Iron(II) Complexes of 2,6-Di[4-(ethylcarboxy)pyrazol-1-yl]pyridine with Reversible Guest-Modulated Spin-Crossover Behavior

• Published in: Crystal growth & design 2023-04, Vol.23 (4), p.2730-2738
• Main Authors: García-López, Víctor, El Jastimi, Hanane El Mansour, Juráková, Jana, Clemente-León, Miguel, Coronado, Eugenio
• Format: Article
• Language: English
• ISSN: 1528-7483; 1528-7505
• DOI: 10.1021/acs.cgd.2c01524

Three solvatomorphs of the iron­(II) complex of 2,6-di­[4-(ethylcarboxy)­pyrazol-1-yl]­pyridine (bpCOOEt2p) of formulas [Fe­(bpCOOEt2p)2]­(ClO4)2·1.5MeNO2 (1), [Fe­(bpCOOEt2p)2]­(ClO4)2·MeNO2 (2), and [Fe­(bpCOOEt2p)2]­(ClO4)2·2MeNO2 (3) have been prepared and characterized. They show interesting spin-crossover (SCO) properties ranging from partial to complete thermal spin transitions and a light-induced excited spin-state trapping (LIESST) effect. In solvatomorph 2, a robust structure is formed with channels that enable the entrance or removal of solvent molecules by vapor diffusion without losing the crystallinity. Thus, solvent-exchanged samples [Fe­(bpCOOEt2p)2]­(ClO4)2·MeNO2 (2·MeNO 2 ), [Fe­(bpCOOEt2p)2]­(ClO4)2·MeCN (2·MeCN), [Fe­(bpCOOEt2p)2]­(ClO4)2·0.5Me2CO (2·Me 2 CO), and [Fe­(bpCOOEt2p)2]­(ClO4)2·MeCOOH (2·MeCOOH) were prepared by vapor diffusion of the solvents in a crystal of the compound previously heated to 400 K in a single-crystal to single-crystal (SCSC) fashion. Interestingly, this causes a change of spin state with a stabilization of the low-spin state in 2·Me 2 CO and the high-spin state in 2·MeCN. Therefore, the SCO properties of 2 can be tuned in a reversible way by exposure to different solvents.