Question

A coordination complex (or coordination compound) consists of a central metal ion surrounded by ions or neutral molecules called ligands. The name of the complex specifies the number and types of ligands, as well as the name and oxidation number of the metal. Here are some common ligands and their names:

Ligand	Name
Cl−	chloro
F−	fluoro
CO32−	carbonato
O2−	oxo
CN−	cyano
en	ethylenediamine
NH3	ammine
H2O	aqua
CO	carbonyl

To get an idea of how coordination complexes are named, consider the following examples:

[Pt(NH3)2(H2O)2]2+= diamminediaquaplatinum(II),

[PtCl4]2−= tetrachloroplatinate(II),

K2[PtCl4]= potassium tetrachloroplatinate(II), and

[Pt(en)2]2+= bis(ethylenediamine)platinum(II).

Notice that "platinum" becomes "platinate" only if the complex has an overall negative charge. Here are some metals and their names in complex anions.

Metal	Anion name	Metal	Anion name
Aluminum	Aluminate	Iron	Ferrate
Chromium	Chromate	Manganese	Manganate
Cobalt	Cobaltate	Nickel	Nickelate
Copper	Cuprate	Platinum	Platinate
Gold	Aurate	Zinc	Zincate

Similarly, copper, gold, and iron become cuprate, aurate, and ferrate, respectively, in complex anions. Also note that for the ethylenediamine ligand, en, the prefixes bis, tris, and tetrakis are used instead of di, tri, and tetra.

Part A

Name the complex ion [Cu(NH3)2(H2O)2]2+. The oxidation number of copper is +2.

Part B

Name the complex CoCl2(en)2. The oxidation number of cobalt is +2.

Part C

Name the salt [Ni(H2O)3(CO)]SO4. The oxidation number of nickel is +2.

Some ligands that have multiple donor atoms may act as monodentate or bidentate ligands, depending on the molecule. For example, although the carbonate ion CO32− has up to two donor atom sites, sometimes only one donor atom is used. You can sometimes use the coordination number of a metal ion to determine the number of donor atoms. Since cobalt(III) most frequently has a coordination number of 6, carbonate is most likely acting as a bidentate ligand in [Co(CO3)(NH3)4]3+. However, since platinum(II) has a coordination number of 4, carbonate is most likely acting as a monodentate ligand in [Pt(CO3)(NH3)3]3+.

Part E

Name the salt K4[Pt(CO3)2F2] given that the carbonate ion acts as a monodentate ligand in the complex. The oxidation number of platinum is +2.

Answer 1

Coordination complex consists of central metal atom/ion which is bonded to electron rich species, called as ligands via coordinate covalent bonds.

The nomenclature of Coordination complexes:

1. Calculation of the oxidation state of the metal atom/ion.

2. The ligands attached to the metal atom/ion is written in English alphabet order. Prefix- di, tri, tetra are added to denote the number of ligand molecules present in the complex.

3. Ligands like ethylene diamine contains di in its name. Thus, to denote the number of such ligands, bis, tris, etc. are used.

4. The positive part is written first followed by the negative part of the complex.

5. The complex can be neutral or ionic. For the ionic complex compounds, 'ion' is written in the name. For the neutral ones, the positive charge and the negative charge are written separately.

6. If the coordination sphere contains negative charge, then suffix -ate is written to the metal atom/ion. For example, copper is written as cuprate, iron is written as ferrate.

7. Ligand names are written followed by the metal atom/ion and the oxidation state of it is written in roman number in brackets.

(a)

Given,

The complex ion: [Cu(NH₃)₂(H₂O)₂]²⁺

The oxidation number of copper is +2.

The complex contains ligands NH₃ and H₂O.

NH₃ is written as ammine and H₂O as aqua. NH₃ is written first because ammine will come before aqua in the English alphabet.

2 molecules of NH₃ are acting as ligands in the complex. So, written as: diammine

2 molecules of H₂Oare acting as ligands in the complex. So, written as: diaqua

The name of the complex is:

diamminediaquacopper(II) ion

(b)

Given,

The complex ion: CoCl₂(en)₂

The oxidation number of cobalt is +2.

The complex contains ligands Cl₂ and en which means ethylene diamine.

Cl₂ is written as chloro and en as ethylene diamine. Cl₂ is written first because chloro will come before ethylene diamine in the English alphabet.

2 molecules of Cl₂ are acting as ligands in the complex. So, written as: dichloro

2 molecules of enare acting as ligands in the complex. So, written as: bis(ethylene diamine).

The name of the complex is:

dichlorobis(ethylene diamine)cobalt(II)

(c)

Given,

The complex ion: [Ni(H₂O)₃(CO)]SO₄

The oxidation number of nickel is +2.

The complex contains ligands H₂O and CO

H₂O as aqua and COis written as carbonyl. H₂Ois written first because aqua will come before carbonyl in the English alphabet.

2 molecules of H₂Oare acting as ligands in the complex. So, written as: diaqua

1 molecule of COare acting as ligands in the complex. So, written as: carbonyl

Sulfate ion is acting as spectator negative ion

The name of the complex is:

diaquacarbonylnickel(II) sulfate

(d)

Given,

The complex ion: K₄[Pt(CO₃)₂F₂]

The carbonate ion acts as a monodentate ligand in the complex.

The oxidation number of platinum is +2.

The complex contains ligands H₂O and CO₃

CO₃ as carbonato and Fis written as fluoro. CO₃ is written first because carbonato will come before fluoro in the English alphabet.

2 molecules of CO₃ are acting as ligands in the complex. So, written as: dicarbonato

2 molecules of F are acting as ligands in the complex. So, written as: difluoro

Potassium ion is acting as spectator positive ion.

The coordination sphere is of negative charge is platinum is written as platinate.

The name of the complex is:

potassium dicarbonatodifluoroplatinate(II)