadrupole resonance data are presented for a number of compounds containing tetrahedral ZnX42- ions, where X = Cl, Br, and I. Characteristic mean frequencies are: for 35Cl in ZnCl42- 8.9 MHz ; for 81Br in ZnBr42- 60 MHz; and for 127I in ZnI42- 75 and 150 MHz. The number and relative intensities of the resonances for any compound is found to be a useful indication of the site symmetry of the ZnX42- ion, and compounds of unknown structure are examined in this light. 35Cl data are also presented for Cs2CuCl4, which has a mean frequency of 10.6 MHz at 298°K.

Nuclear Magnetic Resonance of the Aquated Proton. II. Chloroauric Acid Tetrahydrate. Phase Transitions and Molecular Motion

Abstract: Proton and deuterium nuclear magnetic resonance and chlorine‐35 nuclear quadrupole resonance of chloroauric acid tetrahydrate, H5O2+AuCl4−· 2H2O has been studied from 180 to 300°K. Phase transitions are observed at 290°K (Solid I↔ Solid II) and at 218°K (Solid II↔ Solid III) in ordinary chloroauric acid tetrahydrate. In the deuterated compound the lower‐phase transition shifts upward by 33° to 252°K; an upper‐phase transition was not detected below 300°K. The chlorine‐35 NQR consists of two lines (1:1 intensity ratio) above the Solid II—III phase transition and three lines (1:2:1 intensity ratio) below this transition. The proton spin—lattice relaxation time T1 of H5O2+AuCl4−· 2H2O exhibits a minimum at 273°K which is assigned to the interbond jump motion of the bridging proton in the H5O2+ ion. The activation energy for this process is 5.7 kcal mole−1 in Solid II and 11.7 kcal mole−1 in Solid III. Rotating frame relaxation times have minima at 200 and 233°K which are assigned to the interbond jump proces...

Investigation of the Rotary Lattice Mode in R2PtCl6 Compounds. I. From Measurements of the 35Cl Nuclear Quadrupole Resonance Frequency

Abstract: Measurements of the temperature and pressure variation of the 35Cl nuclear quadrupole resonance (NQR) frequency in Rb2PtCl6 and Cs2PtCl6 are reported. The resonance frequency is measured at atmospheric pressure for temperatures from 4 to 500 K and at four temperatures between 290 and 380 K for pressures to 5000 kg cm−2. Previously published data for K2PtCl6 are also included in the analysis. Static lattice NQR frequencies are deduced. The differences between the static lattice frequencies are compared with the calculations of Smith and Stoessiger. Thermal averaging of the electric field gradient at a chlorine site is assumed to be dominated by the Q3, Q4, Q5, and Q6 internal modes of the PtCl6 octahedra and by the rotary lattice mode. The rotary mode frequencies are deduced; they are of similar magnitude and increase in the same sequence as the frequencies deduced from infrared and Raman data. An analysis of the pressure dependence of the NQR frequencies leads to pressure coefficients for the rotary mode ...

35Cl Nuclear Quadrupole Resonance of Alkyl Chloroformates, Alkyl Acid Chlorides, and Carbamyl Chlorides

Abstract: The 35Cl nuclear quadrupole resonance (n.q.r.) frequencies at 77 °K of twenty-two chloroformates, twenty-eight acid chlorides, two thiocarbonyl molecules, and five carbamyl chlorides are reported.

Erratum: Nuclear Quadrupole Resonance of 14N of the CN Group in Some para‐Substituted Benzonitriles

Abstract: The NQR of 14N of the –CN group in some benzonitriles with electron‐releasing as well as electron‐withdrawing para‐substituent groups, has been studied. The experimentally obtained values of (e2qQ)z, the quadrupole coupling constant, and of Γ, the asymmetry parameter of the electric field gradient, are discussed on the basis of the Townes and Dailey theory. The discussion may be developed further, with some assumptions, to obtain the electron populations of the two p‐type orbitals describing the π bonds between the nitrogen and the carbon atoms of the cyano group. The variations of such electron populations when changing the para substituent is obtained. A good correlation was also found between the values of the electron populations of the p‐type orbital orthogonal to the benzene ring and the variations of the electron distribution on the ring, as described by the Hammett σ values for the corresponding para‐substituent groups.

Nuclear Quadrupole Resonance Spectroscopy. Part Two--Instruments.

Abstract: This article is concerned with recent developments in the kinds of instrument that can be used to detect and record nuclear quadruple resonance signals in the solid state.

35Cl nuclear quadrupole resonance of the N—Cl bond

Abstract: The 35Cl n.q.r. frequencies of seven N-chloro molecules are reported and with those of five additional molecules in the literature, interpreted using BEEM and BEEM-π. The frequency is dependent on the hybridization of the N atom: with tr1tr1tr1π2 hybridized N the 35Cl frequency is around 55 MHz, with tr1tr1tr2π1hybridized N around 46 MHz and with te1te1te1te2 hybridized N at 44 MHz.

