1-Acetamido-propylidene-1, 1-diphosphonic acid (S-186) and 1-propionamido-ethylidene-1, 1-diphosphonic acid (S-106) were synthesized and their chelation with alkaline earth metal ions was studied by pH method at 30+/-0.1 C. The complexes MHL, ML, ML2 and M2L were formed in aqueous solutions, when the molar proportion of metal to ligand varied from 10:1 to 1:2. Their stability constants were determined and it was found that the complexes of S-186 were more stable than those of S-106 and that there was a close relationship between the stability of the complexes and basicity of the ligands. It was also noticed that their binuclear complexes with Sr(II) were more stable than those with other alkaline earth metal ions.

Key words: PHOSPHONIC ACID P, PHOSPHONIC ACID P, COMPLEX COMPOUNDS, NUMBERS, ETHYLIDENE, PROPANAMIDE P, ISOPROPYLIDENE, ALKALINE EARTH METAL COMPLEX, CHELATE EFFECT, ACETAMIDO GROUP