Effect of the Crystal Packing and LIESST Effect of a Two-Dimensional Iron(II) Spin-Crossover Complex: [FeII(HLH,Me)2](CF3SO3)2 (HLH,Me: 8-(Imidazol-4-ylmethylideneamino)-2-methylquinoline)

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Abstract A 2D iron(II) spin-crossover (SCO) complex, [FeII(HLH,Me)2](CF3SO3)2, was synthesized, where HLH,Me: 8-(imidazol-4-ylmethylideneamino)-2-methylquinoline, and its structures and magnetic properties were investigated. The complex [FeII(HLH,Me)2](CF3SO3)2 has no crystal solvent and has structure isomorphous to the complex [FeII(HLH,Me)2](ClO4)2·1.5MeCN, and shows a gradual and reversible one-step SCO between the HS (S = 2) and LS (S = 0) states at T1/2 = 215 K without hysteresis. The T1/2 value is higher than that of corresponding desolvated ClO4− compound, [FeII(HLH,Me)2](ClO4)2, about 35 K, although the spin transition is more gradual than that of ClO4− compound and the hysteresis is absent, which is observed in ClO4− compound. The crystal structures were determined at 296 (HS state) and 100 K (LS state), where the crystal system and space group showed no change between these temperatures. The structures at both temperatures have the same 2D layered structure, which is constructed of both the bifurcated NH···O− hydrogen bonds between two CF3SO3− ions and two neighboring imidazole NH groups of the [FeII(HLH,Me)2]2+ cations and the π–π interactions between the two quinolyl rings of the two adjacent cations. This network structure is the same as that of ClO4− compound. 600 nm light irradiation at 10 K induced the LIESST effect.