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−
  2·0.5CH₃CN, 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
  5)₄N⁺·2Na⁺·2Cl−
  ·2C
  10N
  4O2−
  2·CH
  3CH
  2OH, orange, loses 1 ethanol and 2 TBA 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