How To Give A Name To A Coordination Complex Species

It is a tricky job to name a coordination
complex because a such type of complex is consist of many parts i.e. a central
metal ion, counter ions, ligands, where ions (may be +ve or -ve) mainly fulfill
the primary valencies, which in turn counterbalance the charge of the
coordination sphere (Central atom + ligands) and ligands mainly satisfy the
secondary valency. Ligands can be neutral, positively charged (cationic ligand)
or negatively charged (anionic ligand). So, there are some rules approved by
IUPAC (International Union of Pure and Applied Chemistry)
to name the central ion, ligands and ions to get an appropriate nomenclature of
the coordination complex. Here we will basically learn the rules and how to
apply them for such nomenclature.

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Before going to the rules we can take a
look to the different part of a coordination compound.

Now come to the rules.

Rule 1: The naming should start with
ligands maintaining alphabetic order if there are more than one type of ligands
and after that central metal ion should be named.

Rule 2:

i. For anionic
ligands, the name should end with “o”. For anions ending with “ide” (chloride,
bromide etc.), ”ate” (nitrate, sulphate etc.) and “ite” (nitrite, sulphite
etc.), the changes will be “ido” (Chlorido, bromido etc.), “ato” (nitrato,
sulphato etc.) and “ito” (nitrito, sulphito) respectively.

ii. For neutral
ligands, common name of the molecules should be used. (Some exceptions are
there: water is named as aqua, ammonia is named as ammine, CO is named as
carbonyl and N2 and O2 are named as dinitrogen and
dioxygen respectively.)

Rule 3: When more than one ligands are
connected to the central metal ion then di, tri, tetra, penta etc. prefixes are
attached with the ligand name. When the ligand name contains already these
prefixes then bis, tris, tetrakis, pentakis etc. are used instead of di, tri,
tetra, penta respectively.

Rule 4:  Cation name should be written first and then
anion name should be written for an ionic coordination complex.

Rule 5: Oxidation number should be written
in roman digit with sign in a first bracket () after the central metal ion
name.

Rule 6: For cationic or neutral complex,
the usual name of the central metal ion should be used. But in case of anionic
complex, the “ate” suffix is attached with the usual metal name. (e.g. copper
is changed cuprate, molybdenum is changed to molybdate etc.)

Rule 7: In case of ambidentate ligand (one
having two donor site), the naming of the ligand depends upon which donor site
is binding to the central metal ion, e.g. SCN- (donor atom S) is
called as thiocyanato or S-thiocyanato and NCS- (donor atom N) is called as
isothiocyanato or N-thiocyanato etc.

In GAMSAT following type of question can
be asked with suitable vignette. Have a look.

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