Study of complex formation in the manganese(II)/azide system

The complex formation between Mn(II) cations and N-3(-) anions was studied in aqueous medium at 25 degrees C and ionic strength 2.0 M (NaClO4). Data of average ligand number, (n) over bar (Bjerrum's function), were obtained from pH measurements on the Mn(II)/N-3(-)/HN3 system followed by integration to obtain Leden's function, F-0(L). Graphical treatment of data and a matrix solution of simultaneous equations have given the following overall formation constants of mononuclear stepwise complexes: beta(1) = 4.15 +/- 0.02 M(-1), beta(2) = 6.61 +/- 0.04 M(-2), beta(3) = 3.33 +/- 0.02 M(-3), beta(4) = 0.63 +/- 0.01 M(-4). A linear plot of log K-n vs. (n-1) shows no change in the configuration during complex formation. Slow spontaneous oxidation of solutions to Mn(III) occurs when the N-3(-) concentration is greater than 1.0 M.