Homoleptic Organocobalt(III) Compounds with Intermediate Spin

Homoleptic organocobalt­(III) compounds with formula [NBu4]­[CoIII(C6X5)4] [X = F (3), Cl (4)] were obtained in reasonable yields by chemical oxidation of the corresponding divalent species [NBu4]2­[CoII(C6X5)4] [X = F (1), Cl (2)]. The [CoIII(C6X5)4]−/[CoII(C6X5)4]2– couples are electrochemically related by quasi-reversible, one-electron exchange processes at moderate potential: E 1/2 = −0.29 (X = F) and −0.36 V (X = Cl) versus saturated calomel electrode. The [CoIII(C6X5)4]− anions in salts 3 and 4 show an unusual square-planar geometry as established by single-crystal X-ray diffraction methods. According to their stereochemistry, these CoIII derivatives (d6) are paramagnetic non-Kramers systems with a large zero-field splitting contribution and no observable electron paramagnetic resonance (EPR) spectrum. The thermal dependence of their magnetic susceptibilities can be explained in terms of a spin-Hamiltonian formalism with S = 1 ground state (intermediate spin) and substantial spin–orbit contribution. The magnetic properties of the square-planar d7 parent species [NBu4]2­[CoII(C6X5)4] were also thoroughly studied both at microscopic (EPR) and macroscopic levels (alternating current and direct current magnetization measurements). They behave as S = 1/2 (low spin) systems with mainly (dz2)1 electron configuration and a certain degree of s-orbital admixture that has been quantified. The electronic structures of all four open-shell [Co­(C6X5)4]q− compounds (q = 1, 2) accounting for their respective magnetic properties are based on a common orbital energy-level diagram.

通过对相应二价配合物物种[NBu4]2[CoII(C6X5)4] [X = F (1), Cl (2)]进行化学氧化，以可观产率得到了通式为[NBu4][CoIII(C6X5)4] [X = F (3), Cl (4)]的全同配体有机钴(III)（homoleptic organocobalt(III)）化合物。[CoIII(C6X5)4]−/[CoII(C6X5)4]2– 氧化还原对可通过准可逆单电子转移过程在中等电位下实现电化学关联：相对于饱和甘汞电极（saturated calomel electrode）的半波电位E1/2分别为−0.29 V（X=F）和−0.36 V（X=Cl）。盐3和4中的[CoIII(C6X5)4]−阴离子呈现出反常的平面正方形几何构型，该构型通过单晶X射线衍射（single-crystal X-ray diffraction）方法得以确证。根据其立体化学特征，这些d6构型的Co(III)衍生物属于顺磁性非克拉默体系，具有较大的零场分裂（zero-field splitting）贡献，且未观测到电子顺磁共振（Electron Paramagnetic Resonance, EPR）信号。其磁化率的热依赖性可通过自旋哈密顿量（spin-Hamiltonian）形式进行解释，基态为S=1的中间自旋态，且存在显著的自旋-轨道耦合贡献。本研究还从微观（EPR）和宏观（交流与直流磁化强度测量）层面，对平面正方形d7构型的母体物种[NBu4]2[CoII(C6X5)4]的磁学性质进行了全面研究。该类配合物表现为S=1/2的低自旋体系，电子构型主要为(dz2)1，且存在一定程度的s轨道混杂，该混杂程度已被定量表征。上述四种开壳层[Co(C6X5)4]q−化合物（q=1,2）的电子结构均基于统一的轨道能级图，该图可合理解释其各自的磁学性质。