Question

In complexes of weak field ligands, ${\Delta _0} < P$ (pairing energy), the energy difference between ${t_2}g$ and eg sets is relatively less. Under the influence of strong-field ligands, ${\Delta _0} > P$ (pairing energy), the energy difference between ${t_2}g$ and eg sets is relatively high.
The correct statement regarding ${\left[ {Cr{{\left( {en} \right)}_2}C{l_2}} \right]^ + }$ and ${\left[ {Co{{\left( {{C_2}{0_4}} \right)}_2}{{\left( {N{H_3}} \right)}_2}} \right]^ - }$ complexions is :
A. both are equally stable complexes
B. both have an equal number of stereoisomers
C. both are diamagnetic complexes
D. None of the above

Answer 1

Cobalt and chromium are d- block metals. The d block elements are found in the group 3,4,5,6,7,8,9,10,11and 12 of the periodic table. These are also known as transition metals. The d orbital is filled with an electronic shell $n - 1$ . There is a total of 40 d block elements.

Complete step by step answer:
The given complexes are, ${\left[ {Cr{{\left( {en} \right)}_2}C{l_2}} \right]^ + }$ and ${\left[ {Co{{\left( {{C_2}{0_4}} \right)}_2}{{\left( {N{H_3}} \right)}_2}} \right]^ - }$ .
It is given that in complexes of weak field ligands, ${\Delta _0} < P$ (pairing energy), the energy difference between ${t_2}g$ and eg sets is relatively less. Under the influence of strong-field ligands, ${\Delta _0} > P$ (pairing energy), the energy difference between ${t_2}g$ and eg sets is relatively high.
The number of unpaired electrons in ${\left[ {Co{{\left( {{C_2}{0_4}} \right)}_2}{{\left( {N{H_3}} \right)}_2}} \right]^ - }$ is zero as ${C_2}{0_4}^{ - 2}$ is a strong field ligand. On the other hand, the number of unpaired electrons in ${\left[ {Cr{{\left( {en} \right)}_2}C{l_2}} \right]^ + }$ the complex is 3. So ${\left[ {Cr{{\left( {en} \right)}_2}C{l_2}} \right]^ + }$ is paramagnetic and ${\left[ {Co{{\left( {{C_2}{0_4}} \right)}_2}{{\left( {N{H_3}} \right)}_2}} \right]^ - }$ is diamagnetic in nature.
These two compounds have two bidentate ligands. Therefore, these two compounds are $[M{(AA)_2}]{a_2}{]^{n \pm }}$ type. So, they should have the same number of stereoisomers.

So, the correct option is C.

Additional information:
A complex is a substance in which a metal atom or ion in the center is associated with a group of ligands. Ligands may be neutral or anionic. The coordination compounds are named as per IUPAC nomenclature rules.
1.In naming the complexion, the name of the ligand is written first in alphabetical order, then the metal atom or ion.
2.For neutral ligands like water, ammonia, carbon monoxide has a common name called aqua, ammine, carbonyl respectively.
3.We use Greek prefixes to designate the number of each type of ligand in the complexion. Example- di, tri, tetra, etc.
4.After naming the ligands, we name the central metal atom. If the complex is a cation, the metal is named the same as the element name. and if the complexion is an anion, the name of metal has a suffix-ate.
5.Following the name of the metal, we write the oxidation state of the metal in the complex as a Roman numeral in parentheses.

Note: Transition elements show a magnetic moment due to the presence of unpaired electrons to their d orbitals. With increasing the number of unpaired electrons, the spin magnetic moment value increases and vice-versa. . If there is no unpaired electron then it is diamagnetic.