Bivariate Metal–Organic Frameworks with Tunable Spin‐Crossover Properties.

Gong, Yu; Li, Zhi‐Hua; Yan, Xiaodong; Wang, Ya‐Qin; Zhao, Chen‐Yang; Han, Wang‐Kang; Hu, Qing‐Tao; Lu, Hui‐Shu; Gu, Zhi‐Guo

In this work, pyrazine (A), aminopyrazine (B), quinoxaline (C), and 5,6,7,8‐tetrahydroquinoxaline (D) have been screened out among a large number of pyrazine derivatives to construct Hofmann‐type metal–organic frameworks (MOFs) Fe(L)[M(CN)4] (M=Pt, Pd) with similar 3D pillared‐layer structures. X‐ray single‐crystal diffraction reveals that the alternate linkage between M and FeII ions through cyano bridges forms the 2D extended metal cyanide sheets, and ligands A–D acted as vertical columns to connect the 2D sheets to give 3D pillared‐layer structures. Subsequently, a series of bivariate MOFs were constructed by pairwise combination of the four ligands A–D, which were confirmed by 1H NMR, PXRD, FTIR, and Raman spectroscopy. The results demonstrated that ligand size and crystallization rate play a dominant role in constructing bivariate Hofmann‐type MOFs. More importantly, the spin‐crossover (SCO) properties of the bivariate MOFs can be finely tuned by adjusting the proportion of the two pillared ligands in the 3D Hofmann‐type structures. Remarkably, the spin transition temperatures, Tc↑ and Tc↓ of Fe(A)x(B)1−x[Pt(CN)4] (x=0 to 1) can be adjusted from 239 to 254 K and from 248 to 284 K, respectively. Meanwhile, the width of the hysteresis loops can be widened from 9 to 30 K. Changing Pt to Pd, the hysteresis loops of Fe(A)x(B)1−x[Pd(CN)4] can be tuned from 9 (Tc↑=215 K, Tc↓=206 K) to 24 K (Tc↑=300 K, Tc↓=276 K). This research provides wider implications in the development of advanced bistable materials, especially in precisely regulating SCO properties.

METAL-organic frameworks; METAL cyanides; HYSTERESIS loop; SPIN crossover; RAMAN spectroscopy; CYANIDES; COORDINATION polymers; TRANSITION metals

Chemistry - A European Journal, 2020, Vol 26, Issue 54, p12472

0947-6539

Academic Journal

10.1002/chem.202002544