Thermodynamics of formation of magnesium, calcium, strontium and barium complexes with 2,2'-bipyridyl and 1,10-phenanthroline, at different ionic strengths in aqueous solution.

The formation constants for the complexes of Mg(2+), Ca(2+), Sr(2+) and Ba(2+) with 2,2'-bipyridyl and 1,10-phenanthroline have been determined from pH measurements in aqueous solution, at 10, 25 and 40 degrees and various ionic strengths in the range 0.05-0.95M. The species [MtL)](2+) was found in all systems. The dependence on ionic strength was calculated for all the stability constants, and DeltaH degrees values have been calculated from the temperature dependence of the stability constants. The formation constants are in the order MgL(2+) > CaL(2+) > SrL(2+) > BaL(2+) and M-10, 10-phenanthroline > M-2,2'-bipyridyl.