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Naming of Co-ordination Compounds

Just like nomenclature of organic compounds, nomenclature is important in Coordination Chemistry also. Naming of coordination compounds is needed for providing an unambiguous method for representing and describing formulas and names of coordination compounds systematically. The nomenclature becomes even more important when dealing with the isomers of the same coordination compound.

The formulas and names which are used for coordination compounds are based on the rules of the International Union of Pure and Applied Chemistry (IUPAC).

Before we learn how to write name of any coordination compounds, lets firs learn how to write the formula of any coordination compound

The formula of a coordination compound is a tool which is used for providing  basic information regarding the constitution of the coordination compound in a brief,convenient and meaningful manner.

In coordination compounds,  

  • Within the coordination entities the central atom/ion is listed first followed by the ligands

  • The ligands are then listed after the central metal atom/ion in alphabetical order.

  • The formula of coordination entity, is written in square brackets.

  • Ligand abbreviations are also writtenin parentheses.

  • There should be no space between the ligands and the metal within a coordination sphere.

  • The charge on  the cation(s) is balanced by the charge of the anion(s).

Let’s have a look at these IUPAC rules for nomenclature of organic compounds one by one.

Rule 1:

While naming a coordination compound, cation is always named before the anion irrespective of the fact that whether the complexion is cation or anion.

For example:

Na[Co(NH)4 (Cl)2] →  Na is to be named first followed by [Co(NH)4 (Cl)2]

Sodium tetramminedichlorocoblatate(I)

[Co(NH)4 (Cl)2]SO4 →  [Co(NH)4 (Cl)2] is to be named first followed by SO4

Tetraamminedichlorocobalt(0) sulphate.

Rule 2:

  • If there are more than one type of ligands present in any coordination compound, the name of the ligands is to be done in alphabetic order followed by the name of central metal atom/ion.

  • Name of the anionic ligands, ends with ‘o”.
    For example, Chloride → Chlorideo, Nitrate → Nitrito

  • For neutral ligands, their common name are used as such e.g.
    H2NCH2CH2NH2 → ethylenediamine
    H2O → aqua,
    NH3 → ammine,
    CO → carbonyl
    N2  → dinitrogen|
    O2 → dioxygen.

Anionic ligands

Neutral ligands

Br 

Bromo

NH3

Ammine

F

Fluoro

H2O

Aqua

O2–

Oxo

NO

Nitronyl

OH

 Hydroxo

CO

Carbonyl

CN

Cyano

O2

Dioxygen

C2O42–

Oxalato

 N2

Dinitrogen

CO32–

Carbonato

H2NH2C | H2NH2C

Ethylene diamine

CH3COO

Aceto

Rule 3:

If the names of the ligands already contains a numerical prefix , then the terms, bis, tris, tetrakis are used and the ligand to which they refer being placed in parentheses.
For example,
[NiCl2(PPh3)2] is named as dichloridobis(triphenylphosphine)nickel(II)

Rule 4: 

After naming the ligand in alphabetic order, name the central metal atom/ion is written.

  • If the complex ion is a cation, metal is named same as the element.

  • If the complex is an anion, the name of metal ends with the suffix -ate for Latin name.

English name

Latin name

Anion name

Copper

Cuprum

Cuprate

Gold

Aurum

Aurate

Iron

Ferrum

Ferrate

Lead

Plumbum

Plumbate

Silver

Argentum

Argentate

Tin

Stannum

Stannate

Rule 5: 

The oxidation state of the metal in the complex is given as a roman numeral in parentheses.

Rule 6:

The neutral complex molecule is named similar to that of the complex cation.

Rule 7:

These are some ligands which  may be attached to the central metal atom/ion through different atoms. For example NO2, CN etc..

Thus M-NO2 → nitro

M-ONO →  nitrito.

M-SCN →  thiocyanato

M-NCS →  isothiocyanato

Refer to the followinbg video for naming of coordination compounds

Solved Problem

llustration 1: IUPAC name  of K2[Fe(NC)3Cl2(NH3)2]

Solutions:                 
The positive part is named first followed by the negative part. In
the negative part the names are written in alphabetical order followed
by metal. So the name is Potassiumdiamminedichlorotricyano-N-
ferrate (III)

Illustration 2: IUPAC name of [Co(NH3)4(NO2)2]Cl
Solution:
In the earlier two examples the negative part was the complex part while in this case the positive part is the complex. So it is named first with ligands in alphabetical order followed by metal (but not ending in –ate as the metal belong to the positive part of the complex). This is followed by the negative part. So the name is Tetraamminedinitrocobalt (III) chloride.

Illustration 3: Write IUPAC name of [Pt(Py)4][PtCl4].

Solution:             
Here both the positive and negative part has the same metal. Procedure is same earlier are the IUPAC name. Tetrapyridineplatinum(II) tetrachloroplatinate(II).

Illustration 4: Write the IUPAC name of [Fe(NH3)4O2C2O4]Cl

Solution:             
In this charge on the complex part is +1. The ligand oxalato has a charge of –2, so iron should be in  +3 state meaning O2 to be neutral. Now had O2 been superoxo (O2) or peroxo (O2– – ) the negative charge of the ligands should have been –3 and –4 respectively. In that case Iron has to be +4 and +5 which is not possible. So O2 will behave as a neutral ligand and IUPAC name is Tetraammineoxalatodioxygeniron (III) chloride.

Related Resources

To read more, Buy study materials of Coordination Compounds comprising study notes, revision notes, video lectures, previous year solved questions etc. Also browse for more study materials on Chemistry here.

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