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 lum...