Cooperative Spin Crossover above Room Temperature in the Iron(II) Cyanoborohydride-Pyrazine Complex

Yurii S Bibik; Sergiu Shova; Aurelian Rotaru; Sergii I Shylin; Igor O Fritsky; Rostyslav D Lampeka; Il'ya A Gural'skiy

doi:10.1021/acs.inorgchem.2c02177

Cooperative Spin Crossover above Room Temperature in the Iron(II) Cyanoborohydride-Pyrazine Complex

Inorg Chem. 2022 Sep 19;61(37):14761-14769. doi: 10.1021/acs.inorgchem.2c02177. Epub 2022 Sep 6.

Authors

Yurii S Bibik¹, Sergiu Shova², Aurelian Rotaru³, Sergii I Shylin⁴, Igor O Fritsky¹, Rostyslav D Lampeka¹, Il'ya A Gural'skiy¹

Affiliations

¹ Department of Chemistry, Taras Shevchenko National University of Kyiv, 64 Volodymyrska St., 01601 Kyiv, Ukraine.
² "Petru Poni" Institute of Macromolecular Chemistry, Aleea Gr. Ghica Voda 41A, 700487 Iaşi, Romania.
³ Faculty of Electrical Engineering and Computer Science & MANSiD Research Center, Ştefan cel Mare University, Universitatii St. 13, 720229 Suceava, Romania.
⁴ Department of Chemistry - Ångström Laboratory, Uppsala University, Box 523, 75120 Uppsala, Sweden.

PMID: 36067517
DOI: 10.1021/acs.inorgchem.2c02177

Abstract

Hysteretic spin crossover in coordination complexes of 3d-metal ions represents one of the most spectacular phenomena of molecular bistability. In this paper we describe a self-assembly of pyrazine (pz) and Fe(BH₃CN)₂ that afforded the new 2D coordination polymer [Fe(pz)₂(BH₃CN)₂]_∞. It undergoes an abrupt, hysteretic spin crossover (SCO) with a T_1/2 of 338 K (heating) and 326 K (cooling) according to magnetic susceptibility measurements. Mössbauer spectroscopy revealed a complete transition between the low-spin (LS) and the high-spin (HS) states of the iron centers. This LS-to-HS transition induced an increase of the unit cell volume by 10.6%. Meanwhile, a modulation of multiple [C-H^δ+···H^δ--B] dihydrogen bonds stimulates a contraction in direction c (2.2%). The simplicity of the synthesis, mild temperatures of transition, a pronounced thermochromism, stability upon thermal cycling, a striking volume expansion upon SCO, and an easy processability to composite films make this new complex an attractive material for switchable components of diverse applications.