Ligand indexing

F. Spindler, M. Studer, A. Togni, Topics in Catalysis 2002, 39, 3 and information on commercial ligands in http // www.solvias.com/english/products-and-services/chemicals/ligands/index.html... 

In the case of permutation isomers with some indistinguishable ligands and/or with skeletal symmetry there are different but equivalent ligand permutations leading to the reference isomer of the configuration. Among the numerically ordered equivalent ligand index permutations that one is chosen for the descriptor which contains the lowest number of transpositions ). 

The structures in Figures 2-6 illustrate the utility of a ligand index-based stereochemical notation for coordination compounds. 

As an illustration, consider the oxidation of acyclic phosphines by bis (2-hydroxyethyl) disulfide which proceeds with retention of configuration at phosphorus. The essential portion of this reaction, and appropriate ligand indexing, are shown in Eq. (13) for the oxidation of (/ )-methylphenyl-propylphosphine (29). 

In empirical formulas of inorganic compounds, electropositive elements are listed first [3]. The stoichiometry of the element symbols is indicated at the lower right-hand side by index numbers. If necessary, the charges of ions are placed at the top right-hand side next to the element symbol (e.g., S "). In ions of complexes, the central atom is specified before the ligands are listed in alphabetical order, the complex ion is set in square brackets (e.g., Na2[Sn(OH)+]). 

Figure 2-80. The permutation matrix oFthe reference isomer the second line gives the indices of the sites of the skeleton and the first line the indices of the ligands (e.g.. the ligand with index 3 is on skeleton site 3).

Fig. 2. Yellowness index vs two-roU mill heat stabiUty, where the mercaptide ligands, — SCH2COOR (A), —SCH2CH2COOR ( ), and —SCH2CH2C00R + HSCH2CH2C00R ( )) IT 9, and 6% Sn, respectively. R = CgH. R = H33. ...

The development of ligands selective for individual receptor subtypes relevant to a targeted disease could decrease these toxic effects thereby improving the therapeutic index. Two new arotinoids are already available for topical use in skin diseases. These are tazarotenic acid (tazarotene) and 6-[3-(l-adamanty 1)-... 

Index of Review Articles and Specialist Texts Table 3 Complexes According to Ligand... 

Entries where the oxidation state of a metal has been specified occur after all the entries for the unspecified oxidation state, and the same or similar entries may occur under both types of heading. Thus cyanide appears under Chromium complexes, Chromium(O) complexes, Chromium(I) complexes, etc. More specific entries, such as Chromium, hexacyano-, may also occur. Similar ligands may also occur in different entries. Thus a carboxylic acid-metal complex may occur under Carboxylic acid complexes, under entries for specific carboxylic acids, and under the specific metal. Coordination complexes may also be listed in the Cumulative Formula Index. 

The element symbols within each formula are arranged according to a modified Hill system in which the order is metal(s), C, H and then any remaining symbols arranged alphabetically. Compounds containing two (or more) different metals appear twice (or more), being listed under each metal. Common ligand abbreviations which appear in the text have also been used in the index. These include acac (acetylacetone), bipy (2,2 -bipyridyl), diars [o-phenylenebis(dimethyl-arsine)], dien (diethylenetriamine), etc. 

The idea of ligand efficiency was extended by considering other molecular descriptors. Abad-Zapatero and Metz [56] introduced a percentage efficiency index, a binding efficiency index and a surface-binding efficiency index by normalizing... 

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