Department of Chemistry and Center for Theoretical and Computational Chemistry, University of Tromsø, N-9037 Tromsø, Norway, and Department of Chemistry, University of the Free State, 9300 Bloemfontein, Republic of South Africa.
J Chem Theory Comput. 2008 Oct 14;4(10):1576-84. doi: 10.1021/ct800118c.
Low-coordinate architectures sustain unusual chemistry for middle and late transition metals, of which imido complexes are an excellent example. Recent DFT studies have uncovered a number of unusual features in the bonding in trigonal-planar and pseudotetrahedral imido complexes. Herein, we have extended these studies to a unique, distorted square-planar iron-imido complex with a pincer-type pyridine-2,6-diimine (PDI) supporting ligand. DFT calculations indicate that the iron center in the formally Fe(II) complex Fe(PDI)(NPh) is better described as intermediate-spin Fe(III), antiferromagnetically coupled to a b2-symmetry PDI π-anion radical. A comparative analysis of the major classes of low-coordinate imido complexes has uncovered a certain similarity between Fe(PDI)(NPh) and a trigonal-planar Fe(III)-nacnac-imido complex. Both ligand architectures afford a total of four energetically accessible d orbitals, resulting in intermediate-spin Fe(III) centers.
低配位结构可以维持中晚期过渡金属的特殊化学性质，其中亚胺配合物就是一个很好的例子。最近的密度泛函理论研究揭示了三角平面和拟四面体亚胺配合物中键合的一些不寻常特征。在此，我们将这些研究扩展到一个独特的、扭曲的正方形平面铁-亚胺配合物，该配合物具有钳式吡啶-2,6-二亚胺（PDI）支载配体。密度泛函理论计算表明，在形式上为 Fe(II)配合物 Fe(PDI)(NPh)中的铁中心更好地描述为中间自旋 Fe(III)，与 b2 对称性的 PDI π-阴离子自由基反铁磁耦合。对主要类别的低配位亚胺配合物的比较分析表明，Fe(PDI)(NPh)与三角平面 Fe(III)-nacnac-亚胺配合物之间存在一定的相似性。两种配体结构总共提供了四个能量上可及的 d 轨道，导致中间自旋 Fe(III)中心。
