Department of Chemistry, Molecular Sciences Research Hub, Imperial College London, London, UK.
Chemical Crystallography, Chemistry Research Laboratory, University of Oxford, Oxford, UK.
Nature. 2019 Oct;574(7778):390-393. doi: 10.1038/s41586-019-1616-2. Epub 2019 Oct 9.
Transition-metal complexes are widely used in the physical and biological sciences. They have essential roles in catalysis, synthesis, materials science, photophysics and bioinorganic chemistry. Our understanding of transition-metal complexes originates from Alfred Werner's realization that their three-dimensional shape influences their properties and reactivity, and the intrinsic link between shape and electronic structure is now firmly underpinned by molecular-orbital theory. Despite more than a century of advances in this field, the geometries of transition-metal complexes remain limited to a few well-understood examples. The archetypal geometries of six-coordinate transition metals are octahedral and trigonal prismatic, and although deviations from ideal bond angles and bond lengths are frequent, alternative parent geometries are extremely rare. The hexagonal planar coordination environment is known, but it is restricted to condensed metallic phases, the hexagonal pores of coordination polymers, or clusters that contain more than one transition metal in close proximity. Such a geometry had been considered for [Ni(PBu)]; however, an analysis of the molecular orbitals suggested that this complex is best described as a 16-electron species with a trigonal planar geometry. Here we report the isolation and structural characterization of a simple coordination complex in which six ligands form bonds with a central transition metal in a hexagonal planar arrangement. The structure contains a central palladium atom surrounded by three hydride and three magnesium-based ligands. This finding has the potential to introduce additional design principles for transition-metal complexes, with implications for several scientific fields.
过渡金属配合物在物理和生物科学中得到了广泛的应用。它们在催化、合成、材料科学、光物理和生物无机化学中具有重要作用。我们对过渡金属配合物的理解源于阿尔弗雷德·维尔纳（Alfred Werner）的认识，即它们的三维形状会影响它们的性质和反应性，并且形状和电子结构之间的内在联系现在已经牢固地建立在分子轨道理论基础上。尽管在这个领域已经取得了一个多世纪的进展，但过渡金属配合物的几何形状仍然仅限于少数几个理解得很好的例子。六配位过渡金属的典型几何形状是八面体和三角双锥，尽管偏离理想键角和键长的情况很常见，但替代的母体几何形状极为罕见。六方平面配位环境是已知的，但它仅限于凝聚金属相、配位聚合物的六方孔或含有多个紧密相邻过渡金属的簇。这种几何形状曾被认为存在于[Ni(PBu)]中；然而，对分子轨道的分析表明，这个配合物最好被描述为具有三角双锥几何形状的 16 电子物种。在这里，我们报告了一种简单配位配合物的分离和结构表征，其中六个配体以六方平面排列与中心过渡金属形成键。该结构包含一个被三个氢化物和三个镁基配体包围的中心钯原子。这一发现有可能为过渡金属配合物引入额外的设计原则，对几个科学领域都有影响。
