Knowledge Bank

Infrared spectra of $B(OH)3,HOBO$ and $(HOBO)3$ have been obtained in neon, argon and nitrogen matrices near $4\circ K$ over the region $250-4000cm-1$. The various isotopically enriched molecules containing $B10(96.3\%),B11(98.3\%)$ and $H2(99.7\%)$ have also been studied. The metaboric acid monomer molecules were generated by the reaction $B2O3(1)+H2O\rightleftarrows 2HOBO$ (g) at temperatures near $1400\circ K$. The fundamental vibrations have been assigned assuming $C\ast \ast \ast \ast$ symmetry (linear heavy atom array). Force constants and thermodynamic functions have been calculated and will be discussed. The orthoboric acid monomer molecules were generated by the reaction: $B(OH)3(C)⟶\Delta B(OH)3(g)$ at $293\circ K$. The infrared active modes of all the isotopic species have been carefully measured. Values for the infrared inactive modes were obtained by studying the mixed $[B(OH)(OD)2$ and $B(OH)2(OD)]$ molecules and applying an isotopic correction factor. Force constants and thermodynamic functions have been calculated. The hydrogen frequency differences between isolated and crystalline boric acid, ca. $400cm-1$ for the stretching and ca. $200cm-1$ for the bending modes, suggest moderately strong hydrogen bonds in the crystal. Trimeric metaboric acid was produced via vaporization of the crystalline material: $(HOBO)3(c)⟶\Delta (HOBO)3(g)$ near $440\circ K$. A qualitative assignment of the infrared data has been made and interpretation of the results will be discussed.