作者:Ivan Šalitroš、Olaf Fuhr、Andreas Eichhöfer、Robert Kruk、Ján Pavlik、Lubor Dlháň、Roman Boča、Mario Ruben
DOI:10.1039/c2dt11906d
日期:——
The mononuclear compound (1) [FeII(L)2](BF4)2 (L = 4-ethynyl-2,6-bis(pyrazol-1-yl)pyridine) was prepared and structurally as well as magnetically characterised. The crystallisation revealed the formation of two polymorphs – the orthorhombic 1A and the tetragonal form 1B. A third, intermediate phase 1C was found exhibiting a different orthorhombic space group. Reversibility of the phase transition between 1A and 1C was studied by variable-temperature single-crystal and powder X-ray diffraction studies, while an irreversible phase transition was observed for the transition of 1B→1C. The magnetic studies show that the 1A↔1C transition is accompanied by a very abrupt spin transition (ST) with 8 K hysteresis width (T1/2(↓) = 337 K, T1/2(↑) = 345 K). The ST was confirmed by Mössbauer spectroscopy as well as by DSC studies. In contrast, the 1B polymorph remained low-spin up to 420 K. In conclusion, a full cycle of intertwined phase- and spin-conversions of three polymorphs could be proven following the general scheme 1B→1C↔1A.
制备了单核化合物(1)[FeII(L)2](BF4)2(L = 4-乙炔基-2,6-双(吡唑-1-基)吡啶),并对其结构和磁性进行了表征。结晶显示形成了两种多晶型——正交晶型1A和四方晶型1B。还发现了第三种中间相1C,其具有不同的正交晶格。通过变温单晶和粉末X射线衍射研究,研究了1A和1C之间的相变可逆性,同时观察到1B→1C的不可逆相变。磁性研究表明,1A↔1C的相变伴随着一个非常突然的磁畴转变(ST),其滞后宽度为8 K(T1/2(↓) = 337 K,T1/2(↑) = 345 K)。磁畴转变通过莫斯堡尔谱和DSC研究得到了证实。相比之下,1B多晶型在420 K之前保持低磁畴。总之,三种多晶型的相变和磁畴转变的完整循环可以按照1B→1C↔1A的一般方案进行证明。