Infrared and raman spectra of orthorhombic,monoclinic and cubic metaboric acid and their relation to the “strength” of the hydrogen bond present

Infrared and Raman spectra of the three forms of metaboric acid (orthorhombic, monoclinic and cubic) are presented and discussed. The behaviour of the asymmetric stretching vibration v_oh and of the in-plane and out-of-plane deformations δ_OH and γ_OH shows that hydrogen bonds of different “strengths” are present in the three forms of metaboric acid, in accordance with X-ray diffraction measurements. This phenomenon is explained in a qualitative way by a valence bond treatment of the structural centres present in the three forms of metaboric acid. The remaining vibrational modes are related to the analogous modes present in borates and polyborates of known structure.