分光化学系列
Metal complexes are very attractive compounds because of their physical properties such as the electronic, magnetic and the optical phenomena can be explained by means of the ligand field splitting of the d- and/or f-electron orbitals of the central metal atom. The physical properties can be controlled continuously by changing the substituent of the ligand molecules. So many coordination chemists are studying how to control freely the ligand field splitting width by changing the chemical modification to the ligand. There are some basically textbook examples of the ligand field splitting such as the crystal field theory, ligand field theory, Tanabe-Sugano diagram, and the Tsuchida's spectrochemical series that is the most powerful strategic system for the metal complexes including the bidentate ligands with almost of trivalent cobalt (Co(III)) and chromium (Cr(III)). But these theoretical systems are not appropriate for many other complexes. On the other hand, the central metal dependence of the spectrochemical series has also been reported, which should be suitable for the hexaammine complexes [M(NH3)6]n+ and the hexaaqua ones [M(H2O)6]n+. Unfortunately, it is also well knows that the metal atom dependence of the spectrochemical series is not suitable for any other ligand molecules except in the cases of these ammonia and water. There are no developments of the discussions of ligand field splitting and the spectrochemical series during these 30-40 years, whereas the Tsuchida's spectrochemical series mentioned above was reported more than 70 years ago. Therefore, we are trying to review the ligand dependence and/or metal dependence of the spectrochemical series separately, and the concept of the novel 2D universalspectrochemical series, which can be applied for any combinations of the central metals and the ligand molecules, should be introduced.
