Metal Complexes with a New N₄O₃ Amine Pendant-Armed Macrocyclic Ligand: Synthesis, Characterization, Crystal Structures, and Fluorescence Studies

The synthesis of a new oxaaza macrocyclic ligand, L, derived from O1,O7-bis(2-formylphenyl)-1,4,7-trioxaheptane and tren containing an amine terminal pendant arm, and its metal complexation with alkaline earth (M = Ca2+, Sr2+, Ba2+), transition (M = Co2+, Ni2+, Cu2+, Zn2+, Cd2+), post-transition (M = Pb2+), and Y3+ and lanthanide (M = La3+, Er3+) metal ions are reported. Crystal structures of [H2L](ClO4)2·3H2O, [PbL](ClO4)2, and [ZnLCl](ClO4)·H2O are also reported. In the [PbL] complex, the metal ion is located inside the macrocyclic cavity coordinated by all N4O3 donor atoms while, in the [ZnLCl] complex, the metal ion is encapsulated only by the nitrogen atoms present in the ligand. π−π interactions in the [H2L](ClO4)2·3H2O and [PbL](ClO4)2 structures are observed. Protonation and Zn2+, Cd2+, and Cu2+ complexation were studied by means of potentiometric, UV−vis, and fluorescent emission measurements. The 10-fold fluorescence emission increase observed in the pH range 7−9 in the presence of Zn2+ leads to L as a good sensor for this biological metal in water solution.