Kinetics and Mechanism of the Substitution Reaction of Amine in (bis(Acetyle Acetonato) Ethylenediimine) (Diamine)Cobalt(III) Perchlorate with N3-, Br- and NCS-

Document Type : Research Note


1 Islamic Azad University, Varamin Branch, Varamin, I.R. IRAN

2 Islamic Azad University, Shahre Ray Branch, Tehran, I.R. IRAN

3 Department of Chemistry, Amir Kabir University of Technology, Tehran, I.R. IRAN

4 Department of Chemistry, Zanjan University, Zanjan, I.R. IRAN


A series of complexes of the type trans-[Co(acacen)(amine)2]ClO4, where (acacen) is the (bis(acetyleacetone) ethylenediimine) and the amines are Benzyl amine (bzlan) 1, 2-amino pyrimidine (2ampy) 2, N-methylpipirazine (nmpip) 3, 3-methyl pyridine (3mpy) 4, p-toluidine (p-toldn) 5, has been synthesized and characterized by uv-vis. and FT-IR. The kinetics of the substitution reaction of [Co(acacen)(p-toldn)2]ClO4 with N3- , Br- and NCS- ions has been investigated in an aqueous solution by using UV-vis. spectroscopy. It has been found that the reaction occurs in two steps, hydrolysis and ligation. The first order rate constants for hydrolysis and ligation reactions in 313K have been determined. The rate of reaction is almost independent of the type and the concentration of anion. So, the interchange dissociative (Id) mechanism is suggested. The reaction has been carried out in several temperatures and the activation energy for hydrolysis and ligation (for NCS- anion) reactions have been calculated about 55 and 95 kJ/mol respectively.  


Main Subjects

[1] Aly M.M., Recent Developments in the Metallosupramolecular and Molecular Structures of the Cobalt, Iron and Vanadium Complexes of the Dianionic Tetradentate Schiff Base Ligands of Salicylideneimine and Acetylacetoneimine, J. Coord. Chem., 43, p. 89 (1998).
[2] Bu X.R., Jachson C.J., Derveer D.V., You X.Z., Meng Q.J., Wang R.X., New Copper(II) Complexes Incorporating Unsymmetrical Tetradentate Ligands with cis-N2O2 Chromophores: Synthesis, Molecular Structure, Substituent Effect and Thermal Stability, Polyhedron, 16, p. 2991 (1997).
[3] Liu H.Y., Scharbert B., Holm R.H.,An Initial Approach to Biologically Related Bridged Assemblies: Pyridinethiolate-Linked Iron Fe4S4-Fe Complex Systems, J. Am. Chem. Soc., 113, p. 9529 (1991).
[4] Amirnasr M., Vafazadeh R., Mahmoudkhani A.H., Synthesis, Structure, and Electrochemistry of Cobalt(III) Complexes with Bis(Benzoylacetone) Ethylenediimine Schiff Base, Can. J. Chem.,. 80, p. 1196 (2002).
[5] Rybak-Akimova E.V., Otto W., Deardorf P., Roenser R., Busch D.H., Kinetics and Equilibria of Dioxygen Binding to a Vacant Site in Cobalt(II) Complexes with Pentadentate Ligands, Inorg. Chem., 36, p. 2746 (1997).
[6] Alcock N.W., Busch D.H., Iron and Cobalt "Lacunar" Complexes as Dioxygen Carriers, Chem. Rev., 94,
p. 585 (1994).
[7] Glusker J.P., Wagner T., Afshar C.E., Carrel H.L., Englert U., Hogenkamp H.P.C., ifluoromethylcobalamin: Structural Aspects of an Old Tree with a New Branch, Inorg. Chem., 38, p. 1785, 1999.
[9] Marzilli L.G., Cini R., Moore S.J., Difluoromethylcobalamin: Structural Aspects of an Old Tree with a New Branch, Inorg. Chem.,. 37, p. 6890 (1998).
[11] Huilan C., Deyan H., Hong Y., Wenxia T., Chen J., Zheng P., Chen C., Synthesis and Crystal Structure of Organocobalt(III) Complexes with Secondary Alkyls or Bulky Schiff Base Equatorial Ligands, Inorg. Chem., 35, p. 1502 (1996).
[12] Pratt J.M.,The B12-dependent Isomerase Enzymes; How the Protein Controls the Active Site,,Chem. Soc. Rev., 14, p. 161 (1985).
[13] Randaccio L., Pahor N.B., Zangrando E., Structural Properties of Organocobalt Coenzyme B12 ModelsChem. Soc. Rev., 18, p. 225 (1989).
[14] Amirnasr M., Vafazadeh R., Trans Ligand Influence in Cobalt(III) Schiff Base Complexes: Electronic and Steric Effects on the Kinetics of Hydrolysis,Int. J. Chem. Kinet., 34, p. 387 (2002).
[16] Marzilli L.G., Summers M.F., Zangrando E., Pahor N.B., Randaccio L., Unusually Detailed Insight into the Dynamic Behavior of Coordinated Ambidentate Ligands. Factors Influencing the Binding Bode of 2-Aminopyridines in B12 Bodels, J. Am. Chem. Soc., 108, p. 4830 (1986).
[17] McCarthy P.J. et al, J. Am. Chem. Soc., 80, p. 1100 (1958).
[18] Cotton F.A., Wilkinson G., Murillo C.A., Bachmann M., “Advanced Inorganic Chemistry” 6th Edition, John Wiley and Sons, pp. 830-833 (1999).
[19] Wilkins R.G., “Kinetics and Mechanism of Reactions of Transition Metal Complexes” 2nd Revised Edition, VCH, p. 156 (1991).
[20] Miessler G.L., “Inorganic chemistry”Third edition, Perntice Hall, pp. 412-426 (1983).