copper-polyphenol complexes

Ingredients

tannic acid, gallic acid, copper(II) sulfate

Preparation Steps

Original Recipe Text

Prepared by mixing polyphenol solutions with copper(II) sulfate pentahydrate following a protocol similar to the iron complexation, typically at a molar ratio corresponding to the coordination requirements of the specific polyphenol (p. 27939, 27946).

Evidence

"The interaction with Cu2+ ions induces similar spectral changes on GA as observed for the GA–iron interaction. The most intense bands are observed at 1492 and 1319 cm−1, corresponding to the ν1 and ν2 modes... However, the suspension adopted a reddish color due to the blueshift of the absorbance maximum."

Remarks

Copper complexes were investigated as a secondary metal component often found in historical vitriol used for IGIs. The copper-gallic acid complex shows Raman bands at 1492 (ν1) and 1319 (ν2) cm−1 (p. 27946). The ν3 band corresponding to the Cu−O interaction appears at 270 cm−1, similar to what is observed in copper oxide (p. 27946). These complexes result in a reddish color rather than the deep black of iron gallate (p. 27946).