The interaction of 2-amino-2-hydroxymethyl-1,3-propanediol with cobalt(II)and manganese(II) ions

The stepwise complex formation between 2-amino-2-hydroxymethyl-1,3-propaned iol (TRIS) with Co(II) and Mn(II) was studied by potentiometry at constant ionic strength 2.0 M (NaClO4) and T =(25.0 +/- 0.1)degrees C, from pH measu rements. Data of average ligand number (Bjerrum's function) were obtained f rom such measurements followed by integration to obtain Leden's function, F -0(L). Graphical treatment and matrix solution of simultaneous equations ha ve shown two overall stability constants of mononuclear stepwise complexes for the Mn(II)/TRIS system (beta(1) = (5.04 +/- 0.02)M-1 and beta(2) = (5.4 +/- 0.5) M-2) and three for the Co(IT)/TRIS system (beta(1) =(1.67 +/- 0.0 2) x 10(2) M-1, beta(2) =(7.01 +/- 0.05)x 10(3) M-2 and beta(3) = (2.4 +/- 0.4) x 10(4) M-3). Slow spontaneous oxidation of Co(II) solutions by dissol ved oxygen, accelerated by S(IV), occurs in a buffer solution TRIS/HTRIS+ 0 .010/0.030M, with a synergistic effect of Mn(II).