Controlling the confinement of fullerene C60 molecules using a saddle shape Ni(II) macrocycle

Article abstract of DOI:10.1039/b718937k

A saddle-shaped Ni-macrocycle bearing flexible benzyl arms, Ni(TBTAA), 1, has been prepared and structurally authenticated in the solid state as a toluene adduct, with the toluene residing in the extended cavity of the macrocycle, close to two of benzylic substituents. The Ni-macrocycle forms a crystalline inclusion complex with fullerene C₆₀, {C₆₀∩(1) ₂}·(toluene)₅, 2, which has each fullerene encapsulated by two macrocycles involving π...π interactions to the phenyl lined face of the macrocycles, as well as CH...π from the benzyl groups and toluene molecules closing up the fullerene surface. The CH...π for the benzyl groups effectively increases the steric demands of the macrocycle over the surface of the fullerene, circumventing any fullerene...fullerene interactions. The nature of the interactions in the fullerene complex has been probed using Hirshfeld surface analysis. The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.

Full text of DOI:10.1039/b718937k

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PAPER
www.rsc.org/njc | New Journal of Chemistry
Controlling the confinement of fullerene C60 molecules using a saddle
shape Ni(II) macrocyclewz
Marck Norret, Mohamed Makha, Alexandre N. Sobolev and Colin L. Raston*
Received (in Durham, UK) 10th December 2007, Accepted 13th March 2008
First published as an Advance Article on the web 27th March 2008
DOI: 10.1039/b718937k
A saddle-shaped Ni-macrocycle bearing flexible benzyl arms, Ni(TBTAA), 1, has been prepared
and structurally authenticated in the solid state as a toluene adduct, with the toluene residing in
the extended cavity of the macrocycle, close to two of benzylic substituents. The Ni-macrocycle
forms a crystalline inclusion complex with fullerene C60, {C60-(1)2}ꢀ(toluene)5, 2, which has each
fullerene encapsulated by two macrocycles involving pꢀ ꢀ ꢀp interactions to the phenyl lined face of
the macrocycles, as well as CHꢀ ꢀ ꢀp from the benzyl groups and toluene molecules closing up the
fullerene surface. The CHꢀ ꢀ ꢀp for the benzyl groups effectively increases the steric demands of the
macrocycle over the surface of the fullerene, circumventing any fullereneꢀ ꢀ ꢀfullerene interactions.
The nature of the interactions in the fullerene complex has been probed using Hirshfeld surface
analysis.
porating methyl groups on the aromatic rings of the macro-
Introduction
cycle also affords a 1 : 1 complex, but the interplay of
Understanding and controlling the host–guest interactions
fullerenes is dramatically changed, with a linear arrangement
involving inherently weak interactions is a prime challenge
of supramolecular chemistry,1 requiring design characteristics
of fullerenes, each fullerene having two fullereneꢀ ꢀ ꢀfullerene
interactions.13 Ripmeester and co-workers have partially in-
of the host molecule to optimize its interplay with specific
troduced rigid phenyl substituents onto the nickel macrocycle
guest molecules to enhance the likelihood of forming stable
thereby extending the walls of the shallow cavity resulting in
complexes.2 Fullerene C60 is a spheroidal molecule which is an
limited interactions between fullerene molecules.14
attractive guest molecule in designing effective molecules for
While Ni(TMTAA) and its derivatives mentioned above
its supramolecular confinement. This is important in separa-
demonstrate that the nickel macrocycle is effective in forming
tion technology of the fullerene and changing its properties.3
complexes with fullerene C60, as well as fullerene C70,15 there is
Fullerene C60 readily forms host–guest complexes with a
limited work on incorporating design principles into the
variety of compounds, such as porphyrins,4 calixarenes,5
macrocycle to effectively stabilize the ultimate host–guest
cyclodextrins,6 cyclotriveratrylenes (CTV),7 and concave poly-
arenes.8 A starting point in design principles is the use of a
complex where fullereneꢀ ꢀ ꢀfullerene interplay is sterically in-
accessible. This is the research objective herein, where we
concave host molecules having complimentary of curvature,
report the synthesis and structural characterisation of a novel
then to optimise the non-covalent interactions between the C60
nickel macrocycle, Ni(TBTAA), 1 (Scheme 1).
