A Combined 25Mg Solid-State NMR and Ab Initio DFT Approach to Probe the Local Structural Differences in Magnesium Acetate Phases Mg(CH3COO)2•nH2O (n=0,1,4)

Multinuclear (H-1, C-13, Mg-25) solid-state NMR data is reported for a series of magnesium acetate phases Mg(CH3COO)(2)nH(2)O (n=0 (two polymorphs), 1, 4). The central focus here is Mg-25 as this set of compounds provides an expanded range of local magnesium coordinations compared to what has previously been reported in the literature using NMR. These four compounds provide 10 distinct magnesium sites with varying NMR interaction parameters. One of the anhydrous crystal structures () has an MgO7 site which is reported, to the best of our knowledge, for the first time. For those phases with a single crystal structure, a combination of magic angle spinning (MAS) NMR at high magnetic field (20T) and first principles density functional theory (DFT) calculations demonstrates the value of including Mg-25 in NMR crystallography approaches. For the second anhydrate phase (), where no single crystal structure exists, the multinuclear NMR data clearly show the multiplicity of sites for the different elements, with Mg-25 satellite transition (ST) MAS NMR revealing four inequivalent magnesium environments, which is new information constraining future refinement of the structure. This study highlights the sensitivity of Mg-25 NMR to the local environment, an observation important for several sub-disciplines of chemistry where the structural chemistry of magnesium is likely to be crucial.