Acid-base interaction of 3,7,13,17-tetramethyl-2,8,12,18-tetrabutyl-5,15-di
azaporphyn and its copper complex (H(2)DAP and CuDAP) in CH2Cl2-CF3COOH, CF
3COOH-H2SO4, and CH3COOH-urea-H2SO4 proton-donor media was studied by spect
rophotometric titration. The dissociation constants of the resulting acid f
orms were determined; it was found that the pK(i) concentration values obta
ined in CH2Cl2-CF3COOH coincided with the pK(ai) thermodynamic constants de
termined by the Hammer equation for acetic acid media. In CH2Cl2-CF3COOH, b
oth meso nitrogen atoms of CuDAP were involved in complete acid-base intera
ction, which resulted in the formation of ionic associates of the protonate
d CuDAPH(+) (pK(a1) = +3.32) and CuDAPH(2)(2+) (pK(a2) = +0.58) forms. H(2)
DAP first formed an ionic associate of the H(2)DAPH(+) form monoprotonated
at the meso nitrogen atom (pK(a1) = +3.1.5). Further, this associate transf
ormed into the H(4)DAP(2+) symmetrical dication with protonated endocyclic
nitrogen atoms (pK(a2) = +2.19). Complete acid-base interaction with the me
so nitrogen atoms in the H(4)DAP(2+) dication was only possible in a medium
more acidic than 100% CF3COOH; sequential formation of the H(4)DAPH(3+) tr
ication (pK(a3) = -4.45) and H(4)DAPH(2)(4+) tetracation (pK(a4) = -8.10) w
as observed in a CF3COOH-H2SO4 binary solvent. The electronic absorption sp
ectra of the acid forms of diazaporphyrins are discussed.