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

The compounds [SnCl4(L)(n)] (where L is pyridine (py), 4-methylpyridine (gamma-pico), 3-methylpyridine (beta-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 (Delta(r)Hdegrees), the standard enthalpies of formation (Delta(f)Hdegrees), the standard enthalpies of decomposition (Delta(r)Hdegrees), the lattice standard enthalpies (Delta(M)Hdegrees) and the standard enthalpies for the Lewis acid/base reaction in the gaseous phase (Delta(r)Hdegrees). The mean standard enthalpies of the tin-nitrogen bonds ((D) over bar ((Sn-N))) have been estimated. Based on these last values, the basicity orders: pipd > morph > gamma-pico = beta-pico > py > 4-cyanopy > 3-cyanopy and pipz > quin are obtained. (C) 2002 Elsevier Science B.V. All rights reserved.