35Cl Nuclear Quadrupole Resonance Frequencies Research Articles

Ab initio calculations of nuclear quadrupole resonance frequencies in trichloroacetyl halides: a comparison of DFT and experimental data

Ab initio calculations of 35Cl nuclear quadrupole resonance (NQR) frequencies (νQ) in trichloroacetyl halides (CCl3COHal, where Hal = F, Cl, Br or I) are performed. The estimated νQ values are compared with experimental values obtained by Gordeev et al []. Calculation of the average of 35 Cl NQR frequencies in CCl3COCl demonstrated that the difference between the calculated and experimental values are less than 3.1%. This indicates that the density functional theory is a powerful technique that for predicting unknown electronic states before performing experiments. A linear correlation between Hal-C bond length and νQ is observed. This hence provides a scheme to estimate interatomic distances using NQR frequencies.

Isotope effect on the temperature dependence of the 35Cl NQR frequency in (NH4)2RuCl6

The 35Cl nuclear quadrupole resonance frequencies and spin–lattice relaxation times for (NH4)2RuCl6, (ND4)2RuCl6, (NH4)2SnCl6, and (ND4)2SnCl6 were measured in the temperature range 4.2–300K. In these four compounds, it was confirmed that no phase transition occurs in the observed temperature range. At 4.2K, discrepancies of the NQR frequency between non-deuterated and deuterated compounds, which are attributed to the difference in the spatial distributions of hydrogen (deuterium) atoms in the ground states of the rotational motion of ammonium ion, reached to 24kHz and 23kHz for the ruthenate compounds and the stannate compounds, respectively. The separation between the ground and the first excited states of the rotational motion of the ammonium ion was estimated to be 466Jmol−1 and 840Jmol−1 for (ND4)2RuCl6 and (NH4)2RuCl6, respectively, by least-square fitting calculations of temperature dependence of the NQR frequency. For (ND4)2SnCl6 and (NH4)2SnCl6, these quantities were estimated to be 501Jmol−1 and 1544Jmol−1, respectively. It was clarified that the T1 minimum, which has been observed for the stannate compounds at around 60K as a feature of the temperature dependence, was dependent on a method of sample preparation. It is concluded that the minimum is not an essential character of the ammonium hexachlorostannate(IV) since the crystals prepared in strong acid condition to prevent a partial substitution of chlorine atoms by hydroxyl groups, did not show such T1 minimum.

Stereoelectronic structure of MCl4-benzoyl chloride (M=Si, Ge, Sn) systems resulting from ab initio calculations and NQR 35Cl

Results of quantum-chemical calculations of MCl4–C6H5COCl (M=Si, Ge, Sn) systems of 1 : 1 composition using RHF/3-21 G* and MP2/3-21 G* levels as well as those of 1 : 2 composition using the RHF/3-21 G* level have been represented. MCl4 ← C6H5COCl complexes of 1 : 1 composition are energetically more advantageous. They are formed in solid state provided that the M···O distance in individual systems is considerably less than the sum of van der Waals radii of M and O and their total energies are appreciably less than the sum of total energies of components. These conditions are realized only for M=Sn. In systems of 1 : 2 compositions, calculated M···O distances are practically equal to the sum of covalent radii of M and O. Nonetheless, complexes with such composition are not formed in solid state. Total energy of the system which is lower than the sum of its components’ energies is not an indispensable condition for complex formation. The 35Cl nuclear quadrupole resonance (NQR) frequencies and asymmetry parameters of the electric field gradient at the 35Cl nuclei have been evaluated using the results of ab initio calculations.

Measurement of temperature and temperature gradient in millimeter samples by chlorine NQR

A mini-thermometer based on the 35Cl nuclear quadrupole resonance (NQR) frequency temperature dependence in the chlorates KClO3 and NaClO3 was built and successfully tested by measuring temperature and temperature gradient at 77 K and higher in about 100 mm3 active volume of a mini Joule–Thomson refrigerator. In the design of the tank-circuit coil, an array of small coils connected in series enabled us (a) to achieve a suitable ratio of inductance to capacity in the NQR spectrometer input tank circuit, (b) to use a single crystal of KClO3 or NaClO3 (of 1–2 mm3 size) in one coil as a mini-thermometer with a resolution of 0.03 K and (c) to construct a system for measuring temperature gradients when the spatial coordinates of each chlorate single crystal within an individual coil are known.

