High‐Resolution NMR Spectroscopy in Solids by Truly Magic‐Angle Spinning

Abstract

Right angles: In solid‐state magic‐angle spinning (MAS) NMR spectra, the line widths of carbonyl carbon atoms in polycrystalline cholesteryl acetate are found to be as narrow as 0.039 ppm if the magic angle is adjusted very accurately, that is, within ±0.004° (see picture). The line broadening observed for slightly miss‐set angles is mostly due to residual chemical shift anisotropy (CSA) interactions. Long spin‐echo life times up to ${{{\rm T}{{\prime \hfill \atop 2\hfill}}}}$=3.6 s open the way to sophisticated NMR methods.

Detection and use of small J couplings in solid state NMR experiments

“…Here, the two different a 13 CH 2 directly linked to the two non-equivalent 31 P sites of the inorganic layer are split into doublets by one-bond 31 P-13 C scalar ( 1 J) coupling of ca. 40 Hz (topright inset) and the 13 C of the benzyl ring linked to the 14 N of the amine reveals a broadening due to a dipolar/ quadrupolar cross-term [19,20] (top-left inset).…”

“…ments because there exist small but significant higher order terms including shifts and broadening (secondorder quadrupolar effects, second-order cross-terms between interactions), residual dipolar coupling terms at limited spinning rates, and distribution of the isotropic contributions due to non-ideal ordering or disorder. Nevertheless, a combination of high-frequency spinning, very accurate magic angle setting (AE0.018) [19] and efficient heteronuclear decoupling allows observation of scalar J couplings in perfectly ordered crystalline phases, as illustrated on Fig. 2 with the 13 C CP-MAS spectrum of the (ZnO 3 P C 2 H 4 CO 2 H -0.5 C 6 H 5 NH 2 ) layered phosphonate crystalline compound [18,2].…”

“…The full J-resolved spectra can be perfectly modeled by considering 29 Si isotopic enrichment and strong coupling effects due to small chemical shift differences (adapted from reference [22]). compounds or glasses, and also heteronuclear couplings such as one-bond 19 F-207 Pb [43], 31 P-113 Cd, and 31 P-77 Se [44-46] 1 J couplings, and two-bond 2 J( 29 Si-O-31 P) couplings [47][48][49], among others.…”

“…Because tailoring excitation conditions allows one to selectively excite the central transition as a fictitious I = 1/2 spin using an echo [78,79] the J multiplet of the 93 central transition) sevenfold J multiplet of the 93 Nb resonance characteristic of the sixfold coordination to 19 F nuclei. The 1D MAS NMR 19 F spectrum (Fig.…”

Coherence transfer between spy nuclei and nitrogen-14 in solids

“…During the 13 C acquisition period t 2 a lower 1 H RF amplitude of m RF = 70 kHz was used, with pulse-widths of 5.2 ls and a phase difference of 35°. The magic angle was adjusted within 0.01°using deuterated [D 6 ]a-oxalic acid dehydrate [26]. The chemical shifts for 1 H, 13 C, and 14 N were referred to the external standards of TMS, adamantane, and NH 4 Cl, respectively.…”