Effect of ligands on H ↔ D isotopic exchange rate in Co3+ complexes

By the method of 59Co NMR the isotopic H ↔ D exchange in the complexes (Co(NH3)5NO2)2+ and (Co(Q)3) in D2O (where Q-cysteine and cystamine) has been studied. For the complexes (Co(Q)3) of fac-configuration due to trans effect of sulfur atom deceleration of isotopic exchange as compared with (Co(En)3) is observed. In tris-cystamine complex of mer-configuration, containing two pairs of nonequivalent aminogroups, hydrogen atoms on transcoordinate to sulfur atom are less labilized and are substituted for by deuterium much less actively (one order slower) than protons of aminogroups in cis-positions. The rates of isotopic exchanger reactions are compared, on the basis the change in the strength of cobalt-nitrogen bonds in different Co3+ compounds is discussed