Thermochemistry of adducts of manganese(II) and copper(II) pentane-2,4-dionate with heterocyclic amines

The compounds [M(pd)2(L)] (where M is manganese(II) or copper(II); pd is pentane-2,4-dionate; and L is piperazine (pipz), 4-cyanopyridine (4-cyanopy), quinoline (quin) or 2,2′-bipyridine (bipy)) were synthesized and characterized by elemental analysis, melting points, thermal studies and electronic and IR spectroscopy. The enthalpies of dissolution of adducts, metal pentane-2,4-dionate and ligands in a 1:3 (v/v) mixture of aqueous HCl 1.2 M and 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 reaction (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 reaction in the gaseous phase (ΔrHθ(g)). The mean standard bond dissociation enthalpies of the manganese–nitrogen and copper–nitrogen bonds have been determined.