Piecha-Bisiorek Anna, Bieńko Alina, Jakubas Ryszard, Boča Roman, Weselski Marek, Kinzhybalo Vasyl, Pietraszko Adam, Wojciechowska Martyna, Medycki Wojciech, Kruk Danuta
Faculty of Chemistry, University of Wrocław , 14 F. Joliot-Curie, 50-383 Wrocław, Poland.
Department of Chemistry, FPV, University of SS Cyril and Methodius , Trnava, Slovakia.
J Phys Chem A. 2016 Mar 31;120(12):2014-21. doi: 10.1021/acs.jpca.5b11924. Epub 2016 Mar 18.
(C3N2H5)2[CoCl4] (ICC) was characterized in a wide temperature range by the single-crystal X-ray diffraction method. Differential scanning calorimetry revealed two structural phase transitions: continuous at 245.5 K (from phase I to II) and a discontinuous one at 234/237 K (cooling/heating) (II → III). ICC adopts monoclinic space groups C2/c and P21/c in phase (I) and (III), respectively. The intermediate phase (II) appears to be incommensurately modulated. Dynamic properties of polycrystalline ICC were studied by means of dielectric spectroscopy and proton magnetic resonance ((1)H NMR). The presence of a low frequency dielectric relaxation process in phase III reflects libration motion of the imidazolium cations. The temperature dependence of the (1)H spin-lattice relaxation time indicated two motional processes with similar activation energies that are by about an order of magnitude smaller than the activation energy obtained from dielectric studies. There are no abrupt changes in the (1)H relaxation time at the phase transitions indicating that the dynamics of the imidazolium rings gradually varies with temperature; that is, it does not change suddenly at the phase transition. Negative values of the Weiss constant and the intermolecular exchange parameter were obtained, confirming the presence of a weak antiferromagnetic interaction between the nearest cobalt centers. Moreover, the magnitude of zero field splitting was determined. The AC susceptibility measurements show that a slow magnetic relaxation is induced by small external magnetic field.
通过单晶X射线衍射法在很宽的温度范围内对二氯化钴（ICC）进行了表征。差示扫描量热法揭示了两个结构相变：在245.5 K时连续相变（从相I到相II），以及在234/237 K（冷却/加热）时的不连续相变（II→III）。ICC在相（I）和（III）中分别采用单斜空间群C2/c和P21/c。中间相（II）似乎是无公度调制的。通过介电谱和质子磁共振（（1）H NMR）研究了多晶ICC的动力学性质。相III中低频介电弛豫过程的存在反映了咪唑阳离子的振动运动。（1）H自旋晶格弛豫时间的温度依赖性表明存在两个具有相似活化能的运动过程，其活化能比从介电研究中获得的活化能小约一个数量级。在相变处（1）H弛豫时间没有突然变化，这表明咪唑环的动力学随温度逐渐变化；也就是说，在相变时它不会突然改变。得到了魏斯常数和分子间交换参数的负值，证实了最近的钴中心之间存在弱反铁磁相互作用。此外，还确定了零场分裂的大小。交流磁化率测量表明，小的外部磁场会引起缓慢的磁弛豫。
