Croconate violet

It is an orange crystalline solid that melts at 260–270 °C and dissolves in water to give violet skin-staining solutions.

[2] Croconate violet salts also have interesting electrochemical, semiconducting and photophysical properties, and have been the subject of research in supramolecular chemistry.

In these solids the croconate violet anion is almost planar, with the dicyanomethylene groups slightly twisted out of the mean plane.

The aromatic character of the croconate core is retained or even enhanced, with strongly delocalized π electrons.

[4] The mixed salts of potassium and of certain trivalent lanthanides cations (lanthanum, neodymium, gadolinium, and holmium) exhibit some degree of π-stacking interactions; namely, the π electrons of the croconate rings in one layer form weak bonds with those in the adjacent layers.