Question

Which of the following is not correctly matched? (1) Sodium (ethylenediaminetetraacetato)chromate(II) \(-\mathrm{Na}_{2}\left[\mathrm{Cr}\left(\mathrm{CH}_{3} \mathrm{COO}\right)_{4}(\mathrm{en})\right]\) (2) Dichloridobis(ethane \(-1,2\)-diamine) cobalt(III) ion \(-\left[\mathrm{Co}(\mathrm{Cl})_{2}(\mathrm{en})_{2}\right]^{*}\) (3) Tris(bipyridyl)iron(II)ion \(-\left[\mathrm{Fe}\left(\mathrm{NH}_{4} \mathrm{C}_{5}-\mathrm{C}_{5} \mathrm{H}_{4} \mathrm{~N}\right)_{3}\right]^{2 *}\) (4) Ammineaquadibromidocopper(II) \(\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)\left(\mathrm{H}_{2} \mathrm{O}\right) \mathrm{Br}_{2}\right]\)

Short answer

Option (3) is not correctly matched.

Step-by-step solution

- Analyzing Option (1)

Sodium (ethylenediaminetetraacetato)chromate(II) is given as \(-\mathrm{Na}_{2}\left[\mathrm{Cr}\left(\mathrm{CH}_{3} \mathrm{COO}\right)_{4}(\mathrm{en})\right]\). Here, 'en' stands for ethylenediamine (ethylenediaminetetraacetato is EDTA). The formula has 4 acetate groups, so there seems to be a mismatch in naming for EDTA and acetate groups. But without checking all the options, we may not conclude yet.

- Analyzing Option (2)

Dichloridobis(ethane-1,2-diamine) cobalt(III) ion is given as \(-\left[\mathrm{Co}(\mathrm{Cl})_{2}(\mathrm{en})_{2}\right] \cdot. \) Here, two 'en' ligands (ethane-1,2-diamine) and two chloride ions are correct. It appears correct on first glance.

- Analyzing Option (3)

Tris(bipyridyl)iron(II)ion is given as \(-\left[\mathrm{Fe}\left(\mathrm{NH}_{4} \mathrm{C}_{5} -\mathrm{C}_{5} \mathrm{H}_{4} \mathrm{~N}\right)_{3}\right]^{2 *}\). Bipyridyl ligand is denoted as \quad \left(\mathrm{bpy}\right). There seems to be a mismatch in formula representation since ammonium is not a typical component of bipyridyl.

- Analyzing Option (4)

Ammineaquadibromidocopper(II) is given as \(\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right) \left(\mathrm{H}_{2} \mathrm{O}\right) \mathrm{Br}_{2}\right]\). A copper(II) complex with one ammine, one aqua, and two bromide ions matches correctly.

- Concluding the Incorrect Match

Both options (1) and (3) have mismatches. Sodium (ethylenediaminetetraacetato), and tris(bipyridyl) representations were checked, finding errors in how ligands are shown. Option (3) with bipyridyl error looks more straightforward.

Key concepts

Coordination Compounds

Coordination compounds are a major topic in chemistry. They consist of a central metal atom or ion bonded to surrounding molecules or ions, known as ligands. These compounds are essential in various biological systems, industrial processes, and catalytic reactions. Their unique structures enable them to function in ways that simple molecules cannot. Coordination compounds are notable because they exhibit coloration, magnetic properties, and distinct reactivities.
For example: \(-[\text{Fe(CN)}_6]^{3-}\text{ (hexacyanoferrate(III)) }\) showcases the complex nature of these compounds. The metal center (iron in this case) is surrounded by six cyanide ligands. Understanding these structures requires recognizing how ligands interact with metal centers.

Ligands

Ligands are the molecules or ions that surround the central metal atom in coordination compounds. They bond to the metal center using donor atoms - the atoms in a ligand that donate an electron pair to the metal.
Notable Characteristics:

• Donor Atoms: The specific atoms within the ligand that bond to the metal. Common examples include nitrogen, oxygen, and sulfur.
• Denticity: Refers to the number of donor atoms in a ligand that bind to the metal. For example, monodentate ligands have one donor atom, while bidentate (like ethylenediamine (en)) have two.
• Chelation: When a ligand forms multiple bonds to a metal center, creating a ring-like structure. This can increase the stability of the coordination compound.

Understanding ligands is crucial because the properties of the coordination compound can vary tremendously depending on the type, number, and arrangement of ligands around the metal center.

IUPAC Naming Conventions

Naming coordination compounds follows a set of rules established by the International Union of Pure and Applied Chemistry (IUPAC). The correct naming of such compounds ensures clear communication among chemists. It involves several steps:

• Name the cation first, followed by the anion, regardless of their actual order in the formula.
• Within the coordination sphere, name the ligands alphabetically, before naming the central metal.
• Specify the number of each ligand type using prefixes such as mono-, di-, tri-, tetra-, etc. For complex ligands, prefixes like bis-, tris-, and tetrakis- are used.
• Indicate the oxidation state of the central metal using Roman numerals in parentheses.

For example: \(\text{[Cu(NH}_3\text{)(H}_2\text{O)Br}_2\text{]} \) is named ammineaquabromidocopper(II). A detailed understanding of these conventions is critical. They help in identifying not just the elements in the compound but also their quantity and coordination.