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Solid‐state natural abundance 25Mg NMR studies of Na2MgEDTA·4H2O—a possible new reference compound for 25Mg NMR spectroscopy

Natural abundance solid‐state 25Mg NMR measurements were made of the disodium salt of magnesium ethylenediaminetetraacetate tetrahydrate (Na2MgEDTA·4H2O). Both magic angle spinning (MAS) and static experiments were employed to determine the quadrupole coupling constant (Cq) and the asymmetry parameter (ηq) of the electric field gradient (EFG) tensor associated with 25Mg in this compound, giving the values Cq = 1.675(5) MHz and ηq = 0.15(1). The isotropic chemical shift was determined to be δiso = 0.25(10) ppm (relative to 11 M MgCl2 aqueous solution) and a small chemical shift anisotropy (CSA) contribution (∼− 13 ppm) was detected, one of the first CSA reports in 25Mg NMR. This compound exhibited remarkably good 25Mg NMR sensitivity, due to its fast spin‐lattice relaxation and modest quadrupole coupling, which allowed its use as a secondary shift reference and as a test sample for the implementation and optimisation of signal‐enhancement methods in 25Mg NMR spectroscopy, such as double frequency sweeps (DFS) and the use of adiabatic hyperbolic secant (HS) and WURST pulses. Copyright © 2008 John Wiley & Sons, Ltd.