In chemistry, melem is a compound with formula ; specifically, 2,5,8-triamino-heptazine or 2,5,8-triamino-tri- s-triazine, whose molecule can be described as that of heptazine with the three hydrogen atoms replaced by . It is a white crystalline solid.[
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Preparation
Melem can be prepared by thermal decomposition of various C−N−H compounds, such as melamine C3N3(NH2)3, dicyandiamide H4C2N4, ammonium dicyanamide NH4N(CN)2, cyanamide H2CN2, at 400 to 450 °C.[
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Structure and properties
Crystal structure
Melem crystallizes in the group P21/c (No. 14), with parameters a = 739.92(1) picometre, b = 865.28(3) pm, c = 1338.16(4) pm, β = 99.912(2)°, and Z = 4. The almost-planar molecules are arranged in parallel layers spaced 327 pm apart. The molecule is in the triamino form, rather than one of the possible tautomers.[
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Thermal decomposition
When heated above 560°, melem transforms into a graphite-like C−N material.[
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Melemium cations
Melem accepts up to three protons yielding cations called melemium . Some salts described in the literature are melemium sulfate, • 2, melemium perchlorate, • , melemium hydrogensulfate and two melemium methylsulfonates • and • . The protons can be inserted in any of the six outer nitrogen atoms of the heptazine core, yielding many tautomers of apparently similar energies.[
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See also
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Triazine , with a single C-N ring
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Melamine , triamino triazine
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Melaminium , a cation derived from melamine
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Melam , a condensation dimer of melamine
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Melamium , a cation derived from melam
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Melon , a condensation oligomer of melem
[Tamikuni Komatsu (2001)> ]
[Fabian Karl Keßler (2019), Structure and Reactivity of s-Triazine-Based Compounds in C/N/H Chemistry. Doctoral thesis, Fakultät für Chemie und Pharmazie, Ludwig-Maximilians-Universität München]