Question

Give IUPAC names for each of the following: (a) \(\left[\mathrm{AgI}_{2}\right]^{-}\) (d) \(\left[\mathrm{Cr} \mathrm{Cl}\left(\mathrm{NH}_{3}\right)_{5}\right] \mathrm{SO}_{4}\) (b) \(\left[\mathrm{SnS}_{3}\right]^{2-}\) (e) \(\mathrm{K}_{3}\left[\mathrm{Co}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{3}\right]\) (c) \(\left[\mathrm{Co}(\mathrm{en})_{2}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2}\right] \mathrm{SO}_{4}\)

Short answer

The IUPAC names are (a) diiodoargentate(I), (b) trithiostannate(IV), (c) diaquabis(ethylenediamine)cobalt(III) sulfate, (d) pentaamminechlorochromium(III) sulfate, and (e) potassium tris(oxalato)cobaltate(III).

Step-by-step solution

Naming the complex \( \left[\mathrm{AgI}_{2}\right]^{-} \)

Begin by identifying the central metal and its oxidation state. Silver (Ag) is the metal, and since iodide (I) has a -1 charge each, the total negative charge is -2. As there is one extra negative charge, silver's oxidation state must be +1. The anion iodide is called 'iodo' as a ligand. Since there are two iodides, we use the prefix 'di'. The metal in an anionic complex is named with the suffix '-ate', but since silver retains its Latin name, it is named argentate. The coordination complex name is 'diiodoargentate(I)'.

Naming the complex \( \left[\mathrm{Cr} \mathrm{Cl}\left(\mathrm{NH}_{3}\right)_{5}\right]\mathrm{SO}_{4} \)

Chromium is the central metal. The ammonia ligands are neutral, so the complex charge is due to the single chloride ligand, making the complex cationic. The oxidation state of chromium is +3 (since ammonia is neutral and chloride has a -1 charge). The ligands are listed alphabetically with prefixes denoting their quantity: pentaammine (for the five ammonia molecules) and chloro (for the chloride). The sulfate is the counterion. The final name is 'pentaamminechlorochromium(III) sulfate'.

Naming the complex \( \left[\mathrm{SnS}_{3}\right]^{2-} \)

Tin (Sn) is the central metal. The ligand is sulfide with a -2 charge each, but the overall charge of the complex is -2, meaning the tin must have a +4 oxidation state. In naming, sulfide becomes 'thio', and with three sulfide ions, it becomes 'trithio'. Include the oxidation state of the metal as a Roman numeral in parentheses. The name is 'trithiostannate(IV)'.

Naming the complex \( \mathrm{K}_{3}\left[\mathrm{Co}\left(\mathrm{C}_{2}\mathrm{O}_{4}\right)_{3}\right] \)

Here, cobalt is the central metal in a complex anion. The ligand is oxalate, named 'oxalato'. With three oxalate ligands, use the prefix 'tris'. Since the complex has a 3- charge neutralized by the three potassium ions, the oxidation state of cobalt is +3. The final name is 'potassium tris(oxalato)cobaltate(III)'.

Naming the complex \( \left[\mathrm{Co}(\mathrm{en})_{2}\left(\mathrm{H}_{2}\mathrm{O}\right)_{2}\right] \mathrm{SO}_{4} \)

The central metal is cobalt. The ligands include en (ethylenediamine), a bidentate ligand, and two water molecules. As there is a sulfate counterion, the complex has a +2 charge, giving cobalt a +3 oxidation state. The prefix for two ethylenediamine ligands is 'bis', and for two water molecules, 'diaqua'. The name is 'diaquabis(ethylenediamine)cobalt(III) sulfate'.

Key concepts

Coordination Chemistry

Coordination chemistry is a branch of inorganic chemistry that deals with the structure, properties, and reactivity of coordination compounds, which are complex molecules with a metal atom or ion at their center, surrounded by multiple ligands. Ligands are ions or molecules that can donate pairs of electrons to the metal, forming coordinate covalent bonds.

In understanding coordination compounds such as those in the exercise, it's essential to recognize that the central metal and the ligands work together to form a stable arrangement. The metal's ability to act as a Lewis acid (an electron-pair acceptor) combined with the ligands acting as Lewis bases (electron-pair donors) results in the formation of these distinctive compounds. The overall charge of the compound can be neutral, positive, or negative, and its proper name depends on the combination of the metal's oxidation state and the nature and number of the ligands, as demonstrated in the naming process for the provided compounds.

Coordination chemistry not only includes naming these compounds but also exploring their applications, such as in catalysis, biological systems, and material science. The structure and naming of these compounds form a fundamental part of the understanding of coordination chemistry.

Oxidation States

The oxidation state, or oxidation number, of an atom within a compound, indicates the degree of oxidation of that atom. It is defined as the charge an atom would have if all bonds to atoms of different elements were completely ionic. Understanding oxidation states is crucial in coordination chemistry when identifying the chemical makeup of coordination compounds.

Oxidation states allow us to comprehend how electrons are distributed in a compound which directly influences a compound's reactivity and properties. For example, when determining the oxidation state of the central metal in a coordination compound, it's obvious that the charge on the complex and the charges of the individual ligands are intimately related to it. Silver, for instance, has an oxidation state of +1 in 'diiodoargentate(I)' because each iodide ion carries a -1 charge, canceling out the silver’s +1 charge in the overall anionic complex.

The oxidation state of a metal can affect the compound's color, magnetic properties, and how it interacts with other molecules. It's a foundational concept that enables students to better predict and explain the outcomes of chemical reactions involving coordination compounds.

Ligand Nomenclature

The nomenclature of ligands in coordination compounds forms a critical aspect of the naming conventions in coordination chemistry. Ligands are named before the metal center, and their names often derive from their base ions or molecules, with specific prefixes and suffixes used to indicate their number and type.

In the IUPAC system of nomenclature, neutral ligands are named using their usual organic or common name (e.g., 'NH₃' becomes 'ammine'). Anionic ligands are denoted with an 'o' ending (e.g., 'Cl^-' becomes 'chloro'). When dealing with multiple ligands of the same type, numerical prefixes are used, such as 'di-' for two, 'tri-' for three, and so forth. However, for ligands that already contain a numerical prefix in their name, such as 'ethylenediamine (en)' or 'oxalate', special prefixes like 'bis-', 'tris-', and 'tetrakis-' are used, which prevent confusion.

Properly naming ligands is not only essential for clear communication in chemistry but also for understanding the symmetry, geometry, and potential reactivity of the corresponding coordination compounds.

Metal Complexes

Metal complexes consist of a central metal atom or ion bonded to surrounding ligands via coordinate covalent bonds. These complexes, a central topic in coordination chemistry, can have various geometries and properties dictated by the metal center and the number and type of ligands attached to it.

Metal complexes are incredibly diverse; they can range from simple structures with just a few ligands to intricate setups with multiple ligands creating large macromolecular compounds. For example, in 'potassium tris(oxalato)cobaltate(III)', cobalt forms a complex with three oxalate ligands creating a 3-dimensional structure. The charge on the metal center, its possible oxidation states, the type of ligands attached, and how they're arranged are all fundamental in determining a complex's properties.

In metal complexes, it's the central metal's properties, such as the number of available orbitals for bonding and its oxidation state, which will largely decide which ligands can bind and in what arrangement. Understanding these complexes enables the study of various chemical processes, including those important to industrial catalysis and bioinorganic chemistry.