The compounds [MBr2(L)(2)] (where M is Mn(II), Fe(II), Co(II), Ni(II), Cu(II) or Zn(II); L = beta-picoline N-oxide (beta-picoNO)) 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 beta-picoNO in methanol or aqueous 1.2M HCl 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(r)Hdegrees), the standard enthalpies of formation (Delta(f)Hdegrees), the standard enthalpies of decomposition (Delta(D)Hdegrees), the lattice standard enthalpies (Delta(M)Hdegrees) and the standard enthalpies of the Lewis acid/base reactions in the gaseous phase (A(r)Hdegrees(g)). The mean bond dissociation enthalpies of the metal(II)-oxygen bonds ((D) over bar ((M-O))) have been estimated. (C) 2004 Elsevier B.V. All rights reserved.