Nomenclature of Inorganic Chemistry, IUPAC Recommendations 2005 is the 2005 version of Nomenclature of Inorganic Chemistry (which is informally called the Red Book). It is a collection of rules for naming inorganic compounds, as recommended by the International Union of Pure and Applied Chemistry (IUPAC).
The 2005 edition replaces their previous recommendations Nomenclature The Red Book of Inorganic Chemistry, IUPAC Recommendations 1990 (Red Book I), and "where appropriate" (sic) Nomenclature of Inorganic Chemistry II, IUPAC Recommendations 2000 (Red Book II).
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 (PIN), 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.
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Throughout the recommendations the use of the electronegativity of elements for sequencing has been replaced by a formal list which is loosely based on electronegativity.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" (with the addition of elements 112 through 118, that had not yet been named in 2005, to their respective groups):
|mono-atomic?||molecular?||metal present?||Bond to carbon?||transition metal
|main group metal|
groups 1, 2, 3-6?
|Treat each component separately
|Use solids naming||No||No|
|Element or monatomic cation/anion/radical naming||No||Yes||Yes|
|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
for groups 1-2 organometallics
|Use additive naming for coordination complexes||No||Yes||No||Yes||Yes||No||Yes|
|Choose either substitutive or additive||No||Yes||No||Yes||No||No|
Note "treat separately" means to use the decision table on each component
An indeterminate sample simply takes the element name. For example a sample of carbon (which could be diamond, graphite etc or a mixture) would be named carbon.
This is specified by the element symbol followed by the Pearson symbol for the crystal form. (Note that the recommendations specifically italicize the second character.)
Examples include Pn,. red phosphorus ; Asn, amorphous arsenic.
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. (See IUPAC numerical multiplier.) 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.
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(s) are designated as electronegative.
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, (optional for 1−) 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.
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(1/10). 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.
This naming method generally follows established IUPAC organic nomenclature. Hydrides of the main group elements (groups 13-17) 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.
(hydrogen sulfide or dihydrogen sulfide)
(hydrogen selenide or dihydrogen selenide)
(hydrogen telluride or dihydrogen telluride)
(hydrogen polonide or dihydrogen polonide)
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 (i.e single rings consisting of one element):
The stoichiometric name is followed by the number of hydrogen atoms in brackets. For example B2H6, diborane(6). 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 ? symbol.
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 (indicating a molecular aggregate) or compositional naming. Examples are:
However the recommendation notes that future nomenclature projects will be addressing these compounds.
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:
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 do not change name with the exception of the following:
|D−or 2H−||deuterido or [2H]hydrido|
|MeCOO−||acetato or ethanoato|
|MeCONH2||acetamide (not acetamido)|
|MeCONH−||acetylazanido or acetylamido (not acetamido)|
|MeNH−||methylazanido, or methylamido, or methanaminido|
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 ? 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.
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 ?4 describes the bridging of the central oxide ion. (Note the use of the kappa convention to describe the bridging of the acetate ion where both oxygen atoms are involved.) 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. ?3 bridging before ?2 bridging.
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, ?. 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. (This is formally dealt with in the recommendations). 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.
The use of ? to denote hapticity is systematised. The use of ?1 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 (SP-4-3)-(acetonitrile)dichlorido(pyridine)platinum(II) the (SP-4-3) 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.
Additive nomenclature is generally recommended for organometallic compounds of groups 3-12 (transition metals and zinc, cadmium and mercury).
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 bis(?5-cyclopentadienyl)metal (and ring-substituted analogues), 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 Ba(C5H5)2 or Sn(C5H5)2.
Examples of compounds that meet the criteria are:
Examples of compounds that should not be named as metallocenes are:
In polynuclear compounds with metal-metal bonds these are shown after the element name as follows: (3 Os--Os) in Decacarbonyldihydridotriosmium. A pair of brackets contain a count of the bonds formed (if greater than 1), followed by the italicised element atomic symbols separated by an "em-dash".
The geometries of polynuclear clusters can range in complexity. A descriptor e.g. tetrahedro or the CEP descriptor e.g. Td-(13)-?4-closo] can be used. this is determined by the complexity of the cluster. Some examples are shown below of descriptors and CEP equivalents. (The CEP descriptors are named for Casey, Evans and Powell who described the system.
|number of atoms||descriptor||CEP descriptor|
or tri-?-carbonyl-1:2?2C;1:3?2C;2:3?2C-nonacarbonyl- 1?2C,2?2C,3?2C,4?3C-tetrahedro-tetrarhodium(6 Rh--Rh)
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 (hydrogen sulfide) 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 (hydrogen atoms). If this information is to be conveyed then the additive name should be used (see the list below for examples).
The recommendations give a full list of acceptable names for common acids and related anions. A selection from this list is shown below.
|acid acceptable name||related anions- acceptable names|
and additive names
|dihydrogenphosphite dihydroxidooxidophosphate(1-))||hydrogenphosphite, hydroxidodioxidophosphate(2-)||phosphite, |
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., for a mixture of and and for a mixture of and . The recommendation is to use the following generalised method e.g.
Note that cation vacancies in could be described by
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 (the element vanadium).
To specify the crystal form of a compound or element the Pearson symbol may be used. The use of Strukturbericht (e.g. A1 etc) 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 (e.g. for where the two forms zincblende (cubic) and wurtzite (hexagonal)), as and respectively.