Question

Using IUPAC norms write the formulae for following:
(a) Potassium trioxalatoaluminate - (II)
(b) Dichloridobis (ethane - 1, 2 - diamine) cobalt (III)

Answer 1

Rules for IUPAC nomenclature of coordination compound

(a) The formula of cation is written first followed by anion.

(b) If there is more than one similar ligand, then prefixes di, tri, tetra, etc. are used to indicate the number of ligands.

(c) All ligands whether +ve charged, -ve charged, or neutral is written alphabetically followed by the name of the metal ion.

(c) If the complex is cationic or neutral the name of the central metal is written as such, followed by oxidation state in Roman numeral.

(d) If the complex is anionic, the name of the central metal ends in ‘ate’ followed by oxidation state in the Roman numeral.

(a) Potassium trioxalatoaluminate - (II)

Potassium trioxalatoaluminate - (II) contain

trioxalato means three oxalate ions$\left(C_2{O}_4^{2-}\right)$.

Roman numeral (II) indicates that the oxidation state of $Al=+2$

Let the charge on the complex is $‘x^{\prime }$

$+2+3(-2)=x$

$x=-4$

Hence, the formula of the anionic complex is $\left[Al\right(C_2{O}_4{)}_3{]}^{4-}$. Hence, to balence, the negative charge four potassium ions is added as counter ions.

Therefore, formula of complex is $K_4\left[Al\right(C_2{O}_4{)}_3]$

(b) Dichloridobis (ethane - 1, 2 - diamine) cobalt (III)

Dichloridobis (ethane - 1, 2 - diamine) cobalt (III) contain

trichloridoo means two chloride ions$\left(C{l}^{-}\right)$.

bis(ethane-1,2-diamine) means two ethane-1,2-diamine molecules$\left(en\right)$.

Roman numeral (IIi) indicates that the oxidation state of $Co=+3$

Let the charge on the complex is ${}^{\prime }{x}^{\prime }$.

$2(-1)+2\left(0\right)+3=x$

$x=+1$

Hence, the formula of cationic complex is $\left[Co\right(en{)}_{2}C{l}_2{]}^{+}$