The IUPAC nomenclature of the compound LiAlH4 is?

Analysis

The question asks for the IUPAC (International Union of Pure and Applied Chemistry) name for the compound $\text{LiAlH}_4$. This compound is a well-known reducing agent in organic chemistry.

Concept: IUPAC Nomenclature for Complex Hydrides

To name complex inorganic compounds like $\text{LiAlH}_4$, we follow these rules:

1. Identify the Cation: The metal outside the complex bracket (or the first part of the formula) is named first. Here, it is Lithium.
2. Identify the Anion (Complex Ion): The complex part is $[\text{AlH}_4]^-$. • The ligand (the group attached to the central metal) is the hydride ion ($\text{H}^-$). In IUPAC nomenclature, when hydrogen acts as a ligand, it is called hydrido. Since there are four of them, we use the prefix tetra-. • The central metal is Aluminium. Because it is part of an anionic complex (the whole bracket has a negative charge), we add the suffix -ate to the metal name, making it aluminate.
3. Determine Oxidation State: We calculate the oxidation state of the central metal (Aluminium). • $\text{Li} = +1$ • $\text{H} = -1$ (since it is a hydride) • Let $x$ be the oxidation state of $\text{Al}$: $(+1) + x + 4(-1) = 0$ $1 + x - 4 = 0$ $x - 3 = 0 \implies x = +3$ • The oxidation state is written in Roman numerals in parentheses: (III).

Step-by-Step Solution

1. Name the cation: Lithium.
2. Name the ligands: Four hydrides = tetrahydrido.
3. Name the central metal: Aluminium becomes aluminate.
4. Combine: Put the parts together in the order: [Cation] + [Ligand prefix] + [Ligand name] + [Metal name] + [Oxidation state].
5. Result: Lithium + tetrahydrido + aluminate + (III) = Lithiumtetrahydridoaluminate (III).

Conclusion

Comparing our result with the given options, we find that option A matches our systematic derivation. Note that while "Lithium aluminium hydride" is the common name used in laboratories, the formal IUPAC name is "lithiumtetrahydridoaluminate (III)".

Exam Tip

When naming complex ions, always remember that if the complex ion is an anion (negative), the central metal must end in -ate (e.g., aluminate, ferrate, cuprate). If it were a cation, the metal name would remain unchanged.