IUPAC nomenclature of inorganic chemistry 2005


Nomenclature of Inorganic Chemistry, IUPAC Recommendations 2005 is the 2005 version of Nomenclature of Inorganic Chemistry. It is a collection of rules for naming inorganic compounds, as recommended by the International Union of Pure and Applied Chemistry.

Summary

The 2005 edition replaces their previous recommendations Nomenclature The Red Book of Inorganic Chemistry, IUPAC Recommendations 1990 , and "where appropriate" Nomenclature of Inorganic Chemistry II, IUPAC Recommendations 2000 .
The recommendations take up over 300 pages and the full text can be downloaded from IUPAC. Corrections have been issued.
Apart from a reorganisation of the content, there is a new section on organometallics and a formal element list to be used in place of electronegativity lists in sequencing elements in formulae and names. The concept of a preferred IUPAC name, a part of the revised blue book for organic compound naming, has not yet been adopted for inorganic compounds. There are however guidelines as to which naming method should be adopted.

Naming methods

The recommendations describe a number of different ways in which compounds can be named. These are:
Additionally there are recommendations for the following:
For a simple compound such as AlCl3 the different naming conventions yield the following:
Throughout the recommendations the use of the electronegativity of elements for sequencing has been replaced by a formal list which is loosely based on electronegativity. The recommendations still use the terms electropositive and electronegative to refer to an element's relative position in this list.

A simple rule of thumb ignoring lanthanides and actinides is:
The full list, from highest to lowest "electronegativity" :
ActionAddition
compound?		Definite
stoichiometry?		mono-atomic?molecular?metal present?Bond to carbon?transition metal
group 3–12?		main group metal
groups 1, 2, 3–6?
Treat each component separately
use compositional
Use solids naming
Element or monatomic cation/anion/radical naming
Divide components into "electropositive"/"electronegative"
Treat each component separately
Use generalised stoichiometric naming
Use Blue book
'
Use additive naming for
group 3- 12 organometallics
Use substitutive naming for
group 3–6 organometallics
Use compositional
for groups 1–2 organometallics
Use additive naming for coordination complexes
Choose either substitutive or additive

Note "treat separately" means to use the decision table on each component

Element names

Sample of indeterminate structure

An indeterminate sample simply takes the element name. For example a sample of carbon would be named carbon.

Specific allotrope

Molecular

This is specified by the element symbol followed by the Pearson symbol for the crystal form.
Examples include
Pn,. red phosphorus ; Asn, amorphous arsenic.

Compounds

Compositional names impart little structural information and are recommended for use when structural information is not available or does not need to be conveyed.
Stoichiometric names are the simplest and reflect either the empirical formula or the molecular formula. The ordering of the elements follows the formal electronegativity list for binary compounds and electronegativity list to group the elements into two classes which are then alphabetically sequenced. The proportions are specified by di-, tri-, etc. Where there are known to be complex cations or anions these are named in their own right and then these names used as part of the compound name.

Binary compounds

In binary compounds the more electropositive element is placed first in the formula. The formal list is used. The name of the most electronegative element is modified to end in -ide and the more electropositive elements name is left unchanged.

Taking the binary compound of sodium and chlorine: chlorine is found first in the list so therefore comes last in the name. Other examples are
The following illustrate the principles.

The 1:1:1:1 quaternary compound between bromine, chlorine, iodine and phosphorus:
The ternary 2:1:5 compound of antimony, copper and potassium can be named in two ways depending on which element are designated as electronegative.

Cations

Monatomic cations are named by taking the element name and following it with the charge in brackets e.g
Sometimes an abbreviated form of the element name has to be taken, e.g. germide for germanium as germanide refers to.
Polyatomic cations of the same element are named as the element name preceded by di-, tri-, etc., e.g.:
Polyatomic cations made up of different elements are named either substitutively or additively, e.g.:
Monatomic anions are named as the element modified with an -ide ending. The charge follows in brackets, e.g.:
Some elements take their Latin name as the root e.g
Polyatomic anions of the same element are named as the element name preceded by di-, tri-, etc., e.g.:
or sometimes as an alternative derived from a substitutive name e.g.
Polyatomic anions made up of different elements are named either substitutively or additively, the name endings are -ide and -ate respectively e.g. :
A full list of the alternative acceptable non-systematic names for cations and anions is in the recommendations.
Many anions have names derived from inorganic acids and these are dealt with later.

Radicals

The presence of unpaired electrons can be indicated by a "·". For example:
The use of the term hydrate is still acceptable e.g. Na2SO4·10H2O, sodium sulfate decahydrate. The recommended method would be to name it sodium sulfate—water. Similarly other examples of lattice compounds are:
As an alternative to di-, tri- prefixes either charge or oxidation state can be used. Charge is recommended as oxidation state may be ambiguous and open to debate.

