A Molecular‐Mechanics Approach for the Prediction of the Geometry of High‐Spin FeIII Complexes with Oxygen and Nitrogen as Coordinating Atoms

A method for the prediction of geometries and the de novo design of oligodentate ligands for octahedral high‐spin Fe^III complexes with chemically diverse coordinating functions is described. Based on a set of 23 complexes with two nitrogens and four oxygens as coordinating atoms, a computational method was elaborated that describes and predicts the geometries of high‐spin Fe^III complexes, including small variations in bond length and angles. The method uses partial atomic charges of the ligand, which are obtained from ab initio calculations, and empirically derived angular and dihedral constraints, which are added to a molecular‐mechanics force field. Conformational analyses of the complex geometries were performed. The method was iteratively optimized by fitting calculated geometries into the corresponding crystal structures of the Fe^III complexes. Three representative examples of calculated structures superimposed on the crystal structure are shown to illustrate the accuracy of the method.