A novel fabrication of [Fe(HB(pz)3)2]@MIL-101 hybrid material via diffusion and the lower temperature shift on its spin transition behavior

Abstract

[Fe(HB(pz)3)2], a well-studied spin-crossover (SCO) complex, has been entrapped in NH2-MIL-101(Al) metal–organic framework (MOF) via gas diffusion method. [Fe(HB(pz)3)2] would sublimate when temperature exceeds 100 °C, especially at low pressure. Thus, in the selected condition, [Fe(HB(pz)3)2] molecules can be sublimated to a gas phase and diffused into the pores of NH2-MIL-101(Al), which yield [Fe(HB(pz)3)2]@MIL-101 hybrid materials. The identity of composites, with a loading of iron complex at ~ 8 wt%, was characterized by X-ray diffraction and spectroscopic attestation. The hybrid materials demonstrate a gentle spin transition curve from 300 to 400 K, which is different from the SCO behavior of [Fe(HB(pz)3)2]. And for the pure [Fe(HB(pz)3)2] sample at 400 K, only 60% of Fe(II) is in HS, while in hybrid samples, HS state is complete. This interesting phenomenon might indicate that the spin transition in the hybrid sample can be triggered at lower temperature. The composite samples were thoroughly studied by X-ray diffraction, IR spectroscopy, atom absorption spectroscopy, nitrogen physisorption, and magnetic measurements. Thereby, a novel MOF-based material with isolated SCO units is proposed, which demonstrate a salient ‘matrix-effect’ on spin-crossover behavior of [Fe(HB(pz)3)2].