Thermochemistry of piperidine adducts of some bivalent transition metal bromides

The adducts [MBr₂(pipd) _n ] (where M = Mn(II), Fe(II), Co(II), Ni(II), Cu(II), or Zn(II); pipd = piperidine; n = 1/2, 1, or 3/4) were synthesized and characterized by melting points, elemental analysis, thermal studies, and IR and electronic spectroscopy. From calorimetric studies in solution, the standard enthalpies of formation and several other thermochemical parameters of them were determined. The mean standard enthalpies of the metal–nitrogen bonds were calculated, as well as the enthalpies of the adduct formation in the gaseous phase. Using the values obtained for the enthalpies of reaction, the acidity order of the salts is obtained: FeBr₂ > MnBr₂ and CoBr₂ > NiBr₂. Comparing with pyridine adducts, the ligand piperidine is more basic than the ligand pyridine: pipd > py.