ELECTRONIC STRUCTURE OF COMPLEXES OF LANTHANIDE IONS WITH CROWN ETHERS
Li Zhenxiang Ni Jiazuan ( Changchun Institute of Applied Chemistry, Academia Sinica ) Xu Guangxian Ren Jingging ( Department of Chemistry, Beijing University)
The total energy of molecules, electronic structure, charge distribution and Mulliken' s bond orders in the complexes of lanthanide nitrate or chloride with crown ethers have been calculated using an INDO method. The cause of structural difference between La(NO3)315-C-5 and La(NO3)318-C-6 is related to the cavity of crown ethers. The configuration with the three nitrate groups on one side and crown ring on the other side of La is energetically the most preferable. At coordination the charge transfer O(Cr) Ln leads to the shift of orbital levels and weakening of the bond of Ln-O(NO3) or Ln-Cl. The ligand constituents are dominant in the occupied MO's (except for 4f), while the Ln constituents are dominant in low unoccupied MO's. The occupied MO's may be classified into six groups. Benzene ring linked with crown ether makes frontier MO's shown n character. The covalent bonding is mainly due to the participation of 5d, and a lesser extent, 6p and 6s. The 4f orbitals almost do not participate in covalent bonding. The chemical bonding and stabilization factors of the complexes at high coordination numbers were discussed.