Kappa convention

Fig. 25 A Molecule that Uses the Kappa Convention in IUPAC Nomenclature...

As well as finessing the use of p and r in "inorganic" nomenclature, the proposed nomenclature discards the entire kappa convention [48]+. The molecule illustrated in Figure 25, which has the IUPAC name [2(-diphenylphosphino-Kp)-phenyl-KC1]hydrido (triphenylphosphine-Kp)nickel(II), using the phenyl abbreviation described in the footnote on page 55, would be named ... 

Not only are some inorganic compounds named using the kappa convention, others augment this kappa convention with a "priming" convention [49], All of these are, similarly, made obsolete by the proposed system. For example, the ion illustrated in Figure 25, which IUPAC names as aqua[(l,2-ethanediyldinitrilo-K2N,N ) (tetraacetato-K30,0",0 " )]cobaltate (1-) would be named as ... 

The chief sdvani of the kappa convention seems to be that it denotes Ugeiing... 

Where the precise positions of ligation are unknown, the kappa convention cannot be used. 

IR-9.2.3.1 Sequence of symbols within the coordination formula IR-9.2.3.2 Use of enclosing marks IR-9.2.3.3 Ionic charges and oxidation numbers IR-9.2.3.4 Use of abbreviations IR-9.2.4 Specifying donor atoms IR-9.2.4.1 General IR-9.2.4.2 The kappa convention... 

IR-9.2.4.3 Comparison of the eta and kappa conventions IR-9.2.4.4 Use of donor atom symbol alone in names IR-9.2.5 Polynuclear complexes IR-9.2.5.1 General IR-9.2.5.2 Bridging ligands IR-9.2.5.3 Metal-metal bonding IR-9.2.5.4 Symmetrical dinuclear entities IR-9.2.5.5 Unsymmetrical dinuclear entities... 

The central atom is the atom in a coordination entity which binds other atoms or groups of atoms (ligands) to itself, thereby occupying a central position in the coordination entity. The central atoms in [NiC F COJ, [Co(NH3)6]3+ and [PtCLJ2- are nickel, cobalt and platinum, respectively. In general, a name for a (complicated) coordination entity will be more easily produced if more central atoms are chosen (see Section IR-9.2.5) and the connectivity of the stmcture is indicated using the kappa convention (see Section IR-9.2.4.2). 

These systems may be used in names, but they are not always suitable for use in formulae. The use of donor atom symbols is possible in the formulae of simple systems (see Section IR-9.2.3.4), but care must be taken to avoid ambiguity. The kappa convention is not generally compatible with the use of ligand abbreviations. 

The kappa convention is used to specify bonding from isolated donor atoms to one or more central atoms. 

In certain cases the kappa convention may be simplified. Donor atoms of a ligand may be denoted by adding only the italicized symbol(s) for the donor atom (or atoms) to the end of the name of the ligand. Thus, for the 1,2-dithiooxalate anion, ligand names such as 1,2-dithiooxalato-K5,K5,/ and l,2-dithiooxalato-KO,K5 may, with no possibility of confusion, be shortened to l,2-dithiooxalato-5,5 and l,2-dithiooxalato-0,5, respectively. Other examples are thiocyanato-iV and thiocyanato-5, and nitrito-iV and nitrito-O. 

The kappa convention is used together with p when it is necessary to specify which central atoms are bridged, and through which donor atoms. The kappa descriptor counts all donor atom-to-central atom bonds so that in Example 2 below the descriptor 1 2 3k3S specifies all three bonds from the sulfur atom bridging central atoms 1, 2 and 3. 

N-coordinated or 0-coordinated modes. To indicate the alternative donor atom through which an ambidentate ligand is coordinated in a particular complex, we may use the kappa convention, indicating the atomic symbol (in italics) of the donor atom by that Greek letter. Thus, we could refer to the nitrito ligand as NO2-KN or NO2-KO (Scheme 1). 

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