Templated synthesis of copper(II) azacyclam complexes using urea as a locking fragment and their metal-enhanced binding tendencies towards anions.
Copper(II) azacyclam complexes 3(2+) and 4(2+) were obtained through a metal-templated procedure involving the pertinent open-chain tetramine, formaldehyde and a phenylurea derivative as a locking fragment. Both metal complexes can establish interactions with anions through the metal centre and the amide NH group. Equilibrium studies in DMSO by a spectrophotometric titration technique were carried out to assess the affinity of 3(2+) and 4(2+) towards anions. While the NH group of an amide model compound and the metal centre of the plain Cu(II)(azacyclam)(2+) complex do not interact at all with anions, 3(2+) and 4(2+) establish strong interactions with oxo anions, profiting from a pronounced cooperative effect. In particular, 1) they form stable 1:1 and 1:2 complexes with H(2)PO(4) (-) ions in a stepwise mode with both hydrogen-bonding and metal-ligand interactions, and 2) in the presence of CH(3)COO(-), they undergo deprotonation of the amido NH group and thus profit from axial coordination of the partially negatively charged carbonyl oxygen atom in a scorpionate binding mode.
Boiocchi
Massimo
M
Centro Grandi Strumenti, Università di Pavia via Bassi, 27100 Pavia, Italy.
Fabbrizzi
Luigi
L
Garolfi
Mauro
M
Licchelli
Maurizio
M
Mosca
Lorenzo
L
Zanini
Cristina
C