Nanometer-sized doubly bonded diamondoid dimers and trimers, which may be viewed as models of diamond with surface sp(2)-defects, were prepared from corresponding ketones via a McMurry coupling and were characterized by spectroscopic and crystallographic methods.. The neutral hydrocarbons and their radical cations were studied utilizing density functional theory (DFT) and ab initio (MP2) methods, which reproduce the experimental geometries and ionization potentials well. The van der Waals complexes of the oligomers with their radical cations that are models for the self-assembly of diamondoids, form highly delocalized and symmetric electron-deficient structures. This implies a rather high degree of sigma-delocalization within the hydrocarbons, not too dissimilar to delocalized pi-systems. As a consequence, sp(2)-defects are thus also expected to be nonlocal, thereby leading to the observed high Surface charge mobilities of diamond-like materials. In order to be able to use the diamondoid,oligomers for subsequent surface attachment and modification, their C-H-bond functionalizations were studied, and these provided halogen and hydroxy,derivatives with conservation of unsaturation.