Question

Write the names of the following compounds, using the standard nomenclature rules for coordination complexes: (a) \(\left[\mathrm{Rh}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{Cl}_{2}\right] \mathrm{Cl}\) (b) \(\mathrm{K}_{2}\left[\mathrm{TiCl}_{6}\right]\) (c) \(\mathrm{MoOCI}_{4}\) (d) \(\left[\operatorname{Pt}\left(\mathrm{H}_{2} \mathrm{O}\right)_{4}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)\right] \mathrm{Br}_{2}\)

Short answer

The names of the given coordination complexes are as follows: (a) tetraamminedichlororhodium(III) chloride (b) potassium hexachlorotitanate(IV) (c) oxotetrachloromolybdenum(VI) (d) tetraaqua(oxalato)platinum(IV) bromide

Step-by-step solution

Identify the Central Atom

Look for the metal ion in each coordination complex. It will be the central atom and the species surrounding it will be the ligands.

Identify the Ligands

Identify the ligands surrounding the central atom. Ligands are species that can donate one or more lone electron pairs to the central metal atom.

Follow IUPAC Nomenclature Rules

Name the complex using the IUPAC nomenclature rules: list the ligands alphabetically in the formula, name the anionic ligands before the neutral ligands, use proper prefixes and ligand names, and use Roman numerals to express the oxidation state of the central atom. (a) $\left[\mathrm{Rh}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{Cl}_{2}\right] \mathrm{Cl}$ - Central Atom: Rh - Ligands: 4 \(\mathrm{NH}_{3}\) (ammine) and 2 \(\mathrm{Cl}^{-}\) (chloro) - Name: tetraamminedichlororhodium(III) chloride (b) \(\mathrm{K}_{2}\left[\mathrm{TiCl}_{6}\right]\) - Central Atom: Ti - Ligands: 6 \(\mathrm{Cl}^{-}\) (chloro) - Name: potassium hexachlorotitanate(IV) (c) \(\mathrm{MoOCI}_{4}\) - Central Atom: Mo - Ligands: 1 \(\mathrm{O}^{2-}\) (oxo) and 4 \(\mathrm{CI}^{-}\) (chloro) - Name: oxotetrachloromolybdenum(VI) (d) \(\left[\operatorname{Pt}\left(\mathrm{H}_{2}\mathrm{O}\right)_{4}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)\right]\mathrm{Br}_{2}\) - Central Atom: Pt - Ligands: 4 \(\mathrm{H}_{2}\mathrm{O}\) (aqua) and 1 \(\mathrm{C}_{2}\mathrm{O}_{4}^{2-}\) (oxalato) - Name: tetraaqua(oxalato)platinum(IV) bromide

Key concepts

IUPAC Nomenclature Rules

Understanding the principles of naming coordination complexes is essential for clear communication in chemistry. The International Union of Pure and Applied Chemistry (IUPAC) developed standardized rules for the nomenclature of coordination compounds to ensure consistency and clarity.

The IUPAC naming conventions involve several steps: First, when naming a coordination complex, the ligands are listed before the metal center. Anionic ligands typically end with an '-o' suffix, while neutral and cationic ligands are generally called by their common names. Prefixes such as 'mono', 'di', 'tri', etc., are used to indicate the number of each type of ligand in the complex.

• If there is more than one type of ligand, they are named in alphabetical order.
• The metal's name is followed by its oxidation state given in Roman numerals within parentheses.
• For charged complexes, the cation precedes the anion.

When naming anionic complexes, the metal name ends in '-ate'. Moreover, if the compound is an optical isomer, the prefixes 'cis-', 'trans-', 'fac-', or 'mer-' are used to denote the geometry of the complex.

Central Atom Identification

The central atom in a coordination complex is typically a transition metal ion or a metalloid. It serves as the core of the complex to which ligands are coordinated, usually through dative, or coordinate covalent bonds.

To identify the central atom, look for the metal in the formula. It will be in square brackets if it's part of the coordination sphere or outside if it's a counter ion. The metal's oxidation state is important for nomenclature and determining the formula of the complex. It's especially critical to note the metal when naming the complex, as the central atom will influence the overall name.

Ligand Identification

Ligands are ions or molecules that bind to the central atom in a coordination complex. They are characterized by the presence of lone electron pairs that can be donated to the metal, forming coordinate covalent bonds.

To identify ligands in a given complex, look for species within the square brackets besides the central atom. Each ligand's name is modified when part of a coordination complex: negatively charged ions typically take an -o ending, such as 'chloro' for Cl- or 'oxo' for O2-. Neutral molecules retain their common names, such as 'water' becoming 'aqua' and 'ammonia' turning into 'ammine'. Polydentate ligands, which can attach at multiple binding sites, are given special names like 'ethylenediamine' for en or 'oxalate' for ox.

Oxidation State Determination

The oxidation state of the central atom is essential to correctly name a coordination complex. It can be calculated by considering the overall charge of the complex and the charges of each ligand.

To determine the oxidation state, assign charges to known ions and neutral molecules first. For example, NH3 as 'ammine' is neutral, while Cl- as 'chloro' has a charge of -1. Then, sum these charges; the oxidation state of the central metal is what would be necessary to balance the overall charge of the coordination complex. In naming, the oxidation state is indicated in Roman numerals in parentheses right after the metal's name. For instance, if a metal center has an oxidation state of +3, it would be represented as '(III)'. Understanding this aspect is critical for accurate nomenclature and chemical communication.