Beryllium-chrome-azurol-S complexes
Complex formation between the aquated beryllium cation and the tetrabasic dyestuff chrome-azurol-S (H4CAS) has been studied by spectrophotometric, potentiometric, electrophoretic, and ion-exchange techniques. At least two complexes are shown to exist within the pH range 3-6. The major species is the anionic complex BeHCAS- for which log β11, = 4.66 � 0.08 at 25� and at ionic strength 0.lM (NaClO4) Coordination of beryllium is considered to occur at the quinonoid-,). carboxylato site in the HCAS8- ligand. The stability constant for the dinuclear species Be2CASO is shown to be log β21 = 15.8 � 0.1 under the same medium conditions. The dinuclear complex interferes with spectrophotometric measurements at beryllium concentrations exceeding 2.5 x 10-4. The acidity constants of H4CAS were determined at 25� and at an ionic strength 0.IM (NaClO,) as pK2a = 2.25 � 0.10,pK3a, = 4.88 � 0.05, pK4, = 11.75 � 0.05, whilst pK1a = -1.2 � 0.4.