Structure-Property Relationships in Crystal Structures of Polar Molecules

Graham Tizzard

Supervisor: Mike Hursthouse

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

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

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

Dataset

Constructed from Cambridge Structural Database1 (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, 380-388, 2002..

Analyses

XPac2: 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 v1.2.13) + modelling of electrostatic charges (Spartan’04 for windows4) 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] Spartan’04; Wavefunction, Inc.; Irvine, CA, USA.

4’-Bromo-trans-1,4-dihydro-4-tritylbiphenyl (BAWSAT)

2 polymorphs identified from CSD: BAWSAT & BAWSAT01

BAWSAT01 is non-centrosymmetric

[5][5]Reference

1.00.5Z’

24Z

1167.3092343.211Cell Volume / Å3

9090γ / º

108.9890β / º

9090α / º

8.46310.431c / Å

16.18717.264b / Å

9.01113.012a / 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.

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?...

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.

-0.0412.3590.136788H22 :70.155091H4

-0.0412.3590.155091H4 :80.136788H22

-0.0562.8440.155091H4 :8-0.191035C28

-0.0562.844-0.191035C28 :70.155091H4

-0.0582.3420.104592H13 :60.120092H19

-0.0582.3420.120092H19 :50.104592H13

-0.082.970.097207H3 :4-0.117756Br1

-0.082.97-0.117756Br1 :30.097207H3

-0.0862.3140.130679H8 :20.136779H24

-0.0862.3140.136779H24 :10.130679H8

Length-VdW / Å

Length / Å

Electrostatic charge 2

Atom2Electrostatic charge 1

Atom1

BAWSAT01

-0.0022.8980.078478C5 :40.097207H3

-0.0022.8980.097216H5 :40.078511C3

-0.0022.8980.097207H3 :50.078478C5

-0.0022.8980.078511C3 :50.097216H5

-0.032.370.104592H13 :80.104591H18

-0.032.370.104591H18 :70.104592H13

-0.1022.2980.097207H3 :60.097216H5

-0.1022.2980.097216H5 :50.097207H3

-0.122.280.155091H4 :40.104591H18

-0.122.280.104592H13 :30.155091H4

-0.122.280.104591H18 :20.155091H4

-0.122.280.155091H4 :10.104592H13

Length-VdW / Å

Length / Å

Electrostatic charge 2

Atom2Electrostatic charge 1

Atom1

BAWSAT

2-(α-p-Bromophenyl-β-nitroethyl)-cyclohexanone (BPNECH)

2 polymorphs identified from CSD: BPNECH & BPNECH01

BPNECH01 is non-centrosymmetric

[7][6]Reference

1.01.0Z’

44Z

1448.1751473.234Cell Volume / Å3

9090γ / º

9090.30β / º

9090α / º

30.77730.570c / Å

8.4958.560b / Å

5.5395.630a / Å

P212121 (19)P21/c (14)Space Group (No.)

orthorhombicmonoclinicCrystal System

BPNECH01BPNECHCSD code

[6] M. Calligaris, F. Giordano, L. Randaccio; Ric. Sci., Parte 1; 36; 1333; 1966. [7] D. Seebach, I. M. Lyapkalo, R. Dahinden; Helv Chim Acta; 82; 1829; 1999.

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 21 screw operation

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

-0.0592.661-0.451598O3 :20.12995H2

-0.0592.6610.12995H2 :1-0.451598O3

-0.0632.9870.093177H5 :8-0.05641Br1

-0.0632.987-0.05641Br1 :70.093177H5

-0.0842.636-0.447545O1 :60.106818H7

-0.0842.6360.106818H7 :5-0.447545O1

-0.1242.596-0.434661O2 :40.130828H1

-0.1242.5960.130828H1 :3-0.434661O2

-0.2122.5080.203696H12 :1-0.434661O2

-0.2122.508-0.434661O2 :20.203696H12

-0.2222.498-0.434661O2 :20.166816H13

-0.2222.4980.166816H13 :1-0.434661O2

Length-VdW

LengthElectrostatic charge 2

Atom2Electrostatic charge 1

Atom1

BPNECH01

-0.0292.691-0.451598O3 :90.062736H3

-0.0292.6910.062736H3 :8-0.451598O3

-0.0482.6720.06238H9 :3-0.434661O2

-0.0482.672-0.434661O2 :40.06238H9

-0.0573.313-0.447545O1 :7-0.05641Br1

-0.0573.313-0.05641Br1 :7-0.447545O1

-0.0962.6240.106818H7 :6-0.447545O1

-0.0962.624-0.447545O1 :50.106818H7

-0.1452.5750.12995H2 :3-0.451598O3

-0.1452.575-0.451598O3 :40.12995H2

-0.2242.4960.1308282H12 :3-0.434661O2

-0.2242.496-0.434661O2 :40.1308282H12

-0.272.45-0.434661O2 :40.1308283H13

-0.272.450.1308283H13 :3-0.434661O2

-0.3262.3940.130828H1 :2-0.434661O2

-0.3262.394-0.434661O2 :10.130828H1

Length-VdWLengthElectrostatic charge 2Atom2Electrostatic charge 1Atom1

BPNECH

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

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

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)