P. L. W. Tregenna-Piggott and Hans-Ueli Güdel
Influence of Jahn-Teller Coupling on the Magnetic Properties of Transition Metal Complexes with Orbital Triplet Ground Terms: Magnetization and Electronic Raman Studies of the Titanium(III) Hexa-Aqua Cation
Inorg. Chem. 40, 5497-5506 (2001)                 

Abstract: Magnetization and electronic Raman data are presented for salts of the type Cs[Ga:Ti](SO₄)₂·12H₂O, which enable a very precise definition of the electronic structure of the [Ti(OH₂)₆]³⁺ cation. The magnetization data exhibit a spectacular deviation from Brillouin behavior, with the magnetic moment highly dependent on the strength of the applied field at a given ratio of B/T. This arises from unprecedented higher-order contributions to the magnetization, and these measurements afford the determination of the ground-state Zeeman coefficients to third-order. The anomalous magnetic behavior is a manifestation of Jahn-Teller coupling, giving rise to low-lying vibronic states, which mix into the ground state through the magnetic field. Electronic Raman measurements of the 1%-titanium(III)-doped sample identify the first vibronic excitation at ~18 cm^–1, which betokens a substantial quenching of spin-orbit coupling by the vibronic interaction. The ground-state Zeeman coefficients are strongly dependent on the concentration of titanium(III) in the crystals, and this can be modeled as a function of one parameter, representing the degree of strain induced by the cooperative Jahn-Teller effect. This study clearly demonstrates the importance that the Jahn-Teller effect can have in governing the magnetic properties of transition metal complexes with orbital triplet ground terms.