Sun Yu-Chen, Chen Feng-Li, Wang Kang-Jie, Zhao Yue, Wei Hai-Yan, Wang Xin-Yi
State Key Laboratory of Coordination Chemistry, Collaborative Innovation Center of Advanced Microstructures, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China.
Jiangsu Key Laboratory of Biofunctional Materials, School of Chemistry and Materials Science, Nanjing Normal University, Nanjing 210023, China.
Inorg Chem. 2023 Sep 18;62(37):14863-14872. doi: 10.1021/acs.inorgchem.3c01188. Epub 2023 Sep 7.
Cooperative spin crossover transitions with thermal hysteresis loops are rarely observed in cobalt(II) complexes. Herein, two new mononuclear cobalt(II) complexes with hysteretic spin crossover at relatively high temperatures (from 320 to 400 K), namely, [Co(terpy-CHOH)]·X (terpy-CHOH = 4'-(hydroxymethyl)-2,2';6',2″-terpyridine, X = SCN() and SeCN ()), have been synthesized and characterized structurally and magnetically. Both compounds are mononuclear Co complexes with two chelating terpy-CHOH ligands. Magnetic measurements revealed the existence of the hysteretic SCO transitions for both complexes. For compound , a one-step transition with = 334.5 K was observed upon heating, while a two-step transition is observed upon cooling with (1) = 329.3 K and (2) = 324.1 K (at a temperature sweep rate of 5 K/min). As for compound , a hysteresis loop with a width of 5 K ( = 391.6 K and = 396.6 K, at a sweep rate of 5 K/min) can be observed. Thanks to the absence of the crystallized lattice solvents, their single crystals are stable enough at high temperatures for the structure determination at both spin states, which reveals that the hysteretic SCO transitions in both complexes originate from the crystallographic phase transitions involving a thermally induced order-disorder transition of the dangling -CHOH groups in the ligand. This work shows that the modification of the terpy ligand has an important effect on the magnetic properties of the resulting cobalt(II) complexes.
在钴（II）配合物中很少观察到具有热滞回环的协同自旋交叉转变。在此，合成了两种在相对较高温度（320至400 K）下具有滞后自旋交叉的新型单核钴（II）配合物，即[Co(terpy-CHOH)]·X（terpy-CHOH = 4'-(羟甲基)-2,2';6',2″-三联吡啶，X = SCN⁻和SeCN⁻），并对其进行了结构和磁性表征。两种化合物都是具有两个螯合terpy-CHOH配体的单核钴配合物。磁性测量表明两种配合物都存在滞后的自旋交叉转变。对于化合物[Co(terpy-CHOH)]SCN，加热时观察到一步转变，T₁/₂ = 334.5 K，而冷却时观察到两步转变，T₁ = 329.3 K和T₂ = 324.1 K（温度扫描速率为5 K/min）。至于化合物[Co(terpy-CHOH)]SeCN，在扫描速率为5 K/min时，可以观察到宽度为5 K的滞后回环（T₁ = 391.6 K和T₂ = 396.6 K）。由于不存在结晶晶格溶剂，它们的单晶在高温下足够稳定，可以在两种自旋态下进行结构测定，这表明两种配合物中的滞后自旋交叉转变源于晶体学相变，涉及配体中悬垂-CHOH基团的热诱导有序-无序转变。这项工作表明三联吡啶配体的修饰对所得钴（II）配合物的磁性有重要影响。
