Magnetic parameters (g-factors, hyperfine coupling constants a(25Mg) and a(31P)) of paramagnetic pyrophosphate and hydrate magnesium complexes, which model those in catalytic site of the ATP synthesizing enzymes, are calculated. Both g-factors and HFС constants a(31P) of the paramagnetic pyrophosphate magnesium complexes are identical to those of the pyrophosphate radical. It demonstrates that namely terminal PO3 group of the liganded ADP in the complex Mg2+(ADP)3− donates electron to the ion in the primary reaction of the ion-radical mechanism of enzymatic ATP synthesis.