Anomalous Behavior of 18O-Labeled Compounds. VI. The Vibrational Spectra of Isotopic Metaborates

The infrared absorption spectrum of an aqueous solution of ¹⁸O‐labeled sodium metaborate shows the antisymmetric $\mathrm{B}{–}^{18}\mathrm{O}$ stretching ν₃ fundamental of its $\mathrm{B}(\mathrm{OH}{)}_4^{-}$ ions at 982 cm⁻¹, as compared with the frequency of 958 cm⁻¹ observed for the respective normal borate vibration. The Raman spectrum of aqueous solutions of these borates exhibits their symmetric $\mathrm{B}–\mathrm{O}$ stretching ν₁ fundamental in both cases at 744 cm⁻¹. The fact that the ν₁ and ν₃ frequencies of the hydrated $\mathrm{B}{(}^{18}\mathrm{OH}{)}_4^{-}$ ions are not decreased by the ¹⁶O–¹⁸O exchange is taken to indicate that the hydrogen bonding between the $\mathrm{B}(\mathrm{OH}{)}_4^{-}$ ions and their solvating water molecules is appreciably lower in the case of the ¹⁸O‐labeled ions than in the case of the $\mathrm{B}{(}^{16}\mathrm{OH}{)}_4^{-}$ ions.