Supramolecular Control of Spin Crossover in Iron(III) Complexes: Parallel versus Angled Chains

• Published in: Crystal growth & design 2022-03, Vol.22 (3), p.1543-1547
• Main Authors: Díaz-Torres, Raúl, Phonsri, Wasinee, Murray, Keith S, Harding, Phimphaka, Harding, David J
• Format: Article
• Language: English
• ISSN: 1528-7483; 1528-7505
• DOI: 10.1021/acs.cgd.2c00040

Crystal packing is known to strongly influence spin crossover (SCO) behavior. The influence of the halogen substituent on the crystal structure and magnetic behavior is investigated in the series, [Fe­(qsal-X)2]­NTf2 (qsal-X = 4-X-2-[(8-quinolylimino)­methyl]­phenolate; X = Cl 1, Br 2, and I 3; NTf2 = CF3SO2NSO2CF3). Compounds 1 and 2 are stabilized in the low spin state (LS), whereas 3 shows an abrupt hysteretic SCO. Anion conformational change upon SCO is observed in the previously reported compound 3, whereas 1 and 2 exhibit an unchanged syn conformation supported by halogen bonds. However, the key factor is the orientation of the 1D π–π chains. For 1 and 2, the 1D chains are connected by C–H···X interactions giving rise to angled chains (ca. 15°) that lock the iron­(III) centers in the LS state. For 3, the 1D chains are parallel to each other connected by C–H···π interactions that allows SCO. Hirshfeld surface analysis supports these findings. Interestingly, this trend is applicable to a large number of qsal-X complexes with 1D π–π chains.