The reaction and structure of the complexes of alkaline earth metals (Ca, Sr, Ba) with 2-(4'-chloro-2'-phosphonazo)-7-(2',6'-dibromo-4'-chlorophenylazo) 1,8-dihydroxy-3, 6-naphthalene disulfonic acid (Chlorophosphonazo-DBC) were studied. This ligand has eight forms under different acidity. The protonation reactions take place at [H+] > 0.36 mol/dm3. The ligand begins dissocns. at pH > 0.5. Two protons are released in the complexes formation reactions (M2+ + 2HI t ML2 + 2H+). The stability constants of the complexes of Ca, Sr, and Ba were determine by Yoe-Jone method, Majumder-Chakrabertty method and calculation method. The order of the stability of complexes is as follows: Sr > Ba > Ca. The structure of the complexes was also studied by IR spectroscopy, Laser Raman spectroscopy, NMR, and EPR. The results show that these groups of N=N, PO3H2 and OH are active groups in the complex reactions. The structure of the complexes of Sr, Ba, and Ca with chlorophosphonazo-DBC are represented and the reaction and the complex bonds are discussed.

Key words: REACTION MECHANISM, INFRARED SPECTROPHOTOMETRY, NMR SPECTROMETRY, STABILITY CONSTANT, STERIC EFFECT, MOLECULAR ORBITAL THEORY, CALCIUM COMPLEX, BONDING, CHLOROPHOSPHONAZO, FOURIER TRANSFORM