Question

How would the following molecules or ions be named as ligands when writing the name of a complex ion? (a) \(\mathrm{C}_{2} \mathrm{O}_{4}^{-}\) (c) \(S^{2-}\) (b) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{NH}\) (dimethylamine) (d) \(\mathrm{Cl}^{-}\)

Short answer

The names of the ligands in complex ions are: (a) oxalato, (c) sulfido, (b) dimethylamine, (d) chlorido.

Step-by-step solution

- Naming the Oxalate Ion

When naming the ligand based on the oxalate ion \(\mathrm{C}_{2} \mathrm{O}_{4}^{-}\), it will be referred to as 'oxalato' in the naming of a complex ion, following the convention for anions where the ending '-ate' is changed to '-ato'.

- Naming the Sulfide Ion

The sulfide ion \(S^{2-}\) is named 'sulfido' as a ligand in a complex ion. The 'ide' ending of a simple negative ion is generally replaced with 'ido' when referred to as a ligand.

- Naming Dimethylamine

Since dimethylamine \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{NH}\) is a neutral molecule, its name remains the same when it is a ligand in a complex ion. Therefore, it will be called 'dimethylamine'.

- Naming the Chloride Ion

The chloride ion \(\mathrm{Cl}^{-}\) as a ligand in the name of a complex ion is called 'chlorido'. Here, the '-ide' suffix is replaced by '-ido'.

Key concepts

Ligand Nomenclature

Understanding how to properly name ligands is crucial in coordination chemistry and ensures clear communication among chemists. A ligand can be described as an ion or molecule that donates a pair of electrons to a metal atom or ion to form a coordination complex. The name of the ligand changes slightly when it becomes part of such a complex.

For negatively charged ligands, the endings often change to help identify them as ligands. For example, in the case of the oxalate ion \(\mathrm{C}_2\mathrm{O}_4^{-}\), it is referred to as 'oxalato'. This alteration from '-ate' to '-ato' is common practice for anionic ligands in coordination complexes. Similarly, the sulfide ion \(S^{2-}\) would be called 'sulfido' when it acts as a ligand, morphing the '-ide' ending to '-ido'.

Neutral ligands, on the other hand, like dimethylamine \(\left(\mathrm{CH}_3\right)_2\mathrm{NH}\), typically retain their molecular name. Nevertheless, there are exceptions, such as water being named as 'aqua' and ammonia as 'amine' in ligand nomenclature.

Naming ligands correctly is an exercise in recognizing the types of molecules or ions involved and applying systematic changes to their endings based on their charges and roles within a complex ion.

Coordination Chemistry

Coordination chemistry is a branch of chemistry that deals with the study of compounds formed between metal atoms or ions and ligands. These compounds, known as coordination complexes, feature a central metal atom or ion surrounded by a number of ligands.

The understanding of coordination compounds starts with recognizing their structure, which is often described by coordination numbers and geometry. The coordination number is the total number of ligand-attachment sites to the metal, which can vary widely across different metals and ligands, resulting in diverse structural arrangements such as octahedral, square planar, and tetrahedral.

Moreover, the formation of these complexes involves chemical bonding that includes both ionic and covalent character, often represented by Lewis acid-base interaction. Metal ions act as Lewis acids (electron pair acceptors), while ligands function as Lewis bases (electron pair donors).

The study of coordination chemistry is not only fundamental for understanding inorganic compounds but also plays a significant role in biological systems, catalysis, and materials science. The ability of metals to coordinate with different ligands can lead to a vast array of chemical reactivity and properties that are studied and utilized across multiple scientific disciplines.

Inorganic Nomenclature

Inorganic nomenclature is the systematic naming of inorganic chemical compounds. It is a standardized way to ensure that each compound is uniquely identified and understood globally among chemists. The rules for naming inorganic compounds are outlined by the International Union of Pure and Applied Chemistry (IUPAC), which codifies the naming process to avoid ambiguity.

When naming an inorganic compound, particularly a complex ion, it is important to start with the name of the central atom or ion, followed by its oxidation state in roman numerals within parentheses. This task is followed by the listing of the ligands in alphabetical order, with any prefixes needed for indicating the number of each type of ligand. For example, 'chlorido' from chloride ions \(\mathrm{Cl}^{-}\) would be placed in the name before other ligands like 'oxalato' or 'sulfido' if also part of the complex.

Naming complex ions is a step-by-step process involving the identification of the central metal and its oxidation state, the coordination number, the ligands involved, and their respective numbers, all of which have to be stated in a precise and orderly fashion to accurately represent the chemical species. This systematic approach ensures clarity and consistency across the diverse field of inorganic chemistry.