Dear Phuntsong;

The formation of the complex compound EDTA with ion is accompanied by a decrease in the Gibbs energy of the reaction. Solvent (water) affected by this value. Say "hydration stabilizes the complex." Without water will not complex of iron with hemoglobin.

Mrs/Miss Dolkar,

The high probability to find closely disposed suitable for coordination donation centre

we can tell simply as forming coordination bonds and its greater stability attributed with chelation or crab like bond formation.