Vibrational spectra of crystalline malononitrile

The infrared and Raman spectra of the four solid phases of malononitrile have been recorded. The crystal structures of these solids are now relatively well established from the present results and from previous X-ray and nuclear quadrupole resonance data. Phase I belongs to the P21/n space group of the monoclinic system, with four molecules per unit cell. In phase II, the molecules occupy two sets of general positions in a crystal of P21 symmetry. The molecular site symmetry is Cs in phase III which is highly symmetric. The structure of the low-temperature metastable phase IV appears to be very similar to that of phase I.