Temperature-Induced Single-Crystal-to-Single-Crystal Transformations with Consequential Changes in the Magnetic Properties of Fe(III) Complexes

The present article
deals with an one-to-one structure–property
correspondence of a dinuclear iron complex, [Dipic­(H2O)­FeOH]2·H2O (1) (Dipic = pyridine-2,6-dicarboxylic
acid). Variable-temperature X-ray single-crystal structural analysis
confirms a phase transition of complex 1 to complex 2 ([Dipic­(H2O)­FeOH]2) at 120 °C.
Further, single-crystal-to-single-crystal (SCSC) transformation was
monitored by temperature-dependent single crystal X-ray diffraction,
powder X-ray diffraction, time-dependent Fourier-transform infrared
spectroscopy, and differential scanning calorimetry. SCSC transformation
brings the change in space group of single crystal. Complex 1 crystallizes in the C2/c space group, whereas complex 2 crystallizes in the Pi̅ space group. SCSC transformation brings the change
in packing diagram as well. Complex 1 shows two-dimensional
network through H-bonding, whereas the packing diagram of complex 2 shows a zigzag-like arrangement. Phase transformation not
only fetches structural changes but also in the magnetic properties.
Difference in Fe–O–Fe bond angles of two complexes creates
notable variation in their antiferromagnetic interactions with adjacent
metal centers.

本文针对双核铁配合物[Dipic(H₂O)FeOH]₂·H₂O（1）（其中Dipic为吡啶-2,6-二羧酸）的一一对应构效关系展开研究。变温X射线单晶结构分析证实，配合物1在120 ℃条件下可发生相变，转变为配合物2（[Dipic(H₂O)FeOH]₂）。此外，本研究通过变温单晶X射线衍射、粉末X射线衍射、时间分辨傅里叶变换红外光谱以及差示扫描量热法，对单晶到单晶（SCSC）转变进行了监测表征。该SCSC转变会导致单晶空间群发生改变：配合物1的空间群为C2/c，而配合物2的空间群为P-1。同时，晶体的堆积方式也随之改变：配合物1通过氢键构筑二维网络结构，而配合物2的堆积则呈现锯齿状排列。相变不仅引发了结构变化，还对其磁学性质产生影响。两种配合物的Fe-O-Fe键角差异，使其与相邻金属中心之间的反铁磁相互作用存在显著差异。