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Kinetics, Mechanism and Synthesis of Adduct Formation of Tetraaza Schiff Base Cobalt(ΙΙ) Complexes as Donor with Diorganotin(IV)dichlorides as Acceptor

Z. Asadi, M. Asadi* and F. Mosalanezhad

Chemistry Department, College of Sciences, Shiraz University, Shiraz, 71454, Iran

The kinetics and mechanism of the adduct formation of diorganotin(IV)dichlorides (R₂SnCl₂), where R = Ph, Me, Bu, with Co(II) tetraaza Schiff base complexes such as: [Co(appn)]{[N,N'-1,2-propylenebis(o-amino-α-phenylbenzylideneiminato) cobalt(ΙΙ)]} and [Co(cappn)]{[N,N'-1,2-proylenebis(5-chloro-o-amino-α-phenylbenzylideneiminato)cobalt(II)]}, were studied spectrophotometrically. The kinetic parameters and the rate constant values show the acceptor tendency trend for the diorganotin(IV)dichlorides as follows: Ph₂SnCl₂ > Me₂SnCl₂ > Bu₂SnCl_2. Adducts were separately synthesized and fully characterized by ¹¹⁹Sn NMR, IR, UV-Vis spectra and elemental microanalysis (C.H.N) methods. The trend of the rate constants for the adduct formation of the cobalt complexes with a given tin acceptor decreased as follows: Co(appn) > Co(cappn). The linear plots of k_obs vs. the molar concentration of the diorganotin(IV)dichlorides, the high span of the second order rate costant k₂ values and the large negative values of ΔS^‡ suggest an associative (A) mechanism for the acceptor-donor adduct formation. Moreover, [Co(aptn)]{[N,N'-1,3-propylenebis-(o-amino-α-phenylbenzylideneiminato)cobalt(ΙΙ)] and [Co(captn)]{[N,N'-1,3-proylenebis-(5-chloro-o-amino-αphenylbenzylideneiminato)cobalt(II)]} were synthesized and characterized but, their kinetics with R₂SnCl₂ were so fast that it was impossible to follow them using the conventional methods.

Keywords: Diorganotin(IV)dichlorides, Kinetic, Mechanism, Tetraaza Schiff base, Cobalt(II) complex