Spectral study of tris(.beta.-dionato)cobalt(III) chelates. Structure-redox potential relations

Abstract

intensity of the main line) and is lost in the base line. If a hidden higher binding energy peak were comparable in intensity to that of the lower binding energy peak, then the Ru 3d512 intensity derived from the deconvoluted spectrum shown in Figure 1 would be anomalously low compared with that of other complexes while the C 1s line intensity would be anomalously high. Furthermore, the large Ru 3d splitting required to hide the high-binding-energy Ru 3d peak under the C 1s line ought to be observable even in the Ru 2p3/2 spectrum of the complex. We examined these possibilities by comparing Ru 3d5/2/C1 2p and Ru 2p312/CI 2p intensity ratios recorded for 7 with those of all the other ruthenium chloride complexes. The Ru 3d5/?/C1 2p and Ru 2~~,~/ C l 2p intensity ratios for 7 are both within 20% (albeit on the low side of all but one) of all other measured ratios. The Ru 2p3p line width for 7 is normal. Given experimental errors, we find then that at least 80% of the Ru 3d512 intensity expected from two ruthenium centers in 7 is accounted for in the deconvoluted spectrum. Consequently, the metal XP spectrum of 7 is consistent with that of a strongly delocalized class I11 complex. For such a complex a large portion of the total metal core level photoemission intensity resides in a single, low-binding-energy line. From the quality of the spectrum we estimate, using eq 2, that the electron exchange parameter a for 7 must be greater than 0.9. ConclusionsThe diruthenium complexes examined have provided the opportunity to systematically assess the effects of ligand coordination environment, metal oxidation state, and metal-metal interaction on the metal XP spectra. One complex is of particular interest in this series; the symmetric, mixed-valence [Ru(II),Ru(III)] complex [As(p-tol)3]2C1RuC13RuC1[As(p-tol)3]2. Depending onthe strength of the metal-metal interaction, the metal XP spectrum from this complex could give any results along the continuum from two equally intense metal lines separated by 1 eV or more, to unequal intensities from the two lines with the lower binding energy line "stealing" intensity from the higher binding energy line, to a single, narrow metal line (indistinguishable metal centers). The spectrum observed is a function of the extent of unpaired electron delocalization during photoemission. It was found that, to the degree of resolution possible, this complex gives a metal spectrum in which at least 80% of the metal signal is present in a single, low-binding-energy final state. This experimental result reflects more extensive unpaired electron delocalization in this complex compared with that in the Creutz-Taube complex [(NH3)5Ru(pz)Ru(NH3)5]5+, which gives two well-separated metal lines of equal intensity. We estimate the value of a in 7 is greater than 0.9, whereas in the Creutz-Taube complex it is less than 0.10. This work, combined with Hush's theory, suggests that very unusual metal XP spectra ought to be obtained from class I11 mixed-valence complexes having metal-metal spacings between 3.5 an...

Mixed Ligand Complexes of Cobalt(II) – Synthesis, Structure, and Properties of Co4(thd)4(OEt)4

“…From the MS data in Table 2 it is seen that Co(thd)(dpd) is detected right up to 290°C which is highest temperature reached by the present MS apparatus. The existence of the complexes Cr(dpd) 3 [30,31], Fe(dpd) 3 [32,33], Co(dpd) 3 [34,35], and Cu(dpd) 2 [29,36] is already reported. The fragment Co(thd)(C 6 H 9 O 2 ) (true enough in very low abundance in the present MS spectra) indicates the existence of another new mixed-ligand Co II complex with a β-keto aldehyde [C 6 H 9 O 2 abbreviated dbd as a derivative of H(dbd) ϭ 3,3-dimethylbutane-1,2-dione].…”

Enantioselectivities in Electron-Transfer and Excited State Quenching Reactions of a Chiral Ruthenium Complex Possessing a Helical Structure

“…This is because the ferricenium/ferrocene redox potential shifts by 0.25 V (vs SCE) on going from acetonitrile to water while the SCE potential in water is 0.24 V. , The reduction potentials for Ru(menbpy) 3 3+/ * 2+ and Ru(menbpy) 3 * 2+/+ are estimated as −0.45 13 and +1.10 V, respectively. The reduction potentials for Co(acac) 3 and Co(edta) - were determined previously to be −0.34 and +0.13 V vs SCE in CH 3 CN, respectively. Reduction potentials of the substituted ruthenium phenanthroline complexes (RuL 3 3+/2+ and RuL 3 2+/+ ) were measured in CH 3 CN (Table ) and confirmed previously published values. , The values for RuL 3 2+/+ , where L = 5-methylphenanthroline, 5,6-dimethylphenanthroline, and 5-bromophenanthroline, are close to those estimated previously…”

“…Electron-transfer quenching should be sensitive to changes in driving force. The reduction potentials of Ru(menbpy) 3 n + are −0.90, +1.55, and −0.45 V for E 0(2+/+) , E 0(3+/2+) , and E 0(3+/ * 2+) , respectively, − and the reduction potential of Co(acac) 3 is ≈−0.34 V . Thus, the free-energy changes, Δ G °, for the thermal electron-transfer reaction between Ru(menbpy) 3 •+ and Co(acac) 3 and the photochemical electron-transfer reaction between *Ru(menbpy) 3 2+ and Co(acac) 3 are −0.56 and −0.11 eV, respectively.…”

Tris(3-nitropentane-2,4-dionato-κ2O,O′)cobalt(III)

“…For the preparation of derivatized tris(2,4-pentanedionato) metal complexes, see: Collman et al (1962Collman et al ( , 1963; Collman (1965); Schirado et al (1971); James (1974); Shalhoub (1980). For spectroscopic properties of the title compound, see: Singh & Sahai (1967, 1968; Larsson & Eskilsson (1969); Fleming & Thorton (1973, 1975; Tsiamis et al (1987). For crystallographic studies of related compounds, see: Appleton et al (1992); Abrahams et al (1998); Tsiamis et al (1998); von Chrzanowski et al (2007).…”