Chemistry Transition Elements ETEA 2019
PMDC Verified Question 51 of 68
Co-ordination number of \( [Co(en)_{2}Cl_{2}] \) is
A
-2
B
6
C
4
D
None of the above
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: 6
Concept:

The coordination number is the total number of coordinate bonds attached to the central metal. It depends on the denticity (number of binding sites) of the ligands.

Solution:

  • The complex is \([Co(en)_2Cl_2]\). The ligands are ethylenediamine (\(en\)) and Chloride (\(Cl^-\)).


  • \(en\) (ethylenediamine) is a bidentate ligand. It has two nitrogen atoms capable of donating lone pairs. Thus, 2 molecules of \(en\) form \(2 \times 2 = 4\) coordinate bonds.


  • \(Cl^-\) is a monodentate ligand. Thus, 2 molecules of \(Cl^-\) form \(2 \times 1 = 2\) coordinate bonds.


  • Total coordination number = \(4 (from \; en) + 2 (from \; Cl) = 6\).


Why other options are incorrect:

  • 4: This would only be true if \(en\) was incorrectly assumed to be a monodentate ligand (\(2+2=4\)).

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