14403-82-8Relevant articles and documents
Photochemistry of 2+: Wavelength, Pressure, and Medium Dependence of Redox and Aquation
Kirk, A. D.,Namasivayam, C.,Porter, Gerald B.,Rampl-Scandola, M. A.,Simmons, A.
, p. 3108 - 3113 (1983)
The ratio of redox to aquation of 2+ has been shown to be constant at about 2 for irradiation wavelengths (nm) of 254, 275, 313, and 365, falling close to zero at 514.5.With increasing pressure, quantum yields for redox and aquation decrease, the former somewhat faster, and in a wavelength-dependent fashion, so that the apparent volumes of activations (mL mol-1) for redox and aquation are respectively 6.0+/-0.6 and -0.4+/-3.2 at 365 nm and 4.8+/-0.3 and 2.5+/-2.7 at 313 nm.At ordinary pressure at redox yield falls 8-fold and the aquation yield increases 50percent in 40 wtpercent glycerol/water.The equations relating volumes of activation for individual reaction steps to the overall apparent volumes of activation for the lifetime and quantum yield are derived.It is shown that all of the above observations are supportive of a mechanism involving generation of a caged radical pair which has no memory of the excitation enrgy of its progenitor.
Synthesis and reactivity of the pentaamminecobalt(III) linkage isomers of succinimide
Angus, Patricia M.,Jackson, W. Gregory
, p. 4806 - 4813 (2008/10/08)
The linkage isomers of (succinimido)pentaamminecobalt(III) have been selectively synthesized and characterized by 1H and 13C NMR, IR, and UV-visible spectroscopies. The deprotonated imide ligand bonds to the metal through oxygen or nitrogen. The oxygen-bonded isomer is the less stable form. In water (ksON = 1.7 × 10-4 s-1, 25°C) and Me2SO (ksON = 5.1 × 10-5 s-1) it spontaneously isomerizes to the nitrogen-bonded form; in aqueous acid (pKa = 2.7, I = 0.1 M, LiClO4) and acidified Me2SO it protonates and rapidly solvolyzes; the protonated species in water has reactivity comparable (kH = 2.3 × 10-2 s-1, I = 0.1 M, LiClO4, 25°C) to the most reactive isolable [(NH3)5CoX]n+ species known. In aqueous base three competing reactions have been detected, namely solvolysis (40%, 25°C), base-catalyzed O- to N-bonded linkage isomerization (30%), and nucleophilic attack on the coordinated carbonyl group by hydroxide ion leading to the formation of the carboxylate-bonded isomer of (succinamato)pentaamminecobalt(III) (30%) (kOH(obsd) = 9.0 × 10-2 M-1 s-1, I = 0.1 M, KF, 25°C). The individual rates and rate laws for all these reactions have been determined. In acid and base the nitrogen-bonded imido complex is less reactive than the O-bonded form. It is base hydrolyzed relatively slowly, and a term second order with respect to hydroxide ion is dominant in the rate law (kN = 6.1 × 10-3 M-2 s-1, I = 1.0 M, NaClO4, 25°C); 18O studies establish the reversible addition of OH- in the first step. The product is the nitrogen-bonded succinamato complex, which has been characterized through crystallization in its basic and acidic forms (pKa = 1.8 (amide) and 3.55 (carboxylic acid), I = 1.0 M, NaCl, 25°C). The succinimido-N complex is protonated in water and Me2SO only in very strong acid. The protonated species has been crystallized and characterized; it is a strong acid (pKa 1/2 = days, 25°C). A N- to O-bonded isomerization reaction has not been detected. The structure and reactivity of these imide complexes are compared with those of the related amide and urea complexes.
Partitioning of Reaction Paths in Ce(IV) Induced Electron Transfer in Azidopentaamminecobalt(III) Perchlorate
Subramani, K.,Srinivasan, Vangalur S.
, p. 1030 - 1033 (2007/10/02)
Cerium(IV) induces electron transfer in azidopentaamminecobalt(III) perchlorate yielding N2 (ca. 95percent), Co(II) (ca. 20percent) and aquopentaamminecobalt(III) (ca. 80percent) as products.The decrease in absorbance at 520 nm for cobalt(III) complex corresponds to nearly 90percent of initial absorbance, as part of the azide complex becomes aquopentaamminecobalt(III) complex which absorbs to some extent at this wavelength.Though the stoichiometry of cerium(IV) to unbound N3(-) is 1 : 1, the ratio of Ce(IV) to azidocobalt(III) complex is about 1 : 0.87, accounting for about 20percent reduction at one of the Co(III) in dimeric complex, III - N6 - CoIII>(4+).The kinetic and stoichiometric results have been accounted for by a suitable mechanism involving such a dimeric complex.