Reactivity of 2,6-Dichloropurine Ribonucleoside Studied by 35Cl NQR Spectroscopy

2,6-Dichloropurine ribonucleoside is a precursor in the potential synthesis of anticancer and antiviral drugs. 35Cl nuclear quadrupole resonance (NQR) studies on electronic structure and the character of C–Cl bonds may provide a valuable information about the difference in reactivity of chlorine atoms present in this compound. In this work 35Cl NQR frequencies, asymmetry parameters and double-bond character for both C–Cl bonds have been determined experimentally. These parameters were then compared with the corresponding theoretical values obtained by means of the density functional theory.

Pressure and temperature dependence of the chlorine NQR in caesium and sodium chlorates

The (35)Cl nuclear quadrupole resonance (NQR) frequencies (nu(Q)) in caesium and sodium chlorates were measured as a function of temperature, from 77 to 300 K at different pressures up to 5.1 kbar, and the data were analysed to estimate the volume dependence of the electric field gradient (EFG), torsional frequency and also the contributions to the NQR frequency from static and dynamic effects. The variation of spin-lattice relaxation time with pressure at different temperatures was studied in the case of sodium chlorate and at room temperature in case of caesium chlorate. The pressure dependence of the spin-lattice relaxation time (T(1)) suggests that the relaxation is mainly due to the torsional motions.

Anomalous H/D isotope effect on 35Cl NQR frequencies in piperidinium p-chlorobenzoate

Anomalous isotope effects were detected in the 35Cl nuclear quadrupole resonance (NQR) frequency of piperidinium p-chlrobenzoate (C5H10NH· ClC6H4COOH) by deuteration of hydrogen atoms. The atoms were determined to form two kinds of N–H···O type H-bonds in the crystal structure. Large frequency shifts of the 35Cl resonance lines reaching 288 kHz at 77 K and 278 kHz at room temperature were caused upon deuteration, in spite of the fact that the Cl atoms in the molecule do not form hydrogen bonds in the crystal. Results of single crystal X-ray diffraction measurements and density-functional-theorem calculations suggest that a dihedral-angle change of 1.8° between benzene and the piperidine ring contributes to 35Cl NQR anomalous frequency shifts.

On the estimation of the field constant of 35Cl nuclear quadrupole resonance frequency in the series of [R1R2R3AsCl]+M− compounds

The field constant of the NQR frequency of a chlorine atom (35Cl) in a series of arsenic derivatives [R1R2R3AsCl]+M− was estimated from correlations. The field frequency is ∼41.5±3.5 Hz cm kV−1, which is nearly twice as much as that in analogous phosphorus compounds.

Menshutkin's {(Arene)·nSbX3} Molecular CompoundsExploring the Correlation between Crystal Structures and Nuclear Quadrupole Resonance Spectra

By use of data from the literature to assign 35Cl, 81Br, 121Sb, and 123Sb nuclear quadrupole resonance (NQR) frequencies to particular atoms, an attempt is made to correlate crystal structures of a number of {(arene)·nSbX3} (X = Cl, Br) Menshutkin molecular compounds with their NQR spectra. Comparing NQR spectra of crystalline neat SbX3 (X = Cl, Br) with those of the molecular compounds shows well-established effects due to the perturbations introduced by changes in the detailed structures of the networks of SbX3 moieties and in the interactions of Sb atoms with the arene moieties. NQR spectra are much more sensitive in this regard than the changes in interatomic distances that are among the main quantitative outcomes of crystal structure analysis. Although a qualitative pattern can be discerned that associates the frequency of the 35Cl NQR spectra with the different structural roles of the crystallographically independent chlorines, it has not been possible to identify particular interactions with the differences found in the NQR frequencies. Generalizations based on NQR spectra do not appear currently achievable, and it seems likely that the spectra of the various molecular compounds will require explanation on an individual basis.

DTA and NQR studies of polymorphism in p-chlorofluorobenzene

Differential thermal analysis, and the 35Cl Nuclear Quadrupole Resonance frequency ( ν Q) and spin-lattice relaxation time ( T 1) were measured as a function of temperature in p-chlorofluorobenzene. Three different phases were found according to the thermal history of the sample and only one was stable up to the melting point. In one of the phases, the presence of molecular reorientations can be inferred from T 1 data with activation energy of 3.7 kcal/mol. A value of 13.9 kJ/mol for the fusion heat of this compound has been obtained.

