Table 3. Protonation Constants^a (log K_HqL) of H₂L¹ and H₂L².

equilibrium reaction	H2L1	H2L2
L + H+ ⇆ HL	10.86(1)	8.14(1)
HL + H+ ⇆ H2L	9.91(1)	4.98(1)
H2L + H+ ⇆ H3L	6.78(1)	3.22(1)
H3L + H+ ⇆ H4L	4.23(1)	2.14(4)
H4L + H+ ⇆ H5L	2.79(1)
H5L + H+ ⇆ H6L	2.01(6)
H6L + H+ ⇆ H7L	0.37(2)b
∑log KHqL	36.95	18.48

^aValues were obtained from UV potentiometric titrations (25 °C, l = 0.2 cm, and I = 0.16 M NaCl). K_HqL defined as [H_qL]/([H][H_q–1L]).

^bFrom acidic in-batch UV titrations [25 °C, l = 1 cm, I = 0.16 M NaCl (when possible)]. Charges are omitted for clarity.