NOMENCLATURE IV
This supplement deals with complexes. In general, a complex is recognizable because square brackets
[ ] enclose the formula. The square brackets are omitted when the actual structure of the complex is
uncertain.
A complex is composed of a central atom, normally a metal, surrounded by atoms or groups of atoms
called ligands. Below is one way of illustrating the formation of a complex:
Ni2+ + 6 H2O Æ [Ni(H2O)6]2+
In this reaction, the metal behaves as a Lewis acid and accepts a pair of electrons from the Lewis base
(ligand). In this case, the ligand is water with the oxygen atom donating one of its lone pairs to the
nickel. The oxygen atom is the donor atom. In this complex, there are six total donor atoms.
A complex may be ionic or neutral. An ionic complex is a complex ion. A neutral complex is a type
of coordination compound. The only difference in naming coordination compounds or complex ions
is that anionic complex ions have an -ate suffix.
A coordination compound may contain more than one complex ion or material that is not part of the
complex. A coordination compound must have an overall neutral charge. Examples of coordination
compounds are: [Pt(NH3)2Cl2], K2[Mn(C2O4)3], and [Ni(H2O)6]SO4.
When writing formulas the metal (central atom) is always first within the brackets. However, when
writing names the metal name is always last. Name any material not listed within the brackets
separately.
Examples:
[Ru(NH3)5(N2)]Cl2
[Ru(NH3)5(N2)]2+
[PtNH3Cl2(C5H5N)]
[IF6]K[IF6]
Coordination compound
Complex ion (cationic)
Coordination compound
Complex ion (anionic) (the name must end in -ate)
Coordination compound (same -ate ending)
If everything in the formula is within one set of bracket, the entire name will be one word. If there is
material outside the brackets, this outside material has a separate name.
As with simpler compounds, cation names are always before anion names. Thus a cationic complex
would be the first word in the name, and an anionic complex would be the last word in a name (with
an -ate ending).
Examples:
[Ni(H2O)4Cl2]
[Co(NH3)6]Cl3
K2[PtCl4]
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tetraaquadichloronickel(II)
hexaamminecobalt(III) chloride
potassium tetrachloroplatinate(II)
When writing the name a complex, or when writing the formula for a complex, list the ligands
alphabetically. Again, do not forget metals are first in the formula and last in the name.
Names of anionic ligands always end in an -o. Neutral ligands are unchanged. Two common
exceptions in the case of neutral ligands are NH3 = ammine (note the double m), and H2O = aqua.
Other common ligands and their names are in the following list:
Those with more than one donor atom may be chelating.
Ligand
Formula
(or abbreviation)
Azide ion
N3Bromide ion
BrCarbonate ion
CO32Chloride ion
ClCyanide ion
CNEthylenediaminetetraacetate EDTA4Fluoride ion
FHydride ion
HHydrogen sulfide ion
HSHydroxide ion
OHIodide ion
INitrite ion
NO2Oxalate ion
C2O42Oxide ion
O2Peroxide ion
O22Sulfide ion
S2Thiocyanate ion
SCNAmmonia
NH3
Bipyridine
bipy
Carbon monoxide
CO
Dinitrogen
N2
Dioxygen
O2
Ethylenediamine
en
Nitric oxide
NO
ortho-phenanthroline
o-phen
Phosphine
PH3
Pyridine
C5H5N or py
Water
H2O
* May form linkage isomers.
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Ligand Name
Donor atoms
azido
bromo
carbonato
chloro
cyano
ethylenediaminetetraacetato
fluoro
hydrido
mercapto
hydroxo
iodo
nitrito
oxalato
oxo
peroxo
thio
thiocyanato
ammine
bipyridine
carbonyl
dinitrogen
dioxygen
ethylenediamine
nitrosyl
ortho-phenanthroline
phosphine
pyridine
aqua
1
1
1
1
1
6
1
1
1
1
1
1*
2
1
1
1
1*
1
2
1
1
1
2
1
2
1
1
1
Multiple identical ligands have prefixes added to designate the number of such ligands:
2
di3
tri4
tetraExamples:
5
6
7
[Co(NH3)6]Cl3
[Cr(NO)4]
pentahexahepta-
8
9
10
octanonadeca-
Hexamminecobalt(III) chloride
Tetranitrosylchromium(0)
If the ligand name contains a prefix or begins with a vowel (except ammine and aqua), alternate
prefixes are necessary:
2
3
4
bistristetrakis-
5
6
7
pentakishexakisheptakis-
8
9
10
octakisnonakisdecakis-
When using the alternate prefixes, it is common practice to enclose the name of the ligand within
parentheses. Add either type of prefix after the ligands have been alphabetized.
