Aminoethyl pendant arms

L14 incorporates a further aminoethyl pendant arm as a potential donor group, but its Cu11 complex displays a somewhat lower stability than with L11, but at the same time, a much higher tendency to form a monoprotonated [Cu(HL14)]3+ complex (Table 1). This behaviour can be ascribed to the presence in [Cu(L14)]2+ of an uncoordinated aminoethyl pendant arm which can be readily protonated in aqueous solution. 

Fig. 2. pH- and redox-controlled relocation of the aminoethyl pendant arm in the nickel complex of 2. The pendant arm can be sequentially bound to and detached from the metal center, by varying the pH and the oxidation state of the metal center (whether +2 or +3)... 

The protonation constants of the ligands L9, L11, L14, and L1S (Scheme 5), having one, two or three aminoethyl or three aminopropyl pendant arms, respectively, on the [9]aneN3 framework, and the thermodynamic stabilities of their mononuclear complexes with Cu11 and Zn11 have been investigated by potentiometric measurements in aqueous solutions (Table 1) [51],... 

---