Bimolecular electron and energy transfer reactivity of exchange-coupled dinuclear iron(III) complexes.
نویسندگان
چکیده
Bimolecular quenching between photosensitizers and exchange-coupled transition metal complexes has been studied in an effort to experimentally establish a link between Heisenberg spin exchange and chemical reactivity. The acceptors are members of the oxo/hydroxo-biscarboxylato class of dinuclear Fe(III) compounds, where protonation of the oxo bridge provides a means for modulating the magnitude of spin exchange within the cluster. Photoexcitation of solutions containing Ru(II) polypyridyl sensitizers and the Fe(III) complexes results in quenching of emission from the (3)MLCT excited state of the Ru(II) chromophores; nanosecond time-resolved absorption measurements demonstrate that quenching occurs, in part, by electron transfer. Decoupling electron transfer driving force (DeltaG(0)(ET)) from changes in the magnitude of spin exchange was achieved by varying the bridging carboxylate to afford a series of complexes of the form [Fe(2)O(H)(O(2)CR)(2)(Tp)(2)](n)(+) (n = 0, 1, 2). Electrochemical measurements reveal a greater than 500 mV shift in cluster reduction potential across the series (i.e., R = CH(3) to CF(3)), whereas variable-temperature magnetic susceptibility measurements demonstrate a corresponding invariance in spin exchange between the metal centers (J(oxo) = -119 +/- 4 cm(-1) and J(hydroxo) = -18 +/- 2 cm(-1) for H = -2JS(1).S(2)). Structural analyses suggest that reorganization energies (lambda) associated with electron transfer should be identical for all molecules within a given series (i.e., oxo or hydroxo bridged); likewise Deltalambda between the series is expected to be small. A comparison of quenching rates for the two extended series firmly establishes that neither reorganization energy nor electron transfer driving force considerations can account for differences in reactivity between oxo-bridged (large spin exchange) and hydroxo-bridged (small spin exchange) quenchers. Upon consideration of energy transfer contributions, it is determined that reactivity differences between the oxo- and hydroxo-bridged quenchers must lie in the relative rates of Dexter energy transfer and/or electron transfer, with the origin of the latter linked to something other than DeltaG(0)(ET) or lambda. Finally, the extent to which spin exchange within the dinuclear Fe(III) quenchers can be identified as the key variable influencing these reactivity patterns is discussed.
منابع مشابه
The Study of Electrochemical Behavior of Mono and Dinuclear Co(III) Complexes, trans-[pyCo((DO)(DOH)pn)(L)]PF6 and [{pyCo((DO)(DOH)pn)}2(μ-dicyd)](PF6)2
Electrochemical behavior of the new mono and dinuclear Co (III) complexes of the types trans-[pyCo((DO)(DOH)pn )(L)]PF6 and [{py Co((DO)(DOH)pn)}2 (μ-dicyd)] (PF6)2 have been studied in acetonitrile solution. All the mono nuclear complexes show two quasi- reversible reduction couples associate to Co(III/II)an...
متن کاملIntramolecular energy transfer involving heisenberg spin-coupled dinuclear iron-oxo complexes.
The synthesis, structure, and physical properties of a series of oxo-bridged dinuclear Fe(III) complexes containing pendant naphthalene groups are described. The compounds [Fe(2)O(O(2)CCH(2)-C(10)H(7))(tren)(2)](BPh(4))(NO(3))(2) (8), [Fe(2)O(O(2)CCH(2)-C(10)H(7))(TPA)(2)](ClO(4))(3) (9), Fe(2)O(O(2)CCH(2)-C(10)H(7))(2)(Tp)(2) (10), and Fe(2)O((O(2)CCH(2)CH(2))(2)-C(10)H(6))(Tp)(2) (11) (where ...
متن کاملSynthesis, Spectroscopy and Magnetic Characterization of Five Dinuclear Copper(II) Complexes with 2, 3 or 4-Pyridinemethanol as the Ligand
The synthesis, spectroscopy and magnetic characterization of five new dinuclear copper(II) complexes are described. All five compounds have the general formula [Cu2(L)4(O-R)2](Cl)2 or [Cu2(L)2(Cl)2](Cl)2, in which R = CH3 or H, L=2, 3 or 4-pyridinemethanol as L2, L3 or L4, respectively. The title compounds consist of dinuclear units with bridging methoxo groups in [Cu2(L4)4(O-CH3)2](Cl)2, hydro...
متن کاملElectron Transfer and Proton-Coupled Electron Transfer Reactivity and Self-Exchange of Synthetic [2Fe–2S] Complexes: Models for Rieske and mitoNEET Clusters
This report describes the thermochemistry, proton-coupled electron transfer (PCET) reactions and self-exchange rate constants for a set of bis-benzimidazolate-ligated [2Fe-2S] clusters. These clusters serve as a model for the chemistry of biological Rieske and mitoNEET clusters. PCET from [Fe2S2((Pr)bbim)((Pr)bbimH)](2-) (4) and [Fe2S2((Pr)bbim)((Pr)bbimH2)](1-) (5) to TEMPO occurs via concerte...
متن کاملDioxygen Activation by a Non-Heme Iron(II) Complex: Theoretical Study toward Understanding Ferric-Superoxo Complexes.
We present a systematic study using density functional theory (DFT) and coupled cluster (CCSD(T)) computations with an aim of characterizing a non-heme ferric-superoxo complex [(TMC)Fe(O2)](2+) (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) that was proposed to perform allylic C-H activation of cyclohexene (Lee, Y.-M. et al. J. Am. Chem. Soc.2010, 132, 10668). As such, we invest...
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید
ثبت ناماگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید
ورودعنوان ژورنال:
- Inorganic chemistry
دوره 40 26 شماره
صفحات -
تاریخ انتشار 2001