The correct IUPAC name for the complex ion [CoCl \(\left.(\mathrm{ONO})(\mathrm{en})_{2}\right]^{+}\) is (a) Bis(ethylenediamine)chloronitrito-O-cobalt (III) ion (b) Bis(ethylenediamine) chloronitrito-O-cobaltate (III) ion (c) Chlorodiethyldiamine nitrite-O-cobalt(III) ion (d) Chlorodiethyl diamine nitrocobalt(III) ion

Coordination chemistry is a branch of inorganic chemistry dealing with coordination compounds, which are constituted of a central metal atom or ion bonded to surrounding molecules or ions called ligands. These ligands can donate electron pairs to form coordinate covalent bonds. Complexes consist of a diverse array of metal ions and ligands, creating structures with various geometrical and bonding properties.

As coordination compounds play a crucial role in various biological systems and industrial applications, understanding their formation and nomenclature becomes essential. These compounds are not just metal salt aggregates but are structured specifically through ligand coordination where the geometry can significantly impact the compound's reactivity and function.

The oxidation state of a central metal in a coordination compound is the charge it would have if all ligands were removed along with the electron pairs that were shared with the metal. It's instrumental in determining the compound's chemical behavior. In naming coordination compounds, the oxidation state of the metal is indicated by Roman numerals in parentheses immediately following the metal's name.

In the example \(\left.\mathrm{CoCl}(\mathrm{ONO})(\mathrm{en})_{2}\right]^{+}\), the overall charge of the complex (+1) helps determine the oxidation state of cobalt. Calculating the charges from each ligand and applying the principle of charge neutrality allows us to deduce that cobalt must have a +3 oxidation state to balance the charges contributed by the chloride and nitrito ligands.

In coordination chemistry, ligands are the ions or molecules bound to the central metal. The naming of ligands follows specific rules: anionic ligands end in '-o', whereas neutral ligands are usually referred to by their common names. Prefixes like 'di-', 'tri-' are used to denote the number of identical ligands, but sometimes, to avoid confusion, the Greek prefixes 'bis-', 'tris-', are preferred.

In our exercise, 'chloro' represents the chloride ion \(\mathrm{Cl}^{-}\), and 'nitrito-O' signifies the ligand binding through an oxygen atom. Ethylenediamine, being a neutral bidentate ligand, retains its name. The prefix 'bis' is used to indicate there are two ethylenediamine ligands, preventing any confusion with potential ligands that may have repeating syllables in their names.

Complex ions are charged species consisting of a central metal ion surrounded by ligands. The charge of the complex ion is crucial as it influences the complex's name and properties. A positive complex ion retains the metal's name, while a negative complex retains its name with an '-ate' suffix.

In our given complex ion, \(\left.\mathrm{CoCl}(\mathrm{ONO})(\mathrm{en})_{2}\right]^{+}\), cobalt functions as the central metal with a positive charge. Hence, its name remains 'cobalt.' Identifying the charge of complex ions is a fundamental skill in coordination chemistry, essential for students to master for a proper understanding of the subject matter.