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]
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]