Examples:
[Cr(en)3]Cl3
K2[Ge(C2O4)3]
Tris(ethylenediamine)chromium(III) chloride
Potassium tris(oxalato)germanate
Anionic complexes always have names ending in -ate. This will require a change in the name of the
metal. Thus, aluminum would become aluminate, and zinc would become zincate. The only
exceptions to this are some of the metals whose symbols are from Latin or Greek names. These
“exceptions” are:
Metal (Greek
or Latin Name)
Symbol
Anionic Name
Copper (Cuprum)
Silver (Argentum)
Gold (Aurum)
Iron (Ferrum)
Tin (Stannum)
Lead (Plumbum)
Cu
Ag
Au
Fe
Sn
Pb
cuprate
argentate
aurate
ferrate
stannate
plumbate
Examples:
K[Au(CN)4]
(NH4)2[PbCl6]
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Potassium tetracyanoaurate(III)
Ammonium hexachloroplumbate(IV)
If the metal ion may exist in more than one oxidation state, it is necessary to list this oxidation state, in
Roman numerals, immediately after the name of the metal ion. Enclose the Roman numeral in
parentheses and considered the Roman numeral and parentheses part of the same word, and not a
separate grouping. If the metal only occurs in one oxidation state, no such indicator is used. The use
of Roman numerals is the Stock system.
In many cases, complexes may occur as isomers. Isomers are compounds with the same composition,
but different structures. The difference in the structures causes differences in their properties.
Coordination isomers involve placing different ligands within the coordination sphere. Linkage
isomers are those with ligands such as the nitrite ion, which may change donor atoms. Different
optical isomers affect light differently. Geometric isomers involve different positions of the bonded
ligands. In most cases, only minor changes are present in the nomenclatures of the different isomers.
There are no new rules for coordination isomers. The new ligands in the coordination sphere about the
central atom simply replace the original ligands in the name.
Linkage isomers require some indication of the donor atom. Some ligands may use different donor
atoms. Two common examples are the nitrite ion and the thiocyanate ion. Either the nitrogen or one
of the oxygen atoms may serve as the donor atom from the nitrite ion. In the formula, if the nitrogen
is the donor, it appears as -NO2, and if one of the oxygens is the donor, it appears as -ONO. In a
similar manner the thiocyanate ion may donate through the sulfur (-SCN) or the nitrogen (-NCS). At
one time the different means of donating electrons were indicated by different names (-NO2 = nitro; ONO = nitrito; -SCN = thiocyanato; and -NCS = isothiocyanato), now the preferred method is to
include the donor atom in the name to give -NO2 = nitrito-N; -ONO = nitrito-O; -SCN = thiocyanatoS; and -NCS = thiocyanato-N.
Examples:
[Zn(NCS)4]2+
[Cd(SCN)4]2+
Tetrathiocyanato-N-zinc ion
Tetrathiocyanato-S-cadmium ion
There will be no discussion of optical isomers in this discussion other than to say that various letters
before the name of the complex indicate that it is an optical isomer.
The two basic types of geometric isomers are cis/trans and fac/mer pairs. Cis/trans isomers may occur
in square planar or octahedral complexes. In the cis isomer, identical ligands are adjacent to each
other, while in the trans isomers they are on opposite sides. The designation cis- or trans- precedes the
name of the complex. Octahedral complexes may also occur in fac/mer pairs. Fac is an abbreviation
for facial, which is the isomer where three identical ligands occupy the corners of a face of the
octahedron. Mer is short for meridinal, which is the isomer where three identical ligands are not on
the corners of a face of the octahedron. As with cis/trans isomers, the terms fac- or mer- precedes the
name of the complex.
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Name or give the formula for each of the following:
(Answers on the next page)
a. Dichlorobis(ortho-phenanthroline)iron(III) perchlorate ________________________
b. Dibromobis(ethylenediamine)platinum(IV) bromide___________________________
c. Bis(ethylenediamine)zinc tetraiodomercurate(II) _____________________________
d. Hexaamminenickel(II) tris(oxalato)chromate(III) _____________________________
e. Hexaamminechromium(III) nitrate
_____________________________
f. Pentaaquabromomanganese(III) sulfate
_____________________________
g. Potassium diaquatetrabromovanadate(III)
_____________________________
h. Sodium tetrabromo(ethylenediamine)cobaltate(II) _____________________________
i. Tetraamminecarbonatocobalt(III) sulfate
_____________________________
j. Tris(bipyridine)ruthenium(II) nitrate
_____________________________
a. [AlCl4]-
_______________________________________________
b. [Ag(CN)2]-
_______________________________________________
c. cis-[Co(en)2(NO2)2]+
_______________________________________________
d. [Co(NH3)2Br2(en)]Cl
_______________________________________________
e. trans-[Cr(NH3)4(H2O)2]3+ _______________________________________________
f. K3[Fe(C2O4)3]
_______________________________________________
g. K3[IrCl5(S2O3)]
_______________________________________________
h. [Pd(en)2][Cr(NH3)2Br4]2
_______________________________________________
i. [PtCl4(en)]
_______________________________________________
j. trans-[Pt(NH3)2(Br)H]
_______________________________________________
k. [Ru(H2O)Cl5]2-
_______________________________________________
l. [Zn(NH3)4]2+
_______________________________________________
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Answers to the nomenclature problem from the preceding page.
