The financial support of the Natural Sciences and Engineering Research Council of Canada, and the Dow Chemical Company, Midland, Michigan, is greatly appreciated. The EXAFS measurements were carried out at the National Synchrotron Light Source, Brookhaven National Laboratories, which is supported by the US Department of Energy, Division of Material Sciences and the Division of Chemical Sciences. Ö. D. gratefully acknowledges the Scientific and Technical Research Council of Turkey for a graduate scholarship and the Chemistry Department, Middle East Technical University, Ankara, Turkey, for permission to conduct his graduate research at the University of Toronto. We also acknowledge Dr. Neil Coombs and Dr. Rana N. S. Sodhi for technical assistance with SEMEDX and XPS measurements. Discussions with our colleagues at the University of Toronto also proved to be invaluable.