1. Contribution from Istituto FRAE-CNR, via Gobetti 101, 40129 Bologna, Italy, Dipartamento di Chimica “G. Ciamician” dell'Università, via Selmi 2, I-40126, Bologna, Italy, The School of Chemistry, The University of Birmingham, Edgbaston, Birmingham B15 2TT, UK, and The Department of Chemistry, Imperial College, South Kensington, London SW7 2AY, UK