Spin Crossover in [Fe(qsal-5-Br q ) 2 ] + Complexes with a Quinoline-Substituted Qsal Ligand.

Using a quinoline substituted Qsal ligand, Hqsal-5-Br q (Hqsal-5-Br q = N-(5-bromo-8-quinolyl)salicylaldimine), four Fe III complexes, [Fe(qsal-5-Br q ) 2 ]A·CH 3 OH (Y = NO 3 - ( 1 NO3 ), BF 4 - ( 2 BF4 ), PF 6 - ( 3 PF6 ), OTf - ( 4 OTf ), were prepared and characterized. Structure analysis revealed that complex 2 BF4 contained two species ( 2 BF4 ( P 1 ̅) and 2 BF4 ( C 2/ c )). In these compounds except 3 PF6 , the [Fe(qsal-5-Br q ) 2 ] + cations form 1D chains through π-π interactions and other weak interactions. Adjacent chains are connected to form the 2D "Chain Layer" structures and 3D structures through various supramolecular interactions. For 3 PF6 , a "Dimer Chain" structure is formed from the loosely connected dimers. Magnetic studies revealed that compounds 1 NO3 and 2 BF4 ( P 1 ̅) displayed abrupt hysteretic SCO with the transition temperature T 1/2 ↓ = 235 K, T 1/2 ↑ = 240 K for 1 NO3 and T 1/2 ↓ = 230 K, T 1/2 ↑ = 235 K for 2 BF4 ( P 1̅ ), while compounds 3 PF6 and 4 OTf are in the HS state. Desolvation of the complexes significantly modifies their SCO properties: the desolvated 1 NO3 and 2 BF4 show a gradual SCO, desolvated 3 PF6 undergoes a two-step SCO, and desolvated 4 OTf exhibits a hysteretic transition. Overall, this work reported the Fe III -SCO complexes of the quinoline-substituted Hqsal ligand and highlighted the potential of these ligands for the development of interesting Fe III -SCO materials.