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 H(2)O 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 center dot center dot center dot O donor-acceptor distances >2.7 angstrom. The FTIR spectra show two main absorptions. The first at 3,602 cm(-1) is polarized for E perpendicular to c and is assigned to the nu(3) mode. The second, at 3,531 cm(-1), is also polarized for E perpendicular to c and is assigned to nu(1) 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 perpendicular to c, and are assigned to the vibrations of the CO(3) group.