Linkage isomers

The two reported structures of Rh thiocyanate complexes both contain an S-bonded NCS unit.275,283 The N-bonded isothiocyanate complex IrCl(CN)(NCSXCO)(PPh3)2284 is obtained by recrystallization of the S-bonded isomer (linkage isomerization). Its structure could not be refined and of the Ir-NCS fragment only the C—S distance (1.62 A) has been given. 

Ligands such as nitrite can have isomers (linkage isomers see Linkage Isomerism), in which the metal is bound via N in one case (M-NO2) or O (M-ONO) in the other. Complexes such as [Co(en)2XY]"+ can have optical isomers (6) and (7),... 

Coordination isomers Linkage isomers Geometric (cis-trans) Optical isomers... 

Linkage isomers Linkage isomers occur when a ligand species can attach to the metal atom in different orientations. For example, when thiocyanate (SCN ) bonds to a metal, in one isomer the metal can be linked through the nitrogen atom whereas in the other isomer it s linked though the sulfur atom. (The orientation of these links affects the name of the coordination compound, which we describe in the next section.)... 

In an oligonucleotide having n backbone linkages, this gives rise to 2 isomers that vary in their mechanism of action, cellular transport, as well as pharmacokinetics (53). Some of the most frequently encountered backbone modifications are Hsted in Table 1. 

The hydroxypentammine is a useful starting material for the nitro and nitrito linkage isomers, the nitrito form separating under mild conditions but transforming to the nitro isomer on standing, especially when heated. 

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