crystals Article Structure and Properties of 1,3-Phenylenediboronic Acid: Combined Experimental and Theoretical Investigations Agnieszka Adamczyk-Wo´zniak 1,*, Michał K. Cyra ´nski 2, Krzysztof Durka 1 , Jan T. Gozdalik 1, Paulina Klimentowska 2, Rafał Rusiecki 1,3, Andrzej Sporzy ´nski 1 and Dorota Zarzecza ´nska 4 1 Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664 Warsaw, Poland;
[email protected] (K.D.);
[email protected] (J.T.G.);
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[email protected] (A.S.) 2 Faculty of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland;
[email protected] (M.K.S.);
[email protected] (P.K.) 3 Adamed Pharma S.A., Pie´nków, Adamkiewicza 6A, 05-152 Czosnów, Poland 4 Faculty of Chemistry, University of Gda´nsk,Wita Stwosza 63, 80-308 Gda´nsk,Poland;
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[email protected]; Tel.: +48-22-234-6147; Fax: +48-22-628-2741 Received: 16 January 2019; Accepted: 15 February 2019; Published: 19 February 2019 Abstract: The structure and properties of 1,3-phenylenediboronic acid are reported. Molecular and crystal structures were determined by single crystal as well as by powder X-ray diffraction methods. Acidity constant, thermal behavior, and NMR characterization of the title compound were also investigated. In addition to the experimental data, calculations of rotational barrier and intermolecular interaction energies were performed. The compound reveals a two-step acid–base equilibrium with different pKa values. TGA and DSC measurements show a typical dehydration reaction with formation of boroxine.