Theoretical study of the complexassion of bivalent ions: Mg2+, Zn2+, Cu2+ and Fe2+ by 4-hydroxy-3-(1-phenylpropyl)-2H-chromen-2-one(HPCO), 4-hydroxy-3-(3-oxo-1-phenylbutyl)-2H-chromen-2-one(HOCO) and 4-hydroy-6-(1-phenylbutan-2-yl)-3-(1-phenylpropyl)-2H-pyran-2-one(HPPO) in water and in ethanol