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Melem

Chemical compound From Wikipedia, the free encyclopedia

Melem
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In chemistry, melem is a compound with formula C
6N
10H
6; 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.[1]

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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 NH4[N(CN)2], cyanamide H2CN2, at 400 to 450 °C.[1][2]

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.[1]

Thermal decomposition

When heated above 560°, melem transforms into a graphite-like C−N material.[1]

Melemium cations

Melem accepts up to three protons yielding cations called melemium [(NH2)3(C6N7Hx)]x+. Some salts described in the literature are melemium sulfate, [(NH
2)
3(C
6N
7H
2)]SO
4 • 2H
2O, melemium perchlorate, [(NH
2)
3(C
6N
7H)]ClO
4 • H
2O, melemium hydrogensulfate [(NH
2)
3(C
6N
7H
3)](HSO
4)
3 and two melemium methylsulfonates [(NH
2)
3(C
6N
7H
2)](SO
3CH
3)
2 • H
2O and [(NH
2)
3(C
6N
7H)][(NH
2)
3(C
6N
7H
2)](SO
3CH
3)
3 • H
2O. The protons can be inserted in any of the six outer nitrogen atoms of the heptazine core, yielding many tautomers of apparently similar energies.[3]

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See also

  • Triazine H
    3    C
    3    N
    3    , with a single C-N ring
  • Melamine (NH
    2    )
    3    (C
    3    N
    3    )    , triamino triazine
  • Melaminium [H(NH
    2    )
    3    (C
    3    N
    3    )]+
    , a cation derived from melamine
  • Melam ((NH
    2    )
    2    (C
    3    N
    3    ))
    2    NH    , a condensation dimer of melamine
  • Melamium [H((NH
    2    )
    2    (C
    3    N
    3    ))
    2    NH]+
    , a cation derived from melam
  • Melon (NH
    2    )(NH(C
    6    N
    7    H)NH)
    n    H    , a condensation oligomer of melem

References

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