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Structure-Property Relationships in Crystal Structures of Polar Molecules Graham Tizzard Supervisor: Mike Hursthouse.

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Presentation on theme: "Structure-Property Relationships in Crystal Structures of Polar Molecules Graham Tizzard Supervisor: Mike Hursthouse."— Presentation transcript:

1 Structure-Property Relationships in Crystal Structures of Polar Molecules Graham Tizzard Supervisor: Mike Hursthouse

2 Background No. of different attractive forces determine packing in molecular crystals London forces, multipolar forces, H- bonding, CT forces Complex interplay of these + repulsion E many local minima in crystal lattice E Polymorphism - the existence of more than one crystalline form in a substance

3 Polymorphism & H-bonding H-bonds: Highest E interactions in molecular crystals most important attractive force Multiple H-bonding sites different H-bonding topologies polymorphism However: Polymorphism also in systems w.out strong H- bonds (D – H A; D = N, O, S; A = N, O, S, Hal) Weak H-bonds may exist (C – H A, C – H π) Importance of H-bonding in defining polymorphism greatly reduced

4 Aims Detailed study of weak or non H-bonding systems Especially those w. non-centrosymmetric polymorphs V. important for development of materials w. NLO properties Electrostatic interactions expected to exert greater influence on xtal structure

5 Dataset Constructed from Cambridge Structural Database 1 (CSD) v5.25 (November 2003) CSD mined for polymorphic clusters with one non-centrosymmetric member 835 hits made up of 258 polymorphic clusters each comprising of 2-3 different polymorphs [1] F. H. Allen, Acta Crystallogr., B58, ,

6 Analyses XPac 2 : Many polymorphic families of a compound show no similarity when analysed For those that do structure-forming motif may be able to be elucidated from results Short contact analysis (Mercury v ) + modelling of electrostatic charges (Spartan04 for windows 4 ) Correlation between short contact distances & matching of potentials would suggest these are important in a crystal structure [2] XPac; T. Gelbrich; 2002; University of Southampton, UK. [3] Mercury v1.2.1; CCDC, Cambridge, UK. [4] Spartan04; Wavefunction, Inc.; Irvine, CA, USA.

7 4-Bromo-trans-1,4-dihydro-4- tritylbiphenyl (BAWSAT) 2 polymorphs identified from CSD: BAWSAT & BAWSAT01 BAWSAT01 is non-centrosymmetric [5] Reference Z 24Z Cell Volume / Å 3 90 γ / º β / º 90 α / º c / Å b / Å a / Å Pc (7)Pnam (62)Space Group (No.) monoclinicorthorhombicCrystal System BAWSAT01BAWSATCSD code [5] A. K. Cheetham, M. C. Grossel, J. M. Newsam; J. Am. Chem. Soc.; 103; 5363; 1981.

8 XPac Analysis of BAWSAT Views of BAWSAT along the c-axis (top) & BAWSAT01 between the a and c axes (bottom) XPac reveals 1d chain along these respective axes common to both crystal structures (green) In both structures the same chain motif is interspaced (in different ways) between the original (dark green) Is this a structure-forming motif?...

9 Short Contact & Electrostatic Charge Analyses of BAWSAT Each molecule in BAWSAT01 (top) & BAWSAT (bottom) has short contacts w. 8 neighbours None of these is particularly strong ESC & SC data correlation: 4/10 wrt. BAWSAT01; 0 wrt. BAWSAT Suggests electrostatic interactions unimportant in crystal formation Other interactions e.g. simple space-filling may dictate these structures H22 : H H4 : H H4 : C C28 : H H13 : H H19 : H H3 : Br Br1 : H H8 : H H24 : H8 Length-VdW / Å Length / Å Electrostatic charge 2 Atom2 Electrostatic charge 1 Atom1 BAWSAT C5 : H H5 : C H3 : C C3 : H H13 : H H18 : H H3 : H H5 : H H4 : H H13 : H H18 : H H4 : H13 Length- VdW / Å Length / Å Electrostatic charge 2 Atom2 Electrostatic charge 1 Atom1 BAWSAT

10 2-(α-p-Bromophenyl-β-nitroethyl)- cyclohexanone (BPNECH) 2 polymorphs identified from CSD: BPNECH & BPNECH01 BPNECH01 is non-centrosymmetric [7][6]Reference 1.0 Z 44Z Cell Volume / Å 3 90 γ / º β / º 90 α / º c / Å b / Å a / Å P (19)P21/c (14)Space Group (No.) orthorhombicmonoclinicCrystal System BPNECH01BPNECHCSD code [6] M. Calligaris, F. Giordano, L. Randaccio; Ric. Sci., Parte 1; 36; 1333; [7] D. Seebach, I. M. Lyapkalo, R. Dahinden; Helv Chim Acta; 82; 1829; 1999.

11 XPac Analysis of BPNECH Views of BPNECH (top) and BPNECH01 (bottom) along the b-axis XPac reveals 2d sheet along these respective axes common to both crystal structures (green) In BPNECH both highlighted sheets (green & dark green) are identical In BPNECH01 second sheet highlighted (red) is same sheet structure after a 2 1 screw operation

12 Short Contact & Electrostatic Charge Analyses of BPNECH Each molecule in BPNECH01 (top) and BPNECH (bottom) has short contacts w. 8 / 9 neighbours respectively Short contacts are stronger on the whole than in BAWSAT & BAWSAT01 ESC & SC data correlate in both polymorphs Suggests that electrostatic interactions may be significant in formation of both crystal systems O3 : H H2 : O H5 : Br Br1 : H O1 : H H7 : O O2 : H H1 : O H12 : O O2 : H O2 : H H13 : O2 Length- VdW Length Electrostatic charge 2 Atom2 Electrostatic charge 1 Atom1 BPNECH O3 : H H3 : O H9 : O O2 : H O1 : Br Br1 : O H7 : O O1 : H H2 : O O3 : H H12 : O O2 : H O2 : H H13 : O H1 : O O2 : H1 Length- VdW Length Electrostatic charge 2 Atom2 Electrostatic charge 1 Atom1 BPNECH

13 Comments I Several points worth noting: Overall analysis involves several techniques - hard to draw conclusions using them in isolation XPac analysis uses top-down approach - data derived from polymorph crystal structures Modelling of electrostatic charges is bottom-up approach - data derived from molecule One goal of Comb-e-Chem project - combine data from different analyses to derive novel data & develop it into meaningful knowledge

14 Comments II Major bottlenecks throughout project have been workflow related: Data transfer from one application to another Driving applications to obtain the data Methods of automation investigated: perl to write data-transfer scripts Spreadsheets to automate calculations Ultimate aim of providing complete analysis of electrostatic interactions of a molecule in context of its crystal packing as a single callable process

15 Acknowledgements Prof. Mike Hursthouse The Group – Dr. Simon Coles, Dr. Mark Light, Dr. Peter Horton, Dr. Ann Bingham, Dr. Thomas Gelbrich, Dr. Stefan Christensen, Dr. Yang Li, Dr. David Hughes, Suzanna Ward EPSRC E-Science project (GR/R67729, Comb-e-Chem)


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