Formation of a mixed-valence Ru(IV)-Fe(II) binuclear complex via the reaction of [Ru-III(edta)(H2O)](-) and [Fe-III(CN)(6)](3-) in aqueous solution

The combination of [Ru-III(edta)(H2O)](-) (edta(4-) = ethylenediamine-N,N,N 'N'-tetraacetate) and [Fe-III(CN)(6)](3-) in aqueous solution results in th e rapid formation of [Ru-III(edta)(NC)Fe-III(CN)(5)](4-) (1), which has bee n isolated and characterized by physical methods. An aqueous solution of co mplex 1 shows two characteristic absorption maxima in the visible spectral region located at 420 and 620 nm. Examination of the same solution after 72 h shows that a spectral change has occurred, forming a species with a new band maximum at 870 nm. Spectral (IR, UV-Vis, H-1 and C-13 NMR spectra show ing a paramagnetic complex, and time-dependent magnetic susceptibility data ) provide evidence for the formation of a mixed-valence [Ru-IV(edta)(NC)Fe- II(CN)(5)](4-) complex 2 by the process, which causes the appearance of the 870 nm band. The results are compared with the known reactions between [Ru -III(NH3)(5)(H2O)](3+) and [Fe(CN)(6)](3-), which have been reported by Tau be and cc-workers (V.G. Poupopoulu, Z.W. Li, H. Taube, Inorg. Chim. Acta 22 5 (1994) 173) to sequentially form {[Ru-III(NH3)(5)(H2O)](3+), [Fe-III(CN)( 6)](3-)} ion-pairs, converting to a (Ru-III-CN- bridged-Fe-III) binuclear c omplex (an analogue of 1, and upon intramolecular electron transfer, the (R u-IV-CN- bridged-Fe-II) binuclear complex (an analogue of 2). The events re ported for the conversion of 1 into 2 ensue without appreciable accumulatio n of ion pairs as both [Ru-III(edta)(H2O)](-) and [Fe-III(CN)(6)](3-) are a nionic. Magnetic susceptibility data imply that both 1 and 2 are paramagnet ic S = 1 ions. The d electron manifold filling is d(xy)(2)d(xz)(2)d(yz)(1) in 1 and d(xy)(2)d(xz)(1)d(yz)(1) in 2, whereas a filling of d(xy)(2)d(xz)( 2)d(yz)(0) seems to account for the prior observations with the [Ru-IV(NH3) (5)(NC)Fe-II(CN)(5)] system studied by Taube and co-workers. (C) 2000 Elsev ier Science Ltd. All rights reserved.