Thermochemistry of adducts of some bivalent transition metal bromides with pyridine

The compounds [MBr2(py)2] (where M is Mn(II), Co(II), Ni(II), Cu(II) or Zn(II); py = pyridine) were synthesized and characterized by melting points, elemental analysis, thermal analysis and electronic and IR spectroscopy. The enthalpies of dissolution of the adducts, metal(II) bromides and pyridine in 25% (v/v) 1.2 M aqueous HCl 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 reactions (ΔrHθ), the standard enthalpies of formation (ΔfHθ), the standard enthalpies of decomposition (ΔDHθ), the lattice standard enthalpies (ΔMHθ) and the standard enthalpies of the Lewis acid/base reactions in the gaseous phase (ΔrHθ(g)). The mean bond dissociation enthalpies of the M(II)-nitrogen bonds have been estimated as well as the enthalpies of the adducts formation in the gaseous phase.