Question

Give formulas for the following:

a. potassium tetrachlorocobaltate (II)

b. aquatricarbonylplatinum (II) bromide

c. sodium dicyanobis(oxalato)ferrate (III)

d. triamminechloroethylenediaminechromium (III) iodide

Short answer

$$\begin{gathered} potassiumtetrachlorocabaltate\left(II\right)--K_2\left[CoC{l}_6\right] \\ b.aquatricarbonylplatinum\left(II\right)bromide-\left[Pt{H}_{2}O{\left(CO\right)}_3\right]Br \\ c.sodiumdicyanobis\left(oxalate\right)ferrate\left(III\right)-Na\left[Fe{\left(CN\right)}_2{\left(C_2{O}_4\right)}_2\right] \\ d.triamminechloroethylenediaminechromium\left(III\right)idodide-\left[Cr{\left(N{H}_3\right)}_{3}Cl\left(en\right)\right] \end{gathered}$$

Step-by-step solution

Cobalt

In compound (a) cobalt is in +2 and in compound (c) iron is in +3 oxidation state. If the coordination sphere is anion or bears a negative charge then the name of the central metal atom ends in “ate”. Following are examples.

$$\begin{gathered} K_2\left[CoC{l}_6\right]-potassiumtetrachlorocabaltate\left(II\right)inthisClisnegativeligand \\ Na\left[Fe{\left(CN\right)}_2{\left(C_2{O}_4\right)}_2\right]-sodiumdicyanobis\left(oxalate\right)ferrate\left(III\right) \end{gathered}$$

Coordination Sphere

If the coordination sphere is a cation or bears a positive charge, then the name of the central metal atom remains as is. In the following compounds, the metal atom is in a coordination sphere, which is a cation.

$$\begin{gathered} aquatricarbonylplatinum\left(II\right)bromide-\left[Pt{H}_{2}O{\left(CO\right)}_3\right]Br \\ triamminechloroethylenediaminechromium\left(III\right)idodide-\left[Cr{\left(N{H}_3\right)}_{3}Cl\left(en\right)\right] \end{gathered}$$