Question

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

Short answer

The ligands would be named as follows: (a) ammine, (b) azido, (c) sulfato, (d) acetato.

Step-by-step solution

Naming Neutral Ligands

Neutral ligands are named by using the name of the molecule without any additional ending. For ammonia (NH_3), the name of the ligand is simply 'ammine'. The 'e' is added at the end to signify that it is a ligand.

Naming Negatively Charged Ligands

Negatively charged ligands are named using the root of the anion with an 'o' added at the end except where common names are used. For azide (N_3^-), the ligand's name is 'azido'. For sulfate (SO_4^{2-}), the ligand name is 'sulfato'. For acetate (C_2H_3O_2^-), the ligand name is 'acetato'.

Key concepts

Coordination Chemistry

To grasp the fundamentals of naming coordination compounds, a foundational understanding of coordination chemistry is essential. Coordination chemistry is the study of complex compounds where a central metal atom or ion is surrounded by molecules or anions, known as ligands. These ligands donate at least one pair of electrons to the metal, forming a coordination complex.

The number of ligands attached to the metal center is called the coordination number, and the specific spatial arrangement of the ligands is termed the coordination geometry. Understanding these concepts is crucial in predicting the physical and chemical properties of coordination compounds.

The naming of these complexes follows systematic rules which help reveal not only the identity of the metal center but also the type and number of attached ligands. This clarity is paramount for chemists to communicate compound structures effectively and understand their potential reactions.

Ligands in Complex Ions

In coordination compounds, ligands are like the supporting actors to the metal ion star. They are ions or molecules that bind to the metal ion through their lone pairs of electrons, thereby forming complex ions. Each ligand has a specific way of binding, which can range from a single point attachment (unidentate) to multiple points (polydentate).

For instance, ammonia (h{NH_3}) is a neutral molecule that attaches to metal ions through its lone pair of nitrogen, acting as a unidentate ligand. On the other hand, more complex ions like the sulfate ion (h{SO_4^{2-}}) can bind through multiple oxygen atoms.

When naming these structures as part of a complex ion, ligands are named first, followed by the metal. Neutral and negatively charged ligands, as in the exercise, have distinct naming conventions, reflecting their different natures in the bonding environment. The 'ammine' designation for ammonia and 'sulfato' for the sulfate ion are examples of naming these ligands in context with the metal ion they bond to. The careful naming of these ligands ensures a clear and consistent communication of their structure.

Chemical Nomenclature

Chemical nomenclature is the standardized system for naming chemical substances. It allows scientists and educators worldwide to convey information about the composition and structure of chemicals consistently and accurately. In the context of naming coordination compounds, this system ensures each part of the compound's name communicates specific information about the central metal and its surrounding ligands.

For example, neutral ligands often retain the name of the molecule but may have a slight modification, like an added 'e' at the end, to indicate their role in the complex. Conversely, negatively charged ligands typically end in 'o,' such as 'azido' for azide (h{N_3^{-}}) or 'acetato' for acetate (h{C_2H_3O_2^{-}}). In certain cases, traditional names are used, especially when common or historically established.

Naming coordination compounds correctly requires careful attention to detail, including the oxidation state of the metal, the type of ligands attached, and the overall charge of the complex ion. By following the rules of chemical nomenclature, chemists can deduce a significant amount of structural information from the name of a compound alone, essential for studying and working with these substances.