Hydromelonic acid,[1] is an elusive chemical compound with formula C 9H 3N 13 or (HNCN) 3(C 6N 7), whose molecule would consist of a heptazineH3(C 6N 7) molecule, with three cyanamido groups H–N=C=N– or N≡C–NH– substituted for the hydrogen atoms.
The compound had not been properly isolated as of 2010, due to its tendency to polymerize.[3][4] However, removal of three protons yields the melonate[5] (formerly hydromelonate[1]) anion (NCN) 3(C 6N 7)3− , whose salts are stable and have been known since the 19th century. Removal of only two protons yields the divalent hydrogenmelonate anion H(NCN) 3(C 6N 7)2− .[3][5]
Starting in the 1970s, melonates have attracted new interest, motivated by research in cubiccarbon nitride c-C 3N 4.[3] Salts of many cations have been synthesized and studied,[2][10][4][11] including mixed-cation salts[5] and calcium hydrogenmelonateCa[HC 9N 13]·7H 2O.[3] The structure of potassium melonate pentahydrate K 3C 9N 13·5H 2O was elucidated only in 2005.[5]
Alkali melonates are soluble in water without decomposition.[10] Treatment of melonates with alkali gives salts of cyameluric acid.[12]
Potassium melonate pentahydrate has planar sheets of melonate anions with potassium cations between the layers. The same generals structure is seen in the anhydrous salt (except that the melonate ions are asymmetric due to an NHN– group being turned by 180°) and in the salts Rb 3C 9N 13·3H 2O and Cs 3C 9N 13·3H 2O.[3][5]
Melonate salts decompose when melted with cyanates to form tricyanomelaminates, the first selective decomposition reaction leading from heptazines to triazines.[2]
^ abcdeAndreas Sattler and Wolfgang Schnick (2009): "On the Formation and Decomposition of the Melonate Ion in Cyanate and Thiocyanate Melts and the Crystal Structure of Potassium Melonate,K 3[C 6N 7(NCN) 3". European Journal of Inorganic Chemistry, volume 2009, issue 33, pages 4972-4981. doi:10.1002/ejic.200900585
^ abcdefSophia J. Makowski, Daniel Gunzelmann, Jürgen Senker, Wolfgang Schnick (2009): "Protonated Melonate Ca[HC6N7(NCN)3]·7H2O – Synthesis, Crystal Structure, and Thermal Properties". Zeitschrift für anorganische und allgemeine Chemie (ZAAC), volume 635, issue 15, pages 2434-2439. doi:10.1002/zaac.200900231
^ abcCorinna Clauss, Marcus Schwarz, and Edwin Kroke (2010): "Microwave-induced decomposition of nitrogen-rich iron salts and CNT formation from iron(III)–melonate Fe[C 9N 13]". Carbon, volume 48, issue 4, pages 1137-1145. doi:10.1016/j.carbon.2009.11.036
^ abLinus Pauling and J. H. Sturdivant (1937): "The Structure of Cyameluric Acid, Hydromelonic Acid and Related Substances". Proceedings of the National Academy of Sciences, volume 23, issue 12, page 615–620. doi:10.1073/pnas.23.12.615
^ abCorinna Clauss, Jörg Wagler, Marcus Schwarz, Anke Schwarzer, and Edwin Kroke (2010): "Lithium Melonate, Li 3[C 6N 7(NCN) 3]·6H 2O – Synthesis, Crystal Structure and Thermal Properties of a Novel Precursor for Graphitic Carbon Nitrides". 'Zeitschrift für anorganische und allgemeine Chemie (ZAAC), vlume 636, issue 1, pages 196-200. doi:10.1002/zaac.200900326
