Page 72 - Nomenclature of Inorganic Chemistry (IUPAC Recommendations 2005)

IR-4.4 F O R M U L A E

IR-4.4.4 Ligand abbreviations
Since abbreviations are widely u sed in the chemical literature, agreement on their use
and meaning i s d esirable. This Section provides guidelines for the selection of ligand
abbreviations for application in the formulae of coordination compounds (Section
IR-9.2.3.4). Some commonly used ligand abbreviations are listed i n T able VII with
diagrams of most o f t he ligands shown i n T able VIII.
An abbreviation for an organic ligand should be derived from a n ame c onsistent with the
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current rules for the systematic nomenclature of organic compounds. (For some l igands a
non-systematic name i s i ncluded in Table VII i f i t w as the source of the abbreviation and
if that abbreviation is still commonly used.) New abbreviations should further be constructed
according to the following recommendations:

(i) Ligand abbreviations should b e c onstructed so as to avoid confusion and
misunderstanding. Since a r eader may not be familiar with an abbreviation, it
should be explained when first used in a p ublication.
(ii) New m eanings s hould n otbesuggested f orabbreviations o r a cronyms t hat h ave g enerally
accepted meanings, e.g. DNA, NMR, ESR, H PLC, Me (for methyl), Et (for ethyl), etc.
(iii) An abbreviation should readily suggest t he ligand name, e.g. ida for iminodiacetato.
(Ligand names may, however, e ventually violate nomenclature rules as these are
modified, for example i minodiacetate w ill be replaced by azanediyldiacetate i n R ef. 4,
but the ligand abbreviations need not be changed every time the naming rules change.)
(iv) Abbreviations should be as short as practicable, but should c ontain more than one
letter or symbol.
(v) The use of non-systematic names for deriving new ligand abbreviations is discouraged.
(vi) Abbreviations should normally use o nly lower-case letters, with several well-
established exceptions:
(a) abbreviations for alkyl, aryl and similar groups, w hich have the first letter
capitalized with the remaining l etters in lower case, e.g. Me (for methyl), Ac
(for acetyl), Cp (for cyclopentadienyl), etc.;
(b) abbreviations containing atomic symbols, e.g. [ 12]aneS 4 ;
(c) abbreviations containing Roman numerals, e.g. H 2 ppIX for protoporphyrin IX;
(d) abbreviations for ligands containing readily removable hydrons ( see vii).

(N.B. A bbreviations for solvents t hat behave as ligands should a lso be in lower case letters
[e.g. dmso for dimethyl sulfoxide {(methylsulfinyl)methane}, thf for tetrahydrofuran]; the
practice of capitalizing the abbreviation of a s olvent when it does not behave as a l igand is
strongly d iscouraged as an unnecessary distinction.)

(vii) Hydronation of anionic ligands, e.g. ida, leads to acids which may be abbreviated by
the addition of H, e.g. Hida, H 2 ida.
(viii) Ligands which are normally neutral, but which continue to behave as ligands on
losing one or more hydrons, are abbreviated by adding 1H, 2H, etc. ( including the
numeral 1) after the usual abbreviation of the ligand. For e xample, if Ph 2 PCH 2 PPh 2
(dppm) loses one hydron to give [Ph 2 PCHPPh 2 ] its abbreviation is dppm 1H; if it

loses two hydrons, its abbreviation is dppm 2H, etc.

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