Peculiarities of atomic interaction in organic molecules of 3- and 4-coordinated phosphorus using ab initio calculations and 35Cl NQR

The results of ab initio calculations at the MP2/6-31G(d) level of molecules of the series ClPXX′ (X, X′=C 2H 5, N(CH 3) 2, OCH 3) and ClP(M)XX′ (M=O, S; X=CH 3, ?CH 3; X′=C 2H 5, OCH 3) with total optimization of their geometry were presented. They were compared with the obtained earlier results of such calculations at the RHF/6-31G(d) level and with experimental 35Cl nuclear quadrupole resonance (NQR) spectra for these compounds. MP2/6-31G(d) calculations confirm non-inductive influence of heteroatoms on the geminal Cl atom in the non-linear three-atomic Cl–P–M groups. They agree to the conclusion that the abnormal correlation of the 35Cl NQR frequencies for the compounds studied at different X, X′ and M is caused, in general, by the P–Cl bond polarization under the action of the geminal atom partial charges directly through the field. The satisfactory conformity between the experimental 35Cl NQR frequencies and those estimated from 3p-components of the Cl atom valence p-orbitals calculated at the MP2/6-31G(d) level was obtained.

35Cl NQR studies of 1‐chloro‐2,4‐dinitrobenzene and 1,2‐dichloro‐3‐nitrobenzene as a function of pressure and temperature

AbstractThe temperature and pressure dependences of 35Cl nuclear quadrupole resonance (NQR) frequency and spin–lattice relaxation time (T1) were investigated for 1‐chloro‐2,4‐dinitrobenzene and 1,2‐dichloro‐3‐nitrobenzene. T1 was measured in the temperature range 77–300 K. Furthermore, the NQR frequency (ν) and T1 for these compounds were measured as a function of pressure up to 5.1 kbar at 300 K. Relaxation was found to be due to the torsional motion of the molecule and the reorientation motion of the nitro group. By analysing the temperature dependence of T1, the activation energy for the reorientation motion of the nitro group was obtained. The temperature dependence of the average torsional lifetimes of the molecules and the transition probabilities W1 and W2 for the Δm = ±1 and Δm = ±2 transitions, were also obtained. Both compounds showed a non‐linear variation of NQR frequency with pressure. The pressure coefficients were observed to be positive. A thermodynamic analysis of the data was carried out to determine the constant‐volume temperature coefficients of the NQR frequency. The spin–lattice relaxation time T1 for both the compounds was found to be weakly dependent on pressure, showing that the relaxation is mainly due to the torsional motions. Copyright © 2002 John Wiley & Sons, Ltd.

35Cl NQR Studies of Bismuth Trichloride

Abstract The temperature dependence of the 35Cl nuclear quadrupole resonance (NQR) frequency and spin lattice relaxation time (T1) are studied in crystalline BiCl3 , in the range 40-300 K. The positive temperature coefficient observed for one of the 35Cl resonances is explained in terms of the strong intermolecular interactions that exist in this compound. Variation of with temperature is found to be similar at the chemically inequivalent halogen sites. Semiclassical descriptions based on torsional oscillator dynamics are found to be inadequate for explaining the spin lattice relaxation. T1 (T) data follow an AT2 + BT3 type behaviour, indicating that the anharmonic nature of the lattice vibrations plays a significant role in determining the temperature dependence of T1 at high temperatures.

Differential thermal analysis and nuclear quadrupole resonance study on polymorphic 1,4-dichlorobutane

Differential thermal analysis (DTA), and the 35Cl nuclear quadrupole resonance (NQR) frequency (v Q ) and line width (Δv Q ) were measured as a function of the temperature in solid 1,4-Dichlorobutane (DCB). Two crystalline modifications forms I and II, stables above and below T c = 210 K respectively were found according to the thermal history of the sample. A comparative analysis of the NQR frequency in both phases suggests that the crystal structure in form II is closer-packed than in form I. The NQR line width shows the existence of a thermal activated process with an activation energy E a ≃ 20 kJ mol−1, probably related with reorientations of the CH2Cl end groups. Some orientational disorder is expected in the low temperature modification since the line width is twice as much as that in the high temperature phase.

