Thermochemistry of adducts of some transition metals(II) bromides with pyridine N-oxide

The compounds [MBr2(pyNO)n] (where M: Mn, Fe, Co, Ni, Cu or Zn; pyNO is pyridine N-oxide and n=2, 3 or 6) 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 pyNo 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)–oxygen bonds (D̄(MO)) have been estimated.