Organic guests inclusion by tungsten-calix[4]arene hosts

Article abstract of DOI:10.1039/b603006h

The binding mode of a series of lower rim tungsten-calix[4]arenes toward different neutral organic guests has been investigated in the solid state and through ab initio computational studies. From the structure of the inclusion compounds examined it emerges that the metal can be employed as a control element to confer different cone shapes to the calixarene cavity and to act as an additional binding site. the Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2006.

Full text of DOI:10.1039/b603006h

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Organic guests inclusion by tungsten-calix[4]arene hostsw
Arturo Arduini,a Chiara Massera,b Andrea Pochini,*a Andrea Secchia and
Franco Ugozzoli*b
Received (in Montpellier, France) 1st March 2006, Accepted 6th April 2006
First published as an Advance Article on the web 2nd May 2006
DOI: 10.1039/b603006h
The binding mode of a series of lower rim tungsten-calix[4]arenes toward different neutral organic
guests has been investigated in the solid state and through ab initio computational studies. From
the structure of the inclusion compounds examined it emerges that the metal can be employed as
a control element to confer different cone shapes to the calixarene cavity and to act as an
additional binding site.
represent a suitable tool to investigate the use of metal centres
Introduction
to control the shape of the calixarene cavity and to study the
role of the metal as an additional binding site.
Calix[4]arenes possess a p-donor cavity suitable to bind,
through weak host guest CHꢀ ꢀ ꢀp interactions, small organic
guests bearing acid CH groups.1 From the extensive investiga-
tions carried out during the last few decades to single out the
parameters that govern their binding efficiency, it emerged that
the increase of the host rigidity strongly enhances the binding
efficiency of the calixarene cavity.1a,c The macrocycle skeleton
can be blocked in a rigid cone conformation by connecting its
proximal phenolic OH groups with two short diethyleneglycol
chains2 or, alternatively, through the partial functionalization
of the lower rim with alkyl chains.3 By this way the host is able
to act as a monotopic receptor. A further and substantial
increase of binding efficiency can be gained by using hetero-
ditopic calix[4]arene-based hosts, obtained by inserting an
additional binding site onto the upper rim of the calixarene.4
A complementary strategy to insert additional binding sites is
represented by the studies carried out by Reinaud and co-
workers who exploited calix[6]arene derivatives characterised
by the presence of a transition metal centre anchored at the
lower rim.5 The binding properties of these heteroditopic hosts
clearly demonstrated that this arrangement of binding sites can
result in hosts endowed with new and fascinating properties.
In this context, the ability of calix[4]arenes bearing transi-
tion metals covalently linked at the lower rim phenolic oxy-
gens, to act as heteroditopic hosts, remains relatively
unexplored. In fact, despite the rich literature reported so far
on this type of metalla-calix[4]arenes,6 most of the studies have
mainly been devoted to revealing the properties of the metal
centre, considering the calix[4]arene as a new ligand for the
metal. Among the transition metals employed, tungsten-based
calix[4]arenes have been extensively studied.7 Thus, it ap-
peared to us that this class of calix[4]arene derivatives could
Herewith we present an investigation based on X-ray crys-
tallographic data and ab initio calculations on the complexa-
tion properties of a series of calix[4]arene derivatives blocked
in a rigid cone conformation by a tungsten(VI) metal centre,
toward neutral organic guests.
Results and discussion
Design and synthesis of the hosts
Among the tungsten-calix[4]arenes that have been reported so
far in the literature, we selected two series of compounds that
are both characterised by the metal bonded to the four
calixarene oxygens. In one series, the metal is hexo-cavity
bonded through two other oxygens of a pyrocatechol unit,
while in the other, the tungsten is in its oxo form.6c,7a
Calix[4]arenes (1a–c), characterised by the presence of differ-
ent substituents onto their para position, were employed for
the host synthesis. Tungsten(VI) pyrocatechol calix[4]arenes
(3a–c) were prepared in 65–85% overall yield, (see Scheme 1)
by modifying the synthetic procedure devised by Swager and
co-workers.7b,c The series of tungsten(VI) oxo hosts (4a–c)8 was
prepared adapting the procedure published by Floriani and
co-workers.7a According to this latter synthesis, in hosts (4a–c)
a molecule of acetic acid is included inside the calixarene
cavity to ‘‘saturate’’ the coordination sphere of the metal.
