IUPAC Nomenclature of Complex Compounds Preparation and Properties
IUPAC Nomenclature of Complex Compounds :
- The system of nomenclature was suggested by Werner and recommended by IUPAC.
- In order to name complex compounds, certain rules have been framed by IUPAC. These are as follow :
- Like simple salts, the positive part of the complexes is named first and is followed by the name of negative part. The names of cations and anions are separated by a space. In case the complex is non-ionic, it is named as one word.
- In the complex species (cationic or anionic or neutral) ligands are named first followed by the name of central atom.
- The oxidation state of the central metalis indicated by Roman numerls I, II, III, IV ete in brackets immediately after its name.
- The suffix ‘ate’ is added to the name of central metal for anionic complex species. For this, latin names are preferred in place of English name.
- Co → Cobaltate
- Pb → Plumbate
- Ni → Nickelate
- Hg → Mercurate/hydrazinate
- Cr → Chromate
- Ag → Argenate
- Cu → Cuprate
- Sn → Stannate
- Au → Aurate
- Fe → Ferrate
When coordination sphere is either cation or a neutral molecule, the usual name of central metal is used.
→ Naming of Ligands : The different types of differently in a complex compound .
Anionic ligands ending with ido, ito, ato whose name end in ide, ite, ate, i.e., by replacing with ‘o’
→ Some Exceptions : Neutral ligands are given the same names as the neutral molecules.
C5H5N → pyridine (Py)
P(C6H5)3 → tri phenyl phosphine
NH2CH2 – CH2NH2 → Ethylene diamine
However, some exceptions to this rule are :
- H2O → aqua
- NH3 → ammine
- CO → carbonyl
- NO → nitrosyl
- CS → thiocarbonyl
- O2 → dioxygen
→ Name of positive ligands end with ‘ium’
- NH4+ → ammonium
- NO+ → nitrosylium
- NH2 – +NH3 → hydrazinium
- Cl+ → cichloronium
→ When more than one type of ligands are present, they are named in alphabetical order without separation by hyphen.
→ If the number of a particular ligand is more than one in the complex ion, the number is indicated by using Greek numbers such as di, tri, tetra, etc. However, when the ligand includes these numbers. Example: ethylenediamine, dipyridyl etc., then bis, tris, tetrakis etc., are used in place of di, tri, tetra etc.
→ The point of attachment in case of ambidentate ligands, with more than one coordinating atoms is either indicated by using different names for the ligands or by placing the symbol of the donor atom attached.
- CN– → cyano or cyano-C
- NC– → isocyano or cyano-N
- NO2– nitro or nitro-N
- ONO– → nitrito or nitro-O
- SCN– → thiocyanato or thiocyanato-S
- NCS– → isothiocyanato or thiocyanato-N
→ Naming of Bridging ligands : The complexes having two or more metal atoms, are called polynuclear complexes. In these complexes, ligands may simultaneously coordinate with two or more metal atoms, such ligands are called bridging ligands.
→ In naming of such complexes, bridged ligands are separated from the rest of the complex by the using prefix ‘µ’ before their names. If there are two or more bridging groups of the same kind, this is indicated by di, µ, tri – µ etc.
Example : [(NH3)5 Co-NH2 – Co(NH3)5] (NO3)5
Pentaammine cobalt (III)- µ – amido – pentaammine cobalt(III) nitrate
Nomenclature formula to write the names of various types of complexes:
→ Name of coordination compound having positive complex ion
→ Name of coordination compound having negative complex ion
→ Name of neutral complex Ligand + Metal + O.S.
The following examples will make the rules more clear:
Effective Atomic Number (EAN)
→ Sidqwick suggested that after the ligands have donated electron pair to theeentrai metal ion through coordinate bonding, the total number of electrons on central atom is called effective atomic number of the central metal ion.
EAN is calculated by the following relations:
→ EAN = [Atomic no. of metal – Ox. state of metal] + No. of electron gained from the donor atoms of the ligands.
In many cases, EAN is equal to the atomic number of the inert gas of same period.
Complexes in which metals have EAN to next inert gas are stable complexes (EAN rule). But in many stable complexes, it is failed.