Question

Name the following coordination compounds. a. \(\operatorname{Na_t}_{4}\left[\operatorname{Ni}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{3}\right]\) b. \(\mathrm{K}_{2}\left[\mathrm{CoCl}_{4}\right]\) c. \(\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right] \mathrm{SO}_{4}\) d. \(\left[\mathrm{Co}(\mathrm{en})_{2}(\mathrm{SCN}) \mathrm{Cl}\right] \mathrm{Cl}\)

Short answer

The short answer for the given coordination compounds is as follows: a. Tetrasodium bis(oxalato)trinickel(II) b. Dipotassium tetra(chlorido)cobalt(II) c. Tetra(ammine)copper(II) sulfate d. Chlorido-di(ethylenediammine)-thiocyanato-cobalt(III) chloride

Step-by-step solution

1. Compound a: Identify the components

In compound a, the central atom is \(\operatorname{Ni}\) (nickel), and the ligands are \(\mathrm{C}_{2}\mathrm{O}_{4}\) (oxalate). There are four sodium ions \(\operatorname{Na_t}\) as counter ions.

2. Compound a: Name the compound

The ligands take the prefix "bis" since there are three oxalate ligands. Therefore, combining all these elements, compound a can be named as tetrasodium bis(oxalato)trinickel(II). The metal needs to have the oxidation state in roman numerals, which is (II) for nickel in this case.

3. Compound b: Identify the components

For compound b, the metal ion is \(\mathrm{Co}\) (cobalt), and the ligands are four \(\mathrm{Cl}\) (chloride) ions. Additionally, there are two potassium ions \(\mathrm{K}\) as counter ions.

4. Compound b: Name the compound

The ligand should be named as tetra(chlorido), and the oxidation state of cobalt is (II). Hence, compound b can be named as dipotassium tetra(chlorido)cobalt(II).

5. Compound c: Identify the components

In compound c, the central atom is \(\mathrm{Cu}\) (copper) with four \(\mathrm{NH}_{3}\) (ammine) ligands, and the counter ion is sulfate \(\mathrm{SO}_{4}\).

6. Compound c: Name the compound

The ligands are tetra(ammine). The oxidation state of copper is (II). Hence, compound c can be named as tetra(ammine)copper(II) sulfate.

7. Compound d: Identify the components

For compound d, the metal ion is \(\mathrm{Co}\) (cobalt), and the ligands are two \(\mathrm{en}\) (ethylenediamine), one \(\mathrm{SCN}\) (thiocyanato), and one \(\mathrm{Cl}\) (chlorido). There is an additional \(\mathrm{Cl}\) counter ion outside the coordination sphere.

8. Compound d: Name the compound

The ligands should be named as di(ethylenediammine), chlorido, and thiocyanato. As cobalt is the central atom, we should name the ligands in alphabetical order: chlorido first, followed by di(ethylenediammine) and then thiocyanato. The oxidation state of cobalt is (III). Hence, compound d can be named as chlorido-di(ethylenediammine)-thiocyanato-cobalt(III) chloride.

Key concepts

Complex Ion Nomenclature

Naming coordination compounds may seem daunting, but it's straightforward once you know the rules. Here's how it works. The complex name starts with the ligands listed in alphabetical order, followed by the metal. If the complex ion is an anion, the metal takes on the -ate suffix.

Ligands are named first using prefixes like mono-, di-, tri-, etc., to indicate their number. For intricate ligand names, polydentate ligands like ethylenediamine use prefixes such as bis-, tris-. Metals in the complex ion follow, along with their oxidation state in Roman numerals in parentheses.

• For example, \([\operatorname{Ni}\left(\mathrm{C}_{2}\mathrm{O}_{4}\right)_{3}]^{4-}\) is named bis(oxalato)trinatickel(II).
• Counter ions are added as separate words.

Oxidation States

Understanding oxidation states is crucial in naming coordination compounds. They help define how electrons are distributed among atoms. This is especially important for metals in complex ions. The oxidation state is the charge of the metal after accounting for electrons shared with ligands.

To determine it, consider the common charges on each part of the compound. For instance, in \[\mathrm{K}_{2}\left[\mathrm{CoCl}_{4}\right]\],

• Each Cl has a -1 charge.
• Potassium (K) as a counter ion has a +1 charge.
• Co must balance these charges, leading to a +2 charge, written as cobalt(II).

Coordination Chemistry

Coordination chemistry explores compounds formed from a central atom or ion, and surrounding molecules or ions known as ligands. The central atom is typically a metal, which forms coordinate covalent bonds with the ligands.

Key points of coordination chemistry include:

• Understanding the coordination number, which is the number of ligand attachments to a central atom.
• Exploring the geometry, such as octahedral, tetrahedral, or square planar, which affects the properties and reactivity.
• Recognizing ligands can be simple ions like Cl- or more complex molecules like ethylenediamine.

Transition Metals

Transition metals are vital in forming coordination compounds, thanks to their unique electron configuration. They can donate electrons and form stable bonds with various ligands.

Key characteristics of transition metals include:

• The ability to hold multiple oxidation states, allowing diverse interactions with ligands.
• Formation of colored compounds due to d-d electron transitions.
• The central role in catalysis due to their electronic versatility.

Understanding these features helps explain the versatile role of transition metals in chemistry.

Ligands

Ligands play a central role in coordination chemistry by binding to the metal center. They can be neutral molecules like water or ammonia or charged ions like chloride.

Ligands influence the geometry and stability of the complex, and are categorized based on:

• Charge: Neutral or negative.
• Denticity: Monodentate ligands bond through a single site, while polydentate ligands attach through multiple sites.
• Strength: Strong-field ligands like CN- create low-spin complexes, while weak-field ligands like I- form high-spin complexes.

Understanding ligands enhances the comprehension of complex behavior and reactivity.