The structures of the new compounds 3a–c and 4c were
inferred through spectroscopic techniques (see Experimental).
Particularly informative was the observation that in the 1H
NMR spectra, all the tungsten(VI) pyrocatechol calix[4]arene
derivatives 3a–c adopt a distorted cone conformation having a
C2v symmetry. This was clearly evidenced by the two sets of
signals for the aromatic and tert-butyl or cyclohexyl groups
present on the para position of the aromatic rings of 3b and 3c,
respectively. On the contrary, compound 4c assumes a cone
conformation, having a C4v symmetry, as showed by the
presence of one singlet for the four equivalent aromatic
protons and by a unique set of resonances for the cyclohexyl
a
`
Dipartimento di Chimica Organica e Industriale, Universita di
Parma, via G.P. Usberti 17/a, I-43100, Italy. Fax: þ39 0521 905472
b Dipartimento di Chimica Generale ed Inorganica, Chimica Analtica,
Chimica Fisica, Universita` di Parma, via G.P. Usberti 17/a, I-43100,
Italy. E-mail: ugoz@unipr.it; Fax: þ39 0521 905557; Tel: þ39 0521
905417
w Electronic supplementary information (ESI) available: Interaction
energies in the benzene/acetone complex as a function of the Hꢀ ꢀ ꢀCt
distance (Ct = benzene centroid) calculated with the cc-PVDZ and
cc-PVTZ basis sets. See DOI: 10.1039/b603006h
1
moiety in its H NMR spectrum.9
ꢁc
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Solid state complexation studies
The ability of 3a–c and 4a–c to behave as hosts was evaluated
toward a series of small neutral organic molecules representa-
tive of different classes of Volatile Organic Compounds
(VOCs), able to interact with both the p-donor cavity and
the metal centre. The guests used were: ethyl acetate, acetone,
acetonitrile, and N,N-dimethyl formamide. As a working
hypothesis the calix[4]arenes 3a–c, where the tungsten(VI) core
is fully coordinated by six oxygen atoms, should experience a
binding mode related to that of rigid calix[4]arenes,2 and thus
able to interact with the guest only through the aromatic
cavity. On the contrary, in 4a–c, the metal, although hexa-
coordinated, presents a ligand (acetic acid) inside the cavity
that could be exchanged. This could allow a different ligand
(guest) to be recognised by a combination of weak (through
the cavity) and stronger coordinative (through the metal)
intermolecular interactions.
Unfortunately, all attempts to obtain crystals of the tung-
sten(VI) oxo calix[4]arene hosts 4a–c, with the different guests
failed. However, when compounds 3a–c were used as hosts,
crystals suitable for X-ray crystallographic determination of
the corresponding inclusion complexes were obtained from the
slow evaporation of CH2Cl2 solutions of 3a (R = H) with
t
DMF and ethyl acetate, 3b (R = Bu) with acetone, and 3c
(R = cyclohexyl) with acetonitrile. Quite surprisingly, NMR
analysis of the crystals showed that only in the complex with
acetone (acetone C 3b) does the host retain its original
structure. On the contrary, the formation of tungsten(VI) oxo
calix[4]arene derivatives was observed with more strongly
coordinating guests (see Scheme 1), and the following inclu-
sion complexes DMF C 4a, H2O/AcOEt C 4a, and CH3CN
C 4c were isolated.10
Scheme 1
according to the standard rules,11 and by the conformational
parameters f and w and the symbolic representations.12
In acetone C 3b (see Fig. 1), contrary to what is expected,
the guest molecule does not enter inside the cavity with its
oxygen atom, but it prefers to fill the host cavity with the two
