¹⁴N MAS NMR Spectroscopy:  The Nitrate Ion

Abstract

Great efforts have been exercised during the past few years in applying magic-angle spinning (MAS) NMR spectroscopy to the highly abundant 14 N quadrupolar nucleus (99.6% natural abundance, spin I ) 1) in polycrystalline solids. [1][2][3] Obviously a successful outcome of these efforts would be highly appreciated in particular if the resulting spinning sideband (ssb) spectra would be of sufficient quality to allow analysis in a straightforward manner, thereby yielding useful spectral parameters. For example, this could involve the procedures and versatile software programs already developed for the analyses of spinning sideband spectra (the complete manifold and/or individual ssb line shapes) for halfinteger spin (I ) 3 / 2 , 5 / 2 , 7 / 2 , ...) quadrupolar nuclei and 2 H. [4][5][6][7][8][9][10] The potential of a routine determination for the 14 N quadrupole coupling constant (C Q ) and asymmetry parameter (η Q ) from such spectra would constitute a valuable parameter set characterizing the environment of the nitrogen atom in addition to the isotropic/ anisotropic 15 N chemical shift data, oftentimes determined using 15

Direct detection of nitrogen-14 in solid-state NMR spectroscopy

“…Their first publication presented a spectrum obtained from potassium nitrate (Fig. 23), which consisted of a very broad manifold of spinning sidebands spanning a frequency range of over 600 kHz [106]. An extremely high S/N was achieved in an experiment time of 33 hours using single-pulse excitation, allowing an accurate simulation not just of the spinning sideband intensities but also their individual lineshapes (Fig.…”

14N Chemical Shifts and Quadrupole Coupling Constants of Inorganic Nitrates

“…It should be pointed out that this method of averaging the contribution of the second-order effect is a simplified approach. A more comprehensive analysis depends on the simulation of the lineshapes of different spinning sidebands over a fairly large spectral range (17), which was published after the work described here had been completed. When the peak position is measured at two different magnetic fields and denoted as ν 1 and ν 2 , respectively, a set of two simultaneous linear equations is obtained.…”

“…Recently, using a specially designed high-Q probe for lowfrequency nuclei, Jacobsen and co-workers were able to observe all spinning sidebands in a spectral range of 1 MHz (17). By careful simulations of the lineshapes of the spinning sidebands, they were able to obtain both δ and χ at a single resonance frequency.…”

“…The basic features of MAS 14 N NMR have been established in this laboratory (15,16). Recently the simple MAS approach has been greatly improved both experimentally and in data analysis (17).…”

“…Simple broadband MAS probes rather than specially designed high-Q transmission-linetuned low-frequency probes (17) were used for the 14 N NMR study of 14 polycrystalline inorganic nitrates. The reason for choosing inorganic nitrates in this study is that their moderate quadrupole coupling constants (∼0.4-1.0 MHz) make it possible to observe the 14 N peaks without difficulty.…”