Halogen Nuclei Research Articles

Calculation of nuclear magnetic shieldings: infinite-order Foldy–Wouthuysen transformation

A scheme for calculating nuclear magnetic shieldings using the infinite-order Foldy–Wouthuysen (FW) transformation proposed by Barysz and Sadlej (BS) is presented. The nuclear magnetic shieldings of hydrogen halides are calculated by three variant BS schemes; a double finite perturbation method for the external magnetic flux density (B 0) and the nuclear magnetic dipole moment ( μ M ) (BS/FPT-2), a single finite perturbation method for B 0 with analytical differentiation of energy with respect to ( μ M ) (BS/FPT-1), and an approximate analytical differentiation method with respect to both B 0 and μ M (BS/CHF). Although the BS/FPT-2 method is exact theoretically, the actual computation for heavy nuclei includes large error due to reduction of the number of significant figures. The BS/FPT-1 and BS/CHF approaches, on the other hand, yield reasonable values for all of the shieldings. Although several results could not be obtained by the BS/FPT-2 method, no serious contradictions were recognized among these three results. From a comparison of our results with values in the literature, our shieldings for the halogen nuclei are lower than those determined by the four-component relativistic random phase approximation (4-RPA), but the reason for this is not obvious.

Mixed Halide Sodalite Solid Solution Systems, Hydrothermal Synthesis and Structural Characterization by Solid State NMR.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Mixed Halide Sodalite Solid Solution Systems. Hydrothermal Synthesis and Structural Characterization by Solid State NMR

The solid solution behavior of mixed halide (Cl/Br, Cl/I, and Br/I) sodalite systems as prepared by hydrothermal synthesis has been studied in detail by X-ray diffraction and solid-state nuclear magnetic resonance (NMR). At a synthesis temperature of 450 K the rate of halide incorporation into the cages of mixed Cl/Br, Br/I, and Cl/I sodalites depends on the halide stoichiometry in the precursor gel and on the particular halogen anion. 2 3 Na and 2 7 Al NMR spectra acquired with magic angle spinning (MAS) are sensitive to both halide composition and distribution and can be used to monitor the onset of phase separation. The Cl/Br and Br/I sodalites show close to ideal miscibility behavior, whereas in the Cl/I sodalites domain segregation effects prevail. The NMR spectra of the quadrupolar 2 3 Na and the halogen nuclei also serve as sensitive indicators of the local symmetry perturbations caused by the disorder inherent to solid solution systems. Furthermore, the continuous variation of lattice parameters in sodalite solid solutions provides an opportunity to probe the fundamental dependence of chemical shift on Na-halogen distances. In this respect the experimental 2 3 Na NMR data reveal an exponential relationship, in agreement with theoretical calculations based on the Hartree-Fock method. In contrast, for the halogen chemical shifts the correlation is found to be approximately linear, with slopes of 17, 35, and 75 ppm/A for 3 5 Cl, 8 1 Br, and 1 2 7 I, respectively. All of these results reflect the high sensitivity of chemical shifts to the extent of anion-cation overlap for nuclei in ionic environments.

The spin—orbit/Fermi contact effect on 13C substituent chemical shifts in 1-halo-bicyclo[1.1.1]pentanes

In the title compounds, the relativistic spin-orbit corrections to 13C magnetic shielding constants are calculated as a quadratic response to the spin-orbit/Fermi contact (S-O/FC) perturbation. To carry out such calculations, the Gaussian 98 package of programs was properly modified. The FC operator was introduced using the finite perturbation (FPT) approach, while the paramagnetic shielding operator was taken into account within the coupled perturbed Kohn-Sham approach, using a gauge single origin. In all cases the single origin was taken at the halogen nucleus. XH and CH3X (X = F, Cl, Br, I) compounds were taken as test cases to compare results obtained with this modified program to other values taken from the literature. Results obtained with different functionals are also compared. In 1-halo-bicyclo[1.1.1]pentanes, the calculated S-O/FC contributions to 13C magnetic shielding constants correspond to shielding effects for Cα and Cβ, and to deshielding effects for Cγ. Calculated S-O/FC contributions to the Cα magnetic shielding constants are larger than those calculated in CH3X. Such a result is in line with the high s character at the C atom of the C-X bond for the title compounds.

Synthesis and biological activities of some quinoxaline derivatives bearing aromatic halogen nucleus

1-Aryl-3-(3'-chlorophenyl)-2-propen-1-ones (la-j) on reaction with bromine in acetic acid yielded 1-aryl-3-(3'-chloruphenyl)-2,3-dibromopropan-1-ones (2a-j). Reaction of 2a-j with o-phenylenediamine afforded the corresponding 2-(3'-chlorophenyl)-3-substituted-benzylquinoxaline (3a-j). The synthesized compounds were evaluated for their anticancer, antitubercular and antimicrobial activities.

