chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds made of atoms, molecules and ions ...

, melem is a

compound Compound may refer to: Architecture and built environments * Compound (enclosure), a cluster of buildings having a shared purpose, usually inside a fence or wall ** Compound (fortification), a version of the above fortified with defensive struct ...

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 Heptazine, or tri-''s''-triazine or cyamelurine, is a chemical compound with formula , that consist of a planar triangular core group or three fused triazine rings, with three hydrogen atoms at the corners. It is a yellow, weakly fluorescent soli ...

with the three hydrogen atoms replaced by

amino group In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent such a ...

s. It is a white crystalline solid.

Preparation

Melem can be prepared by thermal decomposition of various C−N−H compounds, such as

melamine Melamine is an organic compound with the formula C3H6N6. This white solid is a trimer of cyanamide, with a 1,3,5-triazine skeleton. Like cyanamide, it contains 67% nitrogen by mass, and its derivatives have fire retardant properties due t ...

C₃N₃(NH2)₃, dicyandiamide H₄C₂N₄, ammonium dicyanamide NH₄ (CN)₂

cyanamide Cyanamide is an organic compound with the chemical formula, formula carbon, Cnitrogen, N2hydrogen, H2. This white solid is widely used in agriculture and the production of pharmaceuticals and other organic compounds. It is also used as an alcoho ...

H₂CN₂, at 400 to 450 °C.

Structure and properties

Crystal structure

Melem crystallizes in the

group A group is a number of persons or things that are located, gathered, or classed together. Groups of people * Cultural group, a group whose members share the same cultural identity * Ethnic group, a group whose members share the same ethnic iden ...

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 In chemistry, melem is a chemical compound, 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 gr ...

, • 2,

melemium perchlorate 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 whi ...

, • ,

melemium hydrogensulfate 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 whi ...

and two

melemium methylsulfonate 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 ...

s • and • . The protons can be inserted in any of the six outer

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...

atoms of the heptazine core, yielding many tautomers of apparently similar energies.

References

Barbara Jürgens, Elisabeth Irran, Jürgen Senker, Peter Kroll, Helen Müller, Wolfgang Schnick (2003): "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'', volume 125, issue 34, pages 10288-10300. Tamikuni Komatsu (2001)> "The First Synthesis and Characterization of Cyameluric High Polymers". ''Macromolecular Chemistry and Physics'', volume 202, issue 1, pages 19-25. 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 The Ludwig Maximilian University of Munich (simply University of Munich or LMU; german: Ludwig-Maximilians-Universität München) is a public research university in Munich, Germany. It is Germany's sixth-oldest university in continuous operatio ...

Heterocyclic compounds with 3 rings Nitrogen heterocycles Tricyclic compounds Amines {{Organic-compound-stub