“…Chemical transformations may occur. The most obvious transformations are the ligand substitution reactions of Co(en)32+ and Co(NH3)62+ divalent complexes (Fischer and Bezdek 1973;Mayer et al 1979;Sahami and Weaver 1981). These are apparent from the smaller oxidation (as compared to reduction) peaks observed at both the clay-modified and bare electrodes (Figure 3).…”
Abstract--The roles of molecular structure and charge are examined in the transport of cations within montmorillonite clay films. The series of Ru(NH3)6 3+, Co(NH3) 3+, Co(en)33+, Co(sep) 3+ and Co(bpy)3 3+ are examined in detail via electrochemical and spectrocbemical methods. The electrochemical signal is enhanced both in minimizing the time required to develop the signal and in the magnitude of the signal for Ru(NH3)6 3+. In addition, the potential for the observed reduction peak is shifted negative and the current peak associated with reduction disappears with rinsing of the clay film. These observations are characteristic of a compound that is held by simple electrostatic charge characteristics. In contrast, the compounds Co(NH3) 3+, Co(en)3 3+ and Co(sep) 3+, while showing rapid and enhanced signal development, eventually evolve a signal that is diminished with respect to the bare electrode, consistent with a hydrophobic mode of retention. The signal for Co(bpy)33+ is slow to be observed, is diminished with respect to the bare electrode and is shifted positive in potential, all hallmarks of a strong, non-electrostatic mode of binding within the clay.
“…Chemical transformations may occur. The most obvious transformations are the ligand substitution reactions of Co(en)32+ and Co(NH3)62+ divalent complexes (Fischer and Bezdek 1973;Mayer et al 1979;Sahami and Weaver 1981). These are apparent from the smaller oxidation (as compared to reduction) peaks observed at both the clay-modified and bare electrodes (Figure 3).…”
Abstract--The roles of molecular structure and charge are examined in the transport of cations within montmorillonite clay films. The series of Ru(NH3)6 3+, Co(NH3) 3+, Co(en)33+, Co(sep) 3+ and Co(bpy)3 3+ are examined in detail via electrochemical and spectrocbemical methods. The electrochemical signal is enhanced both in minimizing the time required to develop the signal and in the magnitude of the signal for Ru(NH3)6 3+. In addition, the potential for the observed reduction peak is shifted negative and the current peak associated with reduction disappears with rinsing of the clay film. These observations are characteristic of a compound that is held by simple electrostatic charge characteristics. In contrast, the compounds Co(NH3) 3+, Co(en)3 3+ and Co(sep) 3+, while showing rapid and enhanced signal development, eventually evolve a signal that is diminished with respect to the bare electrode, consistent with a hydrophobic mode of retention. The signal for Co(bpy)33+ is slow to be observed, is diminished with respect to the bare electrode and is shifted positive in potential, all hallmarks of a strong, non-electrostatic mode of binding within the clay.
“…These adducts exhibit weak intervalence-transfer transitions in the low energy visible and near infrared regions which are not present in either reduced or oxidized solutions of either complex alone and which cannot be ascribed to a simple halide ion-to-metal charge transfer originating from the bromide ion formed upon oxidation of the (en) 2 Ru II (bpy) 2+ species. , The spectroscopic transition corresponds to the optical electron-transfer process shown in eq 2 below, and two examples of H-bonded intervalence-transfer (HBIT) spectra are shown in Figure where Ru II (CN)···HN−Ru III is meant here to depict a hydrogen-bonding interaction between the cyano ligand on the Ru(II) complex and one of the N-bound amine hydrogens of ethylenediamine on the Ru(III) complex (the basicity of cyano ligands on Ru(II) is well-established as is the Lewis acidity of the amine hydrogens in metal−en complexes , ). 1 HBIT specta and spectral deconvolutions for (a) [((trpy)(bpy)Ru II (CN)) 2 ,(en) 2 Ru III (bpy)] 5+ and (b)[((bpy) 2 Ru II (CN) 2 ) 2 ,(en) 2 Ru III (bpy)] 3+ in acetonitrile (5 cm path length).…”
Spectroscopic and electrochemical investigations have
been carried out on a collection of hydrogen-bonded
mixed-valence adducts of ruthenium complexes. The electron donors
(H-bond acceptors) are Ru(II) cyano species
and the electron acceptors (H-bond donors) are Ru(III)
ethylenediamine species, and NIR spectroscopic transitions
in the adducts are assigned to intervalence transfer through the
hydrogen bonds holding the adducts together (HBIT).
Spectroscopic studies using Job's method indicate that the
adducts are 2:1 ternary aggregates of formulations such
as
[((trpy)(bpy)RuII(CN))2,(en)2RuIII(bpy)]5+
and
[((bpy)2RuII(CN)2)2,(en)2RuIII(bpy)]3+.
Voltammetric investigations
show substantial repulsion of the redox waves of the parent complexes
in mixtures containing both donor and acceptor.
Comparison with known electronic coupling data for mixed-valence
ruthenium dimers covalently bound through
dithiaspiroalkane bridging ligands indicates that the electronic
coupling through H bonds of this type is 65−75% as
strong as through σ-covalent bonds.
“…This establishes that the homolysis rate of the hydroxo complex is negligibly small (14) The protonation and deprotonation of a nitrogen of L can probably be ruled out at this pH. Also, the deprotonation of a coordinated molecule of H20 in (H20)2CrL3+ is known to have a pKa of 2.9.13 (15) Richens, D. T.; Adzamli, I. K.; Leu pin, P.; Sykes, A. "L = [15]aneN4, *In aqueous solution with 1.0 X 10"2 0.20 M. rReference 5.…”
Section: Resultsmentioning
confidence: 88%
“…1984, 106, 5197. HTMPO, 0.20-1.60 HTMPO, 0.31-1.67 HTMPO, 0.76-2.00 HTMPO, 0.23-1.00 5.0 ± 0.3 5.0 ± 0.4 1.36 ± 0.01 1.24 ± 0.04 1.15 ± 0.01 "At 25.0 °C with [H+] = 1.0 X 10"2 M at µ = 0.20 M and with [RCr( [15]aneN4)(H2O)2+]0 = 0.02-0.35 mM, used always as a limit- intensity of the ESR signal of HTMPO decreased as the homolysis of the isopropylchromium complex proceeded (Figure 1).…”
Section: Resultsmentioning
confidence: 99%
“…Also, the deprotonation of a coordinated molecule of H20 in (H20)2CrL3+ is known to have a pKa of 2.9.13 (15) Richens, D. T.; Adzamli, I. K.; Leu pin, P.; Sykes, A. "L = [15]aneN4, *In aqueous solution with 1.0 X 10"2 0.20 M. rReference 5. ¿[NaOH] = µ = 0.82 .…”
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