Covalent chemistry exerts characteristic changes to the geometric and electronic structures of the carbon allotropes associated with modification of the conjugation. 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; in this case the carbon atoms are removed from conjugation (destructive rehybridization) and (b) covalent chemisorption with formation of an organometallic hexahapto-metal bond that largely preserves the graphitic band structure (constructive rehybridization). ^{1, 2}

We focus our discussion on the organometallic chemistry of the carbon allotropes and the possibility to electronically interconnect graphitic surfaces by means of covalent bonding. This mode of functionalization allows the formation of atomic scale interconnects that consist of bis-hexahapto-metal-bonds between benzenoid ring systems and it may be used to increase the dimensionality of the electronic structure of the materials leading to enhanced conductivity. We will discuss the effect of bis-hexahapto bond formation on the electronic properties of percolating networks of single walled carbon nanotubes, small scale graphite nanoplatelets and graphene.

1. Bekyarova, E.; Sarkar, S.; Wang, F.; Itkis, M. E.; Kalinina, I.; Tian, X.; Haddon, R. C., Effect of Covalent Chemistry on the Electronic Structure and Properties of Carbon Nanotubes and Graphene. Acc. Chem. Res. 2013, 46, 65-76.

2. Bekyarova, E.; Niyogi, S.; Sarkar, S.; Tian, X.; Chen, M.; Moser, M. L.; Ayub, K.; Mitchell, R. H.; Haddon, R. C., Stereochemical Effect of Covalent Chemistry on the Electronic Structure and Properties of the Carbon Allotropes and Graphene Surfaces. Synth. Met. 2015, 210, 80-84.