Adducts of antimony triiodide and 2-aminomethylpyridines: Synthesis, characterization and thermochemistry

Solid adducts of formula SbI3·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 SbI32AxP (where x = 3, 4, 5 and 6, respectively). Decomposition temperatures correlate with metal-ligand bond strength. The enthalpy of reaction: SbI3(c) + nL(c,l) = SbI3·nL (solid) ΔrHm°(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 SbI3·2A3P, SbI3·2A4P, SbI3·2A5P, and SbI3·2A6P were estimated as 175, 135, 154, and 164 kJ mol−1, respectively.