Kinetics of solvolysis of the trans-dichlorotetrapyridinecobalt(III) ion in water and in water + methanol

Abstract

Rates for the first-order solvolysis of the trans-dichlorotetrapyridinecobalt(lll) ion have been measured in water and in mixtures of water and methanol for a range of temperatures. A non-linear dependence of log (rate constant) with reciprocal of dielectric constant suggests that the effects of solvent structure are important and this is confirmed by the comparison of the variation with solvent composition of the transition-state parameters with the variation with solvent composition of a range of physical properties of the solvent mixture. The application of a free-energy cycle relating the process initial state+transition state in water to that in water + methanol shows that changes in solvation of the transition state have a dominant effect on the rate.

Studies on ion-pairing effects of the kinetics of aquation of bromopentaammine cobalt(III) complex in malonate media

“…Log C = Log A + 293.15b (26) where A is the frequency factor, a and b are Akerlof's empirical constants [17]. The plot Log A/K versus E.b/Log C/D as shown in Figure 4, gives a good straight line with a slope approximately equals to 0.052, which is equal to 1/2.302.R = 0.052.…”

1H, 13C, 15N NMR and 13C, 15N CPMAS studies of cobalt(III)-chloride-pyridine complexes, spontaneous py → Cl substitution in trans-[Co(py)4Cl2]Cl, and a new synthesis of mer-[Co(py)3Cl3]

“…The presence of exactly three proton signals in each NMR spectrum proves an equivalency of all py ligands in the trans-[Co(py) 4 n+ formulae (n = 0-2), which contain four equatorial py molecules and two axial chlorides, exhibited a similar shielding of H(2), although the effect was usually weaker, while effects at H(3) and H(4) were of variable sign and magnitude: trans-[Ru(py) 4 Fig. 1 bottom) 6 exhibit three signals in the same order observed for free py (C(2) > C(4) > C(3)), their chemical shifts being nearly independent of the solvent (variations up to ±0.3 ppm); analogous measurements in CDCl 3 have not been performed due to the low solubility of this ionic complex and the conversion of trans-[Co(py) 4 The most characteristic C(2) high-frequency coordination shifts are much larger for the former complex (ca. 7-9 ppm) than the latter one (ca.…”

“…3) remains unknown. In our opinion, this process, generally absent in aqueous media (in water-alcoholic solutions some solvolysis reactions were generally reported for trans-[Co(py) 4 Cl 2 ] + cations [6,65,66]) seems to be favoured just in chloroform due to the two principal reasons: (1) the lack of trans-[Co(py) 4 Cl 2 ]Cl dissociation in this solvent enables stronger interactions between the Co(III) central ion or coordinated py molecules, and the Cl atom located in the outer coordination sphere; (2) the presence of small amounts of HCl (which is well-known to be formed in CHCl 3 upon daylight exposure) may catalyse Cl → py substitution. coordination sphere geometry and character of auxiliary ligands.…”

“…In contrast, mer-[Co(py) 3 15 N CPMAS studies of cobalt(III)-chloride-pyridine complexes, spontaneous py → Cl substitution in trans-[Co(py) 4 Cl 2 ]Cl, and a new synthesis of mer-[Co(py) 3 Cl 3 ] directly prepared by oxidation of aqueous CoCl 2 + py mixtures (which is a common procedure for obtaining Co(III) chloride-azine complexes, e.g. those of cis-[Co(LL) 2 Cl 2 ]Cl formula, where LL = 2,2'-bipyridine or 1,10-phenanthroline [11,12]), because the only product is again trans-[Co(py) 4 Cl 2 ] + [1,5,6,13]. In the past, Shevchenko et al reported mer-[Co(py) 3 Cl 3 ] as the main product of trans-[Co(py) 4 Cl 2 ]Cl·6H 2 O thermal decomposition at o C [14], however, this technique was unsuitable for preparative purposes due to the formation of some other by-products.…”

“…Owing to the lability of py ligands, the former compound, readily prepared by oxidation of trans-[Co(py) 4 Cl 2 ] [3,4] with gaseous chlorine [5,6], is widely used as a facile and versatile precursor for synthesis of more complicated Co(III) species [7]. In contrast, mer-[Co(py) 3 15 N CPMAS studies of cobalt(III)-chloride-pyridine complexes, spontaneous py → Cl substitution in trans-[Co(py) 4 Cl 2 ]Cl, and a new synthesis of mer-[Co(py) 3 Cl 3 ] directly prepared by oxidation of aqueous CoCl 2 + py mixtures (which is a common procedure for obtaining Co(III) chloride-azine complexes, e.g.…”