Question

Which of the following is correct about tetraammine dithiocyanato-s cobalt(III)tris(oxalato)cobaltate(III)?
A) Formula of complex is $[Co{(SCN)_2}{(N{H_3})_4}][Co{(ox)_3}]$
B) It is a chelating complex and shows linkage isomerism.
C) It shows optical isomerism.
D) It shows geometrical isomerism.

Answer 1

A coordination compound can be said as a molecular compound in which the central metal atom or metal ion is linked to a number of ions or neutral molecules by coordinate bonds. The ions or molecules coordinated to the central metal atom or metal ion are called ligands.

Complete step by step answer
Linkage isomerism is due to the difference in the mode of attachment of the ligand to the metal ion or atom.
Hence option B is correct. The $SC{N^ - }$ group can bind to the metal through sulphur or through nitrogen $- NCS$ .
Since in the complex ${[Co{(ox)_3}]^{3 - }}$ do not have any elements of symmetry hence it is optically active. Thus C is correct.
The given complex cation $[Co{(SCN)_2}{(N{H_3})_4}]$ can exist in two different forms cis and trans hence it exhibit geometrical isomerism.
Thus, option D is correct.

Additional Information
The donor atom attached to the metal ion or atom by coordinate bond is different. Linkage isomerism occurs when the ligand has two donor atoms and there are two possible ways of attachment. Geometrical isomerism is due to the difference in the spatial arrangement of ligands coordinated to the metal atom / ion. When two same ligands occupy positions adjacent to each other they are called cis –isomer.

Note
If two same ligands are arranged opposite to each other , it is called trans- isomer. Geometrical isomerism is very common among square planar and octahedral complexes. The compounds which rotate the plane of polarised light are called optically active compounds. An optically active compound exists in at least two different forms. Optical isomers rotate the plane of polarised light in opposite directions. The isomer which rotates the plane of polarised light towards right are dextrorotatory and those which rotates on left side are laevorotatory.