Fig. 2 Structure of the chains of cations observed in the structure of [Cu2(L2)2][PF6]2; hydrogens are omitted except those in the H-bonds.
Fig. 3 Structure of the chains of cations observed in the structure of [Cu2(L2)2]Cl2; hydrogens are omitted except those in the H-bonds.
The corresponding copper(
I
) complex of L2 (which contains
this structure each hydroxy acts as a hydrogen bond donor.
Adjacent cations are connected through two such bridges and all
hydroxys are involved in the hydrogen bonding network. The
anions are now incorporated within the supramolecular chain
rather than lying outside it as in the other structures. Within the
chains each cation possesses the same helicity (leading to chiral
helical chains), while the helicity alternates between chains
rendering the overall structure achiral.
We have demonstrated herein that a metal-directed assembly
process may be harnessed to create not only supramolecular
architectures but also to create multiple H-bond sites using
readily prepared ligands bearing discrete H-bond units. These
multiple H-bond sites may be used to aggregate the metallo-
supramolecules into larger assemblies. Anions can compete
with the hydrogen bonding but this feature can be integrated
into the molecular design to yield arrays in which the anion is
incorporated rather than remote. We are currently exploring
how to integrate further supramolecular interactions to design
more sophisticated assembly pathways based on multiple
recognition events.
ethyl groups on the phenyls of the spacer units) was also
prepared. As expected the introduction of the ethyl groups leads
to the formation of only the rac-isomer (double-helicate); Mass
spectrometry confirms a dinuclear [Cu2(L2)2]2+ formulation and
NMR reveals a single solution species, even at low temperature,
in which the central CH2 resonance is a singlet. Recrystallisa-
tion of the hexafluorophosphate complex from acetonitrile by
diffusion of diethyl ether yielded suitable crystals. The X-ray
crystal structure (Fig. 2) confirms the double-helical structure of
the cations. These double-helical cations are again linked into
infinite chains through hydrogen-bonding interactions (O–
H…O 1.89 Å; O…O 2.71 Å; •OHO 169°). However, in
contrast to the structure with L1, in this structure a single
hydrogen bond links adjacent cations. The other hydroxy
groups engage in hydrogen bonding to fluorine groups from the
anions (O–H…F 2.16, 2.26 Å; O…F 2.99, 3.09 Å; •OHF 166,
169°). Within the chains the helicity of the cations alternates
rendering the chains achiral.
The ‘interference’ of the anions in the hydrogen bonding
motif might at first appear to be a potential problem for
integrating hydrogen-bonding with assembly of cationic met-
allo-supramolecular architectures. While the interference could
potentially be circumvented by using anions without electro-
negative atoms, such as tetraphenylborate, such anions will
inevitably introduce alternate competing supramolecular inter-
actions (for example Dance7 has elegantly demonstrated the use
of tetraphenylborate in aryl crystal embraces). However the
ability of anions to act as H-bond acceptors can be turned to our
advantage by incorporating this feature into the supramolecular
design; how this can be achieved is illustrated by using chloride
as the anion.
Support from EU Marie Curie Fellowships (A.L.; MCFI-
2000-01003; F.T.; MCFI-2000-00403) is acknowledged.
Notes and references
1 J.-M. Lehn, Supramolecular Chemistry – Concepts and Perspectives,
VCH, Weinheim, 1995; Comprehensive Supramolecular Chemistry, Eds.
J. L. Atwood, J. E. D. Davies, J.-M. Lehn, D. D. MacNicol and F. Vogtle,
Pergamon: Oxford, 1996.
2 L. J. Childs, N. W. Alcock and M. J. Hannon, Angew. Chem., Int. Ed.,
2001, 40, 1079–1081; L. J. Childs, N. W. Alcock and M. J. Hannon,
Angew. Chem., Int. Ed., 2002, 41, 4244.
3 M. J. Hannon, C. L. Painting and W. Errington, Chem. Commun., 1997,
1805.
4 M. Vázquez, A. Taglietti, D. Gatteschi, L. Sorace, C. Sangregorio, A. M.
González, M. Maneiro, R. M. Pedrido and M. R. Bermejo, Chem.
Commun., 2003, 1840.
5 E. Breuning, U. Ziener, J.-M. Lehn, E. Wegelius and K. Rissanen, Eur.
J. Inorg. Chem., 2001, 1515; Z. Qin, M. C. Jennings and R. J. Puddephatt,
Chem. Commun., 2001, 2676.
6 M. J. Hannon, C. L. Painting and N. W. Alcock, Chem. Commun., 1999,
2023; M. J. Hannon, C. L. Painting, J. Hamblin, A. Jackson and W.
Errington, Chem. Commun., 1997, 1807.
The comparatively small, spherical chloride anion has strong
potential to act as a hydrogen bond acceptor and can do so to
multiple hydroxy groups. Suitable crystals of the chloride salt
were obtained from methanol solution by diffusion of benzene.
The crystal structure (Fig. 3) again reveals double-helical
cations linked into an infinite chain. However, in contrast to the
hexafluorophosphate salt, the hydroxy units are not hydrogen
bonded to each other but to chloride anions which bridge
between hydroxy groups (O–H…Cl 2.21, 2.28, 2.23, 2.50 Å;
O…Cl 3.04, 3.11, 2.99, 3.02 Å; •OHCl 171, 167, 151, 122°).
Thus, rather than acting alternately as donors and acceptors, in
7 See for example: P. A. W. Dean, M. Jennings, U. Rajalingam, D. C.
Craig, M. L. Scudder and I. G. Dance, CrystEngComm, 2002, U1.
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