Thioethers, resonance structures

An nuclear magnetic resonance (NMR) study of the same complex indicates that the observed hexacoordination in the crystal structure is combined with a fast exchange of the donor thioethers in solution as all carbon atoms of the side chains have equivalent signals. Even at temperatures of 183 K, the signals remain equivalent. This could lead to an extra stability, but despite the high thermodynamic stability the kinetic stability is still too low and slow exchange with serum proteins has been observed. 

The SH group induces much smaller shift changes. The CH2 resonance of carbons adjacent to a thiol group appear around 24-35 ppm according to the presence of other substituents and chain branching. Similar effects are seen in thioethers. Sulfoxides of the type RR SO are chiral because of the pyramidal structure of the sulfoxide group and hence nonequivalence can be seen in the NMR spectra. Methylene carbons adjacent to sulfone groups appear around 55-65 ppm. 

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