methyl groups. This reciprocal host–guest orientation allows
the activation of three (not equivalent) attractive CHꢀ ꢀ ꢀp
interactions between the ‘‘acid’’ hydrogen atoms of the two
methyl groups of the acetone and the electron rich aromatic
nuclei of the host as shown in Fig. 1.13 The shortest Hꢀ ꢀ ꢀCtD
(Ct = ring centroid) separation of 2.77(1) A (see Table 2) is
indicative of a strong CHꢀ ꢀ ꢀp interaction with the aromatic
ring D, while the other two acetone/aromatic separations,
Hꢀ ꢀ ꢀCtB 2.83(1) A and Hꢀ ꢀ ꢀCtC 2.81(1) A, are practically
identical to each other but longer. To clarify whether these
X-Ray studies
As far as the shape of the host is concerned, complex acetone
C 3b adopts a highly flattened cone conformation, as found
for instance in the structure of the complex benzene C 2b.7a In
DMF C 4a the host conformation is flattened, whereas in
H2O/AcOEt C 4a and in CH3CN C 4c the host assumes a
‘‘slightly distorted’’ and an ‘‘ideal’’ cone conformation, respec-
tively. The quantitative and unequivocal description of the
molecular conformation of the host in the four complexes is
summarised in Table 1 by the dihedral angles d, calculated
Table 1 Dihedral anglesa d (1) and conformational parametersb f and w (1) in complexes acetone C 3b, CH3CN C 4c, DMF C 4a and H2O/
AcOEt C 4a
A–B
B–C
C–D
D–A
f
w
f
w
f
w
f
w
Complex
R ^ A
R ^ B
R ^ C
R ^ D
Acetone C 3b
146.6(3) 116.9(2) 158.4(2) 117.9(3) 113(1) ꢂ84(1)
82(1)
ꢂ122(1) 125(1) ꢂ85(1)
82(1)
ꢂ112(1)
CH3CN C 4c
DMF C 4a
127.5(2) 127.5(2) 127.5(2) 127.5(2) 94.2(9) ꢂ93.7(9) 94.2(9) ꢂ93.7(9) 94.2(9) ꢂ93.7(9) 94.2(9) ꢂ93.7(9)
117.1(1) 127.0(2) 117.1(2) 131.2(2) 82.9(7) ꢂ90.1(8) 89.4(7) ꢂ83.8(8) 83.9(7) ꢂ93.0(7) 92.5(8) ꢂ82.0(8)
H2O/AcOEt C 4a 123.8(2) 124.9(2) 125.4(2) 123.8(2) 89.9(9) ꢂ88.1(9) 89.1(9) ꢂ88.9(8) 90.2(7) ꢂ88.4(7) 89.2(8) ꢂ87.9(8)
Dihedral angles between the molecular reference plane R (the weighted least-squares plane through the four CH2 bridges) and the weighted least-
a
b
squares planes of the phenolic rings (A, B, C, D). The symbolic representations of the molecular conformations are: C1 þꢂ, þꢂ, þꢂ, þꢂ, for
acetone C 3b, DMF C 4a, H2O/AcOEt C 4a, and C4 þꢂ for CH3CN C 4c, respectively.
ꢁc
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Fig. 2 Optimised geometry of the acetone–benzene complex in the
Fig. 1 Partial stick view of acetone C 3b.The host is represented in
stick mode; the guest in ball and stick mode. Only the hydrogen atoms
of the guest have been drawn. CHꢀ ꢀ ꢀp interactions are shown by fine
lines.
gas-phase.
attraction by electron correlation [Ecorr = EMP2 ꢂ EHF is
ꢂ20.74 kJ molꢂ1 (cc-PVTZ) against –14.55 kJ molꢂ1 (cc-
PVDZ)] indicates that dispersion is significantly important
for attraction in the CHꢀ ꢀ ꢀp interaction between these two
fragments. From the plot of the interaction energies it is also
evident that (a) the attraction is still substantial up to 3.0 A,
where the binding energy is comparable (EMP2 = ꢂ15.93 kJ
molꢂ1), and (b) in any case the interaction energy profile is
almost flat around the minimum from 2.6 A (EMP2 = ꢂ17.46
kJ molꢂ1) to 3.0 A (EMP2 = ꢂ15.93 kJ molꢂ1).
latter short contacts can be considered true CHꢀ ꢀ ꢀp interac-
tions and in general to evaluate the binding energy between the
‘‘acid’’ hydrogens of acetone and the electron-rich surface of
benzene, we carried out ab initio calculations of the intermo-
lecular interaction energy when an isolated molecule of acet-
one approaches a benzene molecule.
