Problem 62 - Chemistry The Molecular Science

Question

Write the name corresponding to each formula. (a) \(\left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{5}(\mathrm{OH})\right]^{2+}\) (b) \(\left[\mathrm{Mn}(\mathrm{en})_{2} \mathrm{Cl}_{2}\right]\)

Step-by-Step Solution

Answer

(a) Pentaquohydroxo iron(III) ion; (b) Dichlorobis(ethylenediamine) manganese(II).

Step 1: Identify Ligands for Compound (a)

In compound \(\left[\mathrm{Fe}\left(\mathrm{H}_{2}\mathrm{O}\right)_{5}(\mathrm{OH})\right]^{2+}\), the ligands are identified as water \((\mathrm{H}_{2}\mathrm{O})\) and hydroxide \((\mathrm{OH}^-)\). Water is a neutral ligand called aquo, and hydroxide is an anionic ligand called hydroxo.

Step 2: Name the Metal Center for Compound (a)

The metal center in compound (a) is iron (Fe). When naming the complex, we use the name 'ferrate' if the overall charge was negative due to iron's multiple oxidation states, but since this is a cationic complex, we use 'iron' directly.

Step 3: Determine Oxidation State for Iron in Compound (a)

The neutral water ligands do not affect the charge. The overall charge of the complex is +2, and the hydroxide contributes -1. Let \(x\) be the oxidation state of iron. Therefore: \[ x + 0 \times 5 + (-1) = +2 \] Solving this, \(x = 3\). Thus, iron is in the +3 oxidation state, noted as iron(III).

Step 4: Assemble Name for Compound (a)

Combining the previous steps, the name for compound (a) is 'pentaquohydroxo iron(III) ion'.

Step 5: Identify Ligands and Metal for Compound (b)

In compound \(\left[\mathrm{Mn}(\mathrm{en})_{2} \mathrm{Cl}_{2}\right]\), the ligands are ethylenediamine \((\mathrm{en})\) and chloride \((\mathrm{Cl}^-)\). Ethylenediamine is a neutral ligand, while chloride is a negative ion. The central metal is manganese.

Step 6: Determine Oxidation State for Manganese in Compound (b)

In \(\left[\mathrm{Mn}(\mathrm{en})_{2} \mathrm{Cl}_{2}\right]\), there is no overall charge. Let \(x\) be the charge of manganese. The equation becomes: \[ x + 0 \times 2 + (-1) \times 2 = 0 \] Solving for \(x\), we find \(x = +2\). Thus, manganese is in the +2 oxidation state, or manganese(II).

Step 7: Assemble Name for Compound (b)

Using the determined oxidation state and knowledge of the ligands, the name for compound (b) is 'dichlorobis(ethylenediamine) manganese(II)'.

Key Concepts

Ligand Identification

Understanding ligands is fundamental in coordination chemistry, as ligands directly interact with the metal center in a complex. In simple terms, a ligand is an ion or molecule that binds to a central metal atom to form a coordination complex. Ligands can be neutral or carry a charge. Knowing how to correctly identify and name them helps in understanding the structure and function of the complex.

For example, in compound \(\left[\mathrm{Fe}\left(\mathrm{H}_{2}\mathrm{O}\right)_{5}(\mathrm{OH})\right]^{2+}\), the ligands are:

• Water \((\mathrm{H}_{2}\mathrm{O})\) - a neutral ligand, known as aquo.
• Hydroxide \((\mathrm{OH}^- )\) - a negatively charged ligand, known as hydroxo.

Similarly, in compound \(\left[\mathrm{Mn}(\mathrm{en})_{2} \mathrm{Cl}_{2}\right]\), the ligands differ:

• Ethylenediamine \((\mathrm{en})\) - a neutral ligand commonly represented by 'en'.
• Chloride \((\mathrm{Cl}^- )\) - a negatively charged ligand.

Each ligand type affects the name of the complex and impacts other chemical properties like solubility and reactivity.

Oxidation State Determination

Determining the oxidation state of the metal center is an essential task that aids in the proper naming of coordination complexes and helps understand their chemical behavior. The oxidation state is essentially the charge that the metal would have if all ligands were removed.

For compound (a), \(\left[\mathrm{Fe}\left(\mathrm{H}_{2}\mathrm{O}\right)_{5}(\mathrm{OH})\right]^{2+}\), the calculation follows these steps:

• The overall charge of the complex is +2.
• Water ligands contribute 0 as they are neutral.
• The hydroxide ligand contributes -1.

Letting \(x\) represent the oxidation state of iron, the equation is:\[x + 0 \times 5 - 1 = +2\]Solving gives the oxidation state of iron as \(x = +3\), or iron(III).

Similarly, for compound (b), \(\left[\mathrm{Mn}(\mathrm{en})_{2} \mathrm{Cl}_{2}\right]\), where there is no overall charge:

• The chloride ligands contribute a total of -2.
• Ethylenediamine is neutral, contributing 0.

Letting \(x\) be the manganese oxidation state:\[x + 0 \times 2 - 2 = 0\]Upon solving, \(x = +2\), indicating manganese(II). Understanding these calculations is crucial for correctly naming and analyzing the complex.

Chemical Nomenclature

Chemical nomenclature of coordination compounds involves naming both the ligands and the central metal atom in a specific order. It provides a systematic way to name complex structures using standard conventions, making it easier to understand and communicate chemical information.

When naming a coordination compound like \(\left[\mathrm{Fe}\left(\mathrm{H}_{2}\mathrm{O}\right)_{5}(\mathrm{OH})\right]^{2+}\), follow these steps:

• Name the ligands first in alphabetical order: 'aquo' for water and 'hydroxo' for the hydroxide ligand.
• Indicate the number of each ligand with Greek prefixes: 'penta-' for five water molecules and no prefix for one hydroxide.
• State the metal name. For iron with a +3 oxidation state, it becomes 'iron(III)'.

The complete name: 'pentaquohydroxo iron(III) ion'.

For the compound\(\left[\mathrm{Mn}(\mathrm{en})_{2} \mathrm{Cl}_{2}\right]\):

• 'Ethylenediamine' is a neutral ligand, while 'chloride' is an anion, both named in order.
• Use prefixes for quantities: 'bis-' for two ethylenediamine and 'di-' for two chloride ions.
• Manganese with a +2 state is named 'manganese(II)'.

Hence, the complex is named 'dichlorobis(ethylenediamine) manganese(II)'. Correct nomenclature is vital for understanding and working with these compounds.