Single-crystal polarized FTIR spectroscopy and neutron diffraction refinement of cancrinite.

We relate a single-crystal FTIR (Fourier transform infrared) and neutron diffraction study of two natural cancrinites. The structural refinements show that the oxygen site of the H2O molecule lies off the triad axis. The water molecule is almost symmetric and slightly tilted from the (0001) plane. It is involved in bifurcated hydrogen bridges, with Ow...O donor–acceptor distances [2.7 Aengstr . The FTIR spectra show two main absorptions. The first at 3,602 cm-1 is polarized for E perp. c and is assigned to the v3 mode. The second, at 3,531 cm-1, is also polarized for E perp. c and is assigned to v1 mode. A weak component at 4,108 cm-1 could possibly indicate the presence of additional OH groups in the structure of cancrinite. Several overlapping bands in the 1,300–1,500 cm-1 range are strongly polarized for E perp. c, and are assigned to the vibrations of the CO3 group.