Stabilization of Fully Deprotonated Melaminate Anions (C 3 N 6 ) 6– in M 3 (C 3 N 6 ) (M = Cd, Ca)

High Resolution Image Download MS PowerPoint Slide Hydrogen-free melaminate salts M 3 (C 3 N 6 ) (M = Cd, Ca) were synthesized in laser-heated diamond anvil cells at 34–48 GPa and 2000–2500 K. Cd 3 (C 3 N 6 ) was synthesized via a direct reaction between the elements, while Ca 3 (C 3 N 6 ) was obtained following a rational chemical design approach from calcium carbodiimide, Ca(NCN), which served as a single-source precursor. Both compounds contain the fully deprotonated melaminate anion (C 3 N 6 ) 6–, representing a fundamental milestone in nitridocarbonate chemistry. The crystal structures of M 3 (C 3 N 6 ) were solved and refined using synchrotron single-crystal X-ray diffraction data and were fully corroborated by density functional theory calculations. Cd 3 (C 3 N 6 ) crystallizes in the acentric R 3 c and Ca 3 (C 3 N 6 ) in the centrosymmetric R 3̅ c space groups, and both compounds are recoverable to ambient conditions. Extending this design principle, our calculations indicate that Zn and Pb melaminates are thermodynamically accessible under similar conditions, highlighting the general stability of hydrogen-free nitridocarbonates of selected divalent metals.