and the host molecule(s).9 Besides a plethora of host molecules
The methyl-lined face of the parent macrocycle Ni(TM-
possessing cavities as in CTV and polyarenes, suitable concave
TAA) has been extended through the incorporation of benzyl-
surfaces are also found in metal macrocycles such as Ni(TM-
substituents, and its ability to act as a host towards fullerene
TAA),10 which exhibits a unique saddle shape, caused by
C60 is reported. Such a change was expected to lead to
intra-molecular non-bonding interactions.11 The original so-
increased surface area contact between the macrocycle and
C60,14 and consequently enhance complex formation, at the
lid-state studies on complexation behaviour between Ni(TM-
TAA) and C60 showed that the fullerene resides in both of the
shallow cavities of the macrocycle, giving rise to a 1 : 1
complex where the fullerenes are arranged in a corrugated
sheet with five nearest neighbour fullerenes, i.e. each fullerene
has five other fullerenes at the van der Waals limit.12 Incor-
Centre for Strategic Nano-Fabrication, School of Biomedical,
Biomolecular and Chemical Sciences, University of Western Australia,
35 Stirling Hwy, Crawley, WA 6009, Australia. E-mail:
colin.raston@uwa.edu.au; Fax: (+61) 86488 1005; Tel: (+61)
86488 1572
w Contribution dedicated to Prof. Jerry Atwood on the occasion of his
65th birthday.
z CCDC reference numbers 656079 and 656080. For crystallographic
data in CIF or other electronic format see DOI: 10.1039/b718937k
Scheme 1 Synthesis of Ni(TBTAA), 1.
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same time minimizing the ability of the fullerene to be involved
in fullereneꢀ ꢀ ꢀfullerene interactions. This refers to the 1 : 2
complex with the fullerene bound by two macrocycles, with
the extended arms involved in pꢀ ꢀ ꢀp and/or CHꢀ ꢀ ꢀp interac-
tions. We note that the binding of two macrocycles to fullerene
C60 is documented, for example in the binding of p-phenyl-
and p-benzyl-calix[5]arenes,16,17 where the complexes are
dominated by pꢀ ꢀ ꢀp and C–Hꢀ ꢀ ꢀp interactions respectively
for the two macrocycles. The p-benzylcalix[5]arene complex
is particularly relevant to the present study in that the sub-
stituents are also flexible benzyl groups.17 We also report the
Hirshfeld surfaces of the fullerene complex as a probe in
mapping out the interaction between the components in the
crystals. The structure of the parent Ni-macrocycle could not
be analysed using this approach because of disorder associated
with some of the benzyl groups.
Fig. 1 Stacked arrangement adopted by saddle-shaped molecules of
Ni(TBTAA), 1 (toluene molecules shown in red).
stitial space. Stacked rows are arranged in a tetrameric motif,
consisting of antiparallel columns, involving mutual phenyl
embraces, with CHꢀ ꢀ ꢀp short contact distances at 2.656 A,
2.880 A and 2.91 A, Fig. 2.
Results and discussion
The Ni-macrocycle 1 was readily synthesized through con-
densation of o-phenylenediamine, 1,5-diphenyl-pentane-2,4-
dione and nickel(II) acetate tetrahydrate in methanol, as a
‘one pot’ condensation of equimolar amounts of each reagent.
Dissolution of 1 in toluene, followed by slow evaporation
afforded crystals suitable for X-ray crystallography.y The
asymmetric unit contains one molecule of 1, which adopts
the expected saddle shape previously observed in related
compounds,11 and one toluene molecule. The four benzyl
groups are all directed upwards on the same side of the plane
of the central core of the macrocycle, thereby forming ‘‘walls’’
to the phenyl-lined cavity. In the extended packing the macro-
cycles line up in stacked rows with Niꢀ ꢀ ꢀNi distance at 7.975 A
and a toluene molecule residing in the groove formed by four
benzyl groups, two from the individual macrocycles, Fig. 1.
The toluene molecule is held in place with intricate edge-to-
face interactions involving the phenylene and the benzyl
substituents, and CHꢀ ꢀ ꢀp interactions to the benzyl group
from neighbouring stacked molecule with Hꢀ ꢀ ꢀring centroid
short contacts distances of 2.179 and 3.152 A. Two benzyl
groups of each macrocycle are directed edge on towards the
metal centre on a neighbouring macrocycle, with Niꢀ ꢀ ꢀH–Ar
short contacts distances of 3.283 and 2.956 A.
