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.通过对相应二价物种[NBu4]₂[CoII(C6X5)4]（X=F(1)、Cl(2)）进行化学氧化，以合理产率获得了分子式为[NBu4][CoIII(C6X5)4]（X=F(3)、Cl(4)）的同配有机钴(III)化合物。[CoIII(C6X5)4]⁻/[CoII(C6X5)4]²⁻氧化还原电对可通过中等电位下的准可逆单电子转移过程实现电化学互变，其半波电位相对于饱和甘汞电极分别为E₁/₂ = −0.29 V（X=F）与−0.36 V。 盐3与4中的[CoIII(C6X5)4]⁻阴离子呈现出罕见的平面正方形几何构型，该结构经单晶X射线衍射方法确证。基于其立体化学特征，这类d⁶电子构型的CoIII衍生物属于顺磁性非克拉默斯体系，具有较大的零场分裂贡献，且未观测到电子顺磁共振（EPR）信号。 其磁化率的温度依赖性可通过自旋哈密顿量形式进行解释，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。 对于平面正方形d⁷电子构型的母体物种[NBu4]₂[CoII(C6X5)4]，其磁学性质也从微观（EPR）与宏观（交流与直流磁化测量）层面得到了全面研究。该类物种表现为S=1/2的低自旋体系，电子组态主要为(dz²)¹，且存在一定程度的s轨道混合，该混合程度已被定量表征。 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，该结果可合理解释其各自的磁学性质。