High-Temperature Spin Crossover in Two Solvent-Free Coordination Polymers with Unusual High Thermal Stability

Two solvent-free two-dimensional (2D) coordination polymers, ²_∞[Fe­(ptim)₂] (<b>1</b>) and ²_∞[Fe­(ptpy)₂] (<b>2</b>) (Hptim = 2-(5-(4-(1<i>H</i>-imidazol-1-yl)­phenyl)-4<i>H</i>-1,2,4-triazol-3-yl)­pyridine; Hptpy = 2-(5-(4-(pyridin-3-yl)­phenyl)-4<i>H</i>-1,2,4-triazol-3-yl)­pyridine), have been successfully prepared by solvothermal reactions. Their iron atoms are bridged by the corresponding multidentate anionic ligands into dense neutral structures. The magnetic data reveal that complexes <b>1</b> and <b>2</b> are rare examples exhibiting reversible one-step high-temperature spin crossover behaviors with spin transition temperatures of 419 and 416 K, respectively. Moreover, these structures also display remarkable thermal stability up to 714 K (for <b>1</b>) and 690 K (for <b>2</b>), which are confirmed by thermogravimetric and variable-temperature powder X-ray diffraction analyses