1. Contribution from the Centre for Supramolecular and Macromolecular Chemistry, Department of Chemistry, University of Warwick, Coventry CV4 7AL, United Kingdom, the Molecular Structure Laboratory, Department of Chemistry, University of Loughborough, United Kingdom, the Department of Chemistry, University of Newcastle, Newcastle-upon-Tyne, United Kingdom, and the CCLRC Daresbury Laboratory, Warrington, United Kingdom