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In , 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 with the three hydrogen atoms replaced by . It is a white crystalline solid.


Preparation
Melem can be prepared by thermal decomposition of various C−N−H compounds, such as C3N3(NH2)3, dicyandiamide H4C2N4, ammonium dicyanamide NH4N(CN)2, H2CN2, at 400 to 450 °C.


Structure and properties

Crystal structure
Melem crystallizes in the group P21/c (No. 14), with parameters a = 739.92(1) , 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.


Thermal decomposition
When heated above 560°, melem transforms into a graphite-like C−N material.


Melemium cations
Melem accepts up to three protons yielding cations called melemium . Some salts described in the literature are , • 2, melemium perchlorate, • , melemium hydrogensulfate and two melemium methylsulfonates • and • . The protons can be inserted in any of the six outer atoms of the heptazine core, yielding many tautomers of apparently similar energies.


See also
  • , with a single C-N ring
  • , triamino triazine
  • , a cation derived from melamine
  • Melam , a condensation dimer of melamine
  • , a cation derived from melam
  • 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

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