The preparation and standardisation of perchloric acid and sodium perchlorate were as described in ref. 3. Lead@) perchlorate solution was prepared and analysed as in ref. 4 and water purified as in ref. 5. Methods.-The potentiometric approach was as described in ref. 6, studies being carried out at 10, 25, and 40 "C, I = 3.00 mol dm-3 Na[ClO,]. Concentration formation constants were refined from the titration data using the SCOGS 7 and MINIQUAD computer programs. The calorimetry was as described in ref. 3. For all ligands studied, protonation constants a t 25 "C have already been r e p ~r t e d . ~. 93 lo Heats of protonation of the * Defined in the footnote t oTable 2.
the formation constants for the glycylglycinate and glycylglycylglycinate complexes suggests that the atoms 23 ' Hard and Soft Acids and Bases,' ed. R. G.
Die Bildungskonstanten von Komplexen des Cd, Pb und Zn mit EDTA, 1,2‐Bis‐[2‐aminoäthoxy]‐äthantetraessigsäure, Glutathion, Cystein und D‐Penicillamin wurden bei 25°C bestimmt.
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