High-Field, Multifrequency EPR Study of the [Mn(OH2)6]3+ Cation: Influence of (pi)-Bonding on the Ground State Zero-FieldSplitting Parameters

High-field, multifrequency EPR data are presented for the alum CsMn(SO4)2.12D2O, containing the [Mn(OD2)6]3+ cation. The data are interpreted using the conventional S = 2 spin Hamiltonian, and the following parameters determined for the data obtained below 30 K: D = -4.491(7) cm -1, E = 0.248(5) cm -1, gx = 1.981(5), gy = 1.993(5), gz = 1.988(5). Although the deviation of the MnO6 framework from idealized D4h symmetry is small, the magnitude of E/D is significant. The E parameter is related to ligand field parameters derived from the optical absorption spectrum. The rhombic anisotropy is shown to arise as a consequence of the (pi)-anisotropic nature of the manganese(III)-water interaction.