a. Dichlorobis(ortho-phenanthroline)iron(III) perchlorate
[FeCl2(o-phen)2]ClO4
b. Dibromobis(ethylenediamine)platinum(IV) bromide
[PtBr2(en)2]Br2
c. Bis(ethylenediamine)zinc tetraiodomercurate(II)
[Zn(en)2][HgI4]
d. Hexaamminenickel(II) tris(oxalato)chromate(III)
[Ni(NH3)6]3[Cr(C2O4)3]2
e. Hexaamminechromium(III) nitrate
[Cr(NH3)6](NO3)3
f. Pentaaquabromomanganese(III) sulfate
[Mn(H2O)5Br]SO4
g. Potassium diaquatetrabromovanadate(III)
K[V(H2O)2Br4]
h. Sodium tetrabromo(ethylenediamine)cobaltate(II)
Na2[CoBr4en]
i. Tetraamminecarbonatocobalt(III) sulfate
[Co(NH3)4CO3]2SO4
j. Tris(bipyridine)ruthenium(II) nitrate
[Ru(bipy)3](NO3)2
a. [AlCl4]-
Tetrachloroaluminate ion
b. [Ag(CN)2]-
Dicyanoargentate(I) ion
c. cis-[Co(en)2(NO2)2]+
cis-bis(ethylenediamine)dinitrito-N-cobalt(III) ion
d. [Co(NH3)2Br2(en)]Cl
Diamminedibromoethylenediaminecobalt(III) chloride
e. trans-[Cr(NH3)4(H2O)2]3+ trans-tetraamminediaquachromium(III) ion
f. K3[Fe(C2O4)3]
Potassium trisoxalatoferrate(III)
g. K3[IrCl5(S2O3)]
Potassium pentachlorothiosulfatoiridate(IV)
h.[Pd(en)2][Cr(NH3)2Br4]2 Bis(ethylenediamine)palladium(II)
diamminetretrabromochromate(III)
Tetrachloroethylenediamineplatinum(IV)
i. [PtCl4(en)]
j. trans-[Pt(NH3)2(Br)H]
trans-diamminebromohydridoplatinum(II)
k. [Ru(H2O)Cl5]2-
Aquapentachlororuthanate(III) ion
l. [Zn(NH3)4]2+
Tetraamminezinc ion
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PRACTICE SET IV-1
Name the following:
1. K3[Fe(CN)5(NO)]
_______________________________________________
2. [CoCl(en)2(NO2)]Cl
_______________________________________________
3. Na3[Al(C2O4)3]
_______________________________________________
4. cis-[Pt(NH3)2Br2]
_______________________________________________
5. [Ag(NH3)3]+
_______________________________________________
6. [Hg(CN)4]2-
_______________________________________________
7. Ba[BrF4]2
_______________________________________________
8. [Zn(OH)4]2-
_______________________________________________
9. Rb[Cr(CO)2(NCS)4]
_______________________________________________
10. trans-[Pd(NH3)2Cl2]
_______________________________________________
11. cis-[Mo(NH3)2Cl4]
_______________________________________________
12. [NiNH3(Cl2)(C5H5N)]
_______________________________________________
13. [CuCl4]2-
_______________________________________________
14. [Mn(bipy)(en)2]3+
_______________________________________________
15. [V(CO3)3]3-
_______________________________________________
16. [SnI6]2-
_______________________________________________
17. [Cd(H2O)4]2+
_______________________________________________
18. [Hg(N3)4]2-
_______________________________________________
19. [Ru(NH3)5(N2)]2+
_______________________________________________
20. [Re(H)4(PH3)4]+
Re = Rhenium
_______________________________________________
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PRACTICE SET IV-2
Write formulas for each of the following:
1. cis-diamminetriaquahydroxochromium(III) nitrate_____________________________
2. Ammonium diphosphinetetrathiocyanato-S-chromate(III)_______________________
3. Chloronitrito-O-bis(ortho-phenanthroline)cobalt(III) ion________________________
4. Sodium dithiosulfatoargentate(I)
_____________________________
5. Tetrapyridineplatinum(II) tetrachloroplatinate(II) _____________________________
6. Tetraiodonickelate(II) ion
_____________________________
7. Ammonium hexachloroferrate(III)
_____________________________
8. Pentacarbonyliodomanganese(I)
_____________________________
9. Sodium hexachlorophosphate(V)
_____________________________
10. Lithium tetrahydridoaluminate
_____________________________
11. Pentammine(dinitrogen)ruthenium(II) chloride
_____________________________
12. Carbonyldinitrosylnickel(0)
_____________________________
13. Potassium hexacyanoferrate(II)
_____________________________
14. Dichlorobis(ethylenediamine)cobalt(III) ion
_____________________________
15. Tris(bipyridine)iron(II) ion
_____________________________
16. Pentabromocuprate(II) ion
_____________________________
17. Sodium pentafluorodioxouranate(VI)
_____________________________
18. Ammonium nonahydridorhenate(VII)
_____________________________
19. Pentamminethiocyanato-N-cobalt(III) chloride _____________________________
20. Potassium amminedicyanodioxoperoxochromate(VI)
_____________________________
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