Transfer chemical potentials for iron(II)-diimine complexes from water into aqueous methanol

Solvation of iron(II) complexes of hexadentate tris-diimine Schiff base tripod ligands in alcohol?water and DMSO?water mixtures

“…The high stability and substitution-inertness [9,13], the intense colour of these complexes and the low watersolubility of their perchlorate salts makes them excellent candidates for the determination of transfer chemical potentials from solubility measurements. The crystal structures of the perchlorate and tetrafluoroborate [16] salts exhibit identical (within experimental uncertainties) bond distances and angles in the respective [Fe(fpyHg 3 tren)] 2þ cations.…”

“…Such inertness to substitution makes this type of complex extremely useful for kinetic studies, especially of oxidation by such slow oxidants as peroxodisulphate [10] or thallium(III) [11], where often rate-limiting dissociation, with subsequent oxidation of iron(II) intermediates, occurs in parallel with, or faster than, direct oxidation [12], thus making kinetic studies difficult or impossible. We have reported earlier on solvation and the reactivity of cage and linear complexes, and on the intermediate reactivity [9,13] of semi-encapsulated complexes of tripodal ligands (3) [14][15][16]. These ligands are derived from tris(2-aminoethyl)amine and pyridine 2-carboxaldehyde, 2-acetylpyridine, or 2-benzoylpyridine; (3) with R = H, Me, or Ph, respectively.…”

“…Iron(II) complexes of linear [6] and encapsulating [7] hexadentate tris-diimine ligands tend to be exceptionally inert to substitution -cage complexes such as (1) and complexes of linear hexadentate ligands such as (2) have half-lives with respect to base hydrolysis of several hours in 0.33 mol dm À3 hydroxide [8,9], while aquation in acidic media is even slower. Such inertness to substitution makes this type of complex extremely useful for kinetic studies, especially of oxidation by such slow oxidants as peroxodisulphate [10] or thallium(III) [11], where often rate-limiting dissociation, with subsequent oxidation of iron(II) intermediates, occurs in parallel with, or faster than, direct oxidation [12], thus making kinetic studies difficult or impossible.…”

Kinetics of Dissociation of tris-{3-(2-pyridyl)-5,6-bis(2-furyl)-1,2,4-triazine}iron(II)

“…iron(II)-diimine complexes tend to be yet slower [36,42]. Kinetic results for the second stage of base hydrolysis of [Fe(fertri) 3 ] 2+ are collected together in Table 3; Figure 2 shows the dependence of observed rate constants on hydroxide concentration.…”

“…This range may be compared with the even smaller reactivity range for base hydrolysis of [Fe(api) 3 ] 2+ [41], where api is the Schiff base derived from pyridine 2-carboxaldehyde and ammonia, with an increase of nearly 6-fold and of 12-fold for base hydrolysis of [Fe(phen) 3 ] 2+ [45] and of [Fe(HN@CHCH@NH) 3 ] 2+ [46] respectively, and with a decrease of nearly 2-fold for base hydrolysis of [Fe(dapi) 2 ] 2+ [41], where dapi is the terdentate Schiff base derived from 2,6-diacetyl pyridine and ammonia. Further data on trends of base hydrolysis rate constants with solvent composition in methanol-water solvent mixtures are available [42]. These variations are all relatively small, representing the small resultants of rather larger solvent effects on transfer chemical potentials for the initial, i.e.…”