Nuclear Quadrupole Resonance Study of Charge Transfer Complexes: Chloranil Complexes

Abstract: 35Cl nuclear quadrupole resonance frequencies were measured in electron donor-acceptor complexes between chloranil (tetrachloro-p-benzoquinone) and such donors as aromatic hydrocarbons, polyaromatics and amines. Some correlations between the resonance frequencies and infrared spectra were found and discussed in a qualitative way in terms of the π-electron transfer between donors and the chloranil molecule as acceptor. A Zeeman effect experiment was carried out on a single crystal of the 1:2 chloranil-8-hydroxyquinoline complex. The direction of one of the two non-equivalent C-Cl bonds obtained slightly differs from that determined by an X-ray diffraction study. Possible effects of the charge transfer on the resonance frequency and the asymmetry parameter are discussed according to the Mulliken theory of ’weak’ charge-transfer complex. No simple relations could be found between the experimental resonance frequencies and the ionization potential of the donor. This suggests that crystal field effects are rat...

Chlorine nuclear quadrupole resonance of phosphorus–chlorine compounds

Abstract: The 35Cl n.q.r. frequencies at 77 K of two chloro(phenyl)phosphoranes, four cyclic phosphorus esters, four phosphoryl and thiophosphoryl chlorides, and eight chlorophosphates, are reported. The frequencies are used to predict possible molecular structures, and are related to σ- and π-bond effects within the molecules, by use of BEEM.

Nuclear quadrupole resonance studies of boron–chlorine compounds. Part I. Boron trichloride and the phenylboron chlorides

Abstract: The asymmetry parameters of the 35Cl nuclear quadrupole resonance spectra of boron trichloride and phenylboron dichloride have been measured on polycrystalline samples by the method of Morino and Toyama. The value of 0·54 ± 0·02 in boron trichloride is consistent with recent molecular orbital calculations on the boron trihalides and the π-bonding order Bl3 > BBr3≃ BCl3. The extent of s-hybridization of the σ bonding orbitals as estimated by an extension of the SGOBE method is found to be unreasonably high.

Quadrupolar Nuclear Spin–Lattice Relaxation in R2MX6 Compounds

Abstract: The Van Kranendonk theory of quadrupolar nuclear spin–lattice relaxation is adapted to the case of the X nuclei in R2MX6 compounds as observed in a pure nuclear quadrupole resonance experiment. The...

Chlorine nuclear quadrupole resonance in some chloro complexes of divalent copper

Abstract: Nuclear quadrupole resonance for the 35Cl nucleus has been observed in some chloro complexes of divalent copper. Square-planar complexes each show two resonance lines, with the following frequencies (at 77°K): (CH3NH3)2CuCl4, 10.780, 12.157 MHz; (C2H5NH3)2CuCl4, 10.817, 12.074 MHz; (enH2)CuCl4, 10.271, 11.901 MHz; and (C3H7NH3)2CuCl4 at 223°K, 11.290 and 11.781 MHz. NH4CuCl3, containing dimeric Cu2Cl62- units, has resonances, at 77°K, at 11.907, 11.993, and 12.448 MHz. The trigonal pyramidal anion in Co(NH3)6CuCl5 has two resonances at 9.642 and 10.352 MHz at 77°K. These results are compared with previous results for copper chloro complexes, and the implications of covalent bonding are discussed. In particular, it is suggested that the long-bond interaction between units in square-planar complexes amounts to 7-16% of the bonding interaction within the units.

Nuclear Quadrupole Resonance Spectroscopy. Part Three--Pulse Methods: Chemical Applications.

Abstract: The author looks at the contributions made to chemical understanding from the pulse methods.

Nuclear quadrupole resonance studies of boron–chlorine compounds. Part II. Chlorine-35 quadrupole resonance frequencies

Abstract: The 35Cl nuclear quadrupole frequencies of 23 boron-chlorine compounds are presented and discussed in terms of the s-character and charge distribution in the B–Cl band. An approximate order of donor ability for a ligand L in compounds of the type BCl3,L is proposed on the basis of the 35Cl frequencies.

Mutual Orientations of the Principal Axes of the Electric‐Field Gradient Tensors on 14N and 81Br by Combined Zeeman‐Effect Measurements in a Single Crystal of p‐Bromoaniline

Abstract: The Zeeman effect of the nuclear quadrupole resonance of both 14N and 81Br nuclei in a single crystal of p‐bromoaniline was studied. The precision of the technique used here is far greater than that of the few previous works in this field. Measurements were made by means of a newly designed spectrometer, working at both 14N and 81Br NQR frequencies, in which the radio‐frequency assemblies could be interchanged without affecting the crystal position. The relative orientation of the electric‐field gradient tensors at the sites of the nitrogen and bromine nuclei were directly determined. The results are interpreted in terms of known relations between the orientations of the field gradient tensor and the bond directions. The conclusion reached is that the amino group should be nearly coplanar with the benzene ring. Also observed was a large effect on line intensity as a function of the orientation and intensity of the static magnetic field H0 arising from nuclear dipole‐dipole coupling between 14N and the 1H ...