Substitutive nomenclature

This naming method generally follows established IUPAC organic nomenclature. Hydrides of the main group elements are given -ane base names, e.g. borane, BH3. Acceptable alternative names for some of the parent hydrides are water rather than oxidane and ammonia rather than azane. In these cases the base name is intended to be used for substituted derivatives.
This section of the recommendations covers the naming of compounds containing rings and chains.

Base hydrides

BH3boraneCH4methaneNH3azane
H2Ooxidane
HFfluorane
AlH3alumaneSiH4silanePH3phosphane
H2Ssulfane
HClchlorane
GaH3gallaneGeH4germaneAsH3arsane
H2Seselane
HBrbromane
InH3indiganeSnH4stannaneSbH3stibane
H2Tetellane
HIiodane
TlH3thallanePbH4plumbaneBiH3bismuthane
H2Popolane
HAtastatane

Hydrides with non-standard bonding—lambda convention

Where a compound has non standard bonding as compared to the parent hydride for example PCl5 the lambda convention is used. For example:
A prefix di-, tri- etc. is added to the parent hydride name. Examples are:
The recommendations describe three ways of assigning "parent" names to homonuclear monocyclic hydrides :
The stoichiometric name is followed by the number of hydrogen atoms in brackets. For example B2H6, diborane. More structural information can be conveyed by adding the "structural descriptor" closo-, nido-, arachno-, hypho-, klado- prefixes.

There is a fully systematic method of numbering the atoms in the boron hydride clusters, and a method of describing the position of bridging hydrogen atoms using the μ symbol.

Main group organometallic compounds

Use of substitutive nomenclature is recommended for group 13–16 main group organometallic compounds. Examples are:
For organometallic compounds of groups 1–2 can use additive or compositional naming. Examples are:
However the recommendation notes that future nomenclature projects will be addressing these compounds.

Additive nomenclature

This naming has been developed principally for coordination compounds although it can be more widely applied. Examples are:
The recommendations include a flow chart which can be summarised very briefly:

Anionic ligands

If the anion name ends in -ide then as a ligand its name is changed to end in -o. For example the chloride anion, Cl− becomes chlorido. This is a difference from organic compound naming and substitutive naming where chlorine is treated as neutral and it becomes chloro, as in PCl3, which can be named as either substitutively or additively as trichlorophosphane or trichloridophosphorus respectively.

Similarly if the anion names end in -ite, -ate then the ligand names are -ito, -ato.

Neutral ligands

Neutral ligands do not change name with the exception of the following:
Formulaname
Cl−chlorido
CN−cyanido
H−hydrido
D−or 2H−deuterido or hydrido
PhCH2CH2Se−2-phenylethane-1-selenolato
MeCOO−acetato or ethanoato
Me2As−dimethylarsanido
MePH−methylphosphanido
MeCONH2acetamide
MeCONH−acetylazanido or acetylamido
MeNH2methanamine
MeNH−methylazanido, or methylamido, or methanaminido
MePH2methylphosphane
COcarbonyl

Sequence and position of ligands and central atoms

Ligands are ordered alphabetically by name and precede the central atom name. The number of ligands coordinating is indicated by the prefixes di-, tri-, tetra- penta- etc. for simple ligands or bis-, tris-, tetrakis-, etc. for complex ligands. For example:
Where there are different central atoms they are sequenced using the electronegativity list.
Ligands may bridge two or more centres. The prefix μ is used to specify a bridging ligand in both the formula and the name. For example the dimeric form of aluminium trichloride:
This example illustrates the ordering of bridging and non bridging ligands of the same type. In the formula the bridging ligands follow the non bridging whereas in the name the bridging ligands precede the non bridging. Note the use of the kappa convention to specify that there are two terminal chlorides on each aluminium.

Bridging index

Where there are more than two centres that are bridged a bridging index is added as a subscript. For example in basic beryllium acetate which can be visualised as a tetrahedral arrangement of Be atoms linked by 6 acetate ions forming a cage with a central oxide anion, the formula and name are as follows:
The μ4 describes the bridging of the central oxide ion. In the name where a ligand is involved in different modes of bridging, the multiple bridging is listed in decreasing order of complexity, e.g. μ3 bridging before μ2 bridging.

