Meng Yin-Shan, Mo Zhenbo, Wang Bing-Wu, Zhang Yi-Quan, Deng Liang, Gao Song
Beijing National Laboratory of Molecular Science , State Key Laboratory of Rare Earth Materials Chemistry and Applications , College of Chemistry and Molecular Engineering , Peking University , Beijing 100871 , P. R. China . Email:
State Key Laboratory of Organometallic Chemistry , Shanghai Institute of Organic Chemistry , Chinese Academy of Sciences , 345 Lingling Road , Shanghai 200032 , P. R. China . Email:
Chem Sci. 2015 Dec 1;6(12):7156-7162. doi: 10.1039/c5sc02611c. Epub 2015 Sep 10.
The slow magnetic relaxation typical for single-ion magnets has been known for certain low-coordinate 3d metal complexes with d, d, and d electronic configurations, but never for d complexes. Herein, we report a study on two-coordinate d cobalt(i)-N-heterocyclic carbene complexes, for which slow magnetic relaxation behavior was observed for [Co(IMes)][BPh] (IMes: 1,3-dimesitylimidazol-2-ylidene) under an applied dc field. The system represents the first d single-ion magnet, and features a fitted energy barrier of = 21.3 cm and pre-exponential factor of = 6.6 × 10 s. The analog two-coordinate cobalt(i) complexes with different NHC ligands, [Co(sIMes)][BPh] (sIMes: 1,3-dimesitylimidazolin-2-ylidene) and [Co(IAd)][BAr] (IAd: 1,3-dimesitylimidazol-2-ylidene; BAr: tetra(3,5-ditrifluoromethylphenyl)borate), do not show such single-ion magnet behaviour. calculations imply that the dihedral angle between the two NHC planes and the degree of unsaturation of the NHC ligands can dramatically alter the value of the two-coordinate cobalt(i)-NHC ions, possibly changing of the Co-NHC π-interactions, and hence affect the spin-orbit coupling splitting.
单离子磁体典型的缓慢磁弛豫现象在某些具有d⁵、d⁴和d³电子构型的低配位3d金属配合物中已有报道，但在d⁶配合物中从未出现过。在此，我们报道了对二配位d⁶钴（I）-N-杂环卡宾配合物的研究，在施加的直流磁场下，[Co(IMes)][BPh₄]（IMes：1,3-二甲基咪唑-2-亚基）表现出缓慢磁弛豫行为。该体系代表首个d⁶单离子磁体，其拟合能垒为21.3 cm⁻¹，指前因子为6.6×10⁹ s⁻¹。具有不同NHC配体的类似二配位钴（I）配合物，[Co(sIMes)][BPh₄]（sIMes：1,3-二甲基咪唑啉-2-亚基）和[Co(IAd)][BArF₂⁴]（IAd：1,3-二甲基咪唑-2-亚基；BArF₂⁴：四（3,5-二（三氟甲基）苯基）硼酸盐），未表现出这种单离子磁体行为。计算表明，两个NHC平面之间的二面角和NHC配体的不饱和程度可显著改变二配位钴（I）-NHC离子的能垒值，可能改变Co-NHC π相互作用，进而影响自旋-轨道耦合分裂。
