Stereochemical effect of covalent chemistry on the electronic structure and properties of the carbon allotropes and graphene surfaces

• Covalent chemistry affects the geometric and electronic structure of functionalized graphene.
• Addition chemistry leads to σ-bonds to graphene surfaces and removes C-atoms from conjugation.
• Hexahapto-metal bond preserves the graphitic band structure-constructive rehybridization.

We consider the covalent chemistry of the carbon allotropes with an emphasis on the newest member—graphene. We focus on the effect of such chemistry on the geometric and electronic structure of the functionalized materials and the way in which the conjugation is modified by such processes. We conclude that there are two limiting cases: (a) Conventional addition chemistry leading to the formation of σ-bonds to the graphitic surface in which there is full rehybridization of the derivatized carbon atoms from sp2 to sp3; thus these carbon atoms are effectively removed from conjugation and from the electronic band structure (referred to as destructive rehybridization). (b) Covalent chemisorption with formation of an organometallic hexahapto-metal bond that largely preserves the graphitic band structure (constructive rehybridization) and accompanies the formation of bis-hexahapto-metal bonds such as those in (η6-SWNT)Cr(η6-SWNT) which serve to interconnect adjacent graphitic surfaces and significantly reduces the internanotube junction resistance in SWNT networks. The formation of η2 di-hapto bonds represent an intermediate case of covalent chemistry and is known to be important in carbon nanotubes and particularly the fullerenes but this situation has been treated in detail in previous publications.

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