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. Author manuscript; available in PMC: 2019 Mar 28.
Published in final edited form as: Phys Chem Chem Phys. 2018 Mar 28;20(13):8475–8487. doi: 10.1039/c7cp06724k

Figure 3.

Figure 3

Plots illustrating the agreement between experimental 13COOH tensor values for all phases (A2, Bm, Em, and C) and DFT computed values for model structures with various O–H bond distances (r). Plot (a) shows that the best agreement for phases A2, Bm, and Em is a trans structure having O–H bond lengths of 0.93 ± 0.08 Å, 0.86 ± 0.11 Å and 0.96 ± 0.10 Å, respectively. Plot (b) illustrates that phase C agrees with DFT predictions at O–H bond lengths of 1.23 ± 0.06 Å and 1.46 ± 0.03 Å. The δ11 tensor component of phase C corresponds closely to those measured previously in COO− moieties,41 however, elemental analysis indicates that a COOH is present. These conflicting observations are consistent with the presence of COOH hydrogen disorder in which the proton that is dynamically disordered symmetrically about the midpoint between two oxygens separated by 2.63 Å.