Configuration index

Fig. 1. Configurational index a versus ax for self-interacting chains on face centered...

For this case, there are no additional complications, and the configuration index is assigned in the usual way as OC-6-32. 

Attempts to produce descriptors similar to cis and trims for stereochemicidly more complicated coordination entities have tailed to achieve generality, and labels such as foe and mer are no longer recommended. Nevertheless, a diastereoisomeric structure may be indicated for any polyhedron using a configuration index as an affix to the name or formula. Finally, the chiralities of enantiomeric structures can be indicated using chirality symbols. 

Square planar coordination systems (SP-Jt The configuration index is a single digit which b the priority number Tor the ligating atom irons to the ligating atom of priority number l.33... 

The structural formula of this new cytostatic (picoplatin) is shown below. In determining the stereo descriptor, the situation arises here that the highest ranking ligand occurs twice. In such cases the priority number of the ligand coordinated trans to it with the lowest priority (i.e. with the highest priority number) is used as the configuration index (principle of trans maximum difference). 

SP-4-1 ] -(aceionimlc)[Pg.519]

Priming convention. The configuration index is especially useful for bis(tridentate) complexes and for more complicated cases. Bis(tridentate) complexes exist in three di-astereoisomeric forms which serve to illustrate the utility of a priming convention. These isomers are represented below, along with their site symmetry symbols and configuration indexes. For Examples I, 2, and 3, the two ligands are identical and the ligating-atom priority numbers are indicated. 

Clearly a general method is required in order to distinguish between diastereoisomers of compounds in which either other geometries or more than two kinds of donor atoms are present. The configuration index has been developed for this purpose. The next section outlines the method by which a configuration index is obtained for a compound, and the... 

Each donor atom must be assigned a priority number based on the rules developed by Cahn, Ingold and Prelog (the CIP rules).13 These priority numbers are then used to form the configuration index for the compound. The application of the CIP rules to coordination compounds is discussed in detail in Section IR-9.3.5 but, in general, donor atoms that have a higher atomic number have higher priority than those that have a lower atomic number. 

The presence of polydentate ligands may require the use of primes on some of the numbers in the configuration index. The primes are used to indicate either that donor atoms are not part of the same polydentate ligand as those that have unprimed priority numbers, or that the donor atoms belong to different parts of a polydentate ligand that are related by symmetry. A primed priority number means that that donor atom has lower priority than the same kind of donor atom without a prime on the priority number. More detail on the priming convention can be found in Section IR-9.3.5.3. 

The configuration index for a square planar system is placed after the polyhedral symbol (SP-4). It is the single digit which is the priority number for the ligating atom trans to the ligating atom of priority number 1, i.e. the priority number of the ligating atom trans to the most preferred ligating atom. 

The configuration index of an octahedral system follows the polyhedral symbol (OC-6) and consists of two digits. 

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