Table 1 Equilibrium constants and proposed coordination modes for Cu²⁺ complexes at T = 298 K and I = 0.1 M (KCl).

[CuH₂L]⁴⁺

18.21(3)

4.40

N_Im, COO^–

23.06(4)

5.49

2N_Im

[CuHL]³⁺

13.81(2)

5.38

2N_Im, COO^–

17.57(5)

6.30

3N_Im

[CuL]²⁺

8.43(2)

6.59

3N_Im

11.27(7)

6.70

3N_Im, N^–

[CuH_-1L]⁺

1.84(3)

6.88

3N_Im, N^–

4.57(6)

9.44

2N_Im, 2N^–

[CuH_-2L]

 − 5.04(3)

–

2N_Im, 2N^–

 − 4.87(9)

9.91

2N_Im, 2N^–

[CuH_-3L]^–

–

–

–

 − 14.78(7)

–

N_Im, 3N^–

[CuH₅L]⁵⁺

51.38(2)

5.16

2N_Im

[CuH₄L]⁴⁺

46.21(2)

6.21

3N_Im

[CuH₃L]³⁺

40.00(3)

6.90

2N_Im, NH₂

[CuH₂L]²⁺

33.11(2)

7.75

2N_Im, NH₂, N^–

[CuHL]⁺

25.36(3)

9.53

2N_Im, 2N^–

[CuL]

15.83(5)

10.01

2N_Im, 2N^–

[CuH_-1L]^–

5.82(4)

–

N_Im, 3N^–

[CuH_-3L]^3–

 − 15.03(9)

–

N_Im, 3N^–