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Question: Which is a low spin complex? (A) \( {\left[ {Fe{{\left( {CN} \right)}_6}} \right]^{3 - }} \) (B...

Which is a low spin complex?
(A) [Fe(CN)6]3−{\left[ {Fe{{\left( {CN} \right)}_6}} \right]^{3 - }}
(B) [Co(NO2)6]3−{\left[ {Co{{\left( {N{O_2}} \right)}_6}} \right]^{3 - }}
(C) [Mn(CN)6]3−{\left[ {Mn{{\left( {CN} \right)}_6}} \right]^{3 - }}
(D) All of these

Explanation

Solution

Ligands are the part of coordination compounds that are negatively, positively, or neutrally charged molecules or atoms. According to the spectrochemical series, ligands were arranged in the weak field to strong ligands, and some of the examples for strong ligands were cyanide and nitrite groups.

Complete answer:
Complex compounds are also known as coordination compounds. The special property of complex compounds is retaining their identity even dissolved in water or any other organic solvents.
The coordination compound consists of ligand and central metal atoms. Central metal atom accepts electrons from ligands. When the ligands are strong, then the electrons in the metal atom will pair up and result in a low spin complex.
The low spin complex has a small number of unpaired electrons as in the presence of strong-field ligands the pairing of electrons takes place.
High spin complexes have a greater number of unpaired electrons as in the presence of a weak field the pairing of electrons does not take place.
Some of the examples for strong field ligands were cyanide (CN−)\left( {C{N^ - }} \right) and nitrite (NO2−)\left( {N{O_2}^ - } \right) groups.
Thus, the complex compounds consist of cyanide and nitrite ligands are examples of low spin complexes.
From the above explanation, all the given ligands are low spin complexes.
Option D is the correct one.

Note:
Strong field ligands have carbon, nitrogen, and phosphorus as donor atoms. Whereas weak field ligands have oxygen, and sulfur as donor atoms. All the given complex compounds have donor atoms and nitrogen as donor atoms.