The obtained compounds crystallize in stage-1 to stage-3 depending on the nature of host graphite. The thickness of the intercalate, which can be deducted from the repeat distance (I_c) value, generally ranges from 4.50 to 4.85 Å. On the basis of optical reflectivity experiments carried out at Kyoto University, a quantitative interpretation has been proposed using the 2-D band structure model of graphite acceptor compounds (Blinowsky-Rigaux model) [1]. For Cr- and Rh-based materials, the best fitting is obtained for the following Fermi level (E_F) and relaxation time (τ): C₂₁CrF_4.5 E_F = 0.94 ± 0.03 eV; τ = 2.8·10⁻¹⁴ S C₂₈RhF_3.3(HF₂)_1.3 EF = 0.89 ± 0.03 eV; τ = 1.2·10⁻¹⁴ S

The corresponding charge transfer coefficients can be deduced from the E_F values: f_c = 0.024 and f_c = 0.021), respectively. These values can be correlated to a C-C bond length contraction:

• Cr-based GIC: d_c-c = 1.4165 Å → 4 x 10⁻³ Å contraction

• Rh-based GIC: d_c-c = 1.4176 Å → 3.3 x 10₋₃ Å contraction.

This trend is confirmed by the shift towards higher energies observed in Raman E²_2g peak.

The oxidation state of the transition metals has been deduced from ESR, XANES, magnetic and XPS studies, whereas the coordination of Rh and Au has been shown to be octahedral and square planar respectively, using EXAFS spectroscopy.