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Dynamics of ternary complex formation in the reaction of diaquoanthranilato‐N, N‐diacetatonickelate(II) with 2,2′‐bipyridine and 1,10‐phenanthroline
Author(s) -
Das Asim K.
Publication year - 1996
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/(sici)1097-4601(1996)28:4<275::aid-kin5>3.0.co;2-s
Subject(s) - chemistry , ternary operation , phenanthroline , reaction rate constant , bipyridine , crystallography , order (exchange) , 2,2' bipyridine , ternary complex , stereochemistry , kinetics , medicinal chemistry , physics , crystal structure , organic chemistry , enzyme , finance , quantum mechanics , computer science , programming language , economics
Dynamics of ternary complex formation in the reaction of diaquoanthranilato‐ N, N‐ diacetatonickelate(II) with 2,2′‐bipyridine and 1,10‐phenanthroline. $\rm Ni(ada)(H_2O)_2^{‐}$ $+$ $L\rightleftharpoons Ni(ada)(L)^{‐}$ $+$ $2 H_20;$ $‐ {{d[Ni(ada)^{‐}]}\over{dt}}$ $=$ $k_f[Ni(ada)^{‐}][L]+k_d\ [Ni(ada)(L)];$ $\ ada^{3‐}=$anthranilate‐N, N‐diacetate; and L=bipy or phen. The kinetics of formation of ternary complexes by diaquoanthranilato‐ N , N ‐diacetatonickelate(II). [Ni(ada)(H 2 O)] − with 2,2′‐bipyridine (bipy) and 1,10‐phenanthroline (phen) have been studied under pseudo‐first‐order conditions containing excess bipy or phen by stopped‐flow spectrophotometry in the pH range 7.1–7.8 at 25°C and λ = 0.1 mol dm −3 . In each case, the reaction is first‐order with respect to both Ni(ada) − and the entering ligand (ie., bipy, phen). The reactions are reversible. The forward rate constants are: $k^{\rm Ni(ada)}_{\rm Ni(ada)(bipy)}=0.87\times10^3{\rm dm}^3 {\rm mol}^{‐1}{\rm s}^{‐1}$, . $k^{\rm Ni(ada)}_{\rm Ni(ada)(phen)}=1.87\times10^3{\rm dm}^3 {\rm mol}^{‐1}{\rm s}^{‐1}$; and the reverse rate constants are: $k^{\rm Ni(ada)(bipy)}_{\rm Ni(ada)}=1.0{\rm s}^{‐1}$ and $k^{\rm Ni(ada)(phen)}_{\rm Ni(ada)}=2.0{\rm s}^{‐1}$. The corresponding stability constants of ternary complex formation are: $\log K^{\rm Ni(ada)}_{\rm Ni(ada)(bipy)}=2.94$ and $\Delta\log K_M =-4.13; \log K^{\rm Ni(ada)}_{\rm Ni(ada)(phen)}=2.97$ , $\Delta\log K_M =-5.03$ . The observed rate constants and huge drops in stability constants in ternary complex formation agree well with the mechanism in which dissociation of an acetate arm of the coordinated ada 3− prior to chelation by the aromatic ligand occurs. The observations have been compared with the kinetics of ternary complex formation in the reaction Ni(ada) − ‐ glycine in which the kinetics involves a singly bonded intermediate, N(ada)((SINGLE BOND)O(SINGLE BOND)N) 2− in rapid equilibrium with the reactants followed by a sluggish ring closure step. The reaction with the aromatic ligands conforms to a steady‐state mechanism, while for glycine it gets shifted to an equilibrium mechanism. The cause of this difference in mechanistic pathways has been explained. © 1996 John Wiley & Sons, Inc.