Revisiting the crystal structure and thermal properties of NaMgAl(oxalate)₃•9H₂O/Cr(III): An extraordinary spectral hole-burning material

We have reinvestigated the crystal structure and thermal properties of NaMgAl(oxalate)₃•9H₂O. In the thermal gravimetric analysis the steps of dehydration and decomposition/oxidation yield a mass change that is commensurate with 9 water molecules of hydration. Dehydration steps occur at 127, 171, and 201 °C whereas the oxalate ligand decomposes in steps at 403 and 424 °C with a final oxidation step at 692 °C. A refinement of the single crystal X-ray diffraction data taken at 200 K affirms the P3c1 space group with nine water molecules of hydration and unit cell parameters a = b = 16.7349(2) Å and c = 12.6338(1) Å with Z = 6. The structures can be described in terms of modulations of an idealised Z = 1 structure in P3̄lm. T-Cycle experiments of spectral holes in the R ₁-line yield a single Gaussian barrier with T₀ ± σ_T of 46 ± 21 K and three barriers with 40 ± 12, 70 ± 10, 107 ± 5 K for perprotonated and partially deuterated (46%) NaMgAl(oxalate)₃•9H₂O/Cr(iii) 0.5%, respectively.