Geometrical comparison: Table Model] 0 and [Os2-Full] 0 is predicted within 0.02 Å compared to the X-ray result. These results show that the simplification has almost no effect on the structure parameters, thus, the model structure will be used in all electronic structure analysis in this paper. Also, these results indicate that the computational methodology is valid for electronic structure analysis of the {Re[TpMePC]}2 0 and {Os[TpMePC]}2 0 molecules, and consequently for the oxidation and reduction forms. ). The similarity between the bond length of both systems can be explained with similar considerations to that of [Tc2Cl8] 2-/3-complex even though the Tc-Tc bond length of these systems is different as we will see shortly. The formal bond order of the [Tc2Cl8] 2-systems is equal to 4.0 (𝜎 2 𝜋 4 𝛿 2 ) and for the [Tc2Cl8] 3-equal to 3.50 (𝜎 2 𝜋 4 𝛿 2 𝛿 * 1 ). The Tc-Tc bond distance should be shorter in the [Tc2Cl8] 2-systems compare to that in the [Tc2Cl8] 3-. However, the X-ray data and so the quantum chemical calculations show a reverse trend (the computed Tc-Tc bond length for the [Tc2Cl8] 3-system is 2.140 Å compared to the X-ray value of 2.117(2) Å and the Tc-Tc bond length in the [Tc2Cl8] 2-compound calculated of 2.170 Å compared to 2.1560(3) Å of the X-ray). This trend is attributed to many reasons: crystal packing, the 𝜋 component of the Tc-Tc bond is larger in the [Tc2Cl8] 3-, and maybe the 𝛿 bond order is lower in the [Tc2X8] 3-because the single occupation of the 𝛿 * orbital which explains the small internal rotation in the [Tc2Cl8] 3-compound.