Luminescent Lanthanide Coordination Polymers

One-dimensional lanthanide coordination polymers with the formula Ln(isonicotinate)3(H2O)2 (Ln = Ce, Pr, Nd,
Sm, Eu, Tb; 1a−f) were synthesized by treating nitrate or perchlorate salts of Ln(III) with 4-pyridinecarboxaldehyde
under hydro(solvo)thermal conditions. Single-crystal and powder X-ray diffraction studies indicate that these
lanthanide coordination polymers adopt two different structures. While Ce(III), Pr(III), and Nd(III) complexes
adopt a chain structure with alternating Ln−(carboxylate)2−Ln and Ln−(carboxylate)4−Ln linkages, Sm(III),
Eu(III), and Tb(III) complexes have a doubly carboxylate-bridged infinite-chain structure with one chelating
carboxylate group on each metal center. In both structures, the lanthanide centers also bind to two water molecules
to yield an eight-coordinate, square antiprismatic geometry. The pyridine nitrogen atoms of the isonicotinate
groups do not coordinate to the metal centers in these lanthanide(III) complexes; instead, they direct the formation
of Ln(III) coordination polymers via hydrogen bonding with coordinated water molecules. Photoluminescence
measurements show that Tb(isonicotinate)3(H2O)2 is highly emissive at room temperature with a quantum yield
of ∼90%. These results indicate that highly luminescent lanthanide coordination polymers can be assembled
using a combination of coordination and hydrogen bonds. Crystal data for 1a:  monoclinic space group P21/c, a
= 9.712(2) Å, b = 19.833(4) Å, c = 11.616(2) Å, β = 111.89(3)°, Z = 4. Crystal data for 1f:  monoclinic space
group C2/c, a = 20.253(4) Å, b = 11.584(2) Å, c = 9.839(2) Å, β = 115.64(3)°, Z = 8.