Hydrogen-Bonded Structures Formed from the Reaction of 1,3,5-Benzene-triphosphonic Acid and Adamantane

The triphosphonic acid 1,3,5-benzene-triphosphonic acid (BTP; 1,3,5-[(HO)2PO]3C6H3) was allowed to react with different ratios of adamantane. Three compounds with amine to BTP ratios of 2:1, 4:1, and 6:1 were isolated, and their crystal structures were determined by single crystal X-ray diffraction. In the 2:1 compound the BTP molecules transferred two protons to the amines to form a complex of composition [C10H15NH3]22+[C6H3(PO3H)2PO3H2]2−·2H2O. This compound formed zig-zagged chains of BTP molecules hydrogen bonded to each other with the amine cations and water molecules interspersed between the chains. The 4:1 complex also formed chains through hydrogen bonding between the individual BTP molecules, but the chains are separated from each other by a double layer of protonated amines. In the 6:1 compound, all the protons are transferred to the adamantane molecules so that there is no hydrogen bonding between BTP molecules. Rather, a very complex hydrogen bond system between amine−BTP, amine−water and water−BTP results. In all three complexes, all the protonated amino groups hydrogen bond by utilizing all three of their protons as donors. The pKa values of the BTP protons were determined by analysis of the titration curve.