Rylene- and diaza-rylene-derived cobalt clusters for solid-state pyrolysis towards undoped and N-doped carbon nanoparticles.

2,7-Diazapyrene and 2,9-diazaperopyrene tetraalkynes (12 and 13) as well as related non-N-doped pyrene and peropyrene tetraalkynes (14 and 15) of the same shape were used as polyaromatic templates in their metalation by [Co2(CO)8]. Isolated cobalt-rich [(12, 13, 14, 15)Co8(CO)24] clusters were characterized by means of NMR, IR, UV-Vis spectroscopy and X-ray crystallography. Their thermogravimetric behaviour and products of solid-state pyrolysis (SSP) were investigated by TGA, DSC, and scanning electron microscopy (SEM). Despite the same precursor shape, different carbon nanoparticles and nanotubes were formed depending on the extension of the π-system and nitrogen content of the precursors. Diazapyrene and diazaperopyrene complexes formed cauliflower-shaped nanoparticles, and the pyrene complex formed spherical nanoparticles and the peropyrene complex led to multi-walled carbon nanotubes. These results elucidate that the carbon to cobalt ratio and the nitrogen dopant in the precursor have a significant impact on the products of the pyrolysis reaction.