1,2-Bis(dicyanomethylene)squarate

1,2-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 adjacent oxygen atoms by dicyanomethylene groups =C(−C≡N)₂.

The anion can be obtained by reacting squaric acid with n-butanol to obtain the diester 1,2-dibutyl squarate (an oily orange liquid) and treating the latter with metallic sodium and malononitrile (N≡C−)₂CH₂ to give the trihydrated disodium salt 2Na⁺·C
10N
4O2−
2·3H₂O, a yellow 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 the chlorides of other cations in ethanol affords the following salts:^[1]

• dipotassium 2K⁺·K
  2C
  10N
  4O2−
  2, anhydrous, yellow, stable to 300 °C
• dirubidium 2Rb⁺·Rb
  2C
  10N
  4O2−
  2, anhydrous, brown, stable to 300 °C
• magnesium sodium chloride, Mg²⁺·Na⁺·Cl⁻·C
  10N
  4O2−
  2· 4 ¹⁄₂H₂O, dark yellow, dehydrates at 60–106 °C, stable to 461 °C
• calcium disodium, 2Na⁺·Ca²⁺·2C
  10N
  4O2−
  2·9H₂O, yellow, dehydrates at 50–90 °C, stable to 178 °C
• barium, Ba²⁺·C
  10N
  4O2−
  2·2H₂O, yellow, dehydrates at 87 °C, stable to 337 °C
• tetra-n-butylammonium, 2(C₄H₅)₄N⁺·C
  10N
  4O2−
  2·H₂O, yellow, dehydrates at 145 °C, stable to 323 °C

Nuclear magnetic resonance shows that the aromatic character of the squarate core is retained.^[1]

See also

• Croconate violet
• Croconate blue
• 1,3-Bis(dicyanomethylene)squarate

References