Question

Name the following coordination compounds.

$$\begin{gathered} \mathbf{a}\mathbf{.}\mathbf{}{\mathbf{Na}}_{\mathbf{4}}\left[\mathrm{Ni}{\left(C_2{O}_4\right)}_3\right] \\ \mathbf{b}\mathbf{.}\mathbf{}{\mathbf{K}}_{\mathbf{2}}\mathbf{\left[}{\mathbf{CoCl}}_{\mathbf{4}}\mathbf{\right]} \\ \mathbf{c}\mathbf{.}\mathbf{}\left[\mathrm{Cu}{\left({\mathrm{NH}}_3\right)}_4\right]{\mathbf{SO}}_{\mathbf{4}} \\ \mathbf{d}\mathbf{.}\mathbf{}\left[\mathrm{Co}{\left(\mathrm{en}\right)}_2\left(\mathrm{SCN}\right)\mathrm{Cl}\right]\mathbf{Cl} \end{gathered}$$

Short answer

a. Sodium tris (oxalato) nickelate (II)

b. Potassium tetrachloro cobaltate (II)

c. Tetraammine copper (II) sulphate

d. Chloro bis (ethylenediamine) thiosulphato cobalt (II) chloride

Step-by-step solution

Determination of oxidation state of metal ion  

a. ${\mathrm{Na}}_4\left[\mathrm{Ni}{\left({\mathrm{C}}_2{\mathrm{O}}_4\right)}_3\right]$, compound contains four Na⁴⁺ions and three C₂O₄^2- ions. So, Ni has +2 oxidation state.

b. ${\mathrm{K}}_2\left[{\mathrm{CoCl}}_4\right]$compound contains two K⁺ions and four Cl^-ions. So, cobalt has +2 oxidation state.

c. $\left[\mathrm{Cu}{\left({\mathrm{NH}}_3\right)}_4\right]{\mathrm{SO}}_4$compound contains 4 neutral ammonia ligands and SO₄^2- ion. So, Copper has +2 oxidation state.

d. $\left[\mathrm{Co}{\left(\mathrm{en}\right)}_2\left(\mathrm{SCN}\right)\mathrm{Cl}\right]\mathrm{Cl}$compound contains one SCN^- ion and two ethylenediamine neutral ligands and Cl^-ion. So, cobalt has +2 oxidation state.

Identification of cation and anion in the compound

$$\begin{gathered} \mathrm{a}.{{\mathrm{Na}}_4}^{+}{\left[\mathrm{Ni}{\left({\mathrm{C}}_2{\mathrm{O}}_4\right)}_3\right]}^{4-} \\ \mathit{}\mathit{}cation\mathrm{anion} \\ \mathrm{b}.{{\mathrm{K}}_2}^{+}{\left[{\mathrm{CoCl}}_4\right]}^{2-}\mathit{}\mathit{} \\ \mathit{}\mathit{}cation\mathrm{anion} \\ \mathrm{c}.{\left[\mathrm{Cu}{\left({\mathrm{NH}}_3\right)}_4\right]}^{2+}{{\mathrm{SO}}_4}^{2-} \\ \mathit{}\mathit{}\mathit{}\mathit{}\mathit{}cation\mathrm{anion} \\ \mathrm{d}.{\left[\mathrm{Co}{\left(\mathrm{en}\right)}_2\left(\mathrm{SCN}\right)\mathrm{Cl}\right]}^0{\mathrm{Cl}}^{-1} \\ \mathit{}\mathit{}\mathit{}\mathit{}\mathit{}\mathit{}\mathit{}\mathit{}\mathit{}\mathit{}\mathrm{anion} \end{gathered}$$

Naming the ligand and co-ordination sphere

The name of the cation is given first followed by name of the anion. In case of a and b compounds cation is outside the co-ordination sphere.

$$\begin{gathered} {{\mathrm{Na}}_4}^{+}{\left[\mathrm{Ni}{\left({\mathrm{C}}_2{\mathrm{O}}_4\right)}_3\right]}^{4-}\mathrm{Sodium}\mathrm{tris}\left(\mathrm{oxalato}\right)\mathrm{nickelate}\left(\mathrm{II}\right) \\ cation\mathrm{anion} \end{gathered}$$

While naming a coordination sphere, ligands are named first and then the metal atom with its oxidation number. Ligands that are coordinated to the metal ion are listed alphabetical order. Terms like bis, tris, tetrakis, etc. are used to show the number of the ligands whose name already includes a number.

$$\begin{gathered} {\left[\mathrm{Co}{\left(\mathrm{en}\right)}_2\left(\mathrm{SCN}\right)\mathrm{Cl}\right]}^0{\mathrm{Cl}}^{-1} \\ \mathit{}\mathit{}\mathit{}\mathit{}\mathit{}\mathit{}\mathit{}\mathit{}\mathit{}\mathit{}\mathrm{anion} \end{gathered}$$

Chloro bis (ethylenediamine) thiosulphato cobalt (II) chloride

$$\begin{gathered} {\left[\mathrm{Co}{\left(\mathrm{en}\right)}_2\left(\mathrm{SCN}\right)\mathrm{Cl}\right]}^0{\mathrm{Cl}}^{-1}\mathrm{Chloro}\mathrm{bis}\left(\mathrm{ethylenediamine}\right)\mathrm{thiosulphato}\mathrm{cobalt}\left(\mathrm{II}\right)\mathrm{chloride} \\ \mathit{}\mathit{}\mathit{}\mathit{}\mathit{}\mathit{}\mathit{}\mathit{}\mathit{}\mathit{}\mathrm{anion} \end{gathered}$$

Naming the metal ion/atom

Central metal atom’s name is written after the ligands’ name. The oxidation number of the metal atom is shown using roman numerals after writing the name of metal atom such as cobalt (II).

The name of the metal atom depends on the charge present on the coordination sphere.

If the coordination sphere is a cation or a neutral molecule, then the name of the central atom remains unchanged.

E.g - ${\left[\mathrm{Co}{\left(\mathrm{en}\right)}_2\left(\mathrm{SCN}\right)\mathrm{Cl}\right]}^0$Chloro bis (ethylenediamine) thiosulphato cobalt (II)

If the coordination sphere is anion or bears a negative charge then name of the central metal atom ends in “ate”.

${{\mathrm{Na}}_4}^{+}{\left[\mathrm{Ni}{\left({\mathrm{C}}_2{\mathrm{O}}_4\right)}_3\right]}^{4-}$

Sodium tris (oxalato) nickelate (II)