Question 20.4: Determining the Name of a Coordination Compound from Its For......
Determining the Name of a Coordination Compound from Its Formula
Name each of the following:
(a) [Co(NH_3)_6]Cl_3, prepared in 1798 by B. M. Tassaert and generally considered to be the first coordination compound
(b) [Rh(NH_3)_5I]I_2, a yellow compound obtained by heating [Rh(NH_3)_5(H_2O)]I_3 at 100 °C
(c) Fe(CO)_5, a highly toxic, volatile liquid
(d) [Fe(C_2O_4)_3]^{3-}, the ion formed when Fe_2O_3 rust stains are dissolved in oxalic acid (H_2C_2O_4)
STRATEGY
First determine the oxidation state of the metal, as in Worked Example 20.3. Then apply the six rules above to name the compound or ion.
(a) Because the chloride ion has a charge of -1 and ammonia is neutral, the oxidation state of cobalt is +3. Use the prefix hexa- to indicate that the cation contains six NH_3 ligands, and use a Roman numeral III in parentheses to indicate the oxidation state of cobalt. The name of [Co(NH_3)_6]Cl_3 is hexaamminecobalt(III) chloride.
(b) Because the iodide ion has a charge of -1, the complex cation is [Rh(NH_3)_5I]^{2+} and the rhodium has an oxidation state of +3. List the ammine ligands before the iodo ligand, and use the prefix penta- to indicate the presence of five NH_3 ligands. The name of [Rh(NH_3)_5I]I_2 is pentaammineiodorhodium(III) iodide.
(c) Because the carbonyl ligand is neutral, the oxidation state of iron is zero. The systematic name of Fe(CO)_5 is pentacarbonyliron(0), but the common name iron pentacarbonyl is often used.
(d) Because each oxalate ligand (C_2O_4^{2-}) has a charge of -2 and because [Fe(C_2O_4)_3]^{3-} has an overall charge of -3, iron must have an oxidation state of +3. Use the name ferrate(III) for the metal because the complex is an anion. The name of [Fe(C_2O_4)_3]^{3-} is the trioxalatoferrate(III) ion