Phenylphosphonic acid as a building block for two-dimensional hydrogen-bonded supramolecular arrays

The potential use of organic phosphorus acids for the architecture of supramolecular hydrogen-bonded assemblies has been demonstrated by the structural determination of phenylphosphonic acid (1), anilinium phenylphosphonate (2), p-phenylazoanilinium phenylphosphonate (3), ethylenediammonium phenylphosphonate hydrate (4) and hexamethylenediammonium phenylphosphonate hydrate (5). Compounds 1, 2,4 and 5 exhibit layered structures with two-dimensional networks of hydrogen bonds from which the organic tails point out. Compound 3 crystallizes as two concomitant polymorphs showing supramolecular isomerism: a monoclinic phase (3a) with a layered structure and a triclinic phase (3b) in which hydrogen bonds form columns. In these assemblies, there axe supramolecular motifs such as chains and rings of hydrogen-bonded moieties. Water molecules are involved in the formation of hydrogen-bonding networks for compounds 4 and 5. For compound 5, hexamethylenediammonium ions link the adjacent sheets, forming a pillared-layered structure. It has been shown that the phosphonate groups can act as both donor and acceptor of hydrogen bonds. Analysis of the hydrogen bonds of the types (P-)O-(HO)-O-...(-P) and (NHO)-O-...(-P) reveals that they can be regarded as medium to strong hydrogen bonds. (C) 2002 Elsevier Science B.V. All rights reserved.