1. Department of Chemistry, The University of Liverpool, Liverpool L69 7ZD, U.K., ISIS Facility, CLRC Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, OX11 0QX, U.K., Institut Laue-Langevin, 6 rue Jules Horowitz, BP 156, F- 38042 Grenoble Cedex, France, and European Synchrotron Radiation Facility, BP 220, F-38043 Grenoble Cedex, France