1. Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore-560012, India, Centre for Condensed Matter Theory, Department of Physics, Indian Institute of Science, Bangalore-560012, India, CNRS UMR 8640 PASTEUR, Départment de Chimie, Ecole Normale Supérieure, 24 rue Lhomond, 75231 Paris Cedex 05, France, and Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0215