sp Carbon Chains Surrounded by sp3 Carbon Double Helices: A Class of Molecules that are Accessible by Self-Assembly and Models for “Insulated” Molecular-Scale Devices We thank the Deutsche Forschungsgemeinschaft (SFB 583), Johnson Matthey PMC (platinum loan), the Spanish Ministerio de Educación y Ciencia, and the Fulbright Commission (Fellowships, J.M.M.-A.) for support, and Dr. A. M. Arif for assistance with the analysis of one crystal structure.