Kinetics and mechanism of the reactions between the oxygen-bonded complexes 4-, 3-, and 2-pyridinecarboxylatopentaamminecobalt(III) and aquopentacyanoferrate(II)

Abstract

The reactions of 3-and 4-pyridinecarboxylatopentaamminecobalt(IIl) with aquopentacyanoferrate(II) produce binuclear complexes with the iron attached to the pyridine nitrogen. The rate constants for the formation (k¡) and dissociation (k¿) of the binuclear complexes have been measured at 25 °C, µ = 0.10 M (LiC104) and pH 8.0. For the 4-and 3-pyridinecarboxylate complexes the values are: ks = (1.5 ± 0.2) X 103 and (1.9 ±0.1) X 103 M_l s-1; k¿ = (2.54 ± 0.05) X 10-3 and(1.73 ± 0.01) X 10-3 s_1. The metal to ligand charge-transfer band characteristic of the Fe(CN)53_-nitrogen heterocyclic complex is shifted to longer wavelength when the Co(NH3)s3+ moiety is attached to the carboxylate in the 4 position, but to shorter wavelength when the carboxylate is in the 3 position. Because of steric problems, no binuclear complex is produced when 2-pyridinecarboxylatopentaamminecobalt(III) is added to Fe(CN)50H23-. The binuclear complex (NH3)5Co02C(4-pyjV)Fe(CN)s~undergoes intramolecular electron transfer with a rate constant (1.75 ± 0.31) X 10-4 s_1. For the corresponding 3-carboxylate isomer, intramolecular electron transfer is not detected, and the upper limit for the rate constant is 3 X "5 s-'.

Intramolecular electron transfer from pentacyanoferrate(II) to pentaamminecobalt(III) mediated by various 4,4'-bipyridines

“…The data were treated as dexribcd previously. 11 The rate of disappearance of the desired binuclear complex in the presence of pyridine or pyrazine and ascorbic acid was fitted to the two-exponential function A, = A, +fexp[-(kd -I-k,gS)f] + g exp(-k-Lt) by means of a nonlinear least-squares program." Stoichiometric measurements of product solutions were carried out spectrophotometrically as described in detail below.…”

“…In 4-cyanopyridine, the dipole moment vector is reversed relative to pyridine. (11) W. J. Hehre. R. F. Stewart, and J.…”

Kinetic studies of the reactions of pentacyanoferrate(III) complexes with L‐ascorbic acid

“…Anal. for L = py, Calcd for FeC 20 (4,4 -bpy) of the IR spectra further confirmed the formation of Fe(III) complexes [21]. All other chemicals were of reagent grade and were used without further purifications.…”

“…(16)- (20) [5,14], the rate constants k 0 , k 1 , and k 2 can be calculated with the aid of Eqs. (16)- (20). The results are also listed in Table IV.…”

“…(BpyH 2 )[Fe(CN) 5 L] (L = py, isn) were prepared similarly with some modifications. 0.13 g (0.4 m mole) of Na 3 [Fe(CN) 5 NH 3 ] · 3H 2 O [19,20] was added to 20 mL predeaerated solution containing 3 mmole of ligands. The reaction was allowed to proceed for 20 min under argon atmosphere.…”