Slowly cooling a toluene solution of fullerene C60 and 1
afforded crystals suitable for X-ray diffraction studies.y Despite
a 1 : 1 ratio of the two components in solution, the favoured
complex in the solid state is the complex with a 1 : 2 ratio, along
with five molecules of toluene per fullerene. The asymmetric
unit of the structure contains two Ni-macrocycles, one C60 and
five toluene molecules, with the C60 encapsulated between the
two phenyl-lined faces of the Ni-macrocycles, Fig. 3.
No guest is included in the benzyl-lined cavity, contrary to
previously reported structures containing a shallower methyl-
lined cavity, which does include guests.12,13 The host molecules
are not symmetrically placed over the surface of the fullerene,
with the Niꢀ ꢀ ꢀfullerene centroidꢀ ꢀ ꢀNi angle at 153.051. This
skewed arrangement is associated with slightly different closest
The overall packing in 1 consists of four columns of stacked
macrocycles running orthogonal to each other, involving
extensive CHꢀ ꢀ ꢀp interactions with toluene filling the inter-
y Crystal data and refinement details for 1ꢀtoluene: C53H46N4Ni, M =
797.65, F(000) = 1680 e, monoclinic, P21/n (no. 14), Z = 4, T =
100(2) K, a = 7.9746(16), b = 24.528(7), c = 20.765(4) A, b =
92.928(16)1, V = 4056.4(16) A3; Dc = 1.306 g cmꢂ3; mMo = 0.521
mmꢂ1; sin(y/l)max = 0.6462; N(unique) = 7367 (merged from 20 594,
Rint = 0.0408, Rsig = 0.1052), No (I 4 2s(I)) = 4113; R = 0.0721,
wR2 = 0.1934 (A, B = 0.14, 0), GOF = 1.001; |Drmax| = 1.22(9) e
A
ꢂ3. CCDC reference number 656080.
Crystal data and refinement details for 2: {C60-(1)2}ꢀ(toluene)5:
C187H116N8Ni2, M = 2592.30, F(000) = 2700 e, monoclinic, Pn (no.
7), Z = 2, T = 100(2) K, a = 13.7015(8), b = 14.3052(15), c =
32.130(4) A, b = 95.576(8)1, V = 6267.8(11) A3; Dc = 1.374 g cmꢂ3
m
;
Fig. 2 Partial packing diagram of Ni(TBTAA) along the a axis
showing edge-to-face and CHꢀ ꢀ ꢀp interactions in the tetrameric
arrangement of the columns (toluene solvent molecules removed for
clarity and dashed red lines depict CHꢀ ꢀ ꢀp interactions).
Mo = 0.368 mmꢂ1; sin(y/lmax) = 0.5396; N(unique) = 8193 (merged
from 41 816, Rint = 0.0855, Rsig = 0.1144), No (I 4 2s(I)) = 4864; R
= 0.0671, wR2 = 0.1531 (A, B = 0.15, 6.17), GOF = 1.042; |Drmax
|
= 0.88(8) e Aꢂ3. CCDC reference number 656079.
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shaped Ni-macrocycles and C60 have revealed different struc-
tural motifs relating to the fullerenes, such as corrugated
sheets,3 and linear chains.3 The results herein present the first
report of a saddle shape Ni-macrocycle forming an encapsu-
lated fullerene complex (1 : 2 complex) at the expense of a 1 : 1
complex which would allow fullereneꢀ ꢀ ꢀfullerene interactions.
Unlike the columnar tetrameric organisation of the macro-
cycle in 1, the macrocycles in the fullerene complex 2 are
arranged in layers where the macrocyles are in a back-to-back
fashion with the benzyl extended cavities directed outwards for
interplay with fullerene C60, Fig. 5. The back-to-back mode of
association of the macrocycles relates to the associated shallow
cavities with Niꢀ ꢀ ꢀNi separation at 5.085 A. Within the layer,
the back-to-back dimmers are associated with interdigitation
involving CHꢀ ꢀ ꢀp interactions from the benzyl groups to the
phenylene aromatic ring with a short contact of 2.770 A.
