Question

Which one of the following is tris $($ ethane- $1,2$ -diammine $)$ cobalt $(III)$ sulphate?

• A. ${\left[Co(en{)}_2\right]}_2{\left(S{O}_4\right)}_3$
• B. $\left[Co(en{)}_{2}S{O}_4\right]$
• C. $\left[Co(en{)}_3\right]S{O}_4$
• D. ${\left[Co(en{)}_3\right]}_2{\left(S{O}_4\right)}_3$

Answer 1

Answer: (D)

The given name is of cation type complex. Thus, its formula is ${\left[Co(en{)}_3\right]}_2{\left(S{O}_4\right)}_3$ and is named as tris (ethane $1,2$, diammine $)$ cobalt $(III)$ sulphate. The following rules are used while naming the complex :

(i) The cation is named first (if present outside the coordination sphere).

(ii) Then, the ligands are named in an alphabetical order along with their quantity before the name of central atom/ion. (This procedure is reversed for writing the formula).

(iii) The name of central metal is written along with its oxidation state in roman.

(iv) If, name of ligand includes numerical prefix, then, the terms bis for $(2)$ tris for $(3)$ etc. are used and name of ligand is written in parentheses.

(v) If, anion is present outside the coordination sphere, it named without their quantity.

(vi) If the complex ion is a cation, the metal is named as the name of metal but, if the complex ion is an anion, the name of metal ends with suffix-'ate'.

(vii) The neutral complex molecules are named similar to that of complex cation.