Ligand linkage

Another type of isomerism displayed by coordination complexes Is based on the bonding of the ligand. Linkage isomers occur when a ligand can bond to a metal using either of two donor atoms. Figure 20-10 shows the two... 

Different types of protein or ligand linkages to hydroxylic matrices via spacers are shown in the following three examples ... 

The biological and chemical importance of metalloporphyrins has caused much interest in the nature of the metal-ligand linkage in such complexes. Fleischer (1970) has discussed certain structural properties of the porphyrin molecule necessary for understanding such physical properties as its solubility, magnetic susceptibility, and visible absorption, electron spin resonance (ESR), and NMR spectra. He has also... 

The polar and labile nature of RE ligand linkages lends itself to facile acid-base chemistry, p/fa considerations play an important role, and since most hydrocarbyl ligands possess relatively high p/fa values, it follows that in an acid-base reaction, a proligand with a low p/fa will displace... 

Ambidentate ligands possess more than 1 donor atom and can coordinate through either one or the other. This leads to the possibility of linkage isomerism (p. 920). The commonest examples are the ions NO2 (p. 463) and SCN (p. 325). Such ligands can also coordinate via both donor sites simultaneously, thereby acting as bridging ligands. 

Since the coordination number of tantalum or niobium in fluoride and oxyfluoride compounds cannot be lower than 6 due to steric limitations, further decrease of the X Me ratio (lower than 6) leads to linkage between complex ions in order to achieve coordination saturation by sharing of ligands between different central atoms of the complexes. The resulting compounds have X Me ratios between 6 and 4, and form crystals with a chain-type structure. 

A further decrease in the X Me ratio, to 4, leads to linkage of the octahedral units by sharing more than one ligand so as to achieve coordination saturation. Sharing of two vertexes (two comers of the each octahedron) leads to the formation of compounds with layered-type structures. 

A number of tertiary phosphine ligands have been synthesized that also contain an alkene linkage capable of coordinating to a metal. A good example of this kind of coordination is formed in the complex of (tri-o-vinyl-phenyl)phosphine (Figure 2.29) with each alkene acting as a two-electron donor, a noble gas configuration is achieved [67],... 

Less study has been made of complexes with polydentate ligands. Ag-N linkages have been studied in relation to polynucleotide bases and the Ag-DNA interaction could be important in the use of the silver-sulphadiazine complex in burn treatment. Ethylenediamine is a bridging ligand in AgenC104 (2-coordinate silver) but essentially planar 5-coordination... 

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