The compound Rh-2(esp)(2) (esp = alpha,alpha,alpha',alpha'-tetramethyl-1,3-benzenediproponoate) is the most generally effective catalyst for nitrenoid amination of C-H bonds. However, much of its fundamental coordination chemistry is unknown. In this work, we study the effects of axial ligand coordination to the catalyst Rh-2(esp)(2). We report here crystal structures, cyclic voltammetry, UV-vis, IR, Raman, and H-1 NMR spectra for the complexes Rh-2(esp)(2)L-2 where L = pyridine, 3-picoline, 2,6-lutidine, acetonitrile, and methanol. The compounds all show well-defined pi* -> sigma* electronic transitions in the 16500 to 20500 cm(-1) range, and Rh-Rh stretching vibrations in the range from 304 to 322 cm(-1). Taking these data into account we find that the strength of axial ligand binding to Rh-2(esp)(2) increases in the series CH3OH similar to 2,6-lutidine < CH3CN < 3-methylpyridine similar to pyridine. Quasi-reversible Rh-2(4+/5+) redox waves are only obtained when either acetonitrile or no axial ligand is present. In the presence of pyridines, irreversible oxidation waves are observed, suggesting that these ligands destabilize the Rh-2 complex under oxidative conditions.