INDEX tridentate ligands

Bis(tridentate) complexes (i.e. octahedral complexes containing two identical linear tridentate ligands) may exist in three stereoisomeric forms, and there will be more if the tridentate ligands do not themselves contain some symmetry elements. The three isomers of the simplest case are represented below (Examples 1, 2 and 3), along with their polyhedral symbols (Section IR-9.3.2.1) and configuration indexes (Section IR-9.3.3.4). Complexes of A-(2-aminoethyl)ethane-1,2-diamine and iminodiacetate can be described by these diagrams. 

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. 

Tridentate chelation by the tetrafunctional macrocycle in Example 4 is shown by the kappa index following the ligand name. The ligand locants are required in order to distinguish this complex from those where the central atom is bound to other combinations of the four potential donor atoms. 

For polydeniate ligands, a right superscript numeral is added to the symbol k in order to indicate the number of identically bound ligating atoms in the flexidentate34 ligand. Any doubling prefixes, such as bis-, are presumed to operate on the k locant index as well. Examples [I and 2] use tridentate chelation by the linear tetraammine ligand, N,A/ -bis(2-aminoethyl)-l,2-eihanediamine to illustrate these rules. 

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