A series of low-valent Co(III) square planar complexes supported by a dianionic pincer ligand bis(arylamido)pyridine ([NNN]²⁻) was synthesized, including the first structurally characterized square planar hydroxide complex ([NNN]Co(OH), 4) of a 3d transition metal in the +3 oxidation state. The magnetic properties of the Co(III) complexes were highly dependent on the charge of the complex and on the coordination environment of the metal. The diamagnetic cationic complex {[NNN]Co(py)}BF₄ (2) can be converted to neutral paramagnetic complexes [NNN]Co(OR) (R = Ph 3a, iPr 3b, and H 4) by a simple substitution of the ancillary pyridine ligand in 2. The double bond character between the metal and the anilido nitrogen was evident from short Co–N2,3 bond lengths in the solid-state structures, and further supported by density functional theory calculations. Complex 2 showed well-behaved redox processes at −0.93 and +0.70 V assigned to Co^II/III and [NNN]^2−/1− redox couples, respectively. In contrast, both complexes 3a and 4 showed some irreversibility in redox processes on either cobalt or ligands.

中文翻译：

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吡啶双离子钳配体的配位和电子不饱和方形平面钴（III）配合物

合成了一系列由阴离子夹钳配体双（芳基酰胺）吡啶（[NNN] ^2-）支撑的低价Co（III）方形平面络合物，包括第一个结构表征的方形平面氢氧化物络合物（[NNN] Co（OH） ），4）处于+3氧化态的3d过渡金属。Co（III）配合物的磁性能高度依赖于配合物的电荷和金属的配位环境。反磁性阳离子络合物{[NNN] Co（py）} BF ₄（2）可转换为中性顺磁性络合物[NNN] Co（OR）（R = Ph 3a，iPr 3b和H 4）通过2中辅助吡啶配体的简单取代。从固态结构中较短的Co–N2,3键长可以明显看出金属与苯胺氮之间的双键特征，并进一步得到密度泛函理论计算的支持。络合物2在−0.93和+0.70 V处表现良好的氧化还原过程，分别分配给Co ^{II / III}和[NNN] ^{2- / 1-}氧化还原对。相反，络合物3a和4在钴或配体上的氧化还原过程中均表现出一定的不可逆性。