Coordination Chemistry
In the IUPAC nomenclature of coordination compounds, the groups that surround the central atom must be identified in the name. They are listed as prefixes to the name of the central atom along with any appropriate multipliers. Isomerism in Coordination Compounds are mainly of 2 types (A) Stereoisomerism viz: (i) Geometrical isomerism (ii) Optical isomerism and (B) Structural isomerism viz: (i) Linkage isomerism (ii) Coordination isomerism (iii) Ionisation isomerism (iv) Solvate isomerism. Many approaches have been put forth to explain the nature of bonding in coordination compounds viz. Valence Bond Theory (VBT), Crystal Field Theory (CFT), Ligand Field Theory (LFT) and Molecular Orbital Theory (MOT). The magnetic properties of coordination compounds can be measured by the magnetic susceptibility experiments. The results can be used to obtain information about the number of unpaired electrons and hence, structures adopted by metal complexes.
The formula of Hexaamminecobalt(III) sulphate is......
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → [Co(NH3)6]2(SO4)3
To write the formula of a coordination compound from its name:
Write the complex ion in square brackets: central metal first, then the ligands.
Find the charge of the complex ion from the oxidation state of the metal and the charges of the ligands.
Add enough counter ions to make the compound electrically neutral.
Applying this to hexaamminecobalt(III) sulphate:
Six neutral \( \ce{NH3} \) ligands around Co(III): charge of the complex = +3 + 6(0) = +3, i.e. \( \ce{[Co(NH3)6]^{3+}} \).
The counter ion is sulphate, SO42−.
The lowest common multiple of 3 and 2 is 6: 2 complex ions (+6) balance 3 sulphate ions (−6).
\( \displaystyle 2(+3)+3(-2)=0\quad\Rightarrow\quad\ce{[Co(NH3)6]2(SO4)3} \)
Why the other options are incorrect
Option (2) [Co(NH3)6]2(SO4) — Incorrect. Charge = 2(+3) + (−2) = +4; not neutral.
Option (3) [Co(NH3)6](SO4)3 — Incorrect. Charge = +3 + 3(−2) = −3; not neutral.
Option (4) [Co(NH3)6]3(SO4)2 — Incorrect. Charge = 3(+3) + 2(−2) = +5; not neutral.