1,3-Bis(dicyanomethylene)squarate

1,3-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 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−)$2$CH$2$ and sodium ethoxide to give the disodium tetrahydrate salt 2Na$+$··4H$2$O, 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. Reaction of the sodium salt with salts of other cations in ethanol affords the following salts:
 * dipotassium sodium chloride 2K$+$·Na$+$·Cl$−$··$1/2$CH$3$CN, orange
 * rubidium sodium chloride 7Rb$+$·Na$+$·2Cl$−$·3·Ethanol, orange, loses 1 ethanol at 96 °C, stable to 361 °C
 * magnesium disodium nitrate, Mg$2+$·2Na$+$··6H$2$O·, orange, loses 1 ethanol and 6 H$2$O at 78 °C, stable to 482 °C
 * calcium, Ca$2+$··6H$2$O, purple, dehydrates at 63–102 °C, stable to 468 °C
 * barium, Ba$2+$··4H$2$O, orange, dehydrates at 71–96 °C, stable to 457 °C
 * tetra-n-butylammonium sodium, 2$4$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.