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，pyridine-2,6-dicarboxylic acid）的一对一构效关系展开研究。变温X射线单晶结构分析证实，配合物1在120 ℃下发生相变，转化为配合物2（[Dipic(H₂O)FeOH]₂）。此外，通过变温单晶X射线衍射、粉末X射线衍射、时间依赖性傅里叶变换红外光谱及差示扫描量热法，对单晶到单晶（single-crystal-to-single-crystal, SCSC）转变过程进行了追踪表征。该SCSC转变会导致单晶的空间群发生改变：配合物1的单晶空间群为C2/c，而配合物2的单晶空间群为Pi̅。同时，SCSC转变也会改变晶体的堆积模式。配合物1通过氢键形成二维网络结构，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层面的变化，同时也改变了配合物的磁学性能。两种配合物的Fe-O-Fe键角存在差异，这使得其与相邻金属中心之间的反铁磁相互作用出现显著变化。