Molecular and Electronic Structures of Complexes Containing 1‑(2-pyridylazo)-2-phenanthrol (PAPL): Revisiting a Redox-Active Ligand

Herein
we report the molecular structures and electronic properties of neutral,
homoleptic, six-coordinate complexes of the general formula M­(PAPL)2, where PAPL is the monoanion of 1-(2-pyridylazo)-2-phenanthrol
(M = Mn, Ni, Zn). Although, the coordination chemistry of PAPL has
been investigated in a few previous reports in the 1970s and 1980s,
there are, to our knowledge, no reported single crystal X-ray diffraction
studies of any complexes, or any other electronic property or computational
studies of complexes containing the PAPL anion until now. The electronic
structures of the complexes are probed with a combination of cyclic
voltammetry, UV–vis spectroscopy, and spectroelectrochemical
measurements. Density functional theory calculations support the redox-active
nature of the PAPL ligand. In all complexes we observe two reversible
ligand-centered reduction processes, suggesting it may be possible
to access the open-shell radical-anionic state of the ligand.

本文报道了通式为M(PAPL)₂的中性同配体六配位配合物的分子结构与电子性质，其中PAPL为1-(2-吡啶偶氮)-2-菲酚（1-(2-pyridylazo)-2-phenanthrol）的单阴离子，金属中心M为Mn、Ni、Zn。尽管PAPL的配位化学在20世纪70至80年代的少数前期研究中已得到探索，但据我们所知，迄今为止尚未有关于该类配合物的单晶X射线衍射研究，也未报道过含PAPL阴离子的配合物的其他电子性质或计算化学相关研究。本研究结合循环伏安法、紫外-可见（UV-vis）光谱法及光谱电化学测试，对配合物的电子结构进行了表征。密度泛函理论（Density Functional Theory）计算证实了PAPL配体的氧化还原活性。在所有配合物中均观测到两个可逆的配体中心还原过程，表明有望获得该配体的开壳层自由基阴离子态。