High-resolution H-1 and C-13 NMR studies on the linkage isomers [(NH3)(5)CoOC(S)NHCH3](2+) and [(NH3)(5)CoSC(O)NHCH3](2+) reveal that the O-bonded form exists as a 5:1 mixture of Z and E isomers arising from restricted rotation about the C-N bond. Similarly, restricted rotation is observed (at 20 degreesC) for the S-bonded isomer (Z/E ca. 18:1), but not for the isoelectronic carbamate ion [(NH3)(5)CoOC(O)NHCH3](2+), nor for the unsubstituted carbamato complex [(NH3)(5)CoOC(O)NH2](2+). An analysis of the variable-temperature NMR data for the O-bonded carbamato and urea complexes has provided quantitative data on the rotational barriers, and these ions involve much faster C-N bond rotations than the thiocarbamato complexes. The acid-catalyzed reaction of [(NH3)(5)CoC(S)NHCH3](2+) is confirmed, but there is much less parallel hydrolysis (ca. 2%) than previously reported (40 +/- 10%) for 0.1 M HClO4. In 1 M HClO4, [(NH3)(5)CoSC(O)NHCH3](2+) and [(NH3)(5)CoOH2](3+) are formed in parallel as an 83:17 mixture. The kinetic data suggest that the protonated form is at least 20-fold more reactive than the free ion and that the linkage isomerization and hydrolysis pathways are both acid-catalyzed, the latter clearly more so than the rearrangement.