We review the solid-state NMR literature for the 35/37Cl, 79/81Br, and 127I nuclides, with coverage up to August 2008. The theory related to NMR spectroscopy of half-integer quadrupolar nuclei in powdered samples is briefly summarized, as are the experimental methods for recording such spectra. The most recent experimental results demonstrate the increasing feasibility and utility of observing solid-state NMR spectra for these nuclei, particularly chlorine-35/37. Several chlorine chemical shift tensors have been measured recently, along with their orientation relative to the electric field gradient tensor. The increased availability of ultrahigh-field solid-state NMR spectrometers (B0 ≥ 18.8 T) is the dominant factor responsible for the increased number of studies and increased amount of available information. For example, insights have been gained into the hydrogen bonding environment at the chlorine atoms in various organic hydrochloride salts by interpreting trends in the chlorine quadrupolar coupling and chemical shift tensors. The sensitivity of the 35/37Cl NMR parameters to polymorphism and pseudo-polymorphism has also been demonstrated. Important advances in quantum chemistry which are having an impact on the computation of quadrupolar and magnetic shielding tensors for these nuclei are also briefly discussed. Data available from gas-phase molecular beam and microwave spectroscopy experiments are presented. Finally, prospects for future studies of 35/37Cl, 79/81Br, and 127I by solid-state NMR spectroscopy are presented.

Chapter 5 Chlorine, Bromine, and Iodine Solid-State NMR Spectroscopy

NQR spectra due to 35Cl, 127I, and 121Sb in I3Cl2SbCl6 and ICl2SbCl6 have been observed in the temperature range 77 K to melting point. The Zeeman effect on the single crystals of these complexes has been examined. In I3Cl2SbCl6 the η-values for the I atoms contributing to the higher and the lower NQR frequencies are 0.73 to 0.09, respectively, whereas in ICl2SbCl6 the η-value for the I atom is 0.15. In these complexes the 35Cl NQR lines which yield large η-values (0.42 to 0.56) are assigned to the bridging Cl atoms. The η-values for the other Cl atoms, except the Cl atoms in the ICl2+ ion which have η-values of 0.13 to 0.15, are negligibly small. The Sb atoms in both complexes have considerably large η-values (0.39). The orbital populations have been calculated from the NQR parameters. The bonding in the cations is explained on the basis of an approximation using only p orbitals of the I atom.

NQR of 35Cl, 127I, and 121Sb in I3Cl2SbCl6 and ICl2SbCl6

The NQR sepctra due to 81Br and 127I in potassium dibromoiodate and its monohydrate were observed, and the Zeeman effect of 81Br NQR in the monohydrate was examined. The resonance lines indicate that both compounds have two kinds of dibromoiodate ions and that these ions in the anhydride are slightly asymmetric, while those in the monohydrate are symmetric. The difference in frequency between the two resonance lines due to each resonant nucleus in the monohydrate is explained in terms of the I···Br intermolecular interaction. The charge distributions in both compounds were evaluated to be about −0.6e and 0.2e on the terminal and central atoms respectively.

Isamu Tomoyasu

Papers

The Nuclear Quadrupole Resonance of Dibromoiodate Ions

The nuclear quadrupole resonance of dibromoiodate ions