Hirshfeld surfaces and related graphical tools18 provide a
means of exploring the nature of the intermolecular interac-
tions within supramolecular and host–guest systems.19 Hirsh-
feld surfaces analysis was performed on complex 2 in order to
ascertain the environment of C60 in forming a complex with
Ni(TBTAA) and vice versa. Hirshfeld surfaces were mapped
with de, and are shown in Fig. 6. They clearly show the regions
Fig. 3 Projection of complex 2, {C60-(1)2}ꢀ(toluene)5, showing
host–guest interactions and confinement of the C60 within the ben-
zyl-lined concave domain of the macrocycle along with intermolecular
interactions from moieties of neighbouring macrocycles (red: dashed
line represent CHꢀ ꢀ ꢀp contacts, blue: fragment of neighbouring mole-
cules, pink: toluene solvent molecules).
contact distances between the Ni centres of the macrocycle and
the fullerene, at 3.253 and 3.085 A, respectively for the two
macrocycles. The closest contact between C60 and the macro-
cycles is a face-to-face pꢀ ꢀ ꢀp interaction of 3.094 A, measured
from a 6:6 ring junction to an arene in a phenyl-lined cavity.
There are extensive CHꢀ ꢀ ꢀp interactions from the benzyl
groups to the six-membered ring of the fullerene. Analysis of
the extended structure reveals that each fullerene is completely
isolated from neighbouring fullerenes being shrouded by two
macrocycles and toluene molecules, with the closest cen-
troidꢀ ꢀ ꢀcentroid fullerene distance being 13.701 A. This dis-
tance is the closest contact within a distorted hexagonal 2D
array of encapsulated fullerene molecules, Fig. 4. The closest
distance between fullerenes from adjacent hexagonal sheets is
17.671 A. Previous studies on related complexes of saddle-
Fig. 5 Projections of an array of macrocycle in 2 showing the back-
to-back arrangement of the core of the macrocycles, which form
centrosymmetric dimmers associated with non-classical C–Hꢀ ꢀ ꢀp
interactions (shown in red).
Fig. 4 Packing diagram projection down the a axis of complex 2
showing the C60 fullerenes dispersed within the molecular crystal with
intricate intermolecular interactions between the macrocycle moieties.
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Fig. 6 Hirshfeld surfaces for 2: {C60-(1)2}ꢀtoluene, with (a) and (b) focused on the fullerene, the two projections related by a rotation along a
vertical axis of 1801, and similar for (c) and (d) for the macrocycle.
of strong interactions on the VDW surface where the red spots
represent contacts shorter than the van der Waals limits. The
distribution of interactions is associated with pairs of distances
de and di and are accumulated in the form of fingerprints which
are depicted in Fig. 7. The majority of close contacts are
highlighted by the red area, with a limit of de + di ranging
from 2.8 to 3.0 A for the Hirshfeld surface of C60, Fig. 7(a), and
one of the two independent Ni(TBTAA) macrocycle, Fig. 7(b).
The line of isolated fullerene molecules along the a axis in
the crystal, Fig. 4, are interlocked between layers of the Ni-
macrocycle. The intermolecular interactions between the
macrocycles involve predominantly C–Hꢀ ꢀ ꢀp acceptor inter-
actions, 71.3%. For comparison, the inter-atomic contacts for
Cꢀ ꢀ ꢀC, Cꢀ ꢀ ꢀN and Cꢀ ꢀ ꢀNi are 22.8, 4.1 and 1.8%, respectively.
This feature is displayed with colour, as the yellow and red
spots on Fig. 7(a).
and the synthetic protocols described below. Crystals for
compounds 1 were prepared by slow evaporation of a toluene
solution of Ni(TBTAA) (10 mg mlꢂ1) while crystals for
compounds 2 were prepared by slow evaporation of an
equimolar toluene solution of Ni(TBTAA) and C60, with
crystals suitable for single-crystal diffraction studies forming
over a week. Crystal uniformity of each sample was checked
by determining unit cell dimensions on crystals from the same
preparation and from different preparations.
Synthesis of (5,14-dihydro-6,8,15,17-
tetrabenzyldibenzo[b,i][1,4,8,11]tetracyclodecine)nickel(II), (1)
A suspension of Ni(OAc)2ꢀ4H2O (1.48 g, 5.95 mmol) and
o-phenylenediamine (1.29 g, 11.9 mmol) in dry degassed
methanol (5 mL) was heated to reflux for 30 min, then 1,5-
diphenylpentane-2,4-dione (3.00 g, 11.9 mmol) was added in
The analysis of Ni(TBTAA) finger print plots reveals the
character and number of interactions, and are remarkably
similar for the two macrocycles in the asymmetric unit of the
complex, with only that of one of them shown in Fig. 7(b).
