1. Contribution from the School of Chemistry, University of Hyderabad, Hyderabad 500 046, India, Department of Chemistry, University of Durham, South Road, Durham DH1 3LE, U.K., Department of Chemistry, University of Glasgow, Glasgow G12 8QQ, U.K., and ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, U.K.