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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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