Co-ordination of amines to [Fe(CN)5(OH2)]3?

Abstract

Equilibrium constants K for the substitution of co-ordinated H,O in the complex [Fe(CN),(OH,)]'-by amines have been determined in 0.1 rnol dm-' aqueous acetonitrile solution with / = 0.1 rnol dm ' (NaCIO,) at 25 "C by UV/VlS spectrophotometry. The species previously assigned to the NH,OH complex is shown to be the product of some oxidative side-reaction. In the absence of complicating factors, values of log K obey the linear free-energy relation log K = a-pK + b with a = 0.05 and b =

Kinetics of the Aquation of Amminepentacyanoferrate(II). A Volume Profile Analysis

“…Nevertheless, the results established a stoichiometry of 1:1 with log K 2 = 4.7 (pH = 6.5), log K 2 = 4.6 (pH = 7.0), and log K 2 = 4.4 (pH = 7.5). These values agree quite well with those determined in an indirect way (log K 2 = 4.3 at pH = 7.0 and log K 2 = 4.2 at pH = 7.5). At pH > 7.5 the data were more accurate and, for instance, log K 2 = 3.9 at pH = 9.0 (see Figure S4, Supporting Information).…”

“…The linear dependence of k obs on [NH 3 ] at pH = 11.5 (see Figure b) results in a k 2 value of 460 ± 21 M -1 s -1 at 298 K, which is in excellent agreement with a value of 452 ± 5 M -1 s -1 obtained from Figure b under these conditions. The overall equilibrium constant, K 2 = k 2 / k 1 = (1.4 ± 0.1) × 10 4 M -1 (log K 2 = 4.2), calculated from the kinetic data is in good agreement with that determined spectrophotometrically in this and earlier studies 1 Rate and Activation Parameters for the Reaction a k obs × 10 2 (s -1 ) T (K) p (MPa)[NH 4 Cl] = 0[NH 4 Cl] = 0.01M 288.0 0.1 0.72 290.5 1.06 1.11 293.0 1.56 1.62 295.5 2.32 2.30 298.0 3.12 3.20 1.60 b 1.75 c 2.15 d 10 2.90 35 2.50 55 2.29 80 2.15 105 1.77 130 1.46 300.5 0.1 4.33 4.46 303.0 5.90 6.78 308.0 13.0 13.3 313.0 23.6 23.8 Δ H ⧧ (kJ mol -1 ) 102 ± 1 101 ± 1 102 ± 1 b 93 ± 5 c Δ S ⧧ (J mol -1 K -1 ) 68 ± 4 67 ± 4 63 ± 5 b 34 ± 17 c Δ V ⧧ (cm 3 mol -1 ) 16.4 ± 0.6 e 13.5 ± 1.1 a,f a This work, pH = 5.0, I = 0.1 M (NaCl).…”