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

Abstract

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 <O. l I,,/.,I

Ligand substitution reactions of pentacyanoferrate(II) complexes with N-heterocyclic cations in aqueous solution

“…The absorption maxima (t2, + LT* metal-to-ligand charge transfer (MLCT) band) and molar absorptivity coefficients (Table 1) for a number of the complexes in this study have been reported previously (9,12,19,20). The shift in A , , ,…”

“…A fit of the data to eq. [9] yielded pK3 values of 3.6 5 0.1 for (H)CH3BPY2+, 4.6 + 0.2 for (H)CH,BPE2+, and 5.6 + 0.1 for (H)CH3BPA2+. The differences between pK3 and pK1 (H,L~+) for the three species are found to be in the range of 0.1-0.3.…”

“…3 A) separating the coordination site from the carboxylate group. The rate constants for the reactions of F~( C N )~O H~~-with a series of Co(NH3),L3+ complexes (L is a bridging N-heterocycle) depend on the distance between the free nitrogen site and the Co(II1) metal center (6)(7)(8)(9)(10).…”

“…(BPE). These species have been used frequently as bridging ligands in homo-and heterobinuclear complexes containing Fe(CN)5n-(1 1, 12), M(NH3)5n+ ( M = Co(II1) (9), Rh(II1) (13), Ru(I1) and (111) (14)), and M(CO)5 ( M = Mo, W (15)) centers. The kinetics of the formation and dissociation of Fe(CN)5(L-X)n-, where L is BPY, BPE, or BPA and X is a lone pair, H f , CH3+, or Fe(CN)53-, have not, however, been reported in detail previously.…”

β-Cyclodextrin-Assisted Intervalence Charge Transfer in Mixed-Valent [2]Rotaxane Complexes Having Metal Centers Linked by an Interrupted π-Electron System

“…[9,10] The inclusion into the CD cavity also prevents folding of the bpe or bpp units as well as a closed conformation for 5 and 6, as was proposed for [(CN) 5 Fe(bpe)Co(NH 3 ) 5 ]. [11] This excludes any probability of electron transfer ªthrough spaceº because in the absence of folding the two metal centers cannot come closer than 11 which is too large a distance for direct electron transfer through space. Moreover, cyclodextrin is made of carbohydrates and is not expected to mediate electron transfer.…”