Metal Complexes with Macrocyclic Ligands. Part XLI. Nickel(II) and copper(II) complexes with mono-N-functionalized dithiadiazamacrocycles |
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Authors: | Esther Hrmann Pascale C Riesen Markus Neuburger Margareta Zehnder Thomas A Kaden |
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Institution: | Esther Hörmann,Pascale C. Riesen,Markus Neuburger,Margareta Zehnder,Thomas A. Kaden |
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Abstract: | Three N2S2 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 10-methyl-1,4-dithia-7,10-diazacyclododecane-7-ethanamine ( 3 ) and 11-methyl-1,4-dithia-8,11-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 Ni2+) 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 pKa values for the equilibrium ML] + H+?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 ( 10 ), whereas it stabilizes Cu+ for the 12-membered macrocycle ( 3 ). |
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