In addition to the normal oxidation states, the zero oxidation state is also shown by these elements in complexes.

In the highest oxidation states, the transition metal show basic character and form cationic complexes.

In the highest oxidation states of the first five transition elements (Sc to Mn), all the 4s and 3d electrons are used for bonding

Once the d⁵ configuration is exceeded, the tendency to involve all the 3d electrons in bonding decreases.

[Co(en)(NH₃)₂]²⁺

[Co(H₂O)₄(en)]³⁺

[Co(en)₂(NH₃)₂]³⁺

[Co(NH₃)₃Cl]⁺

[Pd (P Ph₃)₂ (NCS)₂] and [Pd (P Ph₃)₂ (SCN)₂]

[Co(NH₃)₅ NO₃]SO₄ and [Co(NH₃)₅ SO₄]NO₃

[Pt Cl₂(NH₃)₄] Br₂ and [Pt Br₂(NH₃)₄] Cl₂

[Cu (NH₃)₄] [Pt Cl₄] and [Pt (NH₃)₄] [CuCl₄]

benzoic acid

salicylaldehyde

salicylic acid

phthalic acid