There are a number of yellow and red spots that can be
associated with a major component of all interactions with
Hꢀ ꢀ ꢀH at 55.1 and 54.6% for molecules A and B, respectively.
The C–Hꢀ ꢀ ꢀp interactions are 15.9% donor and 19.2% accep-
tor, molecule A, and 15.8% donor and 19.8% acceptor for
molecule B.
Experimental
Fig. 7 2-D Histograms (fingerprint plots) of the relative frequency of
points of contacts for C60 (a) and one of the two crystallographically
independent Ni(TBTAA) macrocycles (b).
All solvents and starting materials were purchased from
commercial suppliers and used without further purification
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one portion and the reaction heated at reflux for 48 h. The
resulting green suspension was cooled to RT, filtered, and the
filtercake washed with methanol until washings were colour-
less. The solid was dried under reduced pressure to give 1 (1.81
g, 2.56 mmol, 43%) as a green solid.1H NMR (CDCl3, 500
MHz): dH (ppm) 3.79 (s br, 8H), 4.75 (s br, 2H), 6.44 (dd, J =
6.1, 3.4, 4H), 6.61 (dd, J = 6.0, 3.6, 4H), 7.17 (d, J = 7.2, 8H),
7.20 (t, J = 7.2, 4H), 7.28 (t, J = 7.2, 8H). 13C (CDCl3, 75.5
MHz): dC (ppm) 39.1, 120.2, 122.7, 126.4, 128.7, 128.8, 138.7,
146.9, 157.1. FAB-MS (in CH2Cl2): m/z 704.24 [M]+; Anal.
Found: C, 78.44; H, 5.47; N, 8.01. Calc. for C46H38N4Ni: C,
78.31; H, 5.43; N, 7.94%.
cycle on the surface of the fullerene. This aside, the dispersed
fullerenes form a distorted hexagonal array with the sheets
stacked in an eclipsed fashion such that the centre of one
fullerene in one sheet lies directly over a fullerene in next sheet.
The Hirshfeld surface analysis of the fullerene complex clearly
identifies the nature of interplay of the fullerene with its
nearest neighbours and vice versa for the macrocycle. Inroads
have been made in designing a molecule for controlling the
organisation of fullerenes, in this case, isolated fullerenes. This
has implications in materials science along with potential
applications in photoelectrical devices, which is a trajectory
we are currently pursuing.
Preparation procedure of complex 2
Acknowledgements
To a solution of C60 (5 mg) in toluene (5 mL) was added 1
(5 mg) in toluene (2 mL). The mixture was heated to reflux,
filtered, then allowed to stand for 16 h which resulted in
formation of dark crystals of complex 2. The solution was
filtered and the crystals washed with hexane, yield: 4.5 mg, 45%.
We thank the Australian Research Council and the University
of Western Australia for supporting this work.
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2
dure was used, minimizing w(Fo ꢂ Fc ), with w = [s2(Fo2) +
2
(AP)2 + BP]ꢂ1, where P = (Fo2 + 2Fc )/3. Agreement factors
P
P
P
2
2 2
(R =
||Fo| ꢂ |Fc||/ |Fo|, wR2 = { [w(Fo ꢂ Fc ) ]/
P
P
[w(Fo2)2]}1/2 and GOF = { [w(Fo ꢂ Fc ) ]/(n ꢂ p)}1/2
are cited, where n is the number of reflections and p the total
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2
2 2
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Conclusion
We have prepared a new saddle-shaped macrocycle and
established its complexation with fullerene C60 in the solid
state. By altering one concave surface of the parent divergent
receptor molecule Ni(TMTAA), encapsulation of the globular
fullerene molecule is possible. The flexible benzyl arms are
effective in circumventing fullereneꢀ ꢀ ꢀfullerene interactions,
and it would seem that the associated C–Hꢀ ꢀ ꢀp interaction
with the fullerene increases the steric demands of the macro-
Solution, University of Gottingen, Gottingen, 1997; (b) G. M.
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¨
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¨
¨
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812 | New J. Chem., 2008, 32, 808–812