Dear Dr. Shabas

Thank you very much for your nice question. According to Nernst equation, reduction potential of an electrode depends on temperature and reaction quotient. The later is dependent on the activity of the oxidized species and reduced species of the redox equlibrium. So one can change the reduction potential by changing the temperature and the activity (concentration or partial pressure) of the oxidized and reduced species. You can simply visit the following link.

https://en.wikipedia.org/wiki/Nernst_equation

However, complexation of metal ions with ligands may decrease in the reduction potential also. This is due to the higher stability and lower ionic activity of the complex metal ion than the free one.

Here is another link.

https://www.sciencedirect.com/topics/chemistry/reduction-potential

Best regards

Shafikul Islam

Co(II) is stabilized in tetrahedral geometry by anthranilic acid. The complex is so stable, in fact, that it's used for gravimetric analysis of Co. If solubility is an issue, 2-amino-4-sulfobenzoic acid is a readily available alternative.

Dear Shabas Ahammed many thanks for posting this very interesting technical question. As already mentioned by Shafikul Islam the use of different ligands can greatly influence the reduction potential. In the case of tin, inorganic compounds are stable under normal conditions both in the +2 and +4 oxidation state (e.g. SnCl2 and SnCl4). Organometallic compounds of tin such as Sn(CH3)4 or (CH3)3SnCl normally contain tetravalent tin. In the case of cobalt one can say that simple inorganic cobalt compounds are more stable for Co2+, while the situation is exactly the opposite in the case of coordination compounds. Co3+ forms a vast number of very stable coordination compounds, and e.g. the prototypical complex [Co(NH3)6]Cl3 is significantly more stable than [Co(NH3)6]Cl2.

For more general information about this topic please have a look at the following useful links which might help you in your analysis:

Redox Potentials of Ligands and Complexes – a DFT Approach

This reference is freely available as public full text (see attached pdf file).

and

Factors that Influence Reduction Potential

https://chem.libretexts.org/Bookshelves/Analytical_Chemistry/Supplemental_Modules_(Analytical_Chemistry)/Electrochemistry/Redox_Potentials/Factors_that_Influence_Reduction_Potential

Please also note that there are some closely related questions posted earlier on RG. It might be worth having a look at the answers given to those questions. For example, please see:

What is the correlation between complexation and redox potentials of transition metal redox couple?

https://www.researchgate.net/post/What_is_the_correlation_between_complexation_and_redox_potentials_of_transition_metal_redox_couple

(5 answers)

and

Can you provide an explanation on metal-ligand complexation reactions in terms of redox potential?

https://www.researchgate.net/post/Can-you-provide-an-explanation-on-metal-ligand-complexation-reactions-in-terms-of-redox-potential

(12 answers)

I hope this helps. Good luck with your work and best wishes, Frank Edelmann

thanks for the suggestion. may I please know if in case of tin any such complex can bring the reduction potential? James Demers