X-ray absorption near edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS) were performed to determine the structural stability and atomic local order of transition metal carbonyls Cr(CO)(6) confined into the channel network of MCM-41. These species interact with the surface siloxane groups of the MCM-41 walls as proved by XANES/EXAFS. These Cr species were previously characterized by Fr-IR, Xe adsorption and Si-29 NMR, which confirmed their monodispersity, chemical interaction and confinement into the pore network of MCM-41. In this study, XAS provides additional evidence on the high dispersion of the metal species and symmetry of the Cr sites. Also, the Cr-O bond lengths, Cr coordination and oxidation state were determined after thermal treatments, thus confirming the interaction of the sub-carbonyl species with the siloxane groups. The change of the oxidation state from 0 to almost 3 might explain the unusual catalytic activity for ethylene polymerization of the Cr sub-carbonyl species confined into MCM-41. (c) 2005 Elsevier B.V. All rights reserved.