title: Experimental Electron Density and Neutron Diffraction Studies on the Polymorphs of Sulfathiazole.
abstract: High resolution X-ray diffraction data on forms I-IV of sulfathiazole and neutron diffraction data on forms II-IV have been collected at 100 K and analyzed using the Atoms in Molecules topological approach. The molecular thermal motion as judged by the anisotropic displacement parameters (adp's) is very similar in all four forms. The adp of the thiazole sulfur atom had the greatest amplitude perpendicular to the five-membered ring, and analysis of the temperature dependence of the adps indicates that this is due to genuine thermal motion rather than a concealed disorder. A minor disorder (∼1-2%) is evident for forms I and II, but a statistical analysis reveals no deleterious effect on the derived multipole populations. The topological analysis reveals an intramolecular S-O···S interaction, which is consistently present in all experimental topologies. Analysis of the gas-phase conformation of the molecule indicates two low-energy theoretical conformers, one of which possesses the same intramolecular S-O···S interaction observed in the experimental studies and the other an S-O···H-N intermolecular interaction. These two interactions appear responsible for "locking" the molecular conformation. The lattice energies of the various polymorphs computed from the experimental multipole populations are highly dependent on the exact refinement model. They are similar in magnitude to theoretically derived lattice energies, but the relatively high estimated errors mean that this method is insufficiently accurate to allow a definitive stability order for the sulfathiazole polymorphs at 0 K to be determined.
authors.affiliation: WESTChem School of Chemistry, University of Glasgow , Glasgow G12 8QQ, U.K.
authors.forename: Ioana
authors.initials: I
authors.lastname: Sovago
authors.affiliation: ISIS Facility, STFC Rutherford Appleton Laboratory , Harwell Science and Innovation Campus, Chilton, Didcot, Oxfordshire OX11 0QX, U.K.
authors.forename: Matthias J
authors.initials: MJ
authors.lastname: Gutmann
authors.affiliation: WESTChem School of Chemistry, University of Glasgow , Glasgow G12 8QQ, U.K.
authors.forename: J Grant
authors.initials: JG
authors.lastname: Hill
authors.affiliation: WESTChem School of Chemistry, University of Glasgow , Glasgow G12 8QQ, U.K.
authors.forename: Hans Martin
authors.initials: HM
authors.lastname: Senn
authors.affiliation: Department of Chemistry, University of Bath , Claverton Down, Bath BA2 7AY, U.K.
authors.forename: Lynne H
authors.initials: LH
authors.lastname: Thomas
authors.affiliation: Department of Chemistry, University of Bath , Claverton Down, Bath BA2 7AY, U.K.
authors.forename: Chick C
authors.initials: CC
authors.lastname: Wilson
authors.affiliation: WESTChem School of Chemistry, University of Glasgow , Glasgow G12 8QQ, U.K.
authors.forename: Louis J
authors.initials: LJ
authors.lastname: Farrugia