A New Polymorph of N,N '-Dimethylurea Characterized by X-ray Diffraction and First-Principles Lattice Dynamics Calculations

Martins, D. M. S., Spanswick, C. K., Middlemiss, D. S., Abbas, N., Pulham, C. R. and Morrison, C. A. (2009) A New Polymorph of N,N '-Dimethylurea Characterized by X-ray Diffraction and First-Principles Lattice Dynamics Calculations. Journal of Physical Chemistry A, 113(20), pp. 5998-6003. (doi: 10.1021/jp900141q)

Abstract

In this study we present a combined crystallographic and computational study of a new polymorph of N,N'-dimethylurea (DMU) with P2(1)2(1)2 space group symmetry, along with a revised theoretical study of the previously known phase in its corrected space group (Fdd2). X-ray diffraction studies show crystal structures that are very similar, differing only in the relative orientation of the hydrogen-bonded molecular chains that are common to both phases. The vibrational spectra were obtained from B3LYP hybrid functional lattice dynamics calculations and compared with the experimental data for the known phase. The free-energy difference between the forms is derived from the Gamma-point optical mode frequencies, and amounts to less than 1 kJ mol(-1) across the temperature range of interest. The electronic densities-of-states of both phases are also computed, yielding only marginal differences in valence and conduction band compositions and band gap widths. Taken together, the results highlight the small but important differences separating the two crystal lattices.

• Item Type: Articles
• Keywords: BAND-GAPS CHAIN CRYSTAL Crystal structure Crystal structures CRYSTAL-STRUCTURE CRYSTAL-STRUCTURES DENSITY DESIGN DIFFRACTION DYNAMICS FREE-ENERGY HYBRID HYBRID FUNCTIONAL THEORY LATTICE MOLECULAR-SOLIDS PHASE PRESSURE SPECTRA Structure SYMMETRY TEMPERATURE UREA VALENCE X-RAY X-RAY-DIFFRACTION
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Middlemiss, Dr Derek
• Authors: Martins, D. M. S., Spanswick, C. K., Middlemiss, D. S., Abbas, N., Pulham, C. R., and Morrison, C. A.
• College/School: College of Science and Engineering > School of Chemistry
• Journal Name: Journal of Physical Chemistry A
• ISSN: 1089-5639

Project Code	Award No	Project Name	Principal Investigator	Funder's Name	Funder Ref	Lead Dept
38077	1	Engineering and understanding solid state proton migration and transfer	Charles Wilson	Engineering & Physical Sciences Research Council (EPSRC)	GR/T21615/01	Chemistry