Synthesis, Structure, Luminescence, and Water Induced Reversible Crystal-to-Amorphous Transformation Properties of Lanthanide(III) Benzene-1,4-dioxylacetates with a Three-Dimensional Framework

Abstract

Three crystalline lanthanide(III) coordination polymers and their high quality single crystals with empirical formula [M 2 (BDOA) 3 (H 2 O) 4 ]·6H 2 O [M = Tb ( 1 ), Gd ( 2 ), and Sm ( 3 ); BDOA = benzene-1,4-dioxylacetate] were obtained via the agar gel diffusion method. Their compositions and structures were determined and analyzed in detail by infrared spectroscopy, elemental analysis, and the single-crystal X-ray diffraction method. The ligand has two crystallographically independent coordination modes, L a and L b (L denotes BDOA); the metal centers are connected with L a to form a double helix; these act as secondary building units (SBUs), which are linked by L b resulting in a plane topology geometry with 54-membered macrorings; and each metal ion is saturated by water molecules to form a nine-coordinated sphere. These planes are further constructed into three-dimensional networks by a complicated H-bond system with an inversion center among the water molecules (coordinated and guest), the carboxylate group, and the phenolic O atoms. Investigations of their luminescent properties demonstrate that compound 1 has characteristic emissions of Tb(III) corresponding to electronic transitions from the excited state 5 D 4 to the multiplets 7 F 6, 7 F 5, 7 F 4, and 7 F 3, respectively; however, 2 and 3 have no detectable luminescence under the same conditions. Thermal decomposition and powder X-ray diffraction results indicate that the transformation from the crystal form, [M 2 (BDOA) 3 (H 2 O) 4 ]·6H 2 O, to the amorphous powder, M 2 (BDOA) 3 (H 2 O) 2, is reversible, indicating that the amorphous form, M 2 (BDOA) 3 (H 2 O) 2, may be utilized as an absorbing agent for water and water vapor.