Rationalization of solid-state NMR multi-pulse decoupling strategies: coupling of spin I = ½ and half-integer quadrupolar nuclei

In this paper we undertake a study of the decoupling efficiency of the Multiple-Pulse (MP) scheme, and a rationalization of its parameterization and of the choice of instrumental set up. This decoupling scheme is known to remove the broadening of spin-1/2 spectra I, produced by the heteronuclear scalar interaction with a half-integer quadrupolar nucleus S, without reintroducing heteronuclear dipolar interaction. The resulting resolution enhancement depends on the set-up of the length of the series of pulses and delays of the MP, and some intrinsic material and instrumental parameters. Firstly through a numerical approach, this study investigates the influence of the main intrinsic material parameters (heteronuclear dipolar and J coupling, quadrupolar interaction, spin nature) and instrumental parameters (spinning rate, pulse field strength) on efficiency and resolution enhancement of the scalar decoupling scheme. A guideline is then proposed to obtain quickly and easily the best resolution enhancement via the rationalization of the instrumental and parameter set up. It is then illustrated and tested through experimental data, probing the efficiency of MP-decoupling set up using this guideline. Various spin systems were tested (³¹P-⁵¹V in VOPO₄, ³¹P-⁹³Nb in NbOPO₄, ¹¹⁹Sn-¹⁷O in Y₂Sn₂O₇), combined with simulations results.