These anions retain many of the properties of the parent, including the delocalized bond in the ring and the delocalized charge in the atoms attached to the ring.[1][2][3] Similar anions can be obtained from squarateC 4O2โ 4.[4]
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Alexander J. Fatiadi (1978), Synthesis of 1,3-(dicyanomethylene)croconate salts. New bond-delocalized dianion, "Croconate Violet". Journal of the American Chemical Society, volume 100 issue 8, pages 2586โ2587. doi:10.1021/ja00476a073
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Alexander J. Fatiadi (1980), Pseudooxocarbons. Synthesis of 1,2,3-tris(dicyanomethylene)croconate salts. A new bond-delocalized dianion, croconate blue. Journal of Organic Chemistry volume 45, pages 1338-1339. doi:10.1021/jo01295a044
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Lawrence M. Doane, Alexander J. Fatiadi (2003) Electrochemical Oxidation of Croconate Salts; Evidence of the Chemical Equivalence of the Carbonyl Oxygen Atom and the Dicyanomethylene Groupdoi:10.1002/anie.198206351
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Vanessa E. de Oliveira, Gustavo S. de Carvalho, Maria I. Yoshida, Claudio L. Donnici, Nivaldo L. Speziali, Renata Diniz and Luiz Fernando C. de Oliveira (2009), Bis(dicyanomethylene)squarate squaraines in their 1,2- and 1,3-forms: Synthesis, crystal structure and spectroscopic study of compounds containing alkali metals and tetrabutylammonium ions. Journal of Molecular Structure
Volume 936, Issues 1-3, Pages 239-249 doi:10.1016/j.molstruc.2009.08.002