1. Department of Chemistry, University of Sheffield, Sheffield S3 7HF, United Kingdom, Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, United Kingdom, ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, United Kingdom, and Department of Pharmaceutical Sciences, Institute for Biological Sciences, University of Strathclyde, 27 Taylor Street, Glasgow G4 0NR, Scotland