Christopher J. Groombridge

Nitrogen-15 nuclear magnetic shielding tensors in nitrite and nitrate ion. Experimental and theoretical determinations

Abstract Principal components of the nitrogen shielding tensor are reported for 15 N-enriched sodium nitrite and nitrate, determined by magic angle spinning and static 15 N NMR spectroscopy, and compared with values calculated by local origin methods. The inclusion of electron correlation in SOLO (second-order LORG) improves the results significantly for nitrate as well as nitrite ion, and there is further improvement with the inclusion of six surrounding cations for nitrite ion. The changes in the shieldings with change in molecular dimensions indicate that vibrational corrections are significant. The relative magnitudes of the orbital contributions afford insights into the physical origins of the shielding.

Synthesis and 15N nuclear magnetic resonance shift tensors of bent nitrosyl complexes with N-substituted salicylideneiminate coligands; the shift tensor as a criterion of MNO bond angle

A series of nitrosylcobalt–Schiff base complexes [Co(NO)(asal)2][asal =N-alkyl- or N-aryl-salicylideneiminate, o-OC6H4CHNR, R = Me(msal), Et(esal), Bun(bsal), Ph(phsal) or CH2Ph(bzsal)] has been prepared. Single-crystal X-ray structure analysis of the esal derivative shows the molecule to be pyramidal with a bent apical nitrosyl group [Co–N 1.738(12), N–O 1.16(2)A, Co–N–O 129(1)°] and a trans arrangement of the basal ligands [Co–O 1.833(6), Co–N 1.950(6)A]. The crystals are orthorhombic, space group Pbca, a= 9.544(3), b= 17.000(3), c= 11.359(3)A, Z= 4; the structure was refined to R= 0.059 for 822 observed reflections. The compounds are not very stable in solution, but high-resolution cross-polarisation magic-angle spinning 15N NMR spectroscopy of the [Co(15NO)(asal)2] solids, and also of [Co(15NO)(ketox)2]( ketox =o-OC6H4CMeNOH), shows large isotropic shifts (ca. 730 ppm relative to nitromethane) characteristic of bent nitrosyls. Also characteristic are the nitrogen shift tensors, with one very large component (1100–1960 ppm) reflecting the low energy of the n(N)→π*(NO) circulation. The large ranges of the shielding anisotropy Δ(540–1150 ppm) and the asymmetry parameter η(1.25–2.40) reflect the sensitivity (because of the low excitation energies) of the tensor components to relatively small changes in the geometry of the MNO group, and its relation to the ligands in the basal plane.

13C solid-state n.m.r. spectra of Shanxi coals

Abstract 13 C solid-state n.m.r. spectra of samples of 14 coals and their pyridine residues representative of the three depositions in the Shanxi province of the Peoples Republic of China are described in detail. The results confirm those of previous infrared spectroscopy in showing these vitrinite-inertinite coals to have similar chemical structures and aromaticities to coals of the same rank from Euramerica and Gondwana.

Variable temperature MAS NMR studies of the phase transition in NaTCNQ

13 C MAS NMR spectra of the sodium salt of the radical anion of 7,7,8,8-tetracyanoquinodimethane (Na TCNQ) show changes in both chemical shift position and linewidth of some resonances with temperature, and provide information about the nature of a phase transition at ca. 333 K.

13C and 15N solution and solid-state nuclear magnetic resonance study of the intermolecular interactions in the 1:1 trimethoprim: sulphamethoxazole complex

The combined use of natural-abundance solid-state 13C and 15N n.m.r. shows that the structure of the trimethoprim:sulphamethoxazole complex (TMP:SMZ) is best described by transfer of the proton from N(7) of SMZ to N(1) of TMP. Stabilisation of the complex is achieved by the resulting ionic interaction and by the formation of two intermolecular hydrogen bonds. When the complex is dissolved in dimethyl sulphoxide it is largely dissociated into neutral free base TMP and SMZ.