There is a disagreement in the literature as to the intermediates and final products of the photochemical reaction of diluted aqueous solutions of K4Mo (CN) 8 . In the article we give arguments to support our view that the formula of the red intermediate ion is [Mo(CN)8(H2O)2]4⊖. In particular we give an answer to recent objections by Perumareddi against such an interpretation. In the theoretical part we also reconsider König's interpretation of the electronic spectrum of [Mo(CN)8]4⊖, in terms of a flattened Archimedean antiprism.