NDLI: Kinetics and mechanism of the first aquation stage for the [Cr(pic)$_{3}$]$^{0}$ and [Cr(pic)$_{2}$(OH)]$_{2}$ $^{0}$ complexes in HClO$

Content Provider	Springer Nature Link
Author	Kita, Ewa Szabłowicz, Małgorzata
Copyright Year	2003
Abstract	Aquation of [Cr(pic)$_{3}$]$^{0}$ and [Cr(pic)$_{2}$(OH)]$_{2}$ $^{0}$ in aqueous HClO$_{4}$ solutions leads to formation of the common product – [Cr(pic)$_{2}$(H$_{2}$O)$_{2}$]$^{+}$. The first, reversible stage, the ring opening via Cr—N bond breaking in [Cr(pic)$_{3}$]$^{0}$ is followed by the second, rate-determining step – one-end bonded pic ligand liberation. In the case of the [Cr(pic)$_{2}$(OH)]$_{2}$ $^{0}$ complex, the first faster stage produces the singly bridged dimer, which undergoes cleavage into the parent monomers in the second, much slower step. The subsequent aquation of [Cr(pic)$_{2}$(H$_{2}$O)$_{2}$]$^{+}$ is extremely slow and leads to [Cr(pic)(H$_{2}$O)$_{4}$]$^{2+}$ formation, which practically does not undergo further ligand substitution under the conditions applied. Kinetics of the first aquation stage for [Cr(pic)$_{3}$]$^{0}$ and of the second step for [Cr(pic)$_{2}$(OH)]$_{2}$ $^{0}$ were studied spectrophotometrically in the 0.1–1.0 M HClO$_{4}$ range at I = 1.0 M. The observed pseudo-first order rate constant for [Cr(pic)$_{3}$]$^{0}$ decreases with [H$^{+}$] increase according to the rate law: k $_{obs}$ = k $_{1}$ + k $_{−1}$ Q $_{1}$/[H$^{+}$], where k $_{1}$ and k $_{−1}$ are the rate constants of the forward and the reverse processes in the unprotonated substrate and Q $_{1}$ is the protonation constant of the pyridine nitrogen atom. In the case of the [Cr(pic)$_{2}$(OH)]$_{2}$ $^{0}$ complex, the rate for the singly bridged dimer cleavage does not depend on [H$^{+}$]. The activation parameters for the chelate-ring opening in [Cr(pic)$_{3}$]$^{0}$ and for the singly bridged dimer cleavage have been determined and discussed. Some kinetic data of the slow, second aquation stage for the [Cr(pic)$_{3}$]$^{0}$ complex and of the fast, first aquation stage for the doubly bridged dimer have been studied; for both reactions the rate increases linearly with the increase in [H$^{+}$].
Starting Page	698
Ending Page	706
Page Count	9
File Format	PDF
ISSN	03404285
Journal	Transition Metal Chemistry
Volume Number	28
Issue Number	6
e-ISSN	1572901X
Language	English
Publisher	Kluwer Academic Publishers
Publisher Date	2003-01-01
Publisher Place	Dordrecht
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Inorganic Chemistry Physical Chemistry
Content Type	Text
Resource Type	Article
Subject	Materials Chemistry Metals and Alloys Inorganic Chemistry

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