Thermochimica Acta 438 (2005) 90–94 Adducts of antimony triiodide and 2-aminomethylpyridines: Synthesis, characterization and thermochemistry Adeilton Pereira dos Santos, Maria Gardˆ ennia da Fonseca ∗ , Jos´ e Geraldo de Paiva Esp´ ınola, Severino Francisco de Oliveira, L.N.H. Arakaki Departamento de Quimica, Centro de Ciencias Exatas e da Natureza, Universidade Federal da Para´ ıba, Campus I, 58059-900 Jo˜ ao Pessoa, PB, Brazil Received 3 April 2005; received in revised form 21 July 2005; accepted 3 August 2005 Available online 29 September 2005 Abstract Solid adducts of formula SbI 3 ·L [L = 2-amino-3-methylpyridine (2A3P), 2-amino-4-methylpyridine (2A4P), 2-amino-5-methylpyridine (2A5P), 2-amino-6-methylpyridine (2A6P)] were synthesized and characterized by elemental analysis, IR spectroscopy, thermogravimetry and DSC. Thermochemical parameters of the adducts were determined through solution-reaction calorimetry. The ratio metal–ligand was 1:1 for all adducts based on elemental analysis. Infrared results showed that the ligands coordinate to antimony through the nitrogen atom of the aromatic ring. Thermal degradation of adducts starts at 112, 122, 188, and 137 ◦ C for SbI 3 2AxP (where x = 3, 4, 5 and 6, respectively). Decomposition temperatures correlate with metal–ligand bond strength. The enthalpy of reaction: SbI 3 (c) + nL(c,l) = SbI 3 ·nL (solid)  r H ◦ m (solid) is -97.45, -56.43, -73.56 and -81.45 kJ mol -1 , respectively, for 2A3P, 2A4P, 2A5P and 2A6P adducts. The standard enthalpies of decomposition, as well as the lattice enthalpies and the enthalpies of the Lewis acid–base reaction in the gas phase were calculated through thermochemical cycles. The standard mean antimony-nitrogen bond enthalpies in SbI 3 ·2A3P, SbI 3 ·2A4P, SbI 3 ·2A5P, and SbI 3 ·2A6P were estimated as 175, 135, 154, and 164 kJ mol -1 , respectively. © 2005 Elsevier B.V. All rights reserved. Keywords: Adducts; Aminopyridines; Thermochemistry; Antimony 1. Introduction Several studies report on complexes of pyridine and its derivatives with transition metals [1–12], but no informa- tion about the synthesis and characterization of antimony complexes with 2-aminopyridine is available in the litera- ture. Antimony is an element with biological and pharma- cological importance [13,14], and the bases derived from 2-aminopyridine are used in pharmacology and medicines [15,16]. The aim of this investigation is to contribute to the coordination chemistry of p blocks elements with bases derived from amino methyl pyridines. This paper reports the synthesis and characterization of adducts of general formula SbI 3 ·L where L is 2-amino- 3-methyl-, 2-amino-4-methyl, 2-amino-5-methyl- and 2- ∗ Corresponding author. Tel.: +55 832167591; fax: +55 832167437. E-mail address: mgardennia@quimica.ufpb.br (M.G. da Fonseca). amino-6-methyl pyridine. Attention is focused on determi- nation of thermochemical parameters by solution-reaction calorimetry. This investigation explored the formation of adducts between antimony (III) iodide and heterocyclic bases to evaluate the enthalpies involved. The coordinated bond dis- sociation enthalpies are correlated with other thermochem- ical parameters. The inductive effect on the energy of the antimony–nitrogen bond due to the substitution of hydrogen atoms in the pyridine ring by the electron donor methyl and amino groups is considered. 2. Experimental The solvents used in all preparations were distilled and stored over Linde 4A molecular sieves. All 2- aminomethylpyridines (Aldrich) were used without further purification. The antimony trichloride (Merck) was dried 0040-6031/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.tca.2005.08.006