Unmasking Melon by a Complementary Approach Employing Electron Diffraction, Solid‐State NMR Spectroscopy, and Theoretical Calculations—Structural Characterization of a Carbon Nitride Polymer
Tóm tắt
Poly(aminoimino)heptazine, otherwise known as Liebig's melon, whose composition and structure has been subject to multitudinous speculations, was synthesized from melamine at 630 °C under the pressure of ammonia. Electron diffraction, solid‐state NMR spectroscopy, and theoretical calculations revealed that the nanocrystalline material exhibits domains well‐ordered in two dimensions, thereby allowing the structure solution in projection by electron diffraction. Melon ([C6N7(NH2)(NH)]
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The structure solution was verified by using precession intensity data. Owing to their robustness with respect to sample misalignment and less pronounced dynamical effects the data quality obtained under otherwise identical experimental conditions can be improved. Accordingly Rrimis 20 % and the straightforward structure solution has a figure of merit of 19.5 %. The structure refinement (184 independent reflections no. of reflections/parameter ≈6 dmin.0.78 Å) was less successful due to the large sample thickness which gives rise to stronger dynamical effects (cf. Figure 11 middle).
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