Conformational mobility of 7,16-bis(4-methoxybenzyl)-1,4,10,13-tetraoxa-7, 16-diazacyclooctadecane in molecular and proton-transfer complexes: X-ray and DFT studies

Article abstract of DOI:10.1039/b902953b

For the first time the bibracchial-crown ether 7,16-bis(4-methoxybenzyl)-1, 4,10,13-tetraoxa-7,16-diazacyclooctadecane (1) and its molecular and proton-transfer complexes were isolated and characterized by X-ray single-crystal diffraction. Hydrogen bondin

Full text of DOI:10.1039/b902953b

View Article Online / Journal Homepage / Table of Contents for this issue
New Journal of Chemistry
An international journal of the chemical sciences
Volume 33 | Number 8 | August 2009 | Pages 1621–1792
www.rsc.org/njc
ISSN 1144-0546
PAPER
Marina S. Fonari et al.
Conformational mobility of 7,16-bis(4-
methoxybenzyl)-1,4,10,13-tetraoxa-7,16-
diazacyclooctadecane in molecular and
1144-0546(2009)33:8;1-W
proton-transfer complexes

PAPER
www.rsc.org/njc | New Journal of Chemistry
Conformational mobility of 7,16-bis(4-methoxybenzyl)-1,4,10,13-
tetraoxa-7,16-diazacyclooctadecane in molecular and proton-transfer
complexes: X-ray and DFT studiesw
Marina S. Fonari,*a Eduard V. Ganin,b Yurii M. Chumakov,a
Mark M. Botoshansky,c Kinga Suwinska,d Stepan S. Basoke and Yurii A. Simonova
Received (in Victoria, Australia) 12th February 2009, Accepted 22nd April 2009
First published as an Advance Article on the web 28th May 2009
DOI: 10.1039/b902953b
For the first time the bibracchial-crown ether 7,16-bis(4-methoxybenzyl)-1,4,10,13-tetraoxa-7,16-
diazacyclooctadecane (1) and its molecular and proton-transfer complexes were isolated and
characterized by X-ray single-crystal diffraction. Hydrogen bonding between the neutral molecules
is present in the binary complex 1ꢀ(H2NCS)2 (3) giving rise to a tape structure. The proton
migration from an inorganic acid to a macrocyclic molecule results in doubly protonated cations
(1-H2)2+ and (2-H2)2+ (where 2 is the parent 7,16-dibenzyl-1,4,10,13-tetraoxo-7,16-
diazacyclooctadecane) giving rise to the ionic complexes (1-H2)ꢀ[ClO4]2ꢀ2H2O (4),
(1-H2)ꢀ[NbF6]2ꢀ2H2O (5), (1-H2)ꢀ[TaF6]2ꢀ2H2O (6), (1-H2)ꢀ[BF4]2 (7) and (2-H2)ꢀ[ClO4]2ꢀ2H2O (8)
sustained by a system of charge-assisted hydrogen bonding. The macrocyclic entities in 1–8 differ
by the conformation of the crown ring and the arrangement of the pendant arms. To rationalize
the different conformations of 1 in comparison with the relative compounds based on 2, the
theoretical quantum chemical calculations on the DFT (B3LYP) level were performed.
The contribution of the methoxy group that provides the C–Hꢀ ꢀ ꢀO(OCH3) hydrogen bonding
to the overall system of intermolecular interactions has been estimated by comparison with the
complexes based on 2.
and dynamic when unbound and enveloping when a guest is
complexed.6 The historically first synthesized N,N0-dibenzyl-
1,7,10,16-tetraoxo-4,13-diazacyclooctadecane (N,N0-dibenzyl-
diaza-18-crown-6, 2)4,5,7 has been studied in detail, and it has
Introduction
The crown ether family of macrocyclic compounds has
attracted a huge amount of interest since its discovery in
1967,1,2 especially in the fields of host–guest and coordination
manifested itself as a good complexing agent for a wide range
chemistry. The metal ion complexing abilities of crown ethers
of metals, both inside the cavity acting in its neutral form and
in an outer-sphere coordination. Evans and co-workers8 have
can be improved significantly by their functionalization with
ligating side arms that enhance the cation selectivity and
transport through liquid membranes.3 The C- or N-pivot,
(La–Sm) tend to form inclusion-type compounds with a metal
indicated that the alkaline and lighter lanthanoid species
bibracchial (two arms) lariat ethers (BiBLEs)4,5 were modeled
salt incorporated into the macrocyclic cavity. It results in
on valinomycin complexation and designed to be flexible
different crown conformations: an asymmetric ‘basket-like’
shape with two phenyl substituents situated on the same
a Institute of Applied Physics, Academy of Sciences of Moldova,
side of the macrocyclic cavity as in the cases of NaIꢀ28
Academy str., 5 MD2028 Chisinau R., Moldova.
and Ln(NCS)3ꢀ2 (Ln = La, Nd, Eu),9 a T-shaped arrangement
E-mail: fonari.xray@phys.asm.md; Fax: +373 22 72 58 87;
of two phenyl substituents in the complex AgPF6ꢀ2,10
Tel: +373 22 73 81 54
b Odessa State Environmental University of Ministry of Education and
Science of Ukraine, Lvovskaya str.15, 65016 Odessa, Ukraine.
E-mail: edganin@yahoo.com
and a more symmetric conformation with benzyl arms
splayed up from the both sides of the macrocyclic ring in
c Schulich Faculty of Chemistry, Technion-Israel Institute of
Technology, Technion City, 32000 Haifa, Israel.
E-mail: botoshan@tx.technion.ac.il
catena-((m2-isothiocyanato-N,S)-(m2-thiocyanato-N,S)-bis(2)-di-
potassium).5 In contrast, protonation of the aza-crown ether
inhibits inclusion of the lanthanoid species, affording complex
d Institute of Physical Chemistry Polish Academy of Science,
metal anion species interspersed between the network of crown
dications.8 In a similar way, the recently reported metal-free
Kasprzaka, 44/52, Warsaw, Poland. E-mail: kinga@ichf.edu.pl
e A.V. Bogatsky Physico-Chemical Institute, National Academy of
Science of Ukraine, Lustdorfskaya doroga 86, 650080 Odessa,
Ukraine
w Electronic supplementary information (ESI) available: Overlapping
diagram (Fig. S1) for 1 and 2 in the relative complexes, table of torsion
angles (Table S1) along with the macrocyclic framework of 2 in the
complexes parent to those discussed herein. The coordinates for all
optimized conformers are available from the authors. CCDC reference
numbers 717101–717107. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/b902953b
12
structures of (2-H2)ꢀ[BF4]2ꢀH2O11 and (2-H2)ꢀI8 as well as
[NaꢀN,N0-dipyridyl-bis-aza-18C6]2[(H+)2N,N0-dipyridyl-bis-aza-
18C6][ClO4]ꢀ2H2O13 revealed unusual C–Hꢀ ꢀ ꢀp interactions
between the phenyl substituents and two macrocyclic methylene
protons that effectively anchor the ring into the folded
conformation and inhibit flexing, typical for macrocycles of
this type. Extended studies were devoted to the modification of
ꢁc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2009
1646 | New J. Chem., 2009, 33, 1646–1656

the pendant side arm by the introduction of the fluorescent or
redox switched moieties in the molecule.14 Lariat ethers appear
to be good candidates to analyze the cation–p interactions
with the participation of the pendant arm. The fruitful
conclusion made by Gokel’s group that the arenes should be
placed two carbons from the macrocyclic nitrogen rather than
one permitted them to prove the contribution of one and two
arms to the metal