Hydrothermal synthesis and structural studies of novel 2-D lanthanide coordination polymers with phthalic acid

This paper presents four lanthanide coordination polymers, [Ln(2)(BDC)(3)(H2O)](n) (Ln = La, 1; Ln = Eu, 2; Ln = Tb, 3; BDC = 1,2-benzenedicarboxylate) and [Yb-4(BDC)(6)(H2O)(2)](n) (4) prepared by the hydrothermal technique. They are all 2-D infinite structures with BDC anions connecting adjacent metal ions. In complex 1, La(m) ions are eight- and nine-coordinated, and all La(m) ions are coplanar in the 2-D structure. In complexes 2 and 3, Eu(III) and Tb(III) ions are also eight- and nine-coordinated, but they are distributed in a wave-like 2-D network. In complex 4, the Yb(III) ions have four different coordination numbers (6, 7, 8 and 9), which are rarely found in one lanthanide complex. Both the coordination numbers and the arrangement of Ln atoms in these coordination polymers show the lanthanide contraction. In the four complexes, all the oxygen atoms of BDC take part in coordination with Ln(III) ions, adopting tetra-, penta- and hexadentate coordination modes for the phthalate anions. The luminescent properties of complex 2 have been investigated and the results for the explanation of the chemical environment of the Eu(III) ion are consistent with the X-ray analysis.