Spin-Crossover in a Pseudo-tetrahedral Bis(formazanate) Iron Complex

Spin-crossover in a pseudo-tetrahedral bis­(formazanate) iron­(II) complex (1) is described. Structural, magnetic, and spectroscopic analyses indicate that this compound undergoes thermal switching between an S=0 and an S=2 state, which is very rare in four-coordinate complexes. The transition to the high-spin state is accompanied by an increase in Fe–N bond lengths and a concomitant contraction of intraligand N–N bonds. The latter suggests that stabilization of the low-spin state is due to the π-acceptor properties of the ligand. One-electron reduction of 1 leads to the formation of the corresponding anion, which contains a low-spin (S=1/2) Fe­(I) center. The findings are rationalized by electronic structure calculations using density functional theory.本工作报道了假四面体双(甲脒合)铁(II)配合物(1)的自旋交叉(spin-crossover)现象。结构、磁学与光谱分析结果显示，该化合物可在S=0与S=2两种状态间发生热诱导转变，这类转变在四配位配合物中十分罕见。向高自旋态的转变伴随Fe-N键长的延长，同时伴随配体内N-N键的同步收缩。后者表明低自旋态的稳定源于配体的π电子受体特性。对配合物1进行单电子还原可得到对应的阴离子，该阴离子包含低自旋(S=1/2)的Fe(I)中心。上述研究结果通过密度泛函理论(density functional theory)的电子结构计算得到了合理阐释。