1,3-Bis(dicyanomethylene)squarate

1,3-Bis(dicyanomethylene)squarate is a divalent anion with chemical formula C
10N
4O2−
2 or ((N≡C−)₂C=)₂(C₄O₂)²⁻. It is one of the pseudo-oxocarbon anions, as it can be described as a derivative of the squarate oxocarbon anion C
4O2−
4 through the replacement of two opposite oxygen atoms by dicyanomethylene groups =C(−C≡N)₂.

The anion can be obtained by reacting squaric acid with aniline to form the diester 1,3-dianiline squarate (a yellow solid), before treating the diester with malononitrile (N≡C−)₂CH₂ and sodium ethoxide to give the disodium tetrahydrate salt 2Na⁺·C
10N
4O2−
2·4H₂O, 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.^[1] Reaction of the sodium salt with salts of other cations in ethanol affords the following salts:^[1]

• dipotassium sodium chloride 2K⁺·Na⁺·Cl⁻·K
  2C
  10N
  4O2−
  2· ¹⁄₂CH₃CN, orange
• rubidium sodium chloride 7Rb⁺·Na⁺·2Cl⁻·3Rb
  2C
  10N
  4O2−
  2·CH
  3CH
  2OH, orange, loses 1 ethanol at 96 °C, stable to 361 °C
• magnesium disodium nitrate, Mg²⁺·2Na⁺C
  10N
  4O2−
  2·NO−
  3·6H₂O·CH
  3CH
  2OH, orange, loses 1 ethanol and 6 H₂O at 78 °C, stable to 482 °C
• calcium, Ca²⁺·C
  10N
  4O2−
  2·6H₂O, purple, dehydrates at 63–102 °C, stable to 468 °C
• barium, Ba²⁺·C
  10N
  4O2−
  2·4H₂O, orange, dehydrates at 71–96 °C, stable to 457 °C
• tetra-n-butylammonium sodium, 2(C
  4H
  9)₄N⁺·2Na⁺·2Cl⁻·2C
  10N
  4O2−
  2·CH
  3CH
  2OH, 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.^[1]

See also

• Croconate violet
• Croconate blue
• 1,2-Bis(dicyanomethylene)squarate

References

1. 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 doi:10.1016/j.molstruc.2009.08.002