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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. Reaction of the sodium salt with salts of other cations in ethanol affords the following salts:
2C
10N
4O2−
2· 1⁄2CH3CN, orange
2C
10N
4O2−
2·CH
3CH
2OH, orange, loses 1 ethanol at 96 °C, stable to 361 °C
10N
4O2−
2·NO−
3·6H2O·CH
3CH
2OH, orange, loses 1 ethanol and 6 H2O at 78 °C, stable to 482 °C
10N
4O2−
2·6H2O, purple, dehydrates at 63–102 °C, stable to 468 °C
10N
4O2−
2·4H2O, orange, dehydrates at 71–96 °C, stable to 457 °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.