1,3-Bis(dicyanomethylene)squarate

1,3-Bis(dicyanomethylene)squarate is a divalent anion with chemical formula or ((N≡C−)C=)(CO). It is one of the pseudo-oxocarbon anions, as it can be described as a derivative of the squarate oxocarbon anion through the replacement of two opposite oxygen atoms by dicyanomethylene groups =C(−C≡N).

The anion can be obtained by reacting squaric acid with aniline to form 1,3-dianiline squarate (a yellow solid), before treating the diester with malononitrile (N≡C−)CH and sodium ethoxide to give the disodium tetrahydrate salt 2Na··4HO, an orange water-soluble solid. The hydrated salt loses the water below 100 °C, but the resulting anhydrous salt is stable up to 400 °C. Vanessa E. de Oliveira, Gustavo S. de Carvalho, Maria I. Yoshida, Claudio L. Donnici, Nivaldo L. Speziali, Renata Diniz and Luiz Fernando C. de Oliveira (2009), "Bis(dicyanomethylene)squarate squaraines in their 1,2- and 1,3-forms: Synthesis, crystal structure and spectroscopic study of compounds containing alkali metals and tetrabutylammonium ions". Journal of Molecular Structure Volume 936, Issues 1–3, Pages 239–249 Reaction of the sodium salt with salts of other cations in ethanol affords the following salts:

• dipotassium sodium chloride 2K·Na·Cl··CHCN, orange
• rubidium sodium chloride 7Rb·Na·2Cl·3·, orange, loses 1 ethanol at 96 °C, stable to 361 °C
• magnesium disodium nitrate, Mg·2Na··6HO·, orange, loses 1 ethanol and 6 HO at 78 °C, stable to 482 °C
• calcium, Ca··6HO, purple, dehydrates at 63–102 °C, stable to 468 °C
• barium, Ba··4HO, orange, dehydrates at 71–96 °C, stable to 457 °C
• tetra-n-butylammonium sodium, 2()N·2Na·2Cl·2·, orange, loses 1 ethanol and 2 tetrabutylammonium at 111 °C, stable to 238 °C

Nuclear magnetic resonance shows that the aromatic character of the squarate core is retained.

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