1,2-Bis(dicyanomethylene)squarate
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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.
Nuclear magnetic resonance shows that the aromatic character of the squarate core is retained.[1]
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
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