Isomerism 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. 

Linkage isomerism This is a special type of structural isomerism in which the differences arise from a particular ligand which may coordinate to a metal ion in more than one way. In Table 1-3 we indicated that a ligand such as thiocyanate could bond to a metal through either the nitrogen or the sulfur atom, and the complex ions [Co(NH3)5(ACS)]2+ and [Co(NH3)5(5CN)]2+ are related as linkage isomers. 

The ammonioacetonitrile complex (206) reacts with NH3 to produce the amidine-bonded aminoacetamidine (207) complex, whereas in aqueous base it hydrolyzes to the amid o-A -bo ruled glycinamide complex (208).908 Acid-catalyzed linkage isomerization to first the O-bound form (209) precedes formation ultimately of the amino-bonded isomer (210) as the stable product upon deprotonation of the free amine above pH 6. 

Fe(CN)jSCN]4 displays linkage isomerism. The other isomer is [Fe(CN)5NCS]4... 

There are basically two types of mechanisms which can explain rearrangement of linkage isomers. In the intermolecular mechanism, the ligand giving rise to linkage isomerism (L-L, with two donor centers) dissociates from and recombines with the metal M ... 

Unusual example of bidentate ligand involved in linkage isomerism. Forms characterized by P nmr and x-ray diffraction. (ly isomer favored at 40 °C pH 6.5. No kinetic data on rearrangement. 

An interesting study with BATO compounds concerns the linkage isomerization of coordinated [NCS] in [Tc(NCS)(cdoh)2(cdo)(BMe)] (440). Both a red, N-bond isothiocyanato complex [Tc(NCS)(cdoh)2(cdo)(BMe)] and the brown, S-bond thiocyanato complex [Tc(SCN)(dmg)3(BR)] (441) were isolated from the direct synthesis from [Tc04] . The N-bound (440) was found to be thermodynamically more stable than the S-bound isomer (441) and the conversion was monitored elegantly by spectroscopic methods. The X-ray crystal structure of (440) was determined. The NCS and SCN -substituted analogues exhibited r c N stretch at 2,114-2,124 cm and at 2,055-2,079 cm , respectively. " (Scheme 59). 

For aniline, an equilibrium with Keq close to unity exists between the N-bound and 2,3-C,C-tj2-bound isomers of Os(II). The one-electron oxidation of the latter isomer (E° = 0.16 V versus NHE in acetone) is followed by an arene-to-nitrogen linkage isomerization, proceeding... 

Werner knew of two other examples of linkage isomerism, both nitro-nitrito isomers, and they underwent the same period of skepticism and confirmation as the compounds discussed above although considerably less work was done with diem. A period of more than 50 years passed before Basolo and coworkers attacked the problem with rather amazing results.w Linkage isomerism, once relegated to a few lines as an "exceptional" situation in discussions of isomerism, now boasts an extensive chemistry which continues to develop. The first new linkage isomers prepared were mtro-nitnto isomers of Cr lII), Rh(lll), Ir(lll), and Pt(lV). In all cases except Cr(lll), the nitrito isomer converts readily to the more stable nitro isomer... 

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