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.
Melem can be prepared by thermal decomposition of various CâÂÂNâÂÂH compounds, such as melamine C<sub>3</sub>N<sub>3</sub>(NH<sub>2</sub>)<sub>3</sub>, dicyandiamide H<sub>4</sub>C<sub>2</sub>N<sub>4</sub>, ammonium dicyanamide NH<sub>4</sub>[N(CN)<sub>2</sub>], cyanamide H<sub>2</sub>CN<sub>2</sub>, at 400 to 450 ðC.
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, ò = 99.912(2)ð, 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.
When heated above 560ð, melem transforms into a graphite-like CâÂÂN material.
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.