Zero-Field Nuclear Magnetic Resonance of a Nematic Liquid Crystal

appear which matched those observed by Sanchez and Spiro. Figure 9 shows the time development of the observed Raman spectrum at -0.8 V which at long times became the spectrum of high-spin Fe(I1). The time development of the spectroscopic changes at -0.8 V contrasts the instantaneous changes observed in the reduction of adsorbed hemin and instead tracks the slow reduction of the entire solution volume. Therefore, it is clear that the reduction product of dissolved hemin and adsorbed hemin have different structures. Our surface Raman data support an intermediate-spin 4-coordinate adsorbed Fe(I1)PP and the resonance Raman spectrum of the reduced solution indicates a high-spin more highly coordinated Fe(1I)PP structure. The electrochemical data suggest that a t high Fe(I1) concentrations Fe(I1)PP dimers form in solution (see discussion of wave II,, Figure 3). In the absence of other ligands, the dimerization of dissolved Fe(I1)PP may also explain the observation of low-spin Fe(I1) in the resonance Raman spectrum of the reduced solution. Apparently, the surface-bound reduction products are restrained from aggregating.