Including: 1. Experimental Part for the Synthesis of the [trans-Cl(η η η η 2 -dppe) 2 Ru-C≡C(4-C 6 H 4 )X] n+ Complexes p. S3 2. IR spectra of 1-X and 1-X + (X = NO 2 , H, OMe) in Dichloromethane p. S7 3. UV-vis-Near IR Spectra of 1-OMe in CH 2 Cl 2 p. S7 4. Various LFERs obtained with the [trans-Cl(η η η η 2 -dppe) 2 Ru-C≡C(4-C 6 H 4 )X] n+ Complexes p. S8 5. Slopes of the Various Linear Fits obtained with the [trans-Cl(η η η η 2 -dppe) 2 RuC≡C(4-C 6 H 4 )X] n+ and [(η η η η 2 -dppe)(η η η η 5 -C 5 Me 5 )M-C≡C(4-C 6 H 4 )X] + Complexes (M = Fe, Ru) in LFERs p. S9 6. Selected X-ray Structural Data for Complex 1-NO 2 Compared with Optimized Structural Data for 4-NO 2 p. S10 7. Cartesian Coordinates of All DFT Optimized Geometries p. S11 8. Composition of the Frontier MOs for 4-X/4-X + Complexes p. S21 9. Correlation between IPs computed for 4-X Complexes and E 0 Values Measured for the Related 1-X Complexes p. S23 10. Calculated Dipole Moments for Selected Compounds p. S23

{Cp*(dppe)Fe(C≡C-)}(2)(1,3-C(6)H(4)) is studied both as a neutral molecule, Fe(II)-Fe(II), and as a mixed-valence complex, Fe(II)-Fe(III). Scanning tunneling microscopy (STM) is used to image these species at 77 K under ultrahigh-vacuum conditions. The neutral molecule Fe(II)-Fe(II) has a symmetric, "dumbbell" appearance in STM images, while the mixed-valence complex Fe(II)-Fe(III) demonstrates an asymmetric, bright-dim double-dot structure. This asymmetry results from localization of the electron to one of the iron-ligand centers, a result which is confirmed through comparison to theoretical STM images calculated using constrained density-functional theory (CDFT). The observation of charge localization in mixed-valence complexes outside of the solution environment opens up new avenues for the control and patterning of charge on surfaces, with potential applications in smart materials and molecular electronic devices.