Kappa, κ, convention

The kappa convention is used to specify which ligand atoms are bonding to the central atom and in polynuclear species which atoms, both bridged and unbridged, link to which central atom. For monodentate ligands there is no ambiguity as to which atom is forming the bond to the central atom. However when a ligand has more than one atom that can link to a central atom the kappa convention is used to specify which atoms in a ligand are forming a bond. The element atomic symbol is italicised and preceded by kappa, κ. These symbols are placed after the portion of the ligand name that represents the ring, chain etc where the ligand is located. For example:
Where there is more than one bond formed from a ligand by a particular element a numerical superscript gives the count. For example:
In polynuclear complexes the use of the kappa symbol is extended in two related ways. Firstly to specify which ligating atoms bind to which central atom and secondly to specify for a bridging ligand which central atoms are involved. The central atoms must be identified, i.e. by assigning numbers to them.. To specify which ligating atoms in a ligand link to which central atom, the central atom numbers precede the kappa symbol, and numerical superscript specifies the number of ligations and this is followed by the atomic symbol. Multiple occurrences are separated by commas.
Examples:

Eta, η, convention

The use of η to denote hapticity is systematised. The use of η1 is not recommended. When the specification of the atoms involved is ambiguous the position of the atoms must be specified. This is illustrated by the examples:
For any coordination number above 2 more than one coordination geometry is possible. For example four coordinate coordination compounds can be tetrahedral, square planar, square pyramidal or see-saw shaped. The polyhedral symbol is used to describe the geometry. A configuration index is determined from the positions of the ligands and together with the polyhedral symbol is placed at the beginning of the name. For example in the complex -dichloridoplatinum the at the beginning of the name describes a square planar geometry, 4 coordinate with a configuration index of 3 indicating the position of the ligands around the central atom. For more detail see polyhedral symbol.

Organometallic groups 3–12

Additive nomenclature is generally recommended for organometallic compounds of groups 3-12.

Metallocenes

Following on from ferrocene—the first sandwich compound with a central Fe atom coordinated to two parallel cyclopentadienyl rings—names for compounds with similar structures such as osmocene and vanadocene are in common usage. The recommendation is that the name-ending ocene should be restricted to compounds where there are discrete molecules of bismetal, where the cyclopentadienyl rings are essentially parallel, and the metal is in the d-block. The terminology does NOT apply to compounds of the s- or p-block elements such as Ba2 or Sn2.

Examples of compounds that meet the criteria are:
Examples of compounds that should not be named as metallocenes are:

Metal-metal bonds

In polynuclear compounds with metal-metal bonds these are shown after the element name as follows:
in Decacarbonyldihydridotriosmium.
A pair of brackets contain a count of the bonds formed, followed by the italicised element atomic symbols separated by an "em-dash".

Polynuclear cluster geometry

The geometries of polynuclear clusters can range in complexity. A descriptor e.g. tetrahedro or the CEP descriptor e.g. Td--Δ4-closo] can be used. this is determined by the complexity of the cluster. Some examples are shown below of descriptors and CEP equivalents. -Δ4-closo]56octahedro6triprismo8antiprismo8dodecahedro12icosahedro
Examples:
decacarbonyldimanganese
bis
dodecacarbonyltetrarhodium
tri-μ-carbonyl-1:2κ2C;1:3κ2C;2:3κ2C-nonacarbonyl-
1κ2C,2κ2C,3κ2C,4κ3C--tetrarhodium

or tri-μ-carbonyl-1:2κ2C;1:3κ2C;2:3κ2C-nonacarbonyl-
1κ2C,2κ2C,3κ2C,4κ3C-tetrahedro-tetrarhodium

Inorganic acids

Hydrogen names

The recommendations include a description of hydrogen names for acids. The following examples illustrate the method:
Note that the difference from the compositional naming method as in hydrogen naming there is NO space between the electropositive and electronegative components.

This method gives no structural information regarding the position of the hydrons. If this information is to be conveyed then the additive name should be used.

List of acceptable names

The recommendations give a full list of acceptable names for common acids and related anions. A selection from this list is shown below.

Solids

Stoichiometric phases are named compositionally. Non-stoichiometric phases are more difficult. Where possible formulae should be used but where necessary naming such as the following may be used:
Generally mineral names should not be used to specify chemical composition. However a mineral name can be used to specify the structure type in a formula e.g.
A simple notation may be used where little information on the mechanism for variability is either available or is not required to be conveyed:
Where there is a continuous range of composition this can be written e.g., K for a mixture of KBr and KCl and Cl2 for a mixture of LiCl and MgCl2.
The recommendation is to use the following generalised method e.g.
Note that cation vacancies in CoO could be described by CoO1−x

Point defects (Kröger–Vink) notation

Point defects, site symmetry and site occupancy can all be described using Kröger–Vink notation, note that the IUPAC preference is for vacancies to be specified by V rather than V.

Phase nomenclature

To specify the crystal form of a compound or element the Pearson symbol may be used. The use of Strukturbericht or Greek letters is not acceptable. The Pearson symbol may be followed by the space group and the prototype formula. Examples are:
It is recommended that polymorphs are identified, and wurtzite )as ZnS and ZnS respectively.