Thermochemistry of adducts of tin(IV) chloride with heterocyclic bases

The compounds [SnCl4(L)n] (where L is pyridine (py), 4-methylpyridine (γ-pico), 3-methylpyridine (β-pico), piperidine (pipd), morpholine (morph), piperazine (pipz), 3-cyanopyridine (3-cyanopy), 4-cyanopyridine (4-cyanopy), quinoline (quin) or 2,2′-bipyridine (bipy) and n=2, 1 or 3/2) were synthesized and characterized by elemental analysis, melting points, thermal studies and IR spectroscopy. The enthalpies of dissolution of adducts, tin(IV) chloride and ligands in 1,2-dichloroethane or 25% (v/v) aqueous HCl 1.2 M in methanol were measured and, by using thermochemical cycles, the following thermochemical parameters for the adducts have been determined: the standard enthalpies for the Lewis acid/base reaction (ΔrH°), the standard enthalpies of formation (ΔfH°), the standard enthalpies of decomposition (ΔDH°), the lattice standard enthalpies (ΔMH°) and the standard enthalpies for the Lewis acid/base reaction in the gaseous phase (ΔrH°). The mean standard enthalpies of the tin–nitrogen bonds (D̄(Sn–N)) have been estimated. Based on these last values, the basicity orders: pipd>morph>γ-pico=β-pico>py>4-cyanopy>3-cyanopy and pipz>quin are obtained.