IUPAC Nomenclature of Mononuclear Coordination Compounds

Coordination compounds are chemical compounds that consist of an array of anions or neutral molecules that are bound to a central atom via coordinate covalent bonds. These compounds are also known coordination complexes. These molecules  that are bound to the central atom are referred to as complexing agents or ligands.

Important Points involved in Coordination Compounds

The definitions of some important terms of coordination compounds can be found below as follows-

Coordination Entity

The chemical compound in which the central ion is bound to a set number of atoms or molecules or ions is called a coordination entity.

Some examples of such coordination entity include [CoCl3(NH3)3], and [Fe(CN)6]4-.

Central Atoms and Central Ions

As we know, the atoms and ions to which a set number of atoms, molecules or ions are attached are referred to as the central atoms and the central ions.

In coordination compounds the central atoms or ions are commonly Lewis Acid and can, therefore act as electron-pair acceptors.

Ligand

The atoms or molecules or ions that are connected to the coordination centre or the central atom/ion are referred to as ligands.

The ligand can be a simple ion or molecule (such as Cl– ) or in the form of relatively large molecules such as ethane-1,2-diamine (NH2-CH2-CH2-NH2).

Coordination Number

The coordination number of the central atom in the coordination compound refers to the total number of single bonds through which the ligands are bound to the coordination centre.

In the coordination complex given by [Ni(NH3)4]2+, the coordination number of nickel is 4.

Coordination Sphere

The non- ionizable part of the compound consists of a central transition metal ion surrounded by atoms.

The coordination centre, the ligands attached to the coordination centre, and the net charge of the chemical compound as a whole are the coordination sphere when written together.

The coordination sphere is always accompanied by a counter ion (the ionizable groups that attach to charged coordination complexes).

Example: [Co(NH3)6]C/3 – coordination sphere

IUPAC nomenclature of mononuclear coordination compounds

1. The cation comes first, then the anion. These ions are not in the coordination sphere.
   • diamine silver(I) chloride [Ag(NH3)2]Cl
   • potassium hexacyanoferrate(III) K3[Fe(CN)6]
2. Inner Sphere Complex Ion is enclosed by using brackets. Within the sphere the ligand will be named first and then the metal, however, in writing formulas, the metal ion is written first always.
   • Ligands are named before the metal
   • Metal is written first in the formula
   • A space only between cation and anion
   • No capitalization is needed
     • tetraamminecopper(II) sulfate [Cu(NH3)4]SO4
     • hexaamminecobalt(III) chloride [Co(NH3)6]Cl3
3. These Prefixe denote the number of each type of ligand. The  prefixes and parentheses denoted when the ligand is already containing a prefix.Within this sphere, the ligands should be named before the name of the metal, but in formulas  the metal ion is written first as was the case with sphere.

• dichlorobis(ethylenediamine)cobalt(III) fluoride [Co(en)2Cl2]F
• tris(bipyridine)iron(II) chloride [Fe(bipy)3]Cl2

  Ligands are named in alphabetical order and prefixes are not counted. 

• tetraamminedichlorocobalt(III) [Co(NH3)4Cl2]+ 
• ammine bromo chloro methyl amine platinum(II) [Pt(NH3)BrCl(CH3NH2)]

  Ligand name alterations to consider: 

• Anionic ligands are given with the following  -o suffix: chloro, fluoro, oxo, sulfato
• Neutral ligands will given by these  names: methylamine, bipyridine
• Water becomes aqua
• NH3 becomes that  ammine to keep separate from alkylamines

  One of the two systems can be used  for showing charge or oxidation state of metal ion 

•  The oxidation state is given in Roman Numerals in parentheses after the metal ion name. This is the most common method.
• Ewing-system: charge of the total complex ion is placed in parentheses after the name of the metal ion.
• Both systems will add –ate to the metal name if the complex ion has an overall (-) charge
• [Pt(NH3)4]2+ = tetraammineplatinum(II) or (2+)
  • [PtCl4]2- =tetrachloroplatinate(II) or (2-)
  • [PtCl6]2- =hexachloroplatinate(IV) or (2-)

  Isomer designations are given before the rest of the name  

• cis-diamminedichloroplatinum(II)
• trans-diamminedichloroplatinum(II)

  Bridge forming  ligands are denoted with the prefix μ 

• [(NH3)4Co(OH)(NH2)Co(NH3)4]4+ = μ-amido-μ-hydroxobis(tetraamminecobalt(III))

  Negative charged complexe of metals are given by their Latin names:
Fe = ferrate Ag = argenate Sb = stibate Au = aurate

Pb will be known as plumbate, Sn will be given as stannate Au will given as aurate

The following Exception are Hg still called mercurate (Latin name: hydrargyrum) 

Examples of Naming Coordination Compounds:

Conclusion

1.When you are naming a transition-metal compound, it is necessary to indicate which oxidation number the metal has.

2.The oxidation number appears as a Roman numeral in parentheses after the cation.

3.Coordination compounds contain an ion and an array of ligands.

4.Naming coordination compounds involves a set of rules which includes the oxidation number of the central ion and the chemical composition of the ligand, focusing on the anionic and cationic properties of the molecule.