Aqua ions. 2. Structural manifestations of the Jahn-Teller effect in the β-alums

Abstract

Variable-temperature single-crystal neutron diffraction structures of the alums CsMIII(SO4)2·12D2O, where MIII = Ti, V, Mn, and Ga, are reported. Structural differences are highlighted by the titanium and manganese alums, which undergo cubic (Pa3̄) to orthorhombic (Pbca) phase transitions at ∼13 and ∼156 K, respectively. The structural instability exhibited by these salts is interpreted as arising from cooperative Jahn-Teller interactions, and these measurements characterize the structural changes that result from the coupling between the electronic and vibrational states. Although the symmetry changes associated with the phase transformations are analogous for the Ti and Mn alums, the low-t..