Impurity against non-locality in the incommensurate phase of Rb2ZnCl4: a 35Cl NQR study

The influence of impurities on the phason and amplitudon dynamics in the incommensurate phase of (Rb1-xCsx)2ZnCl4 (for x=0.005 and 0.01) is investigated using 35Cl nuclear quadrupole resonance frequency ( nu ) and spin lattice relaxation time (T1) measurements as a function of temperature. While the paraelectric-to-incommensurate transition temperature (TI) is suppressed by about 8 K, the lock-in transition temperature (observed at 192 K in the pure compound) is not observed down to 77 K for x=0.01. The observation of an additional singularity in the NQR spectrum of the x=0.01 compound is explained as being due to the manifestation of non-locality of the modulation wave with respect to the region of influence of the nuclear spin probe. The phason and amplitudon contributions to the spin lattice relaxation, T1 phi and T1A respectively, are measured by selective excitation of the broadened NQR spectra. While T1A is insensitive to impurities, T1 phi is strongly dependent on temperature and impurity concentration. The temperature dependence of T1 phi is explained as being due to the underdamping of phonon modes in the presence of impurities.

35Cl nuclear quadrupole resonance analysis of the solid 2,3,6-trichloroanisole

The temperature dependences of 35Cl nuclear quadrupole resonance frequencies nu Q, spin-lattice relaxation times T1, linewidth Delta nu and spin-spin relaxation time T2 of the solid 2,3,6-trichloroanisole are reported. Three resonance lines are observed and the experimental measurement of nu Q(T) data are analysed by means of the Bayer-Kushida theory. It appears that only low-frequency lattice modes contribute to the temperature dependence of nu Q(T). The T1(T) relaxation data show a normal behaviour and no thermally activated motion is detected. The linewidth measurements reveal that the electric field gradient affecting the Cl atoms of the molecule undergoes some sort of thermally activated motional narrowing. The T2(T) data are somewhat scarce, showing only a normal temperature behaviour for one of the chlorine atoms of the molecule while for the others it is of the order of T2*.

Nuclear quadrupole resonance in chloromethylphenols

AbstractThe temperature dependences of the 35Cl nuclear quadrupole resonance (NQR) frequencies of 4‐chloro‐3‐methyl‐, 2‐chloro‐5‐methyl‐ and 4‐chloro‐2‐methyl‐phenol were studied in the temperature range from 77 K up to the respective melting points. 4‐Chloro‐2‐methylphenol undergoes a phase transition at ca 185 K, and the presence of trans–cis isomeric forms is inferred. The NQR frequencies of molecules at absolute zero temperature were evaluated.

Dynamic and structural studies on 1,2,3-trichloropropane in the solid phase

35Cl nuclear quadrupole resonance (NQR) frequencies nu Q and spin-lattice relaxation times T1 were measured between 100 and 250 K in 1,2,3-trichloropropane (CH2ClCHClCH2Cl). Three narrow lines were detected in the stable solid phase, indicating that only one of the six possible conformers is present. Also, the three lines were assigned to the three chlorine atoms in the molecule from their distinct temperature behaviours. The dominant mechanism responsible for the relaxation above 200 K is proposed to be the reorientational motion of the CH2Cl end groups, and activation energies of 32.5 and 49.0 kJ mol-1 are determined for the two end groups. The 1H nuclear magnetic resonance lineshape f(H) shows a structure due to the dipolar interaction between the protons of the CH2Cl groups. From the analysis of f(H) a distance dHH=1.68 AA is obtained, which turns out to be quite close to that already determined in solid dichloroethane. Fast cooling of the sample from the liquid state produces very broad NQR signals. The results of differential thermal analysis seem to indicate the existence of a glassy state with a characteristic Tg=144 K.

FIR spectrum and temperature dependence of NQR frequencies in 2,6-dichlorophenol

The torsional modes that contribute to the change in nuclear quadrupole resonance (NQR) frequencies with temperature in 2,6-dichlorophenol are identified by correlating the observed variation of 35Cl NQR frequencies with temperature with the theoretical expectations using the low frequency vibrational modes obtained from the far infrared spectrum.

Analysis of Molecular Motions in SiCl4 by 35Cl NQR Spectroscopy

Abstract The temperature dependence of the 35Cl nuclear quadrupole resonance frequencies, spin-lattice relaxation times and line widths were analyzed for the presence of a solid–solid phase transition in SiCl4. The brittle phase was verified to temperatures approaching the melting point. Evidence suggesting the formation of a plastic phase at elevated temperature is discussed.