Initially, we calculated the minimum-energy structure of the
complex at the MP2/cc-PVDZ level (see Fig. 2). In a second
step, starting from the obtained equilibrium geometry, we
carried out the calculation of the interaction energies as a
function of Hꢀ ꢀ ꢀCt separations in the range 2.2 r Hꢀ ꢀ ꢀCt r
4.4 A at the MP2 level using both cc-PVDZ and cc-PVTZ
basis sets (see ESIw for the calculation details). The plot of the
interaction energies (see Fig. 3) shows that the small cc-PVDZ
basis set underestimates the attraction compared to larger cc-
PVTZ, because the former leads to an underestimate of the
molecular polarizability and the dispersion interactions. The
energy minimum is found at Hꢀ ꢀ ꢀCt = 2.6 A with the cc-
PVDZ basis set and at 2.8 A with the larger cc-PVTZ set. The
angle between the CQO dipole and the benzene ring is 16.81.
However, the energy of binding estimated using cc-PVTZ
(EMP2 = ꢂ17.54 kJ molꢂ1) is 54% higher than that calculated
with cc-PVDZ (EMP2 = ꢂ11.4 kJ molꢂ1). The large gain of
These results help to conclude that, in the structure of
acetone C 3b, the three acetone–aromatic interactions, for
which the Hꢀ ꢀ ꢀCt distances range from to 2.77 to 2.83 A, are
not only all true CHꢀ ꢀ ꢀp interactions, but they are also
practically equivalent from the energetic point of view. It is
noteworthy that the orientation of the CQO dipole of acetone
with aromatic rings are 19.2, 32.4, and 82.61 for rings D, B and
C, respectively, so that the strongest CHꢀ ꢀ ꢀp interaction (with
Table 2 Geometrical parameters for CHꢀ ꢀ ꢀp and OHꢀ ꢀ ꢀp interac-
tions in acetone C 3b, DMF C 4a and H2O/AcOEt C 4aa
Complex
D–Hꢀ ꢀ ꢀAb
Cꢀ ꢀ ꢀCt/A Hꢀ ꢀ ꢀCt/A C–Hꢀ ꢀ ꢀCt/1
Acetone C 3b
C2G–Hꢀ ꢀ ꢀCtB 3.78(1)
C2G–Hꢀ ꢀ ꢀCtD 3.72(1)
C4G–Hꢀ ꢀ ꢀCtC 3.60(1)
2.83(1)
2.77(1)
2.81(1)
171(1)
171(1)
140(1)
DMF C 4a
C1G–Hꢀ ꢀ ꢀCtB 3.190(8) 2.363(8) 154.2(7)
C2G–Hꢀ ꢀ ꢀCtD 3.321(9) 2.661(8) 139.9(7)
˚
˚
Oꢀ ꢀ ꢀCt/A Hꢀ ꢀ ꢀCt/A O–Hꢀ ꢀ ꢀCt/1
Fig. 3 HF and MP2 interaction energies (kJ molꢂ1), calculated with
the cc-PVDZ and cc-PVTZ basis sets, for rigid relative translations of
monomers starting from the equilibrium geometry of the acetone–
benzene complex.
H2O/AcOEt C 4a Ow–Hꢀ ꢀ ꢀCtB 3.42(1)
Ow–Hꢀ ꢀ ꢀCtD 3.43(1)
Ct = centroid. D = donor, A = acceptor.
2.69(1)
2.63(1)
132.5(8)
141.8(8)
a
b
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Fig. 4 Partial stick view of CH3CN C 4c. The host is represented in
stick mode; the guest in ball and stick mode. Only one of the four
different orientations of the hydrogen atoms of the guest has been
drawn.
