Ligand-field analysis of an Er(III) complex with a heptadentate tripodal N4O3 ligand

Polarized absorption and emission spectra of trigonal single crystals of an Er(III) complex coordinated to a heptadentate tripodal ligand are reported at temperatures between 8 and 298 K. The assigned energy levels below the onset of ligand absorption (< 25 000 cm(-1)) are fitted to a parametrized e lectronic Hamiltonian. The C-3 site symmetry of the Er(HI) ion requires eig ht parameters for a full description of the ligand field within a one-elect ron operator description. This compound shows unusually large splittings of the multiplets, and the fitted parameters imply that this heptadentate lig and imparts the largest ligand field reported for an Er(III) complex. The l igand field was also interpreted within the angular overlap model (AOM). We derive the AOM matrix to include both sigma and anisotropic pi bonding and show that a useful description of the C-3 ligand field can be made using o nly five parameters. The success of the AOM description is encouraging for applications on isomorphous complexes within the lanthanide series and in d escribing the ligand field of low-symmetry complexes with less parameters t han in the usual spherical harmonic expansion.