IUPAC nomenclature of inorganic chemistry 2005

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.

• O₂ dioxygen (acceptable name oxygen)
• O₃ trioxygen (acceptable name ozone)
• P₄ tetraphosphorus (acceptable name white phosphorus)
• S₆ hexasulfur (acceptable name ε-sulfur)
• S₈ cyclo-octasulfur (acceptable names for the polymorphic forms are α-sulfur, β-sulfur, γ-sulfur)

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.)

• C_n carbon(cF8) (acceptable name diamond)
• Sn_n tin(tI4) (acceptable name β- or white tin)
• Mn_n manganese(cI58) (acceptable name α-manganese)

Examples include P_n,. red phosphorus ; As_n, amorphous arsenic.

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

• PCl₅ phosphorus pentachloride
• Ca₂P₃ dicalcium triphosphide
• NiSn nickel stannide
• Cr₂₃C₆ tricosachromium hexacarbide

The following illustrate the principles.

The 1:1:1:1 quaternary compound between bromine, chlorine, iodine and phosphorus:

• PBrClI phosphorus bromide chloride iodide (phosphorus is the most electropositive, the others are all designated as electronegative and are sequenced alphabetically)

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.

• CuK₅Sb₂ copper pentapotassium diantimonide, (both copper and potassium are designated as electropositive and are sequenced alphabetically)
• K₅CuSb₂ pentapotassium diantimonide cupride (only potassium is designated as electropositive and the two electronegative elements are sequenced alphabetically) (Note the red book shows this example incorrectly)

Monatomic cations are named by taking the element name and following it with the charge in brackets e.g

• Na⁺
  sodium(1+)
• Cr³⁺
  chromium(3+)

Sometimes an abbreviated form of the element name has to be taken, e.g. germide for germanium as germanide refers to GeH⁻
₃.

Polyatomic cations of the same element are named as the element name preceded by di-, tri-, etc., e.g.:

• Hg²⁺
  ₂ dimercury(2+)

Polyatomic cations made up of different elements are named either substitutively or additively, e.g.:

• PH⁺
  ₄ phosphanium
• SbF⁺
  ₄ tetrafluorostibanium (substitutive) or tetrafluoridoantimony(1+)
• Note that ammonium and oxonium are acceptable names for NH⁺
  ₄ and H
  ₃O⁺
  respectively. (Hydronium is not an acceptable name for H
  ₃O⁺
  )

Monatomic anions are named as the element modified with an -ide ending. The charge follows in brackets, (optional for 1−) e.g.:

• Cl⁻ chloride(1−) or chloride
• S²⁻ sulfide(2−)

Some elements take their Latin name as the root e.g

• silver, Ag, argentide
• copper, Cu, cupride
• iron, Fe, ferride
• tin, Sn, stannide

Polyatomic anions of the same element are named as the element name preceded by di-, tri-, etc., e.g.:

• O₂²⁻ dioxide(2−) (or peroxide as an acceptable name)
• C₂²⁻ dicarbide(2−) (or acetylide as an acceptable name)
• S₂²⁻ disulfide(2−)

or sometimes as an alternative derived from a substitutive name e.g.

• S₂²⁻ disulfanediide

Polyatomic anions made up of different elements are named either substitutively or additively, the name endings are -ide and -ate respectively e.g. :

• GeH₃⁻ germanide (substitutive), or trihydridogermanate(1−) (additive)
• TeH₃⁻ tellanuide substitutive where -uide specifies anion composed of additional hydride attached to parent hydride
• [PF₆]⁻ hexafluoro-λ⁵-phosphanuide (substitutive), or hexafluoridophosphate(1−) (additive)
• SO₃²⁻ trioxidosulfate(2−) (additive), or sulfite (acceptable non-systematic name)

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:

• He^·+ helium(·+)
• N₂^(2·)2+ dinitrogen(2·2+)

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:

• CaCl₂·8NH₃, calcium chloride— ammonia (1/8)
• 2Na₂CO₃·3H₂O₂, sodium carbonate—hydrogen peroxide (2/3)
• AlCl₃·4EtOH, aluminium chloride—ethanol (1/4)

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:

• Water, "aqua"
• Ammonia, "ammine"
• Carbon monoxide bonded via carbon, "carbonyl"
• Nitrogen monoxide bonded via nitrogen, "nitrosyl"

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:

• [CoCl(NH₃)₅]Cl₂ pentaamminechloridocobalt(3+) chloride where ammine (NH₃)precedes chloride. The central atom name(s) come after the ligands. Where there is more than one central atom it is preceded by di- tri-, tetra- etc.
• Os₃(CO)₁₂, dodecacarbonyltriosmium

Where there are different central atoms they are sequenced using the electronegativity list.

