The hydrogen bond linking phenylphosphonic acid dimers in a copper organophosphonate supramolecular complex is investigated using ab initio and density functional theory calculations. Both one- and two-proton structures were modelled and the calculated binding energy values indicated the one-proton model to be more favourable. This structure is consistent with a Cu2+ oxidation state, which was confirmed by additional masNMR experiments. Geometry and energy analysis indicated that the proton is highly delocalised and the hydrogen bond is near-linear. (C) 2003 Elsevier B.V. All rights reserved.