An intermediate neglect of differential overlap (INDO) technique for lanthanide complexes: studies on lanthanide halides

An intermediate neglect of differential overlap method of use for examining the electronic structure of lanthanide complexes is developed. It is characterized by a basis set obtained from relativistic Dirac-Fock atomic calculations, the inclusion of all one-center two-electron integrals, and a parameter set based on molecular geometry. Lanthanide halides MX₂, MX₃ and MX₄ are studied here, as well as initial results for the twelve coordinate Ce(NO₃)₆ ^-2 ion. Geometries obtained are in excellent agreement with experimental values when available. Many MX₃ complexes are found to be pyramidal, and EuCl₂ and YbCl₂ are calculated to be bent even at the SCF level. Models invoking London type forces are therefore not required. Ionization potentials are calculated for the trihalides (δSCF) and are in reasonable agreement with experiment. Contrary to conclusion of others, f-orbital participation, although small, is required - at least in this model - to obtain the spread of metal to halide bond distance observed in these complexes. However f-orbital participation does not seem to be significant even in the twelve coordinate Ce(NO₃)₆ ^-2 complex: rather the large coordination number seems to be a consequence of the relatively large size of the lanthanide ion.