Theory of local distortion in ErO6 cluster:: Spontaneous symmetry reduction in lanthanoid octahedrons

Molecular orbital calculations for an ErO6 cluster predicted a stable C-4v pseudo-octahedron with an Er displacement of similar to0.1 A from the center of the octahedron with an Er=O bond length of 2.27 A. In this particular configuration, the hybridization balance of O 2p-Er 6s with O 2p-Er 5d minimizes electron transfer from the O anion to the Er cation, thereby strengthening the Er=O ionic bond. Excessive O 2p-Er 5d hybridization due to pi-bond formation is found in the shorter Er=O bond range, while insufficient hybridization caused by a weak sigma-bond is obtained in the longer Er=O bond range. Though spontaneous reduction of symmetry has also been confirmed in other LO6 (L=Tb-65-Lu-71) systems, the stablest pseudo-octahedron is obtained for ErO6. (C) 2003 American Institute of Physics.