Generic metallocene Cp₂M type complexes are formed for many from across the 1^st row transition metal series along Sc to Zn. The number of unpaired electrons thus correlates with the number unpaired electrons present in the valence orbital of the metal (Figure 4). Of the complexes of the 1^st row transition metal series, the manganocene exists in two distinct forms, one in a high-spin form with five unpaired electrons, e.g. as in Cp₂Mn and the other in a low-spin form with one unpaired electron, e.g. as in Cp*₂Mn owing to the higher ligand field strength of the Cp* ligand. Cobaltocene, Cp₂Co, has 19 valence electrons (VE) and thus gets easily oxidized to the diamagnetic 18 VE valence electron species, Cp₂Co⁺. Of these metallocenes, the much-renowned ferrocene, Cp₂Fe is a diamagnetic 18 VE complex, whose molecular orbital diagram is shown above (Figure 3).