Steuer Lena, Kaifer Elisabeth, Himmel Hans-Jörg
Anorganisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg, Germany.
Dalton Trans. 2021 Jul 13;50(27):9467-9482. doi: 10.1039/d1dt01354h.
Coordination compounds with redox-active ligands are currently intensively studied. Within this research theme, redox-active guanidines have been established as a new, eminent class of redox-active ligands. In this work the variation of metal-guanidine bonding in dinuclear transition metal complexes with bridging redox-active tetrakisguanidine ligands is analysed. A series of dinuclear complexes with different metals (Mn, Fe, Co, Ni, Cu and Zn) is synthesized, using either newly prepared redox-active tetrakisguanidino-dioxine or previously reported tetrakisguanidino-benzene ligands. The discussion of the bond properties in this work is predominantly based on the trends of structural parameters, derived from determination of single-crystal structures by X-ray diffraction and quantum chemical calculations. In addition, the trends in the redox potentials and magnetometric (SQUID) measurements on some of the complexes are included. Due to their combined σ- and π-electron donor capability, redox-active guanidine ligands are weak-field ligands; the σ- and π-bonding contributions vary with the metal. The results highlight the peculiarity of copper-guanidine bonding with a high π-bond contribution to metal-guanidine bonding, enabled by structural distortion of the coordination mode from tetrahedral in the direction of square-planar, short copper-guanidine bonds and minor displacement of the copper atoms from the ligand aromatic plane.
目前，含有氧化还原活性配体的配位化合物正受到广泛研究。在这一研究主题中，氧化还原活性胍已被确立为一类新型的重要氧化还原活性配体。在本工作中，分析了具有桥联氧化还原活性四胍配体的双核过渡金属配合物中金属 - 胍键的变化情况。使用新制备的氧化还原活性四胍基二恶英或先前报道的四胍基苯配体，合成了一系列含有不同金属（锰、铁、钴、镍、铜和锌）的双核配合物。本工作中对键性质的讨论主要基于结构参数的趋势，这些趋势来自于通过X射线衍射测定单晶结构以及量子化学计算。此外，还包括了对其中一些配合物的氧化还原电位趋势和磁测量（超导量子干涉仪）结果。由于氧化还原活性胍配体具有σ - 和π - 电子供体能力，它们是弱场配体；σ - 和π - 键的贡献随金属而变化。结果突出了铜 - 胍键的特殊性，其对金属 - 胍键具有高π - 键贡献，这是由配位模式从四面体向平面正方形方向的结构畸变、短的铜 - 胍键以及铜原子从配体芳香平面的微小位移所导致的。
