The nature of the axial ligand coordinated to the Yb3+ ion in [Yb(DOTAM)](3+) has profound consequences in the magnetic anisotropy and optical properties of the complex, as evidenced by H-1 NMR and UV-vis spectroscopies. The pseudocontact shifts of H-1 nuclei and the F-2(5/2) <- F-2(7/2) absorption band were found to be very sensitive to the nature of the axial ligand (MeOH, H2O, MeOH, or F). The energy levels of the F-2(5/2) and F-2(7/2) manifolds in [Yb(DOTAM)(X)](3+) (X = MeOH, H2O, or dimethyl sulfoxide (DMSO)) and [Yb(DOTAM)F](2+) complexes were assigned from the analysis of the optical spectra and ab initio calculations based on CASSCF wave functions that considered dynamic correlation through perturbation theory (NEVPT2) and spin-orbit coupling effects. The magnetic anisotropies obtained with ab initio calculations are in good agreement with the experimental values derived from H-1 NMR spectral data, though for the [Yb(DOTAM)(H2O)](3+) and [Yb(DOTAM)F](2+) complexes, the explicit inclusion of a few second-sphere water molecules is required to improve the calculated data. Crystal-field calculations show that the observed pseudocontact shifts do not correlate well with the crystal-field parameter B-2(0), as predicted by Bleaney's theory. The change in the sign of the magnetic anisotropy from prolate (X = MeOH, H2O, or DMSO) to oblate in [Yb(DOTAM)F](2+) is related to the relative energies of the 4f(z)(3) orbital and the 4f(x)(3)/4f(y)(3) pair, which are affected by the coordination ability of the axial ligand.