Metal—ligand bonds Jahn-Teller effect

The coordination chemistry of Cr can be subdivided into the realm of mononuclear coordination compounds, which can be derived (at least formally) from the blue [Cr(OH2)e] ion, and the chemistry of metal-metal bonded species (analogs of Cr2(OAc)4). Most of the former are octahedral high-spin complexes with distinct tetragonal distortions caused by the Jahn - Teller Effect. With strong-field ligands, low-spin octahedral complexes are formed, and there are also some four-coordinate complexes of various coordination geometries. The metal-metal bonded species are described in Section 5. 

M is a hon-Jahn-Teller ion of comparable size and electronic configuration to Cu (e.g. Ni +, Zn2+) or Cu2+ in a statically distorted coordination. The AU s are the differences between the mean square amplitudes of the metal ion and the ligand atom along the Cu(M)-L bond directions. The AU(M—L)gtat, amplitudes for the alkaline earth nitrocomplexes of Ni + and Cu are calculated from the structural data " i) to have values around 20 pm by this procedure, while the AU(Cu—L)dym amplitudes in the case of os-A PbCu(N02)6 [A K, Tl, Cs] are about ten times larger ). The Pmin values as calculated from Eq. (33) are collected in Table 3. In the case of planar dynamic Jahn-Teller effects may be estimated from the U amplitudes in the (001) plane by the modified equation ... 

The CUO2 plane is the xy-plane. The metal-ligand covalent bonds are in the xy-plane because one electron is missing in the antibonding 02p - 3d(x - y ) MO. The CuO distance is therefore smaller in the CUO2 plane than in the perpendicular direction, where the 3dz orbital is fully occupied. This is the Jahn-Teller effect in action, ordering all the copper ions of the plane. The reorganization of the structure due to the number of electrons present at the site has little to do with the Jahn-Teller effect, however. When we apply the Jahn-Teller theorem, the number of electrons is constant. 

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