Charge Density Analysis and Bond Characterization of 3d‐Transition Metal Complexes

Abstract

AbstractChemical bond, which makes molecules from independent atoms, is a very important concept in understanding the molecular behavior. Bond characterization is therefore becoming ever needed for predicting the physical and chemical properties of the molecule and the material. Combined experimental and molecular orbital calculation studies have been used for such purpose in terms of deformation density distribution, natural bond orbital analysis and the topological analysis on the total electron density. These analyses provide not only the distribution of density accumulation and density depletion, but also the information such as bond order, bond type etc. Atom domain in molecule or compound can be defined uniquely. Therefore the combined quantum mechanical calculation and high resolution X‐ray crystallography studies will be extremely useful for characterizing the chemical bond precisely. Bonding in 3d‐transition metal complexes is a major topic in coordination chemistry. The complexity of the 3d orbital splittings subjected in the ligand field is well known and this makes the bonding characterization more interesting and challenging. Charge density analysis on a series of Cr compounds, which contain a Cr‐L multiple bond, will be presented. Detail characterization of Cr‐nitrido, ‐oxo, ‐imido, ‐carbyne and ‐carbene bonds will be described. Metal squarates of late 3d transition elements have been investigated systematically. The valence shell charge concentration (VSCC) around metal ion will be demonstrated by the Laplacian topology, which provides the physical basis for the Lewis structure and valence shell electron pair repulsion (VSEPR). The metal‐metal bond is extremely important for metal clusters; the metal‐metal quintuple bond is rare and a detail analysis will be described. Electronic configurations of the 3d metal ion play important role in coordination chemistry; taking the advantage of the x‐ray absorption spectroscopy available in synchrotron radiation facility, the exact electronic configuration can be monitored. The great recent improvements on both experiment and theory have made the charge density analysis more accessible to even more complicated system, for example, the excited state or the meta‐stable states.