Die Kinetik der Spaltung dinuklearer Tri‐μ‐hydroxo‐kobalt(III)‐Komplexe N₃Co(Oh)₃CoN₃³⁺ (triole) mit Säure

Abstract

ging OH with half life of 0,2, 0,03 and 0,025 sec. respectively (perchlorate medium p = I N , ZOO, pH = 0). The rate of the back reaction could also be determined, yielding ratios of the two rate constants corresponding to pK-values between 0 and 1,5. Whereas Tach-Trio1 is protonated to the di-p-hydroxo-p-quo complex at about p H 1, it is deprotonated to the di-p-hydroxo-p-oxo complex a t about pH 14 (Siroky [16]). The second step of (l), the aquation of the di-p-hydroxo-paquo species to the di-p-hydroxo-diaquo complex (Diol) takes place with half lives between 4 and 9 sec.The final cleavage to the mononuclear triaquo complex needs many hours to go half way and is again initiated by protonation of one of the remaining two OH-bridges. Neither the p-aquo complex produced thereby, nor the Mono-ol [mono-p-hydroxo-tetraaquo complex] formed as an intermediate cause any observable changes of the spectrum. The Mono-ol aquates at a rate which is inverse in [H+] because of the labilisation brought about by deprotonation of its aquo ligands. b 2 t c !-w I 3 ' Q 0

A Structural and Functional Model of Dinuclear Metallophosphatases

“…The pH−rate profile for the hydrolysis of 5b (Figure ) shows no sign of deviation from linearity up to pH 13 (and up to pH 14 at higher ionic strength), indicating that the kinetic p K a of the bridging hydroxide is greater than 14 under our conditions. We estimate the p K a of the bridging hydroxide as 15 by comparison with the p K a for deprotonation of hydroxide in a similar dinuclear Co(III) complex with three bridging hydroxides . The pH−rate profile also shows no deviation from linearity down to pH 5.5 for 5a , indicating that the bridging oxide is the only kinetically significant nucleophile down to at least pH 4.5 (i.e., the bridging hydroxides are not nucleophiles at any pH monitored here).…”