• [ReCo(CO)₉] nonacarbonylrheniumcobalt

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:

Al₂Cl₄(μ-Cl)₂

di-μ-chlorido-tetrachlorido-1κ²Cl,2κ²Cl-dialuminium

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:

[Be₄(μ₄-O)(μ-O₂CMe)₆]

hexakis(μ-acetato-κO:κO′)-μ₄-oxido-tetrahedro-tetraberyllium

The μ₄ 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. μ₃ bridging before μ₂ 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, 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:

• pentaamminenitrito-κO-cobalt(III) specifies that the nitrite ligand is linking via the oxygen atom

Where there is more than one bond formed from a ligand by a particular element a numerical superscript gives the count. For example:

• aqua[(ethane-1,2-diyldinitrilo-κ²N,N′)tris(acetato-κO)acetato]cobaltate(1-), the cobalt anion formed with water and pentadentate edta, which links via two nitrogen atoms and three oxygen atoms. There are two bonds from nitrogen atoms in edta which is specified by -κ²N,N′. The three bonds from oxygen are specified by tris(acetato-κO), where there is one ligation per acetate.

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.

Examples:

di-μ-chlorido-tetrachlorido-1κ²Cl,2κ²Cl-dialuminium, (aluminium trichloride).

tetrachlorido-1κ²Cl,2κ²Cl specifies that there are two chloride ligands on each aluminium atom.

decacarbonyl-1κ³C,2κ³C,3κ⁴C-di-μ-hydrido-1:2κ²H;1:2κ²H-triangulo-(3 Os—Os), (Decacarbonyldihydridotriosmium).

decacarbonyl-1κ³C,2κ³C,3κ⁴C shows that there are three carbonyl groups on two osmium atoms and four on the third.

di-μ-hydrido-1:2κ²H;1:2κ²H specifies that the two hydride bridge between the osmium atom 1 and osmium atom 2.

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:

• Cr(η⁶-C₆H₆)₂, named as bis(η⁶-benzene)chromium as all of the (contiguous) atoms in the benzene ligands are involved their position does not have to be specified
• [(1,2,5,6-η)-cycloocta-1,3,5,7-tetraene](η⁵-cyclopentadienyl)cobalt in this only two (at positions 1 and 5) of the four double bonds are linked to the central atom.

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(η⁵-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:

• vanadocene, [V(η⁵-C₅H₅)₂]
• chromocene, [Cr(η⁵-C₅H₅)₂]
• cobaltocene, [Co(η⁵-C₅H₅)₂]
• rhodocene, [Rh(η⁵-C₅H₅)₂]
• nickelocene, [Ni(η⁵-C₅H₅)₂]
• ruthenocene, [Ru(η⁵-C₅H₅)₂]
• osmocene, [Os(η⁵-C₅H₅)₂]
• manganocene, [Mn(η⁵-C₅H₅)₂]
• rhenocene, [Re(η⁵-C₅H₅)₂].

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

• C₁₀H₁₀Ti
• [Ti(η⁵-C₅H₅)₂Cl₂] is properly named dichloridobis(η⁵-cyclopentadienyl)titanium NOT titanocene dichloride

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)-Δ⁴-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.[4]

Examples:

decacarbonyldimanganese bis(pentacarbonylmanganese)(Mn—Mn)

dodecacarbonyltetrarhodium tri-μ-carbonyl-1:2κ²C;1:3κ²C;2:3κ²C-nonacarbonyl- 1κ²C,2κ²C,3κ²C,4κ³C-[T_d-(13)-Δ⁴-closo]-tetrarhodium(6 Rh—Rh)
or tri-μ-carbonyl-1:2κ²C;1:3κ²C;2:3κ²C-nonacarbonyl- 1κ²C,2κ²C,3κ²C,4κ³C-tetrahedro-tetrarhodium(6 Rh—Rh)

The recommendations include a description of hydrogen names for acids. The following examples illustrate the method:

• HNO₃ hydrogen(nitrate)
• H₂SO₄ dihydrogen(sulfate)
• HSO−4 hydrogen(sulfate)(2−)
• H₂S dihydrogen(sulfide)

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.

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.

• BaTiO₃ (perovskite type)

A simple notation may be used where little information on the mechanism for variability is either available or is not required to be conveyed:

• ~FeS (circa or approximately)

Where there is a continuous range of composition this can be written e.g., K(Br,Cl) for a mixture of KBr and KCl and (Li₂,Mg)Cl₂ for a mixture of LiCl and MgCl₂. The recommendation is to use the following generalised method e.g.

• Cu_xNi_1−x for (Cu,Ni)
• KBr_xCl_1−x for K(Br,Cl)

Note that cation vacancies in CoO could be described by CoO_1−x

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:

• carbon(cF 8 ), diamond
• RuAl(CP22, Pm3m)(CsCl type)