trans‐Configured Ligands Boost Spin Crossover to Room Temperature in Mononuclear Fe(II) Complexes
Guang‐Wen Fu, Yan Kong, Xin Chen, Ying‐Ying Wu, Zi‐Han Yan, Zhao‐Yang Li, Yan‐Hui Shi, Jing‐Wei Dai, Xi‐Guang Han, Feng‐Lei YangAbstract
Seven new mononuclear complexes [Fe(aqin)2(NCS)2] (1), [Fe(aqin)2(NCSe)2] (2), [Fe(aqin)2(NCBH3)2] (3), [Fe(2‐pic)2(NCS)2] (4), [Fe(2‐pic)2(NCSe)2] (5), [Fe(2‐pic)(NCBH3)2] (6), [Fe(tpa)(NCBH3)2] (7), [aqin = 8‐aminoquinoline, 2‐pic = 2‐picolylamine, tpa = tris(2‐pyridylmethyl)amine)] are investigated. Structurally, except for 3, which affords a trans‐configuration, all the complexes adopt a cis‐configuration. Their propensity to crystallize without any solvent molecules facilitates the study of the influence of the “pure” ligand on spin‐crossover (SCO) characteristics. Magnetically, 1, 2, and 4 remain in the high‐spin state, and 3, 5, 6, and 7 display SCO with transition temperatures T1/2 of approximately 310, 162, 262, and 400 K, respectively. The T1/2 values of all the complexes except 3 follow the sequence of ligand‐field strength, whereas the T1/2 value of 3 is increased to room temperature, beyond that of the whole cis‐[Fe(2‐pic)2(NCE)2] family. Theoretical modeling based on the harmonic approximation via Gaussian and periodic DFT+U+D3 calculations via the QE reveals that the lower distortion effect of the trans‐configuration resulted in the LS stabilization increasing T1/2.