Metal Complexes with Macrocyclic Ligands. Part XLI. Nickel(II) and copper(II) complexes with mono-N-functionalized dithiadiazamacrocycles

✍ Scribed by Esther Hörmann; Pascale C. Riesen; Markus Neuburger; Margareta Zehnder; Thomas A. Kaden

• Publisher: John Wiley and Sons
• Year: 1996
• Tongue: German
• Weight: 543 KB
• Volume: 79
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.19960790124

✦ Synopsis

Three N,S2 macrocycles (3,10,12) carrying an amino group as a pendant arm have been synthesized and their complexation properties towards Ni2+ and Cu2+ studied. The crystal structures of the Cu2+ complexes with lO-methyl-l,4-dithia-7,lO-diazacyclododecane-7-ethanamine (3) and 1 1-methyl-1,4-dithia-8,1l-diazacyclotetradecane-8-ethanamine (10) show that, in both cases, the Cu2+ is pentacoordinated by the four donor atoms of the macrocycle and the amino group of the side chain. In aqueous solution, however, two forms of the complexes with stoichiometries [MLH] and [ML] (M = Cu2+ or NiZ+) have been observed. In [MLH], the amino group is protonated and does not bind to the metal ion, whereas in [ML] the amino group is bound, and a pentacoordinated geometry results. The pK, values for the equilibrium [ML] + H+c[MLH]+ decrease in the order 12 > 10 > 3, indicating that the 2-aminoethyl side chain binds better to the Cu2+ than the 3-aminopropyl side chain. Cyclic voltammetry for the Cu2+/Cu+ pair shows that the 2-aminoethyl pendant arm stabilizes the Cu2+ oxidation state, when the metal ion is in the 14-membered ring (lo), whereas it stabilizes Cu' for the 12-membered macrocycle (3).