Toward an Understanding of Diamond sp²-Defects with Unsaturated Diamondoid Oligomer Models

Abstract

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 σ-delocalization within the hydrocarbons, not too dissimilar to delocalized π-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.

Noncovalent interactions in crowded olefinic radical cations

“…Previously, we found that DFT reproduced the experimental ionization potentials of large saturated hydrocarbons well [15 -19]. Correct descriptions of radical cations derived from 1 and 2 require taking into account both electron correlation and noncovalent interactions (NCI) [13,20] between the groups that surround the C=C bonds. Hydrocarbon 1 provides an opportunity to test the applicability of the recently developed DFT implementations to olefinic radical cations, such as 1 •+ , since its X-ray crystal structure is available [13].…”

“…Such a behavior upon ionization makes hydrocarbons 4 and 5 useful for the construction of electronic materials where the structural stiffness of the building blocks upon electron/hole transfer is critical. Derivatives of 4 and 5 may have some advantages over the diamondoid [20,39,40] derivatives previously successfully used for the construction of electron emitters and semiconductors [41 -45].…”

[2](1,3)Adamantano[2](2,7)pyrenophane: A Hydrocarbon with a Large Dipole Moment

“…However, after thermal treatment of natural diamond, C(sp 2 )−C(sp 2 ) bonds (“graphitic islands”) tend to form in the absence of hydrogen, thus leading to electrical conduction . The question whether the electrical conduction occurs only within the sp 2 system or in combination with the sp 3 system is difficult to answer because of a large variety of different sp 2 sites, as well as functionality on the diamond surface and inner defects. Hence, it is useful to study diamond's nanometer‐sized congeners, the diamondoids, which comprise well‐defined hydrogen‐terminated nanodiamonds .…”

Synthesis of 10-Methoxydiamantan-3-One

“…In fact, the diamondoid only exists as hexamantanes and pentamantanes (particle size of 0.6-0.75 nm) for the rod-shaped isomer in limited quantities from oil. Therefore, diamondoids with the desired size larger than 1 nm, in order to explore applications in nanoelectronics [1][2][3][4], for which the present of quantum limitation effects are theoretically presaged, remains problematic at the present time. This can be solved by a coupling reaction using lower diamondoids with various spacers.…”