cm050350q_si_002.cif (10.85 kB)
Thermal Conversion of Guanylurea Dicyanamide into Graphitic Carbon Nitride via Prototype CNx Precursors
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posted on 2005-07-26, 00:00 authored by Bettina V. Lotsch, Wolfgang SchnickGuanylurea dicyanamide, [(H2N)C(O)NHC(NH2)2][N(C⋮N)2], has been synthesized by ion exchange
reaction in aqueous solution and structurally characterized by single-crystal X-ray diffraction (C2/c, a =
2249.0(5) pm, b = 483.9(1) pm, c = 1382.4(3) pm, β = 99.49(3)°, V = 1483.8(5) × 106 pm3, T = 130
K). The thermal behavior of the molecular salt has been studied by thermal analysis, temperature-programmed X-ray powder diffraction, FTIR spectroscopy, and mass spectrometry between room
temperature and 823 K. The results were interpreted on a molecular level in terms of a sequence of
thermally induced addition, cyclization, and elimination reactions. As a consequence, melamine (2,4,6-triamino-1,3,5-triazine) is formed with concomitant loss of HNCO. Further condensation of melamine
yields the prototypic CNx precursor melem (2,6,10-triamino-s-heptazine, C6N7(NH2)3), which alongside
varying amounts of directly formed CNxHy material transforms into layered CNxHy phases without
significant integration of oxygen into the core framework owing to the evaporation of HNCO. Thus,
further evidence can be added to melamine and its condensation product melem acting as “key
intermediates” in the synthetic pathway toward graphitic CNxHy materials, whose exact constitution is
still a point at issue. Due to the characteristic formation process and hydrogen content a close relationship
with the polymer melon is evident. In particular, the thermal transformation of guanylurea dicyanamide
clearly demonstrates that the formation of volatile compounds such as HNCO during thermal decomposition
may render a large variety of previously not considered molecular compounds suitable CNx precursors
despite the presence of oxygen in the starting material.
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CN x H y materialGraphitic Carbon Nitridemelamine yieldsFTIR spectroscopyguanylurea dicyanamidemass spectrometryCN x H y phasesNH 2HNCOcondensation product melemC 6 N 7Thermal Conversionpolymer melonpmgraphitic CN x H y materialsCN x precursorsGuanylurea DicyanamidePrototype CN x Precursors Guanylurea dicyanamide130 Kion exchange reactionhydrogen content823 Kformation processelimination reactionscore frameworkroom temperature
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