Write the reaction mechanism for both reactions:
CoCl2.6H2O + Ethylenediamine -> [Co(en)3]Cl3
[Co(en)3]Cl3 + Na2CO3 + Nitromethane -> [Co(dinosaur)]Cl3
2 – What is the oxidation state of the metal and valence electrons count for the compounds: [Co(en)3]Cl3 and [Co(dinosaur)]Cl3 ?
The Correct Answer and Explanation is :
Reaction Mechanisms
1. Synthesis of ([Co(en)_3]Cl_3):
Reaction:
[ CoCl_2 \cdot 6H_2O + 3(en) \rightarrow [Co(en)_3]Cl_3 + 6H_2O ]
Mechanism:
- Hydrolysis of CoCl(_2): The water molecules around cobalt dissociate, leaving the cobalt center in an octahedral environment.
[ CoCl_2 \cdot 6H_2O \xrightarrow{\text{hydration}} [Co(H_2O)_6]^{2+} + 2Cl^- ] - Ligand Exchange: Ethylenediamine ((en)), a bidentate ligand, displaces water molecules stepwise:
[ [Co(H_2O)_6]^{2+} + 3(en) \rightarrow [Co(en)_3]^{3+} + 6H_2O ] - Addition of Chloride Ions: The solution is neutralized with chloride ions to form the salt ([Co(en)_3]Cl_3).
2. Conversion to ([Co(dinosaur)]Cl_3):
Reaction:
[ [Co(en)_3]Cl_3 + Na_2CO_3 + CH_3NO_2 \rightarrow [Co(dinosaur)]Cl_3 + Byproducts ]
Mechanism:
The ([Co(dinosaur)]^{3+}) complex is synthesized through substitution or addition reactions involving nitromethane ((CH_3NO_2)) and possibly carbonate ((CO_3^{2-})). The exact ligand substitution depends on the structure of the hypothetical “dinosaur” ligand, which might involve a multidentate ligand derived from the reactants.
Oxidation State and Valence Electrons
- For ([Co(en)_3]Cl_3):
- Oxidation state: (+3)
The ethylenediamine ligands are neutral, and each Cl(^-) contributes (-1), leading to a charge balance of (+3) for Co. - Valence electrons: (6)
Cobalt in the (+3) oxidation state has (3d^6) electronic configuration in a low-spin state due to strong ligand field from ethylenediamine.
- For ([Co(dinosaur)]Cl_3):
- Oxidation state: (+3)
The hypothetical “dinosaur” ligand is assumed neutral or anionic, maintaining the (+3) charge on Co for similar charge balance. - Valence electrons: Dependent on ligand field strength. For a strong field ligand, a low-spin (3d^6) configuration would be likely.
300-Word Explanation
The oxidation state is determined by considering the charges contributed by ligands and balancing with the total charge of the complex. In ([Co(en)_3]Cl_3), ethylenediamine is neutral, while three Cl(^-) ions add a (-3) charge. To balance this, Co must have a (+3) oxidation state.
Valence electrons include the (d)-electrons remaining after oxidation. Cobalt has (9) valence electrons in its neutral state ((3d^7 4s^2)). Oxidation to (+3) removes (3) electrons ((4s^2) and (1) from (3d)), leaving (6) valence electrons.
For ([Co(dinosaur)]Cl_3), the same logic applies. The oxidation state is (+3), assuming the dinosaur ligand maintains charge neutrality. Depending on the ligand field strength, the (3d^6) electrons are either low-spin (strong field) or high-spin (weak field).