Biopyrrin pigments, which result from the degradation of heme in biological settings, feature three or two pyrrole rings and characteristic pyrrolin-2-one termini. These scaffolds serve as redox-active ligands and electron reservoirs in coordination compounds. Tripyrrin-1,14-dione coordinates divalent transition metals as a dianionic ligand hosting a delocalized radical. Herein, we report the synthesis and characterization of palladium(II) and platinum(II) tripyrrindione complexes featuring a primary amine (i.e., aniline, tert-butylamine, 1,2-ethylenediamine) at the fourth coordination site within square planar geometries. Interligand hydrogen-bonding interactions are observed between the coordinated amine and the carbonyl groups on the tripyrrindione scaffold. Notably, 1,2-ethylenediamine is employed to link two Pt(II) tripyrrindione complexes. As revealed by optical absorption and electron paramagnetic resonance (EPR) spectroscopy, all resulting complexes present ligand-based radicals that are stable at room temperature and when exposed to air. Spin pairing through multicenter interactions leads to $\pi$-dimerization of the tripyrrindione radicals and a decrease in the EPR signal at low temperatures. Electrochemical measurements indicate that the ligand system undergoes quasi-reversible one-electron oxidation and reduction, thus confirming the ability of tripyrrindione to form square planar complexes in three different redox states.

生物吡啶色素是由生物环境中血红素降解产生的，具有三个或两个吡咯环和特征性的吡咯啉-2-一末端。这些支架在配位化合物中充当氧化还原活性配体和电子库。Tripyrrin-1,14-dione 配位二价过渡金属作为承载离域自由基的双阴离子配体。在此，我们报告了钯（II）和铂（II）三吡啶二酮配合物的合成和表征，该配合物在方形平面几何形状的第四配位位点上具有伯胺（即苯胺，叔丁胺，1,2-乙二胺）。在三吡啶二酮支架上的配位胺和羰基之间观察到配体间氢键相互作用。值得注意的是，1,2-乙二胺用于连接两个 Pt(II) 三吡啶二酮络合物。光学吸收和电子顺磁共振（EPR）光谱显示，所有产生的配合物都呈现基于配体的自由基，这些自由基在室温下和暴露于空气中时是稳定的。通过多中心相互作用的自旋配对导致$\pi$-低温下三吡啶二酮自由基的二聚化和 EPR 信号的减少。电化学测量表明配体系统经历准可逆的单电子氧化和还原，从而证实了三吡啶二酮在三种不同氧化还原态下形成方形平面复合物的能力。