NOMENCLATURE OF COORDINATION COMPOUNDS

Nomenclature of coordination compounds

Detailed guidance on the nomenclature of coordination compounds is beyond the scope of this article and only a general introduction is given here. In fact, the names of complexes often become so cumbersome that inorganic chemists often prefer to give the formula rather than spell out the entire name.

Rules For Nomenclature Of Coordination Compounds

Here are the rules for nomenclature of coordination compounds:

1. For compounds that consist of one or more ions, the cation is named first, followed by the anion (as for simple ionic compounds), regardless of which ion is complex.

2. Complex ions are named with their ligands in alphabetical order (ignoring any numerical prefixes).

Typical ligands and their names:

Nomenclature of coordination compounds

3. The ligand names are followed by the name of the metal with either its oxidation number in parentheses, as in hexaamminecobalt(III) for [Co(NH3)6]3+, or with the overall charge on the complex specified in parentheses, as in hexaamminecobalt(3+).

4. The suffix -ate is added to the name of the metal if the complex is an anion, as in tetrachloridoplatinate(II) for [PtCl4]2-. Some metals, such as iron, copper, silver, gold, tin, and lead, have anion names that derive from the Latin form of the element name (i.e. ferrate, cuprate, argentate, aurate, stannate, and plumbate, respectively).

The number of a particular type of ligand in a complex is indicated by the prefixes mono-, di-, tri-, and tetra-. The same prefixes are used to state the number of metal atoms if more than one is present in a complex, as in octachloridodirhenate(III), [Re2Cl8]2-.

Where confusion with the names of ligands is likely—perhaps because the name already includes a prefix, as with 1,2-diaminoethane—the alternative prefixes bis-, tris-, and tetrakis- are used, with the ligand name in parentheses. For example, dichlorido- is unambiguous but tris(1,2-diaminoethane) shows more clearly that there are three 1,2-diaminoethane ligands, as in tris(1,2-diaminoethane)cobalt(II), [Co(en)3]2+.

Ligands that bridge two metal centres are denoted by a prefix μ (mu) added to the name of the relevant ligand, as in μ-oxido-bis(pentamminecobalt(III)). If the number of centres bridged is greater than two, a subscript is used to indicate the number; for instance, a hydride ligand bridging three metal atoms is denoted μ3-H.

Square brackets are used to indicate which groups are bound to a metal atom and should be used whether the complex is charged or not. The metal symbol is given first, then the ligands in alphabetical order (the earlier rule that anionic ligands precede neutral ligands has been superseded), as in [CoCl2(NH3)4]+ for tetraamminedichloridocobalt(III). This order is sometimes varied to clarify which ligand is involved in a reaction.

Polyatomic ligand formulas are sometimes written in an unfamiliar sequence (as for OH2 in [Fe(OH2)6]2+ for hexaaquairon(II)) to place the donor atom adjacent to the metal atom and so help to make the structure of the complex clear. The donor atom of an ambidentate ligand is sometimes indicated by underlining it, for example [Fe(OH2)5(NCS)]2+. Note that, somewhat confusingly, the ligands in the formula are in alphabetical order of the binding element, and thus the formula and name of the complex may differ in the order in which the ligands appear.

Examples

Examples of some compounds in order to understand the nomenclature of coordination compounds easily.

Cationic Complex

[Co(NH3)6]Cl3                               Hexaamminecobalt(III) chloride

[CoCl(NH3)5]2+                                    Pentaamminechlorocobalt(lll) ion
[CoSO4(NH3)4]NO3                           Tetraamminesulphatocobalt(III) nitrate
[Co(NO2)3(NH3)3]                         Triamminetrinitrito-ᴋNcobalt(III)
[CoCI·CN·NO2·(NH3)3]                Triamminechlorocyanonitrito-ᴋNcobalt(III)
[Zn(NCS)4]2+                                         Tetrathiocyanato-ᴋNzinc(II)
[Cd(SCN)4]2+                                  Tetrathiocyanato-ᴋScadmium(II)

Anionic Complex

Li[AIH4]                                      Lithium tetrahydridoaluminate(III)
Na2[ZnCI4]                                 Sodium tetrachlorozincate(II)
K4[Fe(CN)6]                               Potassium hexacyanoferrate(II)
K3[Fe(CN)5NO]                         Potassium pentacyanonitrosylferrate(II)
K2(OsCl5N]                                 Potassiurn pentachloronitridoosmate(VI)
Na3[Ag(S203)2]                          Sodium bis(thiosulphato)argentate(I)
K2[Cr(CN)2O2(O2)NH3]          Potassium amminedicyanodioxoperoxochromate(VI)

Organic groups

[Pt(py)4][PtCl4]                   Tetrapyridineplatinum(II) tetrachloroplatinate(II)
[Cr(en)3]Cl3                          Tris(ethylenediatnine)chromium(III) chloride
[CuCl2(CH3NH2)2]             Dichlorobis(dimethylamine)copper(II)
Fe(C5H5)2                                    Bis(cyclopentadienyl)iron(II)
[Cr(C6H6)2]                           Bis(benzene)chromium(0)

Bridging groups

[(NH3)5Co-NH2-Co(NH3)5](NO3)5                        µ-amidobis[pentaamminecobalt(III)]nitrate
[(CO)3Fe(CO)3Fe(CO)3]                                        Tri-µ-carbonyl-bis(tricarbonyliron(0))

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