Switching on thermal and light-induced spin crossover by desolvation of [Fe(3-bpp) 2 ](XO 4 ) 2 ·solvent (X = Cl, Re) compounds

• Published in: Inorganic chemistry frontiers Vol. 8; no. 13; pp. 3210 - 3221
• Main Authors: Djemel, Abdelhak, Stefanczyk, Olaf, Desplanches, Cédric, Kumar, Kunal, Delimi, Rachid, Benaceur, Farouk, Ohkoshi, Shin-ichi, Chastanet, Guillaume
• Format: Journal Article
• Language: English
• Published: London Royal Society of Chemistry 29.06.2021
• Subjects: Chemical Sciences; Coordination compounds; Crystal structure; Crystallography; Infrared spectroscopy; Inorganic chemistry; Iron; Material chemistry; Single crystals; Solvents; X ray powder diffraction
• ISSN: 2052-1553; 2052-1545; 2052-1553
• DOI: 10.1039/D1QI00446H

Thermal desolvation is a very attractive method for the post-synthetic modification of the physicochemical properties of switchable materials. In this field of research, special attention has been paid to the possibility of modifying the thermo- and photo-induced spin crossover (SCO) properties of metal complexes as they can act as solvent sensors. Two new [Fe(3-bpp) 2 ](ClO 4 ) 2 ·2.5H 2 O·MeOH ( 1·sol ) and [Fe(3-bpp) 2 ](ReO 4 ) 2 ·3H 2 O ( 2·sol ) compounds, where 3-bpp is 2,6-di-(1 H -pyrazol-3-yl)pyridine, were prepared and structurally characterized, and their solvated and desolvated phases were additionally investigated spectroscopically, magnetically and photomagnetically. Single-crystal X-ray structures of 1·sol and 2·sol consist of similar [Fe(3-bpp) 2 ] 2+ units arranged in π–π stacked layers separated by H-bond-stabilised layers consisting of solvent molecules and anions. Moreover, both materials show desolvation-assisted SCO from a low (LS, S = 0) to high-spin state (HS, S = 2) at around 340 K, followed by a reversible gradual spin conversion with T 1/2 ≈ 210 K and 304 K for 1 and 2 , respectively. Photomagnetic studies of 1·sol and 1 confirmed the efficiency of the light-induced excited spin-state trapping (LIESST) phenomenon with relaxation temperatures T (LIESST) = 82 K and 66 K for the solvated and desolvated phases, respectively. In the case of 2·sol , no LIESST effect was observed while the desolvated phase 2 exhibits a LIESST behaviour at T (LIESST) ≈ 50 K.