ISMSC 2007 - Università degli Studi di Pavia

PSB 61
Molecular Recognition of Electron-Deficient Guests Molecules by Podand
Diazacoronands
Adam Sobczuk a , Marcin Pawlak a , Jarosaw Kalisiak a , Janusz Jurczak a,b
a Institute of Organic Chemistry, Polish Academy of Sciences, Warsaw, Poland
b Department of Chemistry, Warsaw University, Poland
Molecular recognitions, the keystone of supramolecular chemistry, 1 depends on a variety of
noncovalent interaction. Among them an arene-arene interaction play a fundamental role in the
selective complexation of –neutral guests. The interaction between simple arenes compromise
–acid/base (charge-transfer), van der Walls (dispersive), and polar electrostatic (coulombic)
components. 2 The understanding of electron transfer processes is essential for future progress
in many diverse fields of science, spinning from biological enzymes 3 via organic synthesis 4 to
optoelectronic devices. 5
In this communication we would like to present the synthesis and complexation study of Obenzylated
diazacoronands of type 1.
Ar =
N
O
H
Ar
O
O
O
O
H
N
1
N
O O
R = H, OMe, N(Me) 2
O
O
Cl Cl
, , ,
O O
The above-mentioned electron-rich macrocyclic donor compounds with electron-poor acceptor
like nitroarenes, forming charge-transfer complexes. Their formation was confirmed by X-ray
analysis and UV-vis spectroscopy as well as NMR.
[1] J.-M. Lehn, Angew. Chem., Int. Ed. 1990, 29, 1304.
[2] C. A. Hunter, K. R. Lawson, C. J. Urch, J. Chem. Soc., Perkin Trans., 2001, 2, 651.
[3] C. A. Hunter, J. Mol. Biol. 1993, 230, 1025.
[4] J. F. Stoddart, D. J. Williams, J. Org. Chem. 1997, 62, 26.
[5] P. Günter, C. Bosshar , V. Gramlich, Adv. Mater. 1998, 10, 777.
R
An electrochemical sensor for anions based on a tris-imidazolium cage and
on the Co III /Co II PSB 62
redox change
Cristina Spadini a , Valeria Amendola a , Massimo Boiocchi b , Benoît Colasson c , Luigi Fabbrizzi a ,
Maria-Jesús Rodriguez Douton a
a Dipartimento di Chimica Generale, Università di Pavia, 27100 Pavia, Italy
b Centro Grandi Strumenti, Laboratorio di Cristallografia, Università di Pavia, 27100 Pavia, Italy
c LCBPT, Université PARIS V, 75270 Paris Cedex 06, France
Transition metals can be used to direct the assembly of concave receptors, suitable for anion
inclusion. A recent example refers to the system illustrated by the structural formula a, in which
a low-spin Fe II centre induces the formation of a defined cavity, which offers H-bonds from the
CH fragments of three imidazolium subunits. Inclusion of halides (e.g. Br ) and pseudohalides
(e.g. N3 ) has been documented through X-ray and spectroscopic studies [1].
The architectural metal centre can play an additional role in signalling anion inclusion, through
changes of its photophysical (e.g. Ru II ) or electrochemical properties. In this latter perspective,
the Co II complex of the tris-imidazolium-bipyridine (L) ligand has been investigated. Figure b
shows the crystal structure of the [Co II (L)]Cl(PF6)4 . H2O . 2MeCN complex salt. Quite surprisingly,
a water molecule is included within the tris-imidazolium cavity, while the chloride ion stays
outside of the cage, and, being placed between symmetrically related [Co II (L)H2O] 5+
complexes, favours the formation of molecular chains that extends along the a axis in the
crystal. In any case, in a water/MeCN mixture (1:4, v/v), halide and pseudohalides anion are
incorporated into receptor’s cavity through equilibria characterised by unusually high logK
values. The oxidation behaviour of the [Co II (L)] 5+ complex both in pure and in aqueous MeCN, in
presence of a variety of anions, has been investigated through cyclic voltammetry and
differential pulse voltammetry (DPV) studies. Figure c shows the DPV profiles obtained on
titration with chloride of a MeCN solution of [Co II (L)] 5+ (0.1 M [Bu4N]ClO4). On anion addition, the
potential of the Co III /Co II couple becomes distinctly less positive, which reflects the higher affinity
of the anion towards the Co III containing receptor (E = 120 mV for Cl , which corresponds to
logK = 2.0; E = 90 mV and logK = 1.5 for Br ). The redox active [Fe II (L)] 5+ complex cannot
be used as an electrochemical sensor because of the too positive value of the Fe III /Fe II
potential, which exceeds that associated to the X2/X couple (X = halogen).
[1] V. Amendola, M. Boiocchi, B. Colasson, L. Fabbrizzi, M-J. Rodriguez Douton, F. Ugozzoli,
Angew. Chem., Int. Ed., 2006, 45, 6920-6924.