Density functional calculations of nuclear quadrupole coupling constants in the zero-order regular approximation for relativistic effects

The zeroth-order regular approximation (ZORA) is used for the evaluation of the electric field gradient, and hence nuclear quadrupole coupling constants, in some closed shell molecules. It is shown that for valence orbitals the ZORA-4 electron density, which includes a small component density (“picture-change correction”), very accurately agrees with the Dirac electron density. For hydrogen-like atoms exact relations between the ZORA-4 and Dirac formalism are given for the calculation of the electric field gradient. Density functional (DFT) calculations of the electric field gradients for a number of diatomic halides at the halogen nuclei Cl, Br, and I and at the metallic nuclei Al, Ga, In, Th, Cu, and Ag are presented. Scalar relativistic effects, spin–orbit effects, and the effects of picture-change correction, which introduces the small component density, are discussed. The results for the thallium halides show a large effect of spin–orbit coupling. Our ZORA-4 DFT calculations suggest adjustment of some of the nuclear quadrupole moments to Q(79Br)=0.30(1) barn, Q(127I)=−0.69(3) barn, and Q(115In)=0.74(3) barn, which should be checked by future highly correlated ab initio relativistic calculations. In the copper and silver halides the results with the used gradient corrected density functional are not in good agreement with experiment.

Calculation of nuclear magnetic shieldings. XIII. Gauge-origin independent relativistic effects

The gauge-origin independent expression for the relativistic nuclear magnetic shieldings was derived from the Douglas-Kroll transformation of the no-pair equation and the use of the gauge including atomic orbitals (GIAOs) proposed by London. Using our expression the relativistic spin free effect on the nuclear magnetic shieldings was evaluated for the four hydrogen halide molecules, HF, HCl, HBr, and HI, at the coupled Hartree-Fock (CHF) level with uncontracted Cartesian Gaussian-type basis sets. It was found that the GIAO-CHF results are very similar to the shielding values calculated with the fixed gauge origins at the halogen nuclei. The calculated results showed that the spin independent relativistic effect produces high-field shifts at both the halogen nuclei and protons in the hydrogen halides. However, the computed spin free effect was too small to interpret the very large upshield proton shifts observed in HBr and HI molecules.

Calculation of nuclear magnetic shieldings. XII. Relativistic no-pair equation

A Schrödinger-Pauli type two-component perturbation theory has been presented for the calculation of relativistic effects of nuclear magnetic shieldings. The expression for the relativistic nuclear magnetic shieldings are derived from the Douglas-Kroll transformation of the no-pair equation for a molecule, which bears a nuclear magnetic dipole moment, and which is placed in an external magnetic field. The exact form of the relativistic kinetic energy is included in the eigenvalue equation which is solved variationally. We calculated the relativistic mass correction effect on the nuclear magnetic shieldings in the four hydrogen halide molecules, HF, HCl, HBr, and HI, at the coupled Hartree-Fock (CHF) level. It was shown that the mass correction effect increases the nuclear magnetic shieldings of the halogen nuclei. The increments in the shieldings are proportional to about the third power of the atomic numbers of the halogen nuclei. This increase in the shieldings results from the mass correction effect concentrating the electrons in the vicinity of the heavy nucleus, the so-called relativistic contraction.

Determination of the quadrupole moment of the halogen nuclei (Cl,Br,I) from molecular data

The electric field gradients at the halogen nuclei in hydrogen halides are calculated by using the coupled cluster method for the treatment of the electron correlation, and the spin-averaged no-pair approximation for the evaluation of the relativistic contribution. Upon combining these results with microwave spectroscopic data for nuclear quadrupole coupling constants in HCl, HBr, and HI, the following values of the nuclear quadrupole moment of the halide nuclei are obtained: Q(35Cl) = 0.0816 barn, Q(79Br) = 0.2989 barn, and Q(127I) -0.651 barn. The present 'molecular' value of Q(35Cl) agrees with the latest 'atomic' data. The results obtained for 79Br and 127I strongly indicate that the current recommended standard values of their nuclear quadrupole moments need to be revised.

P, π-interaction in the group using the NQR technique and MNDO calculations

The experimental EFG asymmetry parameters at the halogen nuclei in molecules containing the group do not corroborate widespread representations of a p, π-conjugation between the unshared electron pair of the halogen atom and the π-electron double bond system in these molecules. MNDO calculations of ethylene and its derivatives and analysis of p x -orbital populations of the C and Y atoms in the group of these molecules conform to the experimental data in question. These calculations as well as those of XCH=CH 2 (X=F, Cl and CH 3 ) molecules with varying CX bond lengths, and systems XCH=Ch 2 −HF and [XCH=CH 2 ] 1+ − HF with varying distance between the system fragments, conform to an electrostatic mechanism of p x -electron density distribution in such molecules.

