1. Contribution from the Centre for Carbon-Rich Molecular and Nano-Scale Metal-Based Materials Research, Department of Chemistry, and HKU-CAS Joint Laboratory of New Materials, The University of Hong Kong, Pokfulam Road, Hong Kong SAR, People's Republic of China, and Laboratoire de Chimie du Solide et Inorganique Moléculaire, UMR 6511 CNRS-Université de Rennes 1, Institut de Chimie de Rennes, Campus de Beaulieu, F-35042 Rennes, France