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 (Delta H-r(theta)), the standard enthalpies of formation (Delta H-r(theta)), the standard enthalpics of decomposition (Delta H-D(theta)), the lattice standard enthalpies (Delta H-M(theta)) and the standard enthalpies of the Lewis acid/base reactions in the gaseous phase (Delta H-r(theta)(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. (c) 2007 Elsevier B.V. All rights reserved.4561323