Multinuclear NMR: Easy or Difficult? (Tips for Solid-state NMR)

• How easy or difficult NMR measurements are depends on various factors. Sensitivity(S/N ratio) may be estimated in terms of receptivity given by the following formula.
  Large gyromagnetic ratio γ and natural abundance N_abd lead to large receptivity for ¹⁹F and ²⁷Al, for example.
  
• Low-γ nuclei exhibiting low NMR frequencies (∝ γ ), such as ²⁵Mg and ^47,49T_i, may suffer from ringing effects, making their measurements difficult.
• In solid-state NMR, it is easy to obtain high-resolution spectra for the nuclei with spin quantum number of 1/2, like ¹³C and ³¹P, while difficult for those having larger quantum number than 1/2, in general, because of quadrupolar broadening. Half integer spins (I=3/2, 5/2, 7/2, 9/2), such as ¹¹B and ²³Na, may yield high-resolution spectra via special techniques like MQMAS. These techniques are not applicable to integer spins (I=1, 3, …), such as ¹⁰B and ¹⁴N.
• Although ¹H high-power decoupling is widely utilized in solid-state NMR, the nuclei experiencing weak ¹H dipolar interactions like ²⁹Si require not so strong decoupling. It is difficult to decouple ¹H-¹H interactions, rendering solid-state ¹H measurements difficult.
• In solids, chemical shifts vary depending on the nuclear orientations (CSA: chemical shift anisotropy). For the nuclei having large CSA, such as ¹⁹⁵Pt and ²⁰⁷Pb, magic angle sample spinning with realistic speeds cannot remove spinning sidebands.
• Another factor of long longitudinal relaxation times T₁ makes measurements difficult.

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