Solid-state natural abundance Mg-25 NMR studies of Na(2)MgEDTA center dot 4H(2)O - a possible new reference compound for Mg-25 NMR spectroscopy

Freitas, Jair C. C. and Wong, Alan and Smith, Mark E. (2009) Solid-state natural abundance Mg-25 NMR studies of Na(2)MgEDTA center dot 4H(2)O - a possible new reference compound for Mg-25 NMR spectroscopy. Magnetic Resonance in Chemistry, 47 (1). pp. 9-15. ISSN 1097-458X

Abstract

Natural abundance solid-state Mg-25 NMR measurements were made of the disodium salt of magnesium ethylenediaminete-traacetate tetrahydrate (Na(2)MgEDTA center dot 4H(2)O). Both magic angle spinning (MAS) and static experiments were employed to determine the quadrupole coupling constant (C-q) and the asymmetry parameter (eta(q)) of the electric field gradient (EFG) tensor associated with Mg-25 in this compound, giving the values C-q = 1.675(5) MHz and eta(q) = 0.15(1). The isotropic chemical shift was determined to be delta(iso) = 0.25(10) ppm (relative to 11 M MgCl2 aqueous solution) and a small chemical shift anisotropy (CSA) contribution (similar to-13 ppm) was detected, one of the first CSA reports in Mg-25 NMR. This compound exhibited remarkably good Mg-25 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 Mg-25 NMR spectroscopy, such as double frequency sweeps (DFS) and the use of adiabatic hyperbolic secant (HS) and WURST pulses. Copyright (C) 2008 John Wiley Sons, Ltd.