Problem 4 - Chemistry: Introducing Inorganic, Organic and Physical Chemistry

Question

Name the following coordination compounds (Section 28.3 ): (a) \(\left[\mathrm{NiI}\left(\mathrm{NH}_{3}\right)_{5}\right] \mathrm{NO}_{3} ;(\mathrm{b}) \mathrm{K}\left[\mathrm{Co}(\mathrm{ox})_{2}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2}\right] ;(\mathrm{c})\left[\mathrm{Fe}(\text { dien })_{2}\right] \mathrm{SO}_{4}\) (d) \(\mathrm{Na}\left[\mathrm{AuBr}_{2} \mathrm{Cl}_{2}\right]\)

Step-by-Step Solution

Answer

(a) Pentaammineiodonickel(II) nitrate; (b) Potassium diaquabis(oxalato)cobaltate(III); (c) Bis(diethylenetriamine)iron(II) sulfate; (d) Sodium dibromodichloroaurate(III).

Step 1: Understand the Coordination Compound

Coordination compounds consist of a central metal atom or ion surrounded by ligands, which are ions or molecules that donate a pair of electrons to the metal. The compound's name includes details about these ligands and the central metal.

Step 2: Naming the First Compound: \([\mathrm{NiI}\left(\mathrm{NH}_{3}\right)_{5}\] \mathrm{NO}_{3}\)

Identify the ligands and the central metal: - The central metal is Ni (Nickel).- Ligands are five \(\mathrm{NH}_{3}\) (ammine) and one \(\mathrm{I}^{-}\) (iodo).- Anion: \(\mathrm{NO}_{3}^{-}\) is not named in the compound but indicates the charge balance.Naming: 1. Number of ligands: Five ammine and one iodo make it "pentaamminei".2. Name the metal with its oxidation state in Roman numerals; nickel here has +2 oxidation.Thus, the name is **Pentaammineiodonickel(II) nitrate**.

Step 3: Naming the Second Compound: \(\mathrm{K}\left[\mathrm{Co}(\mathrm{ox})_{2}\left(\mathrm{H}_{2}\mathrm{O}\right)_{2}\right]\)

Identify the ligands and the central metal:- Central metal is Co (Cobalt).- Ligands are two \(\mathrm{ox}^{2-}\) (oxalato) and two \(\mathrm{H}_{2}\mathrm{O}\) (aqua).- Counter ion is potassium Naming:1. Mention the cation (potassium) first in the compound name, as it's out of the brackets.2. List ligands in alphabetical order: aqua, then oxalato.3. Oxidation state of cobalt can be deduced from charge balancing (K is +1, oxalato is -2 each) to be +3.4. Name the metal ion and its oxidation state compounds within brackets.Thus, the name is **Potassium diaquabis(oxalato)cobaltate(III)**.

Step 4: Naming the Third Compound: \([\mathrm{Fe}(\text{dien})_{2}]\mathrm{SO}_{4}\)

Identify the ligands and the central metal:- Central metal is Fe (Iron).- Ligand is two dien (diethylenetriamine).- Anion is \(\mathrm{SO}_{4}^{2-}\) (sulfate), balancing the charge.Naming:1. Name the ligands, "bis(diethylenetriamine)" since diethylene is longer.2. Name the metal with its oxidation state in Roman numerals, which is deduced based on SO4 (sulfate) being 2-, so iron oxidation is +2.Thus, the name is **Bis(diethylenetriamine)iron(II) sulfate**.

Step 5: Naming the Fourth Compound: \(\mathrm{Na}\left[\mathrm{AuBr}_{2} \mathrm{Cl}_{2}\right]\)

Identify the ligands and the central metal:- Central metal is Au (Gold).- Ligands are two \(\mathrm{Br}^{-}\) (bromo) and two \(\mathrm{Cl}^{-}\) (chloro).- Counter ion is sodium outside the brackets.Naming:1. List sodium, the cation, first in the name.2. List ligands in alphabetical order: two bromo, then two chloro; hence "dibromo, dichloro".3. Mention the metal ion with its oxidation state in Roman numerals; calculate oxidation state considering ligands.Thus, the name is **Sodium dibromodichloroaurate(III)**.

Key Concepts

Ligands

In the world of coordination compounds, ligands play a fundamental role. They are ions or molecules that attach themselves to a central metal atom or ion through a process called coordinate bonding. This bond involves the donation of one or more pairs of electrons from the ligand to the metal.
While naming coordination compounds, ligands are listed before the central metal in the name. The ligands can be neutral molecules such as water (8_2O, called "aqua") or ammonia (E_3, called "ammine"), or they can be ions like chloride (6l^-) or hydroxide (F8^-). They are named in alphabetical order, regardless of their charge.
It's essential to note that certain ligands have special names when they form part of a coordination compound. For example, CN^- is called "cyano", while C_2O_4^{2-} is an "oxalato" ligand. Knowing these names is crucial for the proper nomenclature of coordination compounds.

Central Metal

The central metal is the pivotal atom in a coordination compound. It is surrounded by ligands, which form a complex arrangement around it. The central metal is typically a transition metal, which can accept electrons from ligands due to its d-orbitals.
When naming these compounds, the metal is named after the ligands. The name of the central metal is modified by its oxidation state, written in Roman numerals. For instance, in 1potassium diaquabis(oxalato)cobaltate(III)2, "cobaltate" refers to the central metal, Cobalt, with an oxidation state of +3.
When the metal has a negative charge in the complex, the suffix "-ate" is often added to its name, such as "ferrate" for iron and "cuprate" for copper. Understanding the behavior and characteristics of the central metal helps in predicting the geometry and properties of the coordination compound.

Oxidation State

The oxidation state is a critical concept when dealing with coordination compounds. It indicates the charge the metal would have if all the ligands and shared electrons were removed. Identifying the correct oxidation state is essential for correctly naming the compound and understanding its reactivity.
The oxidation state is typically represented by Roman numerals immediately following the name of the central metal in a compound's name. For instance, in CPentaammineiodonickel(II)nitrateE, the (II) indicates that the nickel has an oxidation state of +2.
To determine the oxidation state, you must consider the charge contributions of each ligand and any overall charge of the complex. Calculating these charges accurately ensures a correct application of the IUPAC nomenclature and strengthens your understanding of the compound's electronic structure.

IUPAC Nomenclature

The International Union of Pure and Applied Chemistry (IUPAC) has set forth systematic rules for naming chemical compounds to ensure clarity and uniformity. This set of rules extends to the realm of coordination compounds, where its guidelines help in universal identification of compounds across different languages and regions.
When naming coordination compounds following IUPAC rules, you begin with the names of the ligands, listed alphabetically, followed by the central metal's name. After the metal's name, you include the oxidation state of the metal in parentheses using Roman numerals.
For example, CH[aqua, then oxalato, and finishing with cobalt in potassium diaquabis(oxalato)cobaltate(III).E It details the sequence, usage of specific ligand names, and ends with the overall charge balancing elements necessary for completeness.