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The reactions of Fe(CN)50Hz3-with Co(NH3)sL3+ ( L = bis(4-pyridyl)methane, bis(4-pyridyl)ethane, bis(4-pyridyl)propane, bis(4-pyridyl)ethylene, and bis(4-pyridyl) ketone) produce binuclear complexes (NC)5Fe'1LCo1'1(NH3)s that exhibit iron t2g to ligand K* charge transfer bands at (same order) 370, 365, 360, 500, and 555 nm. Comparison of these values with those for the corresponding Fei1(CN)sL3-complexes (370, 365, 360, 460, and 520 nm) suggests that the electron-withdrawing effect of the Co(ll1) moiety attached to the remote N is transmitted to the ring adjacent to the Fe(ll) via T interactions, and that saturated hydrocarbon groups connecting the two pyridine rings insulate electronically the iron and cobalt centers. Rate constants for the formation and dissociation of the binuclear complexes have been measured and a dissociative mechanism is clearly indicated by the LFER of slope -1.0 between rate constants and equilibrium constants for the formation reactions. The rateconstants for intramolecular electron transfer from Fe(ll) to Co(l1l) in the binuclear complexes have been measured. At 25 "C, p = 0. I0 M, the values are (same order of ligands) <0.6 X and

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-'.

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