1,2-Bis(dicyanomethylene)squarate

1,2-Bis(dicyanomethylene)squarate is a divalent anion with chemical formula or ((N≡C−)$2$C=)$2$(C$4$O$2$)$2&minus;$. 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 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−)$2$CH$2$ to give the trihydrated disodium salt 2Na$+$··3H$2$O, 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. Reaction of the sodium salt with the chlorides of other cations in ethanol affords the following salts:
 * dipotassium 2K$+$·, anhydrous, yellow, stable to 300 °C
 * dirubidium 2Rb$+$·, anhydrous, brown, stable to 300 °C
 * magnesium sodium chloride, Mg$2+$·Na$+$·Cl$−$··$4 1/2$H$2$O, dark yellow, dehydrates at 60–106 °C, stable to 461 °C
 * calcium disodium, 2Na$+$·Ca$2+$·2·9H$2$O, yellow, dehydrates at 50–90 °C, stable to 178 °C
 * barium, Ba$2+$··2H$2$O, yellow, dehydrates at 87 °C, stable to 337 °C
 * tetra-n-butylammonium, 2(C$4$H$5$)$4$N$+$··H$2$O, yellow, dehydrates at 145 °C, stable to 323 °C

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