Lanthanide(III) coordination polymers from the exo-coordination of Na+: Syntheses, structures, luminescence, and decay dynamics

[Na2[Ln2(sal)4(CF3SO3)2(H2O)4](CF3SO3)2]n Ln = Nd (1) and Eu (2) were synthesized from the reaction of salicylaldehyde, lanthanide(III) triflates, and sodium hydroxide. The compounds are iso-structural and possess a 2-D supramolecular network built up from discrete dinuclear Ln(III) units [Ln2(sal)4(CF3SO3)2(H2O)4] via exo-coordination of Na(CF3SO3). The sal ligands display μ2-O coordination modes involving both the phenolic and carbonyl oxygen atoms while the triflates function as both μ2 and μ3 bridges. Each Ln(III) in the network is eight coordinate and in bicapped trigonal prism coordination geometry. Luminescence from [Na2[Eu2(sal)4(CF3SO3)2(H2O)4](CF3SO3)2]n showed temperature dependent sensitized emission with significant quadrupolar contribution and decay dynamical studies followed single exponential kinetics. Together these results indicate that in the presence of Na+ ions, sal, and triflate are useful ligands in the construction of Ln(III) coordination polymers with unusual luminescence and structures.