J. Phys. Chem. 1991,95,2101-2103 assumption of a harmonic potential function with zero offdiagonal force constants, and neglect of the dynamical effects of the nonframework alkali-metal cations and chloride anions), it is nevertheless notable that& is smaller thanfm and indeed is small on the scale of typical bending force constants. The smallness of& clearly underlies the conformational flexibility of the sodalite framework, in which the T-0-T angle varies from 125O to 139O to 154O on changing the nonframework cation in the series Li, Na, K.8 We believe these to be the first direct experimental data on the force constants in aluminosilicates, and they confirm the results of a molecular mechanics investigation of the sodalite structure in which it was also concluded thatfm
