Give systematic names for the following formulas: (a) \(\left[\mathrm{Ni}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right] \mathrm{Cl}_{2}\) (b) \(\left[\mathrm{Cr}(\mathrm{en})_{3}\right]\left(\mathrm{ClO}_{4}\right)_{3}\) (c) \(\mathrm{K}_{4}\left[\mathrm{Mn}(\mathrm{CN})_{6}\right]\)

Coordination complexes form when central metal ions join with surrounding ligands to create a larger complex. These complexes can have different geometries like octahedral, tetrahedral, or square planar. Understanding the basic structure helps in identifying the core components of a coordination complex. For example:

• In \(\big[\text{Ni}(\text{H}_2\text{O})_6\big]^{2+}\), nickel (Ni) is the central metal ion, surrounded by six water molecules (H₂O) as ligands forming an octahedral shape.
• In \(\big[\text{Cr}(\text{en})_3\big]^{3+}\), chromium (Cr) is surrounded by three ethylenediamine (en) molecules as ligands, also forming an octahedral structure.
• In \(\big[\text{Mn}(\text{CN})_6\big]^{4-}\), manganese (Mn) is joined by six cyanide (CN^-) ions forming another octahedral complex.

Knowing how these components fit together will make it easier to decode and name coordination complexes.

Ligands are molecules or ions that donate pairs of electrons to the central metal ion, forming bonds. They are named based on their structure and the atoms involved in bonding. Some common ligands include:

• Water (H₂O) is called 'aqua'.
• Ammonia (NH₃) is called 'ammine'.
• Ethylenediamine (en) is a bidentate ligand, meaning it forms two bonds with the central metal ion.
• Cyanide (CN^-) is called 'cyano'.

When naming a complex, the ligands are listed first in alphabetical order before the name of the central metal ion. For instance, in \(\big[\text{Ni}(\text{H}_2\text{O})_6\big]^{2+}\), the ligands are six water molecules, so it's named 'hexaaqua'. Similarly, in \(\big[\text{Cr}(\text{en})_3\big]^{3+}\), three ethylenediamines give 'tris(ethylenediamine)'. The prefix 'tris' is used instead of 'tri' because ethylenediamine is a complex ligand.

The oxidation state of the central metal ion is crucial for naming coordination complexes. It indicates the charge on the metal after accounting for the electrons donated by the ligands. To determine the oxidation state:

• Sum the charges of the ligands and any counter ions present.
• Equal this sum to the overall charge of the complex.

For example:
In \(\big[\text{Ni}(\text{H}_2\text{O})_6\big]^{2+}\), each water ligand is neutral, and the charge of the complex is +2, so the oxidation state of nickel is +2.
In \(\big[\text{Cr}(\text{en})_3\big]^{3+}\), each ethylenediamine is neutral, and the charge of the complex is +3, making chromium's oxidation state +3.
In \(\big[\text{Mn}(\text{CN})_6\big]^{4-}\), each cyanide ligand has a charge of -1, leading to a total charge of -6 from the ligands. If the complex's overall charge is -4, then manganese must be in the +2 oxidation state to balance the charges.

The central metal ion is the core of the coordination complex. The properties and identity of the central metal ion greatly influence the formation and stability of the complex. Notable factors include:

• Metal ions can come from various groups in the periodic table, including transition metals like iron (Fe), nickel (Ni), chromium (Cr), and manganese (Mn).
• The oxidation state of the metal ion affects the coordination number, which is the number of ligand atoms attached to the central metal ion.
• The geometry and physical properties of the coordination complex are also dependent on the metal ion.

The systematic naming of complexes includes the metal name, followed by its oxidation state in parentheses. For example, in \(\big[\text{Ni}(\text{H}_2\text{O})_6\big]^{2+}\), the name is 'nickel(II)', indicating nickel with an oxidation state of +2. This is followed by the names of the ligands to complete the systematic name.