Table2. Rate Constants (Kobs) for the Formation of the Iron(III) Complex. A

Table2. Rate constants (kobs) for the formation of the iron(III) complex. a

[HClO4]T (mol dm-3)

0.010 0.025 0.050 0.100

103[Fe3+]T
(mol dm-3) / 10kobs
(s-1) / 103 [Fe3+]T
(mol dm-3) / 10kobs
(s-1) / 103 [Fe3+]T
(mol dm-3) / 10kobs
(s-1) / 103 [Fe3+]T
(mol dm-3) / 10kobs
(s-1)
1.00 / 1.54 / 1.00 / 1.52 / 2.00 / 2.47 / 5.00 / 2.66
1.50 / 2.13 / 3.00 / 2.85 / 5.00 / 3.85 / 8.00 / 3.38
2.00 / 3.18 / 5.00 / 4.18 / 7.00 / 4.77 / 10.0 / 4.56
2.50 / 3.94 / 7.00 / 5.91 / 11.0 / 6.77 / 13.0 / 5.08
3.00 / 4.80 / 8.00 / 6.85 / 13.0 / 7.55 / 15.0 / 5.69
3.50 / 5.60 / 10.0 / 8.63 / 16.0 / 9.12 / 17.0 / 5.37
4.00 / 6.81 / 17.0 / 9.39

k1 (dm3 mol-1 s-1) 10.6 ± 1.4 b ,c

k2 (dm3 mol-1 s-1) (7.5 ± 0.3) × 102 b ,c

KM-1 6.1 ×10-2 b,c

______

a 25.0 ± 0.1oC, I = 0.3, 10% v/v MeOH + H2O, [L]T = 1.0 × 10-4 mol dm-3, λ = 520 nm.

b KdFeH3L = 2.7 × 10-2 mol dm-3 ( see Table 1). c Σ [10(kcal – kobs)]2 = 4.82.

Table3. Formation of the ternary complexes, [Fe(HL)X]+ ( X = N3–, NCS–, and AcO-). a

N3– / NCS– / AcO-
pH →
[X]T
(mol dm-3) / 3.83 ± 0.05
Aobsb / 4.40 ± 0.04 / 4.87 ± 0.04 / 3.74 ± 0.11 / 4.68 ± 0.05
0.000
0.010
0.020
0.030
0.040 / 0.594
0.674
0.738
0.769
- / 0.557
0.693
0.715
0.837
- / 0.519
-
0.776
0.826
- / 0.624
0.631
0.651
-
0.662 / 0.685
0.655
0.640
0.620
-
0.050
0.070
0.080
0.090
0.100
0.120
0.150
0.180
0.200
0.250 / 0.844
0.957
-
1.045
-
1.092
1.123
-
1.191
- / 0.901
1.008
-
1.101
-
1.143
1.192
-
1.343
1.413 / 0.895
0.985
-
1.027
-
1.078
1.165
-
1.311
- / -
0.680
-
0.717
-
0.757
0.737
-
-
- / 0.570
0.530
0.501
-
0.464
0.433
0.387
0.369
0.344
0.308

N3–NCS–AcO–

Keq (dm3 mol–1) 55.0 ± 2.520.1 ± 5.6 c9.0 ± 2.9 c

KdFe(HL)X (mol dm–3)(2.4 ± 0.2) × 10–5

ε Fe(LH)X(7.15 ± 0.42) × 103(3.78 ± 0.21 ) × 103d (5.7 ± 4.7) × 102d

(dm3 mol–1 cm–1)

ε Fe(L)X(6.20 ± 0.24) × 103

(dm3 mol-1 cm-1)

a29.0 oC, I = 0.3 mol dm–3, 10% MeOH + H2O; complex in situ generated. b λ = 458 nm (N3–, [FeIIIL]T = 2.03 ×10-4 mol dm–3); 480 nm (NCS–, [FeIIIL]T = 2.04 × 10–4 mol dm-3) ; 480 nm(AcO–, [FeIIIL]T = 2.1 ×10–4 mol dm–3). c using KdFe(HL)X = 2.4 × 10–5 mol dm-3. d ε Fe(LH)X = ε Fe(L)X was assumed.