Coordination chemistry problem

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Discussion Overview

The discussion revolves around a coordination chemistry problem involving the properties and characteristics of a ligand in a complex, specifically focusing on chelation, optical activity, oxidation states, and the nature of ligands. The scope includes theoretical reasoning and technical explanations related to coordination complexes.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants propose that the ligand forms chelate rings and is therefore a chelating complex, with implications for optical activity and isomerism.
  • There is a discussion about whether the complexes have different empirical formulas, with some participants questioning this point and suggesting that they may be polymerization isomers if the difference between Br and Cl is not considered.
  • One participant suggests that there should be four octahedra in the complex, while others question this number, proposing only three instead.
  • Participants discuss the contributions of hydroxyl groups to the overall charge of the ligand, with some suggesting that OH groups should be counted as OH- and ammonias as neutral.
  • There is a query about whether a ligand can form chelate rings while also acting as a bridging ligand, with terminology and definitions being debated among participants.
  • Some participants express uncertainty about the oxidation states of chromium in the complex, with calculations leading to conflicting interpretations of the oxidation state based on charge distribution.

Areas of Agreement / Disagreement

Participants generally agree on some aspects of the ligand's properties, such as its chelating nature and optical activity. However, there are multiple competing views regarding the number of octahedra, the empirical formulas, and the nature of the ligands, indicating that the discussion remains unresolved.

Contextual Notes

There are limitations in the discussion regarding assumptions about empirical formulas and the definitions of bridging versus chelating ligands. Additionally, the calculations related to oxidation states are not fully resolved, leading to uncertainty in the conclusions drawn by participants.

Who May Find This Useful

This discussion may be useful for students and professionals in chemistry, particularly those interested in coordination chemistry, ligand behavior, and the complexities of oxidation states in coordination complexes.

Amitkumarr
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Homework Statement
How many of the following are the correct characteristics for the following complex(see attached figure).

(i) It is a chelating complex
(ii) It has two optically active isomer
(iii) It is the polymerisation isomer of(see attached figure).
(iv) It has total three unpaired electrons (v) There are four octahedron in the complex
(vi) All electrons of central metal atoms are present in non axial d-orbitals.
Relevant Equations
No relevant equations.Based on theory.
My attempt-
1)The given ligand forms chelate rings,so it should be a chelating complex.
2)It has no plane of symmetry (P.O.S),so it is optically active(octahedral complex) and should have 2 optically active isomers.
3)They are not polymerisation isomers because they have different emperical formula.
5) According to me there should be 3 octahedron in the complex.
For options 4 and 6,I am unable to get the oxidation state of Cr(central atom) and the overall charge of this ligand.What should be the contribution of the OH groups in the charge of this ligand?
Also,are my justifications correct?
 

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1, 2 - I agree.
3 - Do they have different empirical formulas? What are the EFs? (I assume we're talking about the complex ion, so the difference between Br and Cl doesn't count.)
5 - Only 3?
4, 6 - Count the OHs as OH- and the ammonias as neutral.
 
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mjc123 said:
1, 2 - I agree.
3 - Do they have different empirical formulas? What are the EFs? (I assume we're talking about the complex ion, so the difference between Br and Cl doesn't count.)
5 - Only 3?
4, 6 - Count the OHs as OH- and the ammonias as neutral.
3-They have the same emperical formula(if we don't consider Br and cl),so they are polymerisation isomers,right?
5-I think there should be 4 octahedron,1 on central atom and 3 on side atom.
If we count one OH as OH^- then we have 3×(-2)=-6 as overall charge of this ligand.So,the the oxidation state of Cr(central atom) would be x+(-6)=+6 which means x=+12 ,but that's not possible.
Where am I going wrong?
Note: Solution says only 3 of above options are correct.Which are wrong ones?
 
x = +12, but there are four Cr atoms to divide this charge between.
 
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mjc123 said:
x = +12, but there are four Cr atoms to divide this charge between.
Thanks,I was missing that part.So, each Cr atom is in +3 O.S.
But,I have one more query about the first option.Can any ligand form chelate rings and simultaneously behave as bridging ligand(like in the above question)?
 
It's a long time since I did my degree, and I'm a bit rusty on the terminology, but I would say the OH- ligands are bridging, while the peripheral Cr(OH)2 moieties are chelating the central Cr. Do people agree with that terminology?
 

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