Question

Name each complex ion or coordination compound. a. \(\left[\mathrm{Cu}(\mathrm{en})_{2}\right]^{2+}\) b. \(\left[\mathrm{Mn}(\mathrm{CO})_{3}\left(\mathrm{NO}_{2}\right)_{3}\right]^{2+}\) c. \(\operatorname{Na}\left[\operatorname{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2}(\mathrm{ox})_{2}\right]\) d. \(\left[\mathrm{Co}(\mathrm{en})_{3}\right]\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]\)

Short answer

a. bis(ethylenediamine)copper(II) ion, b. tricarbonyltrinitromanganese(II) ion, c. sodium diaquadioxalatochromate(III), d. tris(ethylenediamine)cobalt(III) hexacyanidoferrate(III)

Step-by-step solution

Name the first complex ion

For \(\left[\mathrm{Cu}(\mathrm{en})_{2}\right]^{2+}\), the metal is copper with an oxidation state of +2 (since the complex has a 2+ charge). The ligand en (ethylenediamine) is a neutral ligand. Since there are two en ligands, we use the prefix 'bis' for naming. The copper ion is in the +2 oxidation state, which is copper(II) in naming. The name of the complex ion is 'bis(ethylenediamine)copper(II) ion'.

Name the second complex ion

In \(\left[\mathrm{Mn}(\mathrm{CO})_{3}\left(\mathrm{NO}_{2}\right)_{3}\right]^{2+}\), manganese has a 2+ charge. The ligands are CO (carbonyl), which is a neutral ligand, and NO2 (nitro), which is also a neutral ligand. With three of each ligand, we use 'tricarbonyl' and 'trinitro'. The name of the complex ion is 'tricarbonyltrinitromanganese(II) ion'.

Name the third coordination compound

For \(\operatorname{Na}\left[\operatorname{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2}(\mathrm{ox})_{2}\right]\), the metal is chromium, and the charge is not indicated, so it takes the charge of the complex after considering the counter ion, Na. There are two water (aqua) ligands, and two oxalate (ox, which is bidentate) ligands. The prefix 'di' is used for both ligands. Because the sodium ion is present, it is named first followed by the complex. The resulting name is 'sodium diaquadioxalatochromate(III)'.

Name the fourth coordination compound

In \(\left[\mathrm{Co}(\mathrm{en})_{3}\right]\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]\), we have two complex ions. The first has cobalt with three en (ethylenediamine) ligands. We use 'tris' for the three ligands. The cobalt is Co(III) because there is no overall charge on the complex. It is named 'tris(ethylenediamine)cobalt(III)'. The second complex has iron with six CN (cyanide) ligands. It is Fe(III) due to matching charges that cancel out. The name for the hexacyanide iron(III) part is 'hexacyanidoferrate(III)'. The full name of the compound is 'tris(ethylenediamine)cobalt(III) hexacyanidoferrate(III)'.

Key concepts

Coordination Compounds

Coordination compounds, also known as coordination complexes, are molecules where a central metal atom is surrounded by non-metal atoms or molecules known as ligands. These ligands are attached to the metal atom via coordinate covalent bonds and play an essential role in determining the properties and reactivity of the compound.

For instance, in the compound \(\left[\mathrm{Cu}(\mathrm{en})_{2}\right]^{2+}\), copper acts as the central metal ion, and ethylenediamine (en) is the ligand creating a coordination complex. These complexes have a wide variety of applications ranging from industrial catalysis to biological systems.

Ligands

Ligands are ions or molecules that donate pairs of electrons to a metal atom or ion to form a coordination compound. They could be anions, cations, or neutral molecules, and they can be monodentate, donating one pair of electrons, like water in \(\mathrm{H}_{2}\mathrm{O}\), or polydentate, donating multiple pairs, such as ethylenediamine. Polydentate ligands form chelates, which wrap around the metal ion like a claw.

The prefixes 'bis', 'tris', etc., are used when naming complexes with polydentate ligands to indicate multiple ligands of the same type, as seen with 'bis(ethylenediamine)copper(II) ion'.

Oxidation State

The oxidation state reflects the total number of electrons that an atom either gains or loses when forming chemical bonds. In coordination complexes, the oxidation state of the central metal ion is significant because it can determine the compound's physical and chemical properties, including color, magnetic behavior, and reactivity.

To determine the oxidation state in coordination compounds, consider the overall charge and the known charges of the ligands. For instance, the copper ion in \(\left[\mathrm{Cu}(\mathrm{en})_{2}\right]^{2+}\) has an oxidation state of +2, discerned by the 2+ charge on the entire complex ion since ethylenediamine is a neutral ligand.

Chemical Nomenclature

The systematic naming of chemical compounds is known as chemical nomenclature. For coordination complexes, the names are formed by first stating the ligands, in alphabetical order, followed by the central metal ion. Ligands are named with special suffixes or prefixes; anionic ligands end in 'o', neutral ligands are named as molecules, and cationic ligands often retain their name. The metal's name is followed by its oxidation state in Roman numerals in parentheses. For example, 'tris(ethylenediamine)cobalt(III)' indicates a cobalt ion with an oxidation state of +3, surrounded by three ethylenediamine ligands.

When naming a salt containing a coordination complex, the cation is named first followed by the anion. In mixed complex ions like \(\left[\mathrm{Co}(\mathrm{en})_{3}\right]\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]\), each complex is named separately, and the cationic complex is written first.