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|Section2= |Section3= |Section4= }} Metaboric acid is the name for a family of inorganic compounds formed by the dehydration of boric acid. These are colourless solids with the empirical formula HBO2.〔Greenwood, N. N.; & Earnshaw, A. (1997). Chemistry of the Elements (2nd Edn.), Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4.〕 ==Preparation== Heating of boric acid at 80-100 °C releases one equivalent of water to give orthorhombic metaboric acid:〔Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 791.〕 3B(OH)3 → (BOH)3O3 + 3H2O This form is molecular, consisting of discrete trimers. This molecule has C3h symmetry and forms a sheet-like structure, similar to that of boric acid itself. It is also called "modification III" of the metaboric acids. Upon heating at 130-140 °C in a sealed ampoule (to prevent dehydration), orthorhombic metaboric acid converts to the monoclinic form: :(BOH)3O3 → B3O4(OH)(H2O) This material, called modification II, has a polymeric structure, and a higher melting point (201 °C) and density (2.045 g/cm3). The structure of this species resembles its precursor except that the rings are connected and 1/3 of the boron centres are tetrahedral.〔W. H. Zachariasen "The crystal structure of monoclinic metaboric acid" Acta Cryst. 1963, vol. 16, pp. 385-389. 〕 : Above 140 °C, boric acid or the other forms of metaboric acid convert to cubic metaboric acid. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Metaboric acid」の詳細全文を読む スポンサード リンク
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