Croconate violet
Croconate violet or 1,3-bis(dicyanomethylene)croconate is a divalent anion with chemical formula C
11N
4O2−
3 or ((N≡C−)2C=)2(C5O3)2−. It is one of the pseudo-oxocarbon anions, as it can be described as a derivative of the croconate oxocarbon anion C
5O2−
5 through the replacement of two oxygen atoms by dicyanomethylene groups =C(−C≡N)2. Its systematic name is 3,5-bis(dicyanomethylene)-1,2,4-trionate. The term croconate violet as a dye name specifically refers to the dipotassium salt K
2C
11N
4O
3.
The anion was synthesized and characterized by Alexander Fatiadi in 1978. He obtained the potassium salt by treating dipotassium croconate K
2C
5O
5 with malononitrile in water solution at 80–90 °C. The dipotassium salt crystallizes from water as a dihydrate in deep blue metallic needles. The water solutions have an intense violet color and strongly stain the skin.
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