Melem Explained

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 amino groups. It is a white crystalline solid.

Preparation

Melem can be prepared by thermal decomposition of various C−N−H compounds, such as melamine C₃N₃(NH₂)₃, dicyandiamide H₄C₂N₄, ammonium dicyanamide NH₄[N(CN)₂], cyanamide 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) pm, 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 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.

See also

• Triazine, with a single C-N ring
• Melamine, triamino triazine
• Melaminium, a cation derived from melamine
• Melam, a condensation dimer of melamine
• Melamium, a cation derived from melam
• Melon, a condensation oligomer of melem

References

^{[1] [2]}

^[3]

Notes and References

1. Jürgens . Barbara . Irran . Elisabeth . Senker . Jürgen . Kroll . Peter . Müller . Helen . Schnick . Wolfgang . 2003-08-01 . Melem (2,5,8-Triamino-tri- s -triazine), an Important Intermediate during Condensation of Melamine Rings to Graphitic Carbon Nitride: Synthesis, Structure Determination by X-ray Powder Diffractometry, Solid-State NMR, and Theoretical Studies . Journal of the American Chemical Society . en . 125 . 34 . 10288–10300 . 10.1021/ja0357689 . 0002-7863.
2. Tamikuni Komatsu (2001)> Komatsu . Tamikuni . 2001-01-01 . The First Synthesis and Characterization of Cyameluric High Polymers . Macromolecular Chemistry and Physics . en . 202 . 1 . 19–25 . 10.1002/1521-3935(20010101)202:1<19::AID-MACP19>3.0.CO;2-G . 1022-1352.
3. 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