title: Towards prediction of stoichiometry in crystalline multicomponent complexes.
abstract: We report on the crystal structure of urea (U) with acetic acid (A), its physical stability and its predictability using computational methods. The crystal structure of urea:acetic acid (U:A) shows hydrogen-bond ribbons and a 1:2 stoichiometry. Crystal structure prediction calculations are presented for two sets of U:A stoichiometries: 1:1 and 1:2. A 1:3 stoichiometry is also partially explored by means of a synthon approach. The calculated lattice energies, along with hydrogen-bond patterns, of crystal structures predicted with the three stoichiometries are presented and analysed to provide a rationalisation for the stoichiometry observed. Exploring stoichiometric diversity using computational methods provides a tool for the rationalisation of stoichiometry preferences in crystalline multicomponent systems and a first step towards their prediction.
authors.affiliation: The Pfizer Institute for Pharmaceutical Materials Science, Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW (UK), Fax: (+44) 122-333-6362.
authors.forename: Aurora J
authors.initials: AJ
authors.lastname: Cruz-Cabeza
authors.affiliation: The Pfizer Institute for Pharmaceutical Materials Science, Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW (UK), Fax: (+44) 122-333-6362.
authors.forename: Graeme M
authors.initials: GM
authors.lastname: Day
authors.affiliation: The Pfizer Institute for Pharmaceutical Materials Science, Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW (UK), Fax: (+44) 122-333-6362.
authors.forename: William
authors.initials: W
authors.lastname: Jones