Breathing Europium-Terbium Co-doped Luminescent MOF as a Broad-Range Ratiometric Thermometer with a Contrasting Temperature-Intensity Relationship.

Solvothermal reactions of lanthanide salts and a semirigid tripodal H3tatab (4,4',4″-s-triazine-1,3,5-triyltri-p-aminobenzoic acid) ligand in mixed water and N-methyl pyrrolidone (NMP) generated novel breathing MOFs [Ln(tatab)]·solvent (Ln = Eu in 1-Eu, Tb in 1-Tb, Eu0.015Tb0.985 in 1-Eu0.015Tb0.985). The framework of 1 was contracted upon removal of guests to form partly desolvated [Ln (tatab)]·3.7H2O·2.5NMP (1'). Single-crystal X-ray analyses demonstrated that 1 has the breathing ability to spontaneously release guests and maintain the same topology. In contrast to as-synthesized 1, the cell volume of 1' decreased markedly upon removal of the guests. Different from linear dicarboxylates, the semirigid tripodal tatab ligand is bridged to an inorganic Ln-O chain, limiting the rotation around the O-O-axis of carboxylate. The breathing mechanism is based on the flexible C-N-C angles of amide bonds in the tatab ligand, causing a change in the solvent-accessible volume in the framework. Interestingly, the luminescence color of breathing co-doped lanthanide MOF 1'-Eu0.015Tb0.985 is blue-shifted and turned from orange to green with an increase in temperature, which can be attributed to a change in the relative intensity of Tb and Eu emissions, and is quite different from that observed for the reported related compounds. The breathing co-doped lanthanide MOF 1'-Eu0.015Tb0.985 can be applied as a high-sensitivity ratiometric thermometer in a broad temperature from 90 to 300 K.