Fe dications

With [Fefri -CsRsKTi -QMeell PFeC R = FI or Me, the three cyclic voltammetry waves coimecting these four oxidation states are chemically and electrochemically reversible. This shows the stability of the sandwich structure along the redox processes between the 17-electron Fe dications and the 20-electron Fe anion. Among these four oxidation states, three of them (Fe -Fe ) have been isolated in crystalline form in the series P eCp (ri -C5Me6)], x = 0, 1 and For the Fe ... 

Stepwise oxidation of [(FTF4)Co202] to the mono- and dications was reported to proceed reversibly in benzonitrile [LeMest et al., 1997] such reversible redox chemistry has not been reported for any O2 adducts of monomeric Co or Fe porphyrins. 

Metallopolymer films have also been prepared by oxidative polymerization of complexes of the type [M(phen)2(4,4 -bipy)2]2+ (M = Fe, Ru, or Os phen= 1,10-phenanthroline, 4,4 -bipy = 4,4 -bipyridine).23 Such films are both oxidatively and reductively electrochromic reversible film-based reduction at potentials below —IV lead to dark purple films,23 the color and potential region being consistent with the viologen dication/radical cation electrochromic response. A purple state at high negative potentials has also been observed for polymeric films prepared from [Ru(L13)3]2+.24 Electropolymerized films prepared from the complexes [Ru(L16)-(bipy)2][PF6]22 and [Ru(L17)3][PF6]226,27 exhibit reversible orange/transparent electrochromic behavior associated with the Run/Ruin interconversion. 

Fig. 12 The room temperature single crystal x-ray structure of the dication in [Fe(HC(pz)3)2](BF4)2. Data obtained from [46]...

The room temperature single crystal x-ray structure of the dication of [Fe(HC(3,5-(CH3)2pz)3)2](BF4)2, see Fig. 15, has been found [46] to be essentially identical [26] to the structure of [Fe(HB(3,5-(CH3)2pz)3)2]. In both complexes the room temperature iron-nitrogen bond distance is 2.17 A, a distance which is indicative of high-spin iron(II). 

A further report dealt with the synthesis, variable temperature magnetic susceptibility measurements, and crystal structure determination at various temperatures (115, 136, 140, 150 and 231 K space group P-1) of [Fe(isoxa-zole)6][Fe(isoxazole)4(H20)2](BF4)4 [73]. The molecular structure of this well-defined double salt consists of two mononuclear Fe(II) dications,... 

The formation of coordinated phenoxyls in the monocations and dications, [Fe(L )]+ and [Fe(L )]2+, is clearly demonstrated by their electronic spectra (142). Fig. 23 displays the spectra of [Fem(LBuMet)]°, [Fe(LBuMet )]+, and [Fem(LBuMet )]2+. Since the spectrum of the neutral tris(phenolato)iron(III) species shows an absorption minimum at -400 nm it is significant that the monocation and dication both display a new intense asymmetric maximum in this region. This intense maximum is the fingerprint of phenoxyl radicals. It is also remarkable that this maximum doubles in intensity on going from the monocation to the dication. On increasing the oxidation level stepwise, the phenolate-to-iron CT band experiences a batho-chromic shift from 513 nm in the neutral species to 562 nm in the monocation and... 

The dication [Fe2(Me4-tpdp)(C6H5C02)(H20)]2+ (Me4-tpdp = JV,A(V/,V -tetrakis (6-methyl-2-pyridyl)methyl -l,3-diaminopropan-2-olate) illustrated in Figure 29 constitutes a further (asymmetric) binuclear Fe(II) model.36... 

Substituent effects in 1,10-phenanthrolines have been comprehensively investigated201,202 from their pA s, stability constants in Fe(III) and Cu(II) complexes, and redox potentials the Ni(II) complexes have also been examined,203 as have other metal complexes.204 p- Values have been obtained for the three successive proton losses (1, 2, 3, respectively) from 4-substituted dications of 10-hydroxy- 1,7-phenanthrolines (23).205... 

The [(tt-C5H5)Co(SR)]2 (R = Me, p-MeC6H4, or p-ClC6H4) complexes undergo voltammetric oxidation to the monocation derivatives, but, unlike the Ni or Fe analogues, they do not form dications.169... 

Kinetic studies have shown that electrophilicity in the iron triad is strongly metal dependent with Fe Ru, Os, and the nucleophilic reactivity order is PPh3 > P(0-tBu)3. Adducts 237 (PR3 = phosphites) react with water to give the cyclohexadienyl phosphonate complexes 239. Complex 235 is a effective catalyst for the conversion of phosphites to HP(0)(0R)2 (99,146,147) [Eq. (29)]. In a similar fashion, benzene ruthenium dications... 

The important point is that [ 4-N2Fl2 Fe(PPr3)(S4)[21 can be oxidized reversibly in two consecutive steps yielding the dication with two Fe(III) centers as indicated in Fig. 23. This finding affords the working hypothesis for attempts to achieve the reduction of N2 under mild and catalytic conditions. 

A different rendering of the relevant core atoms of the dication [Fe, N2H2, S(thiolate) donors] shows that the dicationic diazene complex B and the N2 complex C are potential redox isomers or valence tautomers (Scheme 38). 

Benesi-Hildebrandt plots were linear in a low concentration range however, the linear relationship did not exist between the transition energies and the difference in the half-redox potential of 2V. The solvation of 2,2 -bipyridinium dication is relatively small compared with that of the 4,4 -isomer possessing a symmetrical molecular structure. This decreases the electrostatic interaction to lead to a low transition energy. The CT bands for Bu-V2+ and Bzl-V2+ with [Fe(CN)6]4 ions almost linearly increase in an absorbance upon near-UV irradiation, and the absorbance decreases progressively in the dark and even more rapidly upon heating. 

IV.D. Bonding within [LmMC4M L ]r+ [M Lm, M L ra = Fe(dppe)Cp, Re(NO)(PR3)Cp z = 0-4] has been explored using DFT which confirms the occurrence of cumulenic singlet dications which have nearly isoenergetic triplet states with diyndiyl structures.635 X-ray structures of Fe(dppe) Cp 2(p-C=CC=C) and [ Fe(dippe)Cp 2( r-C4)][PF6]3 are given. 

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