Application of the MAS-J-HMQC experiment to a new pair of nuclei {29Si,31P}: Si5O(PO4)6 and SiP2O7 polymorphs

Efficiency of dipolar and J-derived solid-state NMR techniques for a new pair of nuclei {31P,29Si}. Towards the characterization of Si–O–P mesoporous materials

“…Obviously, the Si(2) build-up curve differs drastically from the one obtained for Si(1), even though Si(1) and Table 2 Estimated T 2 0 ( 29 Si) and T 2 0 ( 31 P) obtained using MAS spin echo experiments and Eq. (1) for the Si 5 O(PO 4 ) 6 phase (Si(1), Si(2), Si(3) and P sites) T 2 0 ( 29 Si) (ms) [26] T 2 0 ( 31 P) (ms) [15] Si (1) 31 Pe 29 Si 2D refocused MAS-J-INEPT pulse sequence. F 1 ¼ þx, þx, þx, þx, þx, þx, þx, þx, Àx, Àx, Àx, Àx, Àx, Àx, Àx, Àx; F 2 ¼ þx, Àx; F 3 ¼ þy, þy, Ày, Ày; F 4 ¼ þx, Àx; F 5 ¼ þx, þx, þx, þx, þy, þy, þy, þy, Àx, Àx, Àx, Àx, Ày, Ày, Ày, Ày; F 6 ¼ þx, Àx, þx, Àx, þy, Ày, þy, Ày; receiver ¼ þx, þx, Àx, Àx, þy, þy, Ày, Ày.…”

“…4a. T 2 0 time constants [15] were measured by spin-echo experiments (90 et 0 e180 et 0 ) under fast MAS for the unique 31 P signal. Such time constants are characteristic of the lifetime of the involved coherences.…”

Low-load rotor-synchronised Hahn-echo pulse train (RS-HEPT)1H decoupling in solid-state NMR: factors affecting MAS spin-echo dephasing times

“…64 The same approach, with -pulses applied during every rotor period, has also been shown to provide effective decoupling in 13 C CP MAS studies of fluorinated polymers. 65,66 It is to be noted that decoupling using -pulses is not a new concept, with Mehring et al having shown that a signal due to NaF appears in a static 19 F solid-state NMR spectrum upon the application of a train of -pulses to the 23 Na spins, 67 while Freeman et al have presented a 13 C liquid-state NMR spectrum of butan-1,2-diol recorded using a repeated sequence of 1 H -pulses. 68 Recently, we have presented 15 N cross-polarisation (CP) spin-echo MAS experiments of guanosine derivatives, where the use of RS-HEPT 1 H 1 D 100 kHz decoupling, with a duty cycle of 6%, allowed spin-echo evolution periods, , out to 200 ms, thereby enabling the accurate determination of a J coupling as small as 3.8 Hz for which the first zero crossing is observed at ¾130 ms. 48 However, good RS-HEPT 1 H decoupling performance at 22.5 kHz MAS was observed only for non-protonated 15 N resonances, with the small T 2 0 values of ¾5 ms obtained for the protonated 15 N resonances preventing the observation of J modulation in these latter cases.…”

Grafting on nanoparticles: is solid-state NMR a convenient tool of investigation?

“…10 Several examples dealing with the 31 P/ 29 Si spin pair will be presented. 3,4,11,12 The MAS-J spectroscopy is one of the latest developments in solid-state NMR. 13,14 The experimental schemes are mainly related to pulse sequences already proposed in the frame of solution state NMR (HMQC, J-Res, INEPT…).…”

“…Their structural characterization involved the set up of J and D techniques, such as 31 P/ 29 Si CP MAS, J-MAS-HMQC, J-MAS-INEPT experiments. 11,12 Triple resonance experiments 1 H/ 31 P/ 29 Si were also implemented in order to characterize double transfers between the involved nuclei. Figure 4 shows a 2D 31 P/ 29 Si HMQC experiment dealing with a complex mixture of silicophosphates.…”