ISMSC 2007 - Università degli Studi di Pavia

OP 15
From non-mesomorphic nature to liquid crystallinity via halogen bonding
Rossana Intenza, a Pierangelo Metrangolo, a Franck Meyer, a Tullio Pilati, b Giuseppe Resnati, a
Giancarlo Terraneo a
a
NFM Lab-DCMIC “G. Natta”, via Mancinelli, 7 I-20131 Milan, Politecnico di Milano, Italy.
b
CNR-Institute of Molecular Science and Technology, University of Milan, via Golgi 19, 20133
Milan, Italy.
Halogen bonding, namely any attractive interactions involving halogens as electrophilic species
[1], can be considered as a first choice intermolecular interaction both reliable and effective to
understand and rationally design self-assembly processes in supramolecular chemistry, crystal
engineering, and materials science [2]. A rather new intermolecular interaction being therefore
accessible, new aggregation processes can be realised with the novelty coming from either the
molecular identity of single modules that are assembled or from the way the modules are
arranged in the supramolecular architecture.
In particular, in the last decade new families of liquid-crystalline materials have been developed
by the identification of non-covalent interactions such as hydrogen bonding, quadrupolar and
charge-transfer interactions that can lead to new mesomorphic supramolecular species by selfassembly
[3].
Recently, Bruce [4] and Metrangolo [5] reported that also halogen bonding is effective in
inducing liquid crystal phase behaviour by combination of nonmesomorphic alkoxystilbazoles
with either iodopentafluorobenzene or diiodoperfluoroalkanes.
Here we report a new class of liquid crystal materials formed thanks to the halogen bonding
occurring between alkoxystilbazoles and 4-iodo-tetrafluoro alkoxystilbenes (Figure 1). A “square
matrix” n x m made of 25 halogen-bonded supramolecular complexes was obtained and
characterized by NMR, X-ray diffraction, hot stage polarising optical microscopy and differential
scanning calorimetry (DSC). Despite both the starting materials are not mesomorphic in nature,
all the 25 supramolecular adducts develop liquid crystal properties.
H 2n+1C nO
n = 4, 6, 8, 10, 12
N
I
Figure 1
F
F
F F
OC mH 2m+1
m = 4, 6, 8, 10, 12
Preliminary results suggest that the mesomorphism of the halogen-bonded
alkoxystibazole/iodotetrafluoroalkoxystilbene complexes is that of a simple, dipolar mesogen,
showing a nematic phase at short chain and a smectic A phase with longer chains.
The generality of this approach will be demonstrated by some other examples of
supramolecular ionic liquid crystals made by halogen bonding-driven self-assembly.
[1]. P. Metrangolo, T. Pilati and G. Resnati, CrystEngComm, 2006, 8, 946 (Front Cover).
[2]. P. Metrangolo, H. Neukirch, T. Pilati and G. Resnati, Acc. Chem. Res., 2005, 38, 386.
[3]. T. Kato, in Handbook of Liquid Crystals, ed. D. Demus, G.WGray, J. Goodby, H.-W. Spiess
and V. Vill, Wiley-VCH, Weinheim, 1998.
[4]. H. L. Nguyen, P. N. Horton, M. B. Hursthouse, A. C. Legon and D. W. Bruce, J. Am. Chem.
Soc., 2004, 126, 16.
[5]. P. Metrangolo, C. Prasang, G. Resnati, R. Liantonio, A. C. Whitwood and D. W. Bruce
Chem. Commun., 2006, 3290 (Hot Paper and Front Cover); Chemical Science, 2006, 7.
Buttressing Effects in Pseudomacrocyclic Metal Extractants
Peter A. Tasker, Ross S. Forgan, David K. Henderson, Fiona McAllister, Simon Parsons and
Peter A. Wood
School of Chemistry, The University of Edinburgh, Edinburgh, EH9 3JJ, UK
E-mail: p.a.tasker@ed.ac.uk
Nearly a third of the world’s copper is now recovered by solvent extraction using salicylaldoxime
derivatives.[1] The strength and selectivity of Cu extraction depends on formation of
pseudomacrocyclic structures. [2]
R
R'
X
N
O
O H
H
H
H
O
O
N
X
R'
R
+Cu 2+
R
R'
N
O
O H
We have found that the nature of the 3-substituent (X above) has a major influence on
extractant strength, with NO2 > Cl > MeO > H Me > t Bu for the extractants with R = t Bu or t Oct.
A favourable buttressing from H-bond acceptor groups such as MeO which favour formation of
bifurcated H-bonds from the oximic OH and an unfavourable destabilising of interligand Hbonding
by large groups such as t Bu account for this order. Solid state structures confirm the
importance of this buttressing effect in stabilizing the pseudomacrocycle structure; cavity sizes
in the dimers (R = H) decrease in the order X = MeO < Cl < H < Me < t Bu. The integrity of these
14-membered pseudomacrocycles is maintained at pressure up to 6 MPa and the compression
of cavity size by up to 6 % should lead to changes in selectivity of metal uptake.
The effect of pressure on the cavity sizes in the metal-free ligand dimers
[1] G. A. Kordosky, ISEC, 2002, p853
[2] P. A. Tasker et al, Comprehensive Coordination Chemistry II, 2004, 9, p759
X
H
Cu
O
O
N
X
R'
OP 16
R
+2H +