Formation equilibria of tin(II) orthophosphate complexes

The complexation equilibria of Sn2+ ion with orthophosphate ions have been studied, at 25 degreesC in 3 M NaClO4 ionic medium. by potentiometric titrations with Sn2+/Sn-Hg and glass electrodes. The concentrations of the metal and of the ligand ranged from 2.5 x 10(-4) to 2.5 x 10(-3) M and from 0.01 to 0.3 M, respectively. The hydrogen ion concentration varied between 0.1 and 10(-5.8) M. The potentiometric data are consistent with the formation of the complexes: SnH2PO4+, Sn(H2PO4)(2)(aq), SnH2PO4HPO4-, SnHPO4(aq), Sn(HPO4)(2)(2-), Sn(HPO4)(3)(4-) and SnPO4-. Stability constants for their formation in 3 M NaClO4 and in dilute solution are reported. (C) 2000 Elsevier Science B.V. All rights reserved.