The Photochemistry of Aqueous Hexacyanoferrate(II) Solutions. I. Photo-aquation Reaction at 3660 Å

The photochemistry of hexacyanoferrate(II) ions in aqueous solutions was studied at 3660 Å in the presence and in the absence of nitrous oxide as an electron scavenger. Only a photo-aquation reaction yielding aquopentacyanoferrate(II) and cyanide ions was observed to occur as the primary process. The formation of aquopentacyanoferrate(II) ions, determined spectrophotometrically after a reaction with sodium azide, was studied as a function of the irradiation time over a wide pH range (0.5 to 13). In neutral or alkaline solutions the amount of aquopentacyanoferrate(II) ions measured was small, because of an efficient thermal back reaction. The initial quantum yield depended on the pH; for example, the yield 0.52 at pH 0.65 and 0.89 at pH 4.0 for 0.01 m solutions at 25 °C. The yield decreased with an increase in the hexacyanoferrate(II) concentration.