Faraday communications. Carbon–halogen second-order quadrupolar and indirect spin–spin coupling effects in high-resolution solid-state13C NMR spectra of halobenzenes

High-resolution solid-state 13C NMR spectra of halobenzenes containing C—X bonds (X = CI, Br, I) are reported and the effects of the second-order quadrupolar interaction and indirect spin–spin coupling between 13C and the quadrupolar halogen nuclei 35/37Cl, 79/81Br and 127I are discussed.

Nuclear magnetic resonance chemical shifts in alkali iodides, cuprous halides and silver halides

NMR chemical shifts of 63Cu, 65Cu, 35Cl, 79Br and 127I nuclei in cuprous halides (CuCl, CuBr and CuI) and silver halides (AgCl, AgBr and AgI) were determined accurately at 294 K using magic-angle-spinning of the sample. The mechanisms of the chemical shifts are discussed qualitatively in terms of the ionic radii and electronegativities. We propose four factors determining the chemical shifts; the nearest neighbor interaction, the next nearest neighbor interaction, isolation and the covalency effect. Temperature dependences of the metal and halogen chemical shifts in alkali iodides, cuprous halides and silver halides were measured for static samples. Positive temperature dependences are observed in LiI ( 7Li and 127I), NaI ( 23Na and 127I), cuprous halides (halogen nuclei), and AgI ( 127I). On the other hand, the dependence is negative in KI ( 39K and 127I), RbI ( 87Rb and 127I), CsI ( 133Cs and 127I), cuprous halides ( 63Cu), AgCl ( 35Cl), and AgBr ( 79Br). These temperature dependences are interpreted qualitatively in terms of lattice vibration, lattice expansion and cation motion.

Relativistic contributions to molecular electric-field gradients in hydrogen halides

Large basis-set calculations are performed for electric-field gradients in HCl, HBr, and HI at the correlated level of approximation and including the relativistic contribution. It is found that even in the case of HCl the relativistic correction to the electric-field gradient at the Cl nucleus is not completely negligible. For HBr and HI, its contribution to the halogen-atom electric-field gradient becomes larger than the corresponding electron-correlation corrections. The calculated values of the electric-field gradient at the halogen nuclei are used to determine the standard “molecular” values of nuclear quadrupole moments for Cl, Br, and I. The results for 35Cl (−8.2 e fm 2) and 79Br(30.5 e fm 2) are among the best available values of the corresponding nuclear quadrupole moments. For the 127I the estimated value of its quadrupole moment is −71.8 e fm 2.

Accurate Determination of NMR Chemical Shifts in Alkali Halides and Their Correlation with Structural Factors

Abstract High-resolution solid-state NMR spectra of alkali halides have been measured using the magic angle spinning (MAS) of the sample, and chemical shifts of 7Li, 23Na, 87Rb, 133Cs, 35Cl, 79Br, and 127I have been determined accurately. The 39K chemical shifts have been determined by NMR without MAS. As the ratio of the cation radius to the anion radius (Rm) increases, the chemical shifts of halogen nuclei show an upfield shift when Rm<0.6, while they show a downfield shift when Rm>0.6. The chemical shifts of the halogen nuclei are explained in terms of the first and the second nearest neighbor interactions, both of which cause a downfield shift. On the other hand, the chemical shifts of alkali nuclei show a downfield shift for the ratio of the anion radius to the cation radius (Rx) less than 1.6, while they show an upfield shift for Rx>1.6. The chemical shifts of the alkali nuclei are expressed by the sum of the nearest neighbor interaction in the absence of the halogen-halogen interaction and the “isolation effect” caused by the halogen-halogen interaction. The “isolation effect” makes the chemical shifts approach to the values of the isolated ions.

Characterisation of the oxo-anions of bromine BrOx–(x= 1–4) by infrared, Raman, nuclear magnetic resonance, and bromine K-edge extended X-ray absorption fine structure techniques

The bromine oxo-anions BrOx–(x= 1–4) have been studied by vibrational and multinuclear n.m.r. spectroscopy and bromine K-edge extended X-ray absorption fine structure (EXAFS) measurements. Raman and/or i.r. data for BrO– and BrO2– are presented, and conflicts in the literature for the latter resolved. Oxygen-17 n.m.r. data for the halogen oxo-anions have been recorded, and an increase in δ(17O) with formal oxidation state of the halogen noted. Coupling to the halogen nucleus has been observed for ClO4–, 1J(35/37Cl–17O)= 85, and for BrO4–, 1J(79/81Br–17O)= 420Hz, but could not be resolved for IO4–. The 81Br n.m.r. resonance of BrO4–(δ= 2 476) and the 127I resonance of IO4–(δ= 4 090 p.p.m.) are reported. Bromine K-edge EXAFS data are presented for all four ions in solution, and for all but BrO– in the solid state, and differences in bond lengths between solid state and solution found to be within experimental error. Bond lengths obtained are: BrO4– 1.61, BrO3– 1.65, BrO2– 1.72, and BrO– 1.81 A. This is the first bond length reported for the hypobromite ion.

