1. School of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
2. Department of Chemistry, McGill University, 801 Sherbrooke St. W., H3A 0B8 Montreal, Canada
3. Faculty of Chemistry, University of Warsaw, 1 Pasteura Street, Warsaw 02-093, Poland
4. EPSRC National Crystallography Service, School of Chemistry, University of Southampton, Highfield, Southampton, UK