1. Molecular Materials Centre, School of Chemical Engineering and Analytical Sciences, University of Manchester, P.O. Box 88, Manchester, M60 1QD, U.K., School of Chemistry, The University of Edinburgh, King’s Buildings West Mains Road, Edinburgh EH9 3JJ, U.K., and ISIS Facility, Rutherford Appleton Laboratory, Chilton, Oxfordshire, OX11 0QX, U.K.