Syntheses, crystal structures and properties of lanthanide complexes featuring infinite molecular rectangle strands constructed from a new macrocyclic metalloligand

Three new double-chain coordination polymers {[Pr(NiL1)2(H2O)3](ClO4)3·2H2O}∞ (1), {[Sm(NiL1)2(H2O)3](ClO4)3·2H2O}∞ (2) and {[Gd(NiL1)2(H2O)3](ClO4)3·2H2O}∞ (3) were prepared and structurally characterized by X-ray single-crystal analyses. L1 denotes the doubly deprotonated form of 2-hydroxyethoxyethyl 5,6,7,8,15,16-hexahydro-6,7-dioxodibenzo[1,4,8,11]tetraazabicyclo[12.4.015,16]-13,18-dicarboxylate. The new mononuclear macrocyclic complex NiL1 acts as the bridging ligand with a monodentate coordination top (one of the alcohol hydroxyls) and a bidentate one (the oxamido carbonyls) between two Ln(III) (Ln = Pr, Sm and Gd in 1, 2 and 3, respectively) nodes to enclose the rectangular Ln2(NiL1)2 subunits. Most of the corresponding metal-to-metal distances in the subunits of the three compounds decrease following the variation trend identical to that of the ionic radii of Pr(III), Sm(III) and Gd(III). The studies with plasmid DNA showed that 1, 2 and 3 induced DNA cleavage. Luminescence investigation displayed that no emission occurred for the three coordination polymers in DMF at room temperature.