title: Search for a predicted hydrogen bonding motif--a multidisciplinary investigation into the polymorphism of 3-azabicyclo[3.3.1]nonane-2,4-dione.
abstract: The predictions of the crystal structure of 3-azabicyclo[3.3.1]nonane-2,4-dione submitted in the 2001 international blind test of crystal structure prediction (CSP2001) led to the conclusion that crystal structures containing an alternative hydrogen bonded dimer motif were energetically competitive with the known catemer-based structure. Here we report an extensive search for a dimer-based crystal structure. Using an automated polymorph screen a new catemer-based metastable polymorph (form 2) and two new catemer-based solvates were found, and concurrent thermal studies reproduced form 2 and identified a plastic phase (form 3), whose powder X-ray diffraction pattern was consistent with the cubic space group I23 (a = 7.5856(1) A). Computational studies on the monomer showed that the imide N-H was a weak hydrogen bond donor, rationalizing the occurrence of the plastic phase which involved the breaking of all hydrogen bonds, and modeling of small clusters showed that dimers could easily reorganize to give the catemer. FTIR spectra confirmed the weakness of the hydrogen bond, with the solute showing no self-assembly in solution. It is concluded that the weakness of the N-H donor, coupled with the globular shape of the molecule, allows unusually facile transformation between alternative hydrogen bonding motifs during aggregation and nucleation.
authors.affiliation: Christopher Ingold Laboratory, Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK.
authors.forename: Ashley T
authors.initials: AT
authors.lastname: Hulme
authors.forename: Andrea
authors.initials: A
authors.lastname: Johnston
authors.forename: Alastair J
authors.initials: AJ
authors.lastname: Florence
authors.forename: Phillipe
authors.initials: P
authors.lastname: Fernandes
authors.forename: Kenneth
authors.initials: K
authors.lastname: Shankland
authors.forename: Colin T
authors.initials: CT
authors.lastname: Bedford
authors.forename: Gareth W A
authors.initials: GW
authors.lastname: Welch
authors.forename: Ghazala
authors.initials: G
authors.lastname: Sadiq
authors.forename: Delia A
authors.initials: DA
authors.lastname: Haynes
authors.forename: W D Samuel
authors.initials: WD
authors.lastname: Motherwell
authors.forename: Derek A
authors.initials: DA
authors.lastname: Tocher
authors.forename: Sarah L
authors.initials: SL
authors.lastname: Price
mesh_terms: D001372:Aza Compounds / Q000737:chemistry*; D001952:Bridged-Ring Compounds / Q000737:chemistry*; D002152:Calorimetry, Differential Scanning; D003460:Crystallization; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008968:Molecular Conformation; D055672:Static Electricity; D013696:Temperature
chemical_list: C519144:3-azabicyclo(3.3.1)nonane-2,4-dione; D001372:Aza Compounds; D001952:Bridged-Ring Compounds