Synthesis, structure and photoluminescent studies of two novel layered uranium coordination polymers constructed from UO(OH) polyhedra and pyridinedicarboxylates

Two new uranium coordination polymers have been obtained from the hydrothermal reaction of (UO₂) (CH₃COO) ₂·2H₂O with 3,4-pyridinedicarboxylic acid (3,4-pydaH₂) or 2,4-pyridinedicarboxylic acid (2,4-pydaH ₂). [(UO₂)₃(μ₃-O) (μ₃-OH)₂-(3,4-pydaH)(3,4-pyda)_0.5] _n (1) crystallizes in the orthorhombic space group Pccn with a = 18.168(2), b = 12.635(1), c = 16.149(1) Å, V = 3707.0(5) ų, and Z = 8. [(UO₂)₃(μ₃- O)(μ₃-OH)(μ₂-OH)(2,4-pyda)(H₂O) ₂]_n·nH₂O (2) is in the orthorhombic space group Pbcn with a = 22.788(2), b = 7.1468(5), c = 21.627(1) Å, V = 3522.1(4) ų, and Z = 8. Complex 1 features a wave-like 2D layer that is constructed by connecting the 1D UO(OH) ribbons by the V-shaped 3,4-pyda or 3,4-pydaH ligands. Complex 2 is a rare hexameric species amongst uranium compounds and features a (4,4) planar "open-layer", which is constructed by the 4-connected hexameric UO(OH) polyhedra and the 2-connected 2,4-pyda ligands. The fluorescence emission (521 nm) of 2 is red-shifted by about 13 nm (emission) and about 40 nm (excitation) compared to that of 1, and the lifetimes increase with the polymerization of UO(OH) polyhedra (145 μs for 1 compared to 24.4 μs for 2).