New Synthesis of Acidopentacyanocobaltate(III) Complexes

Oyetunji

et al. 2009

The kinetics of the reactions between azidopentacyanocobaltate(III), Co(CN) 5 N 3 3-, and iron(II) polypyridyl complexes, Fe(LL) 3 2? (LL = bipy, phen), have been studied in both neutral and acidic aqueous solutions at I = 0.1 mol dm -3 NaCl. The reactions were carried out under pseudo-first-order conditions in which the concentration of Fe(LL) 3 2? was kept constant, and the second-order rate constants obtained for the reactions at 35°C were within the range of 0.156-0.219 dm 3 mol -1 s -1 for LL = bipy and 0.090-0.118 dm 3 mol -1 s -1 for LL = phen. Activation parameters were measured for these systems. The dependence of reaction rates on acid was studied in the range [H ? ] = 0.001-0.008 mol dm -3 . The reaction in acid medium shows interesting kinetics. Two reactive species were identified in acid medium, namely, the protonated cobalt complex and the azido-bridged binuclear complex. The electron-transfer process is proposed to go by mixed outerand inner-sphere mechanisms in acid medium, in which electron transfer through the bridged inner-sphere complex (k 5 ) is slower than through the outer-sphere path (k 4 ).

Section: Methodssupporting

confidence: 85%

Intermediate and ion-pair formation in the outer-sphere reactions between azido-pentacyanocobaltate(III) and iron(II) polypyridyl complexes in aqueous medium

Oyetunji

et al. 2009

“…The purity of the complex was ascertained by its u.v.-visible spectra (k max 380 nm, " ¼ 600 dm 3 mol )1 cm )1 ) and IR bands (1290 cm )1 , 1596 cm )1 , and 2103 cm )1 ). Co(CN) 5 X 3) was prepared using the method of Flor and Casabo [ 13] which involves the treatment of Co(CN) 5 N 3À 3 with KNO 2 in the presence of the coordinating anion X ) . Each complex was purified by dissolving in water and recrystallising from cold EtOH.…”

Section: Methodsmentioning

confidence: 99%

“…Materials K 3 [Co(CN) 5 N 3 ] which is the starting material for the preparation of Co(CN) 5 X 3) , was synthesised as described in the literature [12,13]. The purity of the complex was ascertained by its u.v.-visible spectra (k max 380 nm, " ¼ 600 dm 3 mol )1 cm )1 ) and IR bands (1290 cm )1 , 1596 cm )1 , and 2103 cm )1 ).…”

Section: Methodsmentioning

confidence: 99%

Protonation of Chloro-, Bromo- and Iodo-pentacyanocobaltate(III) Complexes

Ojo

et al. 2006

The reactions between Fe(Phen) 2þ 3 [phen=tris-(1,10) phenanthroline] and Co(CN) 5 X 3) (X=Cl, Br or I) have been studied in aqueous acidic solutions at 25°C and ionic strength in the range I=0.001-0.02 mol dm )3 (NaCl/HCl). Plots of k 2 versus p I, applying Debye-Huckel Theory, gave the values )1.79±0.18, )1.65±0.18 and 1.81±0.10 as the product of charges ðZ A Z B Þ for the reactions of Fe(Phen) 2þ 3 with the chloro-, bromo-and iodo-complexes respectively. Z A Z B of % À2 suggests that the charge on these Co III complexes cannot be )3 but is )1. This suggests the possibility of protonation of these Co III complexes. Protonation was investigated over the range [H + ]=0.0001 )0.06 mol dm )3 and the protonation constants K a obtained are 1.22 · 10 3 , 7.31 · 10 3 and 9.90 · 10 2 dm 6 mol )3 for X=Cl, Br and I, respectively.

“…The purity of the complex was ascertained by its uv-visible (k max 380 nm, e = 600 dm 3 mol )1 cm )1 ) and IR bands (1290 cm )1 , 1596 cm )1 , and 2103 cm )1 ). Co(CN) 3À 5 was prepared using the method of Flor and Casabo´ [13] which involves the treatment of Co(CN) 5 N 3À 3 with KNO 2 in the presence of the coordinating anion X ) . These complexes were purified by dissolving each in water and recrystallising from cold ethanol.…”

Section: Methodsmentioning

confidence: 99%

Ion-pair formation in the outer-sphere electron transfer reactions between tris-(1, 10) phenanthroline iron(II) and the halopentacyanocobaltate(III) complexes in aqueous acidic solutions

Ojo

et al. 2006

The kinetics of the reactions between Fe(phen) 3 2+ [phen = tris-(1,10) phenanthroline] and Co(CN) 5 X 3À (X = Cl, Br or I) have been investigated in aqueous acidic solutions at I = 0.1 mol dm )3 (NaCl/HCl). The reactions were carried out at a fixed acid concentration ([H + ] = 0.01 mol dm )3 ) and the second-order rate constants for the reactions at 25°C were within the range of (0.151-1.117) dm 3 mol )1 s )1 . Ion-pair constants K ip for these reactions, taking into consideration the protonation of the cobalt complexes, were 5.19 Â 10 4 , 3.00 Â 10 2 and 4.02 Â 10 4 mol )1 dm )3 for X = Cl, Br and I, respectively. Activation parameters measured for these systems were as follows: DH* (kJ K )1 mol )1 ) = 94.3 ± 0.6, 97.3 ± 1.0 and 109.1 ± 0.4; DS* (J K )1 ) = 69.1 ± 1.9, 74.9 ± 3.2 and 112.3 ± 1.3; DG* (kJ) = 73.7 ± 0.6, 75.0 ± 1.0 and 75.7 ± 0.4; E a (kJ) = 96.9 ± 0.3, 99.8 ± 0.4, and 122.9 ± 0.3; A (dm 3 mol )1 s )1 ) = (7.079 ± 0.035) Â 10 16 , (1.413 ± 0.011) Â 10 17 , and (9.772 ± 0.027) Â 10 20 for X = Cl, Br, and I respectively. An outer -sphere mechanism is proposed for all the reactions.