Photoluminescent and Magnetic Properties of a Series of Lanthanide Coordination Polymers with 1H-Tetrazolate-5-formic Acid

Reaction of lanthanide oxides and 1 H-tetrazolate-5-ethyl formate in water at 50 degrees C in the presence of pyridine afforded a series of lanthanide coordination polymers, {(Hpy)(2)[Pr-4(tzf)(7)(H2O)(11)]center dot 10H(2)O}(n) (1) and {[Ln(2)(tzf)(3)(H2O)(6)]center dot 4H(2)O}(n), where Ln = Sm (2), Eu (3), Gd (4), Tb (5), Dy (6), Hpy = protonated pyridine, and H(2)tzf = 1H-tetrazolate-5-formate acid. Polymer I features a three-dimensional (3-D) anion framework built up by cross-linkage of tetrameric [Pr-4(tzf)(4)](4+) units and tzf(2-) ligands, showing a six-connected primitive cubic (pcu) topology (4(12).6(3)). Isomorphous polymers 2-6 present a two-dimensional (2-D) neutral structure with a four-connected (4,4) topology. Four new coordination modes of the tzf(2-) ligand are first observed in tetrazolate-5-carboxylate complexes. The lanthanide contraction effect and coordination flexibility of tzf(2-) ligand play a key role in governing the formation of coordination polymers with different polymeric architectures. The photoluminescent analyses for 2, 3, 5, and 6 suggest that ligand-to-Ln(III) energy transfer is efficient, especially for Eu(III) and Tb(III) ions, and the tzf(2-) ligand may act as a good antenna molecule to sensitize Ln(III) emission. The variable-temperature magnetic study shows that magnetic interactions between the Ln(III) ions in 1-6 are mainly ascribed to the antiferromagnetic coupling as well as the depopulation of the Stark levels. The spin-orbit coupling parameters (lambda) for Sm(III) in 2 and Eu(III) in 3 are 259(2) and 344(1) cm(-1), respectively, based on the free-ion approximation.