1. Contribution from the School of Chemistry, University of Edinburgh, The King's Buildings, West Mains Road, Edinburgh EH9 3JJ, United Kingdom, Dipartimento di Chimica “G. Ciamician”, Università degli Studi di Bologna, v. F. Selmi 2, 40126, Bologna, Italy, and Department of Chemistry, University of St. Andrews, St. Andrews KY16 9ST, United Kingdom