Fig. 6 Partial stick view of H2O/AcOEt C 4a. The host is represented
in stick mode; the guest in ball and stick mode. Only the hydrogen
atoms of the guest have been reported. CHꢀ ꢀ ꢀp interactions and
hydrogen bonds are shown by fine lines.
ring D) occurs at an angle close to that found in the ace-
tone–benzene complex (16.81).
In CH3CN C 4c the host has a C4 symmetry, and the
nitrogen of the guest is bonded to the metal, with a Nꢀ ꢀ ꢀW
bond length of 2.328(10) A,14 and lies on the fourfold axis with
the methyl group disordered over four different equivalent
orientations around the C4 axis (see Fig. 4). Apart from van
der Waals interactions, no other weak intermolecular interac-
tions occur between the host and the guest.15
In H2O/AcOEt C 4a (see Fig. 6) one water molecule,
directly coordinated to the metal centre [Wꢀ ꢀ ꢀOw 2.331(4)
A], is further stabilised within the calixarene cavity by two
OHꢀ ꢀ ꢀp interactions with the two opposite phenolic rings B
and D (the water molecule can adjust its orientation within the
cavity by a rigid rotation around the W–OW bond).
In DMF C 4a (see Fig. 5) the guest is held within the
calixarene cavity through its oxygen atom (O1G) coordinated
to the metal centre [Wꢀ ꢀ ꢀO1G 2.310(4) A]. The final orienta-
tion of the guest within the cavity is then adjusted by simple
rotation of the guest itself around the bond O1G–W to bring
the CH hydrogen and one methyl hydrogen of the guest to
interact with the electron-rich surfaces of the two opposite
phenolic rings B and D giving rise to two attractive CHꢀ ꢀ ꢀp
interactions.
The Hꢀ ꢀ ꢀCt separations of 2.63(1) and 2.69(1) A (see Table
2) are only slightly longer than those (2.38 and 2.5 A) observed
in the first example of a OHꢀ ꢀ ꢀp interaction between a water
molecule and the calix[4]arene cavity16 but short enough to
ensure that the OHꢀ ꢀ ꢀp interaction is still attractive. One ethyl
acetate molecule acts as a ‘‘second coordination sphere’’
ligand in the complex. Although located outside the calixarene
cavity, the ethyl acetate is still linked by strong mutual
attraction with the coordinated water molecule in the calixar-
ene cavity: the OC=O of the ethyl acetate acts as an acceptor of
two strong hydrogen bonds from the water molecule. The
geometrical parameters for hydrogen bonds are summarised
in Table 3.
To the best of our knowledge only two other examples of a
second sphere of coordination in metalla-calix[4]arene com-
plexes have been reported. However, the first one is a molyb-
denum complex,17 whereas the second is
a tungsten
calix[4]arene complex in which a disordered aniline molecule
is present in the second coordination sphere.14 This prevents
any other speculation on the intermolecular interaction occur-
ring in this latter complex.
Table 3 Geometrical parameters for hydrogen bonds in H2O/AcOEt
C 4a
Fig. 5 Partial stick view of DMF C 4a. The host is represented in
stick mode; the guest in ball and stick mode. Only the hydrogen atoms
of the guest have been drawn. CHꢀ ꢀ ꢀp interactions and hydrogen
bonds are shown by fine lines.
