Proton-detected solid-state NMR spectroscopy of spin-1/2 nuclei with large chemical shift anisotropy

Dipolar Heteronuclear Correlation Solid-State NMR Experiments between Half-Integer Quadrupolar Nuclei: The Case of 11B–17O

“…The 17 O CT-selective π/2 and π pulse lengths were 10 μs and 20 μs in duration, respectively, corresponding to an 8.3 kHz RF field and 25 kHz CT nutation frequency. 2D 11 B­{ 17 O} D-HMQC experiments were performed with our recently described Arbitrary Indirect Dwell (AID) t 1 acquisition mode and a 25 μs t 1 dwell . RAPT was applied to the 11 B spins with a transmitter offset of ±550 kHz and a 10 kHz RF field prior to the start of NMR experiments. , 11 B­{ 17 O} RESPDOR experiments were performed with a 1.5 rotor period saturation pulse (150 μs for a 10 kHz MAS frequency) with a ca.…”

“…2D 11 B{ 17 O} D-HMQC experiments were performed with our recently described AID t 1 acquisition mode and either a (boric acid) 40 μs or (sodium borate glass) 12.5 μs t 1 dwell. 90 RAPT was applied to the 11 B spins with a transmitter offset of ±500 kHz and either an 83.8 (boric acid) or 46.5 (borate glass) kHz RF field prior to the start of NMR experiments. 87,88 100 kHz 1 H RF field SPINAL-64 heteronuclear decoupling was performed throughout all NMR experiments on boric acid.…”

Solid‐State Nuclear Magnetic Resonance Techniques for the Structural Characterization of Geminal Alane‐Phosphane Frustrated Lewis Pairs and Secondary Adducts

“…has shown that short, hard adiabatic pulses (SHAPs) may be used for the adiabatic inversion of 195 Pt with a linewidth larger than 8000 ppm, using rf nutation frequencies beyond 250.0 kHz. [96] However, WURST pulses may in fact replace the PM pulse for saturation of the S‐spin system in what we have termed the WURST‐RESPDOR (W‐RESPDOR) NMR experiment. The advantage of such an approach is that WURST pulses are straightforwardly implemented and easily accessible via any spectrometer software, for example, the bruker software program Topspin (using Shapetool).…”

“…[95] We note that very recent work by Venkatesh et al has shown that short, hard adiabatic pulses (SHAPs) may be used for the adiabatic inversion of 195 Pt with a linewidth larger than 8000 ppm, using rf nutation frequencies beyond 250.0 kHz. [96] However, WURST pulses may in fact replace the PM pulse for saturation of the S-spin system in what we have 27 Al nuclei. Pulse phases � 1 À � 4 and receiver phase can be found in Ref.…”

Frequency-Swept Ultra-Wideline Magic-Angle Spinning NMR Spectroscopy

“…Synchronization of MAS NMR with Carr–Purcell–Meiboom–Gill (CPMG) acquisition , has resulted in an additional sensitivity enhancement, allowing to probe quadrupolar or generally unreceptive nuclei. − However, the narrow inversion (refocusing) bandwidth of conventional radio-frequency (rf) pulses (∼0.5ν rf , where ν rf is the applied nutation frequency in Hz) drastically compromises the broadband-inversion capabilities of the CPMG technique, which can only in part be compensated for by accepting refocusing pulses with non-ideal flip angles . In particular when strong anisotropic spin interactions are present, the frequency dispersion of the NMR lines can easily exceed ∼250 kHz, requiring the application of either ultrafast MAS conditions with hard pulses (ν rf > 150 kHz) , that may additionally be used with indirect detection schemes, − or static ultra-wideline (UW) NMR methodologies. , For the latter, CPMG acquisition has been combined with wideband uniform rate smooth truncation (WURST) pulses, which employ a linear frequency sweep with an amplitude modulation, to allow for drastically increased excitation/refocusing bandwidths. , The resulting WURST-CPMG (WCPMG) NMR experiment has, to the best of our knowledge, so far only been applied under static NMR conditions. However, an extension of WCPMG to operate under MAS conditions would have clear benefits, including chemical shift resolution of multiple species, signal enhancement via CPMG, and broadband excitation of inhomogeneous broadened NMR lines, which would be of interest for the direct observation of “high- Z ” nuclei relevant to catalysis and other important material science areas. ,, The main reason that the extension to MAS has not been attempted might be found in the complex interference between the time-dependent resonance shift of the different spin orientations modulated by MAS, and the frequency sweep of the WURST pulse.…”