In DMSO containing Br- ions, the heptyl viologen cation radical (HV .(+)) can form two different types of two-dimensional (2D) phase on Hg. Thus, HV .(+) can take a planar conformation relative to the surface; however, depending on the applied potential, it can reorient itself to adopt a conformation where the bipyridine group lies edge-on or tilted relative to the electrode surface. We analyzed the structure and stability of the two phases and found HV .(+) and Br- ions to take part in a 1:1 ratio in both. We also studied the kinetics of formation of the two phases, as well as that of reorientation between them, and found both to involve two-dimensional nucleation and growth mechanisms.