1. Department
of Chemistry, Mansfield
Road, University of Oxford, Oxford OX1 3TA, U.K.
2. Institute
of Chemical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, U.K.
3. Eduard-Zintl-Institut
für Anorganische und Physikalische Chemie, Technische Universität Darmstadt, Alarich-Weiss-Strasse 8, D-64287 Darmstadt, Germany
4. Australian
Centre for Neutron Scattering, Australian Nuclear Science and Technology Organization, Locked Bag 2001 Kirrawee D.C., New South Wales 2232, Australia