Nomenclature of coordination compound


As in any field of study, careful attention to nomenclature is required. The rules for names and formulas of coordination compounds are given here, with examples to
show their use, but we need to be aware of changes in nomenclature with time. In
many cases, the notation used by those who first prepared a compound is retained and
expanded; in other cases, conflicting rules for names are proposed by different people
and only after some time is a standard established. The literature naturally includes
papers using all the possible names, and sometimes careful research is necessary to
interpret those names that had relatively short lifetimes.
Following are the major rules required to name the compounds in this text and
those found in the general literature. Reference to more complete sources may be
needed to determine the names of other compounds.12
Organic (and some inorganic) ligands are frequently named with older trivial
names rather than with IUPAC (International Union of Pure and Applied Chemistry)
names. The IUPAC names are more correct, but trivial names and abbreviations are still
commonly used. Tables 9-2, 9-3, and 9-4 list some of the common ligands. Ligands
with two or more points of attachment to metal atoms are called chelating ligands, and
the compounds are called chelates (pronounced key-lates), a name derived from the Greek (khele, claw of a crab). Ligands such as ammonia are monodentate, with one
point of attachment (literally, one tooth). Other ligands are described as bidentate for
two points of attachment, as in ethylenediarnine (NH2CH2CH2NH2), which can bond
to a metal ion through the two nitrogens. The prefixes tri-, tetra-, penta-, and hexa- are
used for three through six bonding positions, as shown in Table 9-3. Chelate rings may
have any number of atoms; the most common contain five or six atoms, including the
metal ion. Smaller rings have angles and distances that lead to strain; larger rings frequently
result in crowding, both within the ring and between adjoining ligands. Some
ligands can form more than one ring; ethylenediaminetetraacetate (EDTA) can form
five by using the four carboxylate groups and the two amine nitrogens.






Nomenclature rules
1. The positive ion (cation) comes first, followed by the negative ion (anion). This is
also the common order for simple salts.
Examples: diamminesilver(1) chloride, [Ag(NH3)2]Cl
potassium hexacyanoferrate(lII), K3[Fe(CN)6]
2. The inner coordination sphere is enclosed in square brackets in the formula. Within
the coordination sphere, the ligands are named before the metal. but in formulas
the metal ion is written first.
Examples: tetraamminecopper(I1) sulfate, [Cu(NH3)4]SO4
hexaarnminecobalt(II1) chloride, [Co(NH3)6]Cl3
3. The number of ligands of one kind is given by the following prefixes. If the ligand
name includes these prefixes or is complicated, it is set off in parentheses and the
second set of prefixes is used.


Examples: dichlorobis(ethylenediamine)cobalt(III),
[CO(NH2CH2CH2NH2)2CI2]+
tris(bipyridine)iron(II), [Fe(NH4 C5-C5H4N 3)]2+
4. Ligands are named in alphabetical order (according to the name of the ligand, not
the prefix), although exceptions to this rule are common. An earlier rule gave
anionic ligands first, then neutral ligands, each listed alphabetically.
Examples: tetraamminedichlorocobalt(III), [CO(NH3)4CI2]+
(tetraammine is alphabetized by a and dichloro by c, not by the
prefixes)
amminebromochloromethylamineplatinum(II),
Pt(NH3)BrCl(CH3NH2)
5. Anionic ligands are given an o suffix. Neutral ligands retain their usual name.
Coordinated water is called aqua and coordinated ammonia is called ammine.
Examples: chloro, Cl- methylamine, CH3NH2
bromo, Br- ammine, NH3 (the double m distinguishes NH3
sulfato, SO4 fro m alkyl amines)
aqua, H20
6. Two systems exist for designating charge or oxidation number:
a. The Stock system puts the calculated oxidation number of the metal ion as a
Roman numeral in parentheses after the name of the metal. This is the more
common convention, although there are cases in which it is difficult to assign
oxidation numbers.
b. The Ewing-Bassett system puts the charge on thc coordination sphere in
parentheses after the name of the metal. This convention is used by Chemical
Abstracts and offers an unambiguous identification of the species.
In either case, if the charge is negative, the suffix -ate is added to the name of the
coordination sphere.
Examples: tetraammineplatinum(I1) or tetraammineplatinum(2+),
[Pt(NH3)4]2+
tetrachloroplatinate(I1) or tetrachloroplatinate(2-), [PtC14]2-
hexachloroplatinate(1V) or hexachloroplatinate(2-), [PtC16]2-
7. The prefixes cis- and frans- designate adjacent and oppositc geometric locations.
Examples are in Figures 9-1 and 9-5. Other prefixes are used as well and will be
introduced as needed in the text.
Examples: cis- and trans-diamminedichloroplatinum(II), [PtCl2(NH3)2]
cis- and trans-tetraamminedichlorocobalt(III), [CoCl2(NH3)4]+

8. Bridging ligands between two metal ions as in Figures 9-2 and 9-6 have the prefix p-
Examples: tris(tetraammine-p-dihydroxocobalt)cobalt(6+),
[Co(Co(NH3)4(OH)2)3]6+
p-amido- p-hy droxobis(tetramminecobalt)(4 +),
[(NH3)4Co(OH)(NH2)Co(NH3)4]4+

9. When the complex is negatively charged, the names for the following metals are
derived from the sources of their symbols, rather than from their English names:


Examples: tetrachloroferrate(II1) or tetrachloroferrate(1 -), [FeCl4]-
dicyanoaurate(1) or dicyanoaurate(1 -), [Au(CN)2]-
Location: Pakistan

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