Dꢀ ꢀ ꢀA/A
2.60(1)
2.60(1)
Hꢀ ꢀ ꢀA/A
2.07(1)
2.62(1)
D–Hꢀ ꢀ ꢀA/1
113.6(8)
78.5(8)
Ow–H1ꢀ ꢀ ꢀO1G
Ow–H2ꢀ ꢀ ꢀO1G
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Compound 3b. The filtrate was evaporated to dryness under
reduced pressure to afford a red solid residue which was taken
up with ethyl acetate and filtered on Celite. Evaporation of the
filtrate yielded 0.8 g (84%) of a red solid compound (Found:
C, 63.0; H, 6.2. C50H56O6W requires C, 64.1; H, 6.0%). mp 4
300 1C (from ethyl acetate). dH (CDCl3, 300 MHz): 1.18 (18H,
s, –C(CH3)3), 1.37 (18H, s, –C(CH3)3), 3.39 (4H, d, JAX 12,
ArCH2Ar equatorial), 4.66 (4H, d, JAX 12, ArCH2Ar axial),
6.82 and 6.85 (4H, 2s, Ar–H), 6.91 and 7.06 (8H, 2t, Ar–H); dC
(CDCl3, 75 MHz): 31.4, 31.8, 33.9, 34.4, 34.7, 115.3, 123.6,
124.2, 125.9, 126.7, 129.7, 135.5, 145.8, 148.5, 156.5, 161.4; m/z
(CI) 937 (MH1).
Conclusions
These results clearly demonstrate that a transition metal
centre, anchored to the lower rim of a calix[4]arene platform,
can act as an efficient preorganising element. The guest can be
covalently bound to the metal centre within the host cavity
without any other interactions with the host as for the CH3CN
molecule in CH3CN C 4c.
The guest can be linked to the host through cooperatively
strong and weak interactions. The guest can be primarily
covalently linked to the metal centre within the host cavity
and then anchored in to the walls of the host by using multiple
CHꢀ ꢀ ꢀp interactions such as for the DMF molecule in DMF C
4a. Again, a guest can be linked to another guest directly
coordinated to the metal centre within the cavity giving rise to
a ‘‘secondary coordination sphere’’ to the metal. This is the
case for the AcOEt molecule which is linked through hydrogen
bonds to a water molecule coordinated to the tungsten centre
within the cavity as in H2O/AcOEt C 4a. Finally, the metal
centre can be used to force a very flattened cone conformation
of the calixarene to exploit the inner aromatic surfaces of the
calix[4]arene for CHꢀ ꢀ ꢀp interactions with selected guests
which can afford new interaction modes with the aromatic
cavity as verified in acetone C 3b.
Compound 3c. The filtrate was evaporated to dryness under
reduced pressure to afford a red solid residue which was
crystallised from ethyl acetate to yield 0.9 g (86%) of a red
solid compound (Found: C, 66.2; H, 6.3. C58H64O6W requires
C, 66.9; H, 6.2%). mp 4 300 1C (from ethyl acetate). dH
(CDCl3, 300 MHz): 1.2–1.5 and 1.6–1.9 (40H, 2m, cyclohexyl),
2.35 and 2.55 (4H, 2bs, cyclohexyl), 3.35 (4H, d, JAX 13.5,
ArCH2Ar equatorial), 4.62 (4H, d, JAX 13.5, ArCH2Ar axial),
6.87 (4H, bs, Ar–H), 6.92 and 7.08 (8H, 2t, Ar–H); dC (CDCl3,
75 MHz): 26.1, 26.8, 26.9, 29.6, 33.9, 34.5, 34.9, 43.2, 43.5,
44.4, 115.5, 124.2, 124.9, 128.0, 129.7, 135.9, 142.7, 145.4,
156.4, 156.9, 161.8; m/z (CI) 1040 (MH1).
Compound 4c. To a purple suspension of WCl6 (0.4 g, 1
mmol) in dry toluene (15 mL), calix[4]arene 1c (0.2 g, 0.26
mmol) was added. The resulting heterogeneous mixture was
stirred at room temperature for 18 h, then evaporated to
dryness under reduced pressure. The reddish solid residue
was taken up with CH3COOH (15 mL) and a catalytic amount
of AlCl3 was added. The mixture was refluxed under stirring
for a further 6 h, after which it was cooled at room tempera-
ture and filtered to afford a yellow solid residue (0.2 g, 75%)
which did not require further purification (Found: C, 66.2; H,
6.1. C52H60O5W requires C, 65.8; H, 6.4%). mp 4 300 1C
(from ethyl acetate). dH (CDCl3, 300 MHz): 1.2–1.3 (24 H, m,
cyclohexyl), 1.7–1.8 (16 H, m, cyclohexyl), 2.33 (4 H, bs,
cyclohexyl), 3.24 (4H, d, JAX 12.6, ArCH2Ar equatorial),
4.65 (4H, d, JAX 12.6, ArCH2Ar axial), 6.93 (8H, s, Ar–H);
dC (CDCl3, 75 MHz): 26.0, 26.8, 32.7, 34.6, 43.7, 44.4, 126.4,
124.1, 130.0; m/z (CI) 949 (MH1).
