The IR and electronic spectra of 2,7-disubstituted 4,9-dihydroxy-5,10-dioxo-4,5,9,10-tetrahydro-4,9-diazapyrene (R = H, I, NH2, NO2, OH) are studied. Analysis of the IR bands shows that, in crystalline form and in neutral and basic solutions, the compounds exist predominantly in the hydroxamic form. It is established that in sulfuric acid solutions the oxygen atoms of the C=O groups are protonated. The spectral characteristics of the neutral and ionized forms of the compounds are determined. The acid ionization constants are measured by potentiometric titration. © 1993 Plenum Publishing Corporation.