Nuclear Quadrupole Coupling Constant and Conformational Studies

A molecular conformation study on three 3-monosubstituted derivatives of propene has been carried out by evaluating the EFG at the site of the halogen nucleus using a semi-empirical LCAO-MO-SCF method. Calculations are performed on several conformers at INDO and CNDO level, using “sp” and “spd” valence basis sets, with Slater type orbitals as the basis functions. The results obtained for various conformers indicate that the nuclear quadrupole coupling constant is practically independent of the orientation of the CH2X group (X = Cl, Br and I) (Figure 1). The mean value of e2 Qqzz/h (averaged over all conformers) in each system matches favourably with the experimental value, despite the severe approximations that are inherent in the semi-empirical theory as well as in its application in the evaluation of the EFG.

Studies on the intermolecular interactions of metal chelate complexesIX: On the interaction of copper(II) dithiocarbamate with some lewis acids

The intermediate products of the reaction between copper(II) dithiocarbamate complex and some Lewis acids (HgI 2, HgBr 2, GeCl 4, AsBr 3, CoCl 2, C(NO 2) 4) as well as some organometallic compounds (SnEt 4 and PbEt 4) were studied using EPR spectroscopy. In non-polar and non-coordinating solvents HgI 2, HgBr 2 and GeCl 4 formed adducts with Cu(dtc) 2, whereas in polar and coordinating solvents the mixed-ligand complexes of the type Cu(dtc) +…A −(A = HgX 3) were obtained with a complex counterion in the second coordination sphere of copper(II). With C(NO 2) 4 the intermediate reaction product in non-polar solvents was assumed to be Cu(dtc)·NO 2 which dissociates to Cu(dtc) +…NO 2 − in polar solvents. Similar EPR spectra were obtained with SnEt 4 and PbEt 4. The reaction of Cu(dtc) 2 with CoCl 2, AsBr 3 and SbCl 3 yielded the mixed-ligand complexes of the type Cu(dtc)X n ( n = 1 or 2) exhibiting well resolved superhyperfine splitting from one or two halogen nuclei. The influence of the medium on the above interaction is also discussed.

Radiation chemical formation of radical cations of halogenoalkanes and their electron spin resonance spectra and structure

Exposure of dilute solutions of chloro-, bromo- and iodo-alkanes in trichlorofluoromethane to 60Co γ-rays at 77 K gave the corresponding cations. However, for RCI+ and RBr+ the hole is shared with one chlorine atom of a solvent molecule via the formation of a σ bond, as in [RCI[graphic ommitted]CICFCI2]+. For alkyl chlorides the hyperfine coupling constants of the two chlorine nuclei are nearly equal. The (RBr)+ adduct shows e.s.r. spectra consisting of dominant quartet splittings from bromine and additional quartet splittings from chlorine. For the iodo-cations, no clear evidence for such bonding is obtained, and there are very large shifts in the g-values resulting from marked spin-orbit coupling. For more concentrated solutions, the e.s.r. spectra show septet hyperfine patterns arising from coupling to two equivalent halogen nuclei, which indicates the formation of dimer radical cations, (RX)2+, again having the unpaired electron in a σ* orbital. In the particular case of t-butyl chloride, neither the parent cation, nor its complex with a solvent molecule were detected. Instead, a multiline spectrum was obtained which we assign to (Me2CCH2)+ cations weakly complexed with HCl. Theoretical calculations on the parent cations, their dimers, and adducts with CFCl3 support these assignments.

ChemInform Abstract: PARAMAGNETIC TRANSITION METAL CARBONYLS AND CYANIDES. PART 10. ELECTRON ADDITION TO VARIOUS CARBONYL(η5‐CYCLOPENTADIENYL)METAL HALIDES: AN ELECTRON SPIN RESONANCE STUDY

AbstractWerden die Komplexe (I) entweder als reine Verbindungen oder in Lösungsmitteln.

THE 14N, 35Cl, AND 81Br NMR SPECTRA OF SUBSTITUTED PYRIDINIUM CHLORIDES, PERCHLORATES, AND BROMIDES IN AQUEOUS SOLUTION. AN EVIDENCE TO CONTACT ION PAIR FORMATION

Abstract 14N, 35Cl, and 81Br NMR line widths of several chlorides, bromides and perchlorates of 4-substituted pyridinium and related heteroaromatic cations were measured at various concentrations in aqueous solutions. The results were interpreted by assuming the contact ion pair formation, since the calibrated line widths w of halogen nuclei in anions were linearly dependent on the line widths of 14N in respective cations.