Experimental
Materials and methods
All reactions were carried out under nitrogen, and all solvents
were freshly distilled under nitrogen prior to use. All other
reagents were reagent grade quality obtained from commercial
supplies and used without further purification. lH NMR
spectra were recorded at 300 and 400 MHz. 13C NMR were
recorded at 25 and 75 MHz. Chemical shifts (d) are expressed
in ppm from the solvent residual signal. Mass spectra were
recorded in the CI mode (CH4). Compounds 1a,18 1b19 and
1c20 were synthesised according to literature procedures.
General procedure for the synthesis of compounds 3a–3c
To a purple suspension of WCl6 (0.4 g, 1 mmol) in dry toluene
(15 mL), the appropriate calix[4]arene 1a–c (1 mmol) was
added. The resulting heterogeneous mixture was stirred at
room temperature for 24 h, then pyrocatechol (0.1 g, 1 mmol)
and (CH3)3SiCl (0.2 g, 2 mmol) were added. The mixture was
refluxed under stirring for 6–12 h, after which it was cooled at
room temperature and filtered.
Computational Studies
The optimised geometry of the benzene–acetone complex was
obtained by ab initio calculations in the gas phase with the
MP2 method21 by using the cc-PVDZ22 basis set in Gaussian
03.23 The interaction energy pattern as a function of Hꢀ ꢀ ꢀCt
distance was obtained by single point calculations with the
MP2 method using the cc-PVDZ and cc-PVTZ24 basis sets, by
increasing step by step (0.2 A) the Hꢀ ꢀ ꢀCt distance from 2.2 to
4.4 A in the optimised structure of the complex and fixing any
other geometrical parameters. The calculated energy values
were corrected for basis set polarization effects (BSSE).25
Compound 3a. The filtrate was evaporated to dryness under
reduced pressure to afford 0.5 g (65%) of a red solid residue
which did not require further purification (Found: C, 55.8; H,
3.7. C34H24O6W requires C, 57.3; H, 3.4%). mp 4 300 1C
(from toluene). dH (CDCl3, 300 MHz): 3.43 (4H, d, JAX 12,
ArCH2Ar equatorial), 4.66 (4H, d, JAX 12, ArCH2Ar axial),
6.65 (2H, t, J 7.5, Ar–H), 6.90 (2H, t, J 7.3, Ar–H), 6.95 (4H,
bs, Ar–H), 7.05 (4H, d, J 7.5, Ar–H), 7.26 (4H, d, J 7.3, Ar–H);
dC (CDCl3, 75 MHz): 29.7, 115.5, 123.8, 124.7, 125.3, 126.6,
129.8, 130.0, 136.1, 156.3, 158.6, 163.4; m/z (CI) 713 (MH1).
