PARAMAGNETISM OF CESIUM TITANIUM ALUM AND THE JAHN-TELLER INTERACTION

The magnetic properties of [Ti(OH2)(6)](3+) within CsTi(SO4)(2) . 12H( 2)O and doped into a range of isostructural diamagnetic lattices, has been reinvestigated using electron paramagnetic resonance (EPR) and ma gnetic susceptibility measurements. Whereas previous attempts to ratio nalise the variation of the magnetic susceptibility with temperature h ave employed a (2)A(g) trigonal ground term, the data are interpreted within a framework used to describe other tervalent hexa-aqua cations whereby the trigonal field is considerable and of a sign such that the e(g) orbital set is lower lying, resulting in a E-2(g) trigonal groun d term. The magnetic susceptibility is then modeled using a novel appr oach based on the numerical diagonalisation of the vibronic Hamiltonia n. Hence, it is shown that the singular magnetic properties of CsTi(SO 4)(2) . 12H(2)O arise from a delicate balance between spin-orbit and J ahn-Teller coupling. Particular use is made of isotopic substitution t o obtain information regarding the nature of the vibronic interaction. An excellent fit to both the susceptibility data and ground state g v alues is provided by a model in which the Jahn-Teller interaction is d ominated by coupling to phonon modes involving librational modes of su lphate and water coordinated to titanium(III). This interpretation is further supported by Raman data on the corresponding compounds. This a nalysis provides the first satisfactory explanation of the magnetic pr operties of [Ti(OH2)(6)](3+) in the beta-alum lattice. (C) 1997 Americ an Institute of Physics. [S0021-9606(97)01144-6].