Nv. Chizhova et al., Acid-base interactions of tetrabromotetraazaporphin and its complex with zinc(II) in proton-donor media, RUSS J PH C, 73(6), 1999, pp. 889-893
The state of tetrabromotetraazaporphin and its complex with Zn(II) was stud
ied by spectrophotometric titration in AcOH-H2SO4 and AcOH-antipyrine-H2SO4
acetic acid media. An analysis of the electronic absorption spectra was pe
rformed to determine the stability constants of the acid forms of the compo
unds and draw conclusions on their structure. The introduction of electron-
acceptor bromine atoms into the macroring caused a sharp decrease in ligand
basicity and an insignificant decrease in the basicity of the Zn complex;
as a result, acid-base interactions were observed at higher medium aciditie
s than with unsubstituted tetraazaporphin and its complexes with metals. As
distinguished from their unsubstituted counterparts, the tetrabromo deriva
tives participate in acid-base interactions by two meso-nitrogen atoms simu
ltaneously.