State of tetrabromotetraazaporphine and its Zn(II) complex in proton-donormedia

Stability constants in AcOH-H2SO4 and AcOH-antipyrine-H2SO4 media were dete rmined for the acid forms of tetrabromotetraazaporphine and its Zn(IE) comp lex, and some suggestions on the structure of these forms were made. Bromin ation in the macroring was shown to sharply reduce the basicity of the tetr aazaporphine ligand, while the basicity of the zinc complex is reduced only slightly. The acid-base interaction involves in the first stage simultaneo usly two meso nitrogens of tetrabromotetraazaporphine and its zinc complex, which distinguish these compounds from unsubstituted tetraazaporphine and its metal complexes.