Synthesis, characterization, and thermodynamic studies of cobalt Schiﬀ base complexes with amines Mozaﬀar Asadi a, * , Ali Hossein Kianfar b , Susan Torabi a , Khosro Mohammadi c a Chemistry Department, College of Sciences, Shiraz University, Shiraz 71454, Islamic Republic of Iran b Chemistry Department, College of Sciences, Yasouj University, Yasouj, Islamic Republic of Iran c Chemistry Department, Faculty of Sciences, Persian Gulf University, Bushehr 75169, Islamic Republic of Iran Received 3 March 2007; received in revised form 4 August 2007; accepted 14 August 2007 Available online 24 August 2007 Abstract The [N,N 0 -bis(Salicyliden)-2,3-diaminopyridine]tributylphosphinecobalt(III) perchlorate monohydrate, [Co(Salpyr)(PBu 3 )]ClO 4 Æ H 2 O, was synthesized and characterized. For the new ﬁve coordinate complex and some others, such as [N,N 0 -bis(Salicyliden)-1,2-pheny- lenediamine]tributylphosphinecobalt(III) perchlorate monohydrate, [Co(Saloph)(PBu 3 )]ClO 4 Æ H 2 O, [N,N 0 -bis(4-methylSalicyliden)-1, 2-phenylenediamine]tributylphosphine cobalt(III) perchlorate monohydrate, [Co(4-MeSaloph)(PBu 3 )]ClO 4 Æ H 2 O, [N,N 0 -bis(4-nitroSali- cyliden)-1,2-phenylenediamine]tributylphosphinecobalt(III) perchlorate monohydrate, [Co(4-NO 2 Saloph)(PBu 3 )]ClO 4 Æ H 2 O, and [N, N 0 -bis(Salicyliden)-1,2-phenylenediamine]dimethylphenylphosphinecobalt(III) perchlorate monohydrate, [Co(Saloph)(PMe 2 Ph)]ClO 4 Æ H 2 O, the formation constants and the thermodynamic parameters of the interaction of Co(III) Schiﬀ bases with amines were measured spectrophotometrically. Furthermore, the formation constant of these 1:1 adducts in 96% ethanol solvent and in constants ionic strength (I = 0.1 M NaClO 4 ) and at diﬀerent temperatures were determined using the Ketelaar equation. Also the adduct formation of [Co(Sal- oph)(PBu 3 )]ClO 4 Æ H 2 O, with Imidazol, 2-MeImidazol, 4-MeImidazol, 2-EtImidazol, and BzImidazol in 96% ethanol was studied. The formation constants and the thermodynamic parameters for [Co(Salpyr)(PBu 3 )]ClO 4 Æ H 2 O as an acceptor with some aliphatic amines, such as n-butylamine, sec-butylamine, tert-butylamine, benzylamine, and diethylamine as donors were determined in DMA. The com- parison of formation constants and the thermodynamic parameters show that the trend of formation constants of pentacoordinate cobalt(III) Schiﬀ base complexes toward a given donor at lower temperature of the range used (283 and 293) K is as follows: 4-MeSaloph > Saloph > 4-NO 2 Saloph > Salpyr: Also the following binding trend of the donors toward a given cobalt(III) Schiﬀ base complex is in sequence: Im > 4-MeIm > 2- MeIm > 2-EtIm > BzIm and for aliphatic amines is as follows: Benzylamine > sec-butylamine  n-butylamine > tert-butylamine > dieth- ylamine. The formation constants for a given donor change according to the following trend for phosphine axial ligands: PBu 3 < PMe 2 Ph. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Cobalt; Schiﬀ base; Thermodynamic parameter; Amine; Formation constants 1. Introduction Many cobalt derivatives have been prepared and inves- tigated, with particular emphasis on the reactivity of the metal ions in the transmethylation reactions and the revers- ible absorption of molecular oxygen [1–5]. The cobalt com- plexes with tetradentate Schiﬀ base ligands have been extensively used to mimic cobalamin (B 12 ) coenzymes [6– 9], oxygen carriers and oxygen activators [10–13], and enantioselective reduction [14]. Cobalt(III) Schiﬀ base complexes with two amines in axial positions have also been used as antimicrobial agents [15]. The synthesis and 0021-9614/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jct.2007.08.003 * Corresponding author. Tel.: +98 711 228 4822; fax: +98 711 228 6008. E-mail addresses: asadi@susc.ac.ir, mozaﬀarasadi@yahoo.com (M. Asadi). www.elsevier.com/locate/jct Available online at www.sciencedirect.com J. Chem. Thermodynamics 40 (2008) 523–528