Eu3+/Tb3+ and Dy3+ POM@MOFs and 2D coordination polymers based on pyridine-2,6-dicarboxylic acid for ratiometric optical temperature sensing†
LaPOM@MOFs doped with a low percentage of either mixed Eu3+/Tb3+ or Dy3+ as well as mixed Eu3+/Tb3+ and Dy3+ 2D coordination polymers were prepared using a hydrothermal synthesis, where pyridine-2,6-dicarboxylic acid was used as the organic linker, yielding four materials: Eu,TbPOM@MOF, DyPOM@MOF, Eu,Tb 2D sheets, and Dy 2D sheets. These materials were fully characterized employing single crystal XRD and powder XRD and were further evaluated as potential luminescence ratiometric optical temperature sensors. The POM@MOF materials were prepared employing La3+ mixed with a low percentage (10% according to the synthesis) of either mixed Eu3+/Tb3+ or Dy3+. Single crystals were collected after 3 days of reaction. When carrying out the same synthesis, but using 100% Eu3+/Tb3+ or 100% Dy3+ ions, compounds with a different structure (2D coordiation polymers) were acquired. These compounds took much longer to crystalize and single crystals suitable for measurements were collected only after 2 weeks. The pores of the 2D coordination polymers are much smaller than those of the metal organic frameworks (MOFs) obtained when employing La3+ (and small amounts of other Ln3+ ions), and therefore the SiMo12O40 polyoxometalates (POMs) could no longer build into the framework pores of the material. The luminescence ratiometric sensing properties of the two types of materials were evaluated in detail and compared. In both the Eu,TbPOM@MOF and Eu,Tb 2D sheets a significant change of emission color is observed with temperature change.