Crystallography
Data were collected at 295 K on Philips PW 1100 (DMF C 4a
and CH3CN C 4c) and on Siemens AED (acetone C 3b and
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956 | New J. Chem., 2006, 30, 952–958 This journal is the Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2006

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Table 4 Crystal data and experimental details for data collection and structure refinement for acetone C 3b, CH3CN C 4c, DMF C 4a and H2O/
AcOEt C 4a
Compound
Acetone C 3b
CH3CN C 4c
DMF C 4a
H2O/AcOEt C 4a
Empirical Formula
Formula weight
Crystal size/mm
Crystal system
Space group
a/A
b/A
c/A
C
44H52O4W ꢀ C6H4O2 ꢀ C3H6O
C52H60O5W ꢀ CH3CN
982.892
0.3 ꢃ 0.4 ꢃ 0.3
Tetragonal
P4/n
13.292(5)
13.292(5)
13.743(5)
90
90
90
2428(2)
2
1.344
1002
295
0.710 73
2.424
ꢂ14 r h r 14
0 r k r 14
0 r l r 14
3288
1490
0.059
1075
C28H20O5W ꢀ C3H7NO
693.407
0.2 ꢃ 0.2 ꢃ 0.3
Monoclinic
P21/n
8.789(5)
17.600(5)
16.397(5)
90
94.94(1)
90
2527(2)
4
1.823
1368
295
0.710 73
4.620
ꢂ14 r hr 14
0 r k r 28
0 r l r 26
11 745
11 083
0.025
5990
C28H20O5W ꢀ C4H8O2 ꢀ H2O
994.919
0.2 ꢃ 0.3 ꢃ 0.3
Triclinic
P-1
14.243(5)
17.340(5)
10.360(5)
90.99(1)
102.51(1)
98.44(1)
2468(2)
2
1.339
1020
295
0.710 73
2.389
ꢂ16 r h r 16
ꢂ20 r k r 19
ꢂ2 r l r 12
9236
8695
0.034
5339
Fo Z 4s(Fo)
562/24
0.0825
726.434
0.2 ꢃ 0.4 ꢃ 0.3
Monoclinic
P21/n
11.302(5)
14.802(5)
17.226(5)
90
91.05(1)
90
2881(2)
4
1.675
1440
295
0.710 73
4.06
ꢂ12 r h r 10
ꢂ15 r k r 16
ꢂ19 r l r 13
4893
4510
0.030
2845
Fo Z 4s(Fo)
383/3
0.0303
a/1
b/1
g/1
V/A3
Z
r (calcd.)/g cmꢂ3
F (000)
T/K
l/A
m/mmꢂ1
Index ranges
Reflections collected
Independent. Reflections
Rint
Observed
Reflections
Fo Z 4s(Fo)
146/0
0.0402
Fo Z 4s(Fo)
358/0
0.0670
Parameters/restraints
R1
a
wR2
Goodness-of-fitb
0.2154
0.913
0.0995
0.780
0.1801
0.857
0.0689
0.843
a
2
4 1/2
]
b
2
R1 = S8Fo| ꢂ |Fc8/S|Fo|, wR2 = [Sw(Fo ꢂ Fc2)2/SwFo
.
Goodness-of-fit = [Sw(Fo ꢂ Fc2)2/(n ꢂ p)] 1/2, where n is the number of reflections
and p is the number of parameters.
H2O/AcOEt C 4a) diffractometers using graphite-monochro-
mated Mo-Ka radiation (l = 0.710 73 A). Crystal data and
relevant experimental details are presented in Table 4. For
each complex the cell parameters were obtained by a least-
squares fit of 30 I(y,k,f)hkl reflections found in a random
search on the reciprocal lattice. Diffraction data were cor-
rected for Lorentz and polarization effects. Absorption correc-
tion was applied using ABSORB26 at the end of the isotropic
refinement. The structures were solved by direct methods using
SIR9227 and refined by full matrix least-squares on F2 with
SHELX-9728 using anisotropic atomic displacements for all
non-hydrogen atoms except the carbon atoms of the tert-butyl
group on the phenolic rings A and D in acetone C 3b, which
were disordered over two different orientations, and for which
isotropic atomic displacements were used. Generally the hy-
drogen atoms were placed in their calculated position with the
geometrical constraint C–H = 0.96 A and refined with
isotropic atomic displacements ‘‘riding’’ on their parent
atoms. The two water hydrogens in H2O/AcOEt C 4a were
found in the Fourier DF map and refined with isotropic atomic
displacements. All the geometrical calculations were obtained
by PARST97.29
Acknowledgements
This research was partly supported by FIRB (Manipolazione
Molecolare per Macchine Nanometriche), MIUR ‘‘Supramo-
lecular Devices Project’’. Authors thank Centro Interdiparti-
mentale di Misure ‘‘G. Casnati’’ for NMR measurements.
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958 | New J. Chem., 2006, 30, 952–958 This journal is the Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2006