Inorg. Chem. 1980, 19, 3086-3092
3086
tration relative to the other species is low enough to make possible errors in data a serious problem.24 The suggestion of its presence, such as it may be, convinces us that the proposed technique is a valuable addition to other methods in equilibrium analysis.
4t ~~
I
0
4
5
6
7
8
PH Figure 6. Plot of the Sillen sum ( S ) and the residual sums with enH+ and enH?+ deleted (S? and with enH+, enH?’, Cu(en)2+,Cu(en);+, and CuJOH), (see text) deleted (S’?, for the “common point” set.
performing yet another level of residual analysis. The constants for the formation of Cu(en)2+ and Cu(en):+ determined in this study, along with the literature values16 for the copper(I1) hydrolysis constants, were used to further delete contributions to the Sillen sum. The S ” i n Table IIIB indicates of the metal ions participate in the formation that up to 100%~ of complexes other than Cu(en)2+and C ~ ( e n ) ~ * + Figure . 6 shows the three different Sillen sums S, S’, and S”. The nearest integral values of the p”,,,, c”~,and a’’h (Table IIIB) suggest the presence of the dimeric species [(en)Cu(OH)2Cu(en)]2+. We fail to see strong evidence for either C ~ ( e n ) ~ o Hor+ in the pH
