The IUPAC name of \(\left[\mathrm{Ni}\left(\mathrm{NH}_{3}\right)_{4}\right]\left[\mathrm{NiCl}_{4}\right]\) is (A) Tetrachloronickel (II) - tetraamminenickel (II) (B) Tetraamminenickel (II) - tetrachloronickel (II) (C) Tetraamminenickel (II) - tetrachloronickelate (II) (D) Tetrachloronickel (II) - tetraamminenickelate (0)

Coordination chemistry is a branch of chemistry that deals with coordination compounds, which are molecules with a central metal atom or ion bonded to a set of molecules or ions called ligands. These ligands donate pairs of electrons to the metal center, forming coordination bonds.
Coordination compounds exhibit a vast array of colors, geometries, and reactivities, which make them fascinating both for theoretical studies and practical applications, such as in catalysis, material science, and medicine.
A notable feature of coordination compounds is their ability to form stable complex structures, even with transition metals that have partially filled d-orbitals. The arrangement of ligands around the central metal atom is described by coordination geometry, such as octahedral, square planar, or tetrahedral.

Chemical nomenclature is the system of names that chemists use to identify compounds accurately and systematically. For coordination compounds, the IUPAC (International Union of Pure and Applied Chemistry) provides guidelines to ensure that each compound has a unique and universally understood name.
In these naming conventions:

• The ligands are named first, in alphabetical order, irrespective of their charge.
• After the ligands, the central metal atom is named, followed by its oxidation state in Roman numerals enclosed in parentheses.
• If the complex ion is an anion, the metal name often ends with the suffix 'ate'.

It is crucial to use these rules to accurately describe the composition and charge states of the components within a coordination compound.

Ligands are atoms, ions, or molecules that can donate a pair of electrons to a metal to form a coordination bond. They are critical components in the formation of complex ions, which are charged species consisting of a central metal ion surrounded by ligands. Ligands vary greatly in terms of their charge, size, and the number of electrons they donate, which affects the stability and geometry of the corresponding complex ion.
Complex ions can be cationic or anionic, depending on the overall charge. Cationic complexes tend to be formed with neutral or positively charged ligands, while anionic complexes typically contain one or more negatively charged ligands. Understanding the nature of ligands and the structure of complex ions is essential for predicting the properties of coordination compounds, including their reactivity, magnetic behavior, and biological activity.