Electron spectroscopy and density-functional study of `ferric wheel' molecules

Abstract

The Li-centered `ferric wheel' molecules with six oxo-bridged iron atoms form molecular crystals. We probed their electronic structure by X-ray photoelectron and soft X-ray emission spectroscopy, having calculated in parallel the electronic structure of a single `ferric wheel' molecule from first-principles by tools of the density-functional theory, using, specifically, the SIESTA method. The Fe local moments were found to be 4mu(B), irrespective of their mutual orientation. Neighbouring atoms, primarily oxygen, exhibit a noticeable magnetic polarization, yielding effective spin S = 5/2 per iron atom, that can get inverted as a `rigid' one in magnetic transitions. Corresponding energy preferences can be mapped onto the Heisenberg model with effective exchange parameter J of about -80 K. (C) 2003 Elsevier Ltd. All rights reserved.