Kinetics of dissociation of M(II)-aza-oxa cryptates (M=Ni, Cu) in weakly acidic aqueous-acetonitrile media

Ghosh, Tamal ; Bandyopadhyay, Prasun ; Bharadwaj, Parimal K. ; Banerjee, Rupendranath (2001) Kinetics of dissociation of M(II)-aza-oxa cryptates (M=Ni, Cu) in weakly acidic aqueous-acetonitrile media Polyhedron, 20 (5). pp. 477-482. ISSN 0277-5387

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Official URL: http://linkinghub.elsevier.com/retrieve/pii/S02775...

Related URL: http://dx.doi.org/10.1016/S0277-5387(00)00650-1

Abstract

H+ ion promotes dissociation of nickel(II) and copper(II) complexes of a heteroditopic aza-oxa cryptand L, derived from tris(2-aminoethyl)amine (tren). L is a tetradentate ligand and in 50% (v/v) CH3CN---H2O media a tetra acidic base with ligand protonation constants pK1 9.96±0.004, pK2 8.98±0.02, pK3 4.22±0.03 and pK4 2.18±0.02 at 25.0°C; I=0.10 mol dm-3. Kinetics for the H+ ion promoted dissociation of both the complexes are first-order in [H+] and complex concentration. Replacement of H2O with D2O affects the rate insignificantly. At 25.0°C; I = 0.10 mol dm-3 the second order rate constant (dm3 mol-1s-1) for the dissociation of the Ni(II) complex (31.5±0.9) is larger than that for the Cu(II) complex (18.8±0.7) but smaller than that for [Ni(tren)(H2O)2]2+ - a complex thermodynamically much more stable than the Ni(II) cryptate (log K = 8.55±0.02). The results indicate that 'cryptate effect' significantly affects the kinetic lability of transition metal cryptates.

Item Type:Article
Source:Copyright of this article belongs to Elsevier Science.
Keywords:Kinetics; Equilibrium; Nickel(II); Copper(II); Cryptand
ID Code:4925
Deposited On:18 Oct 2010 06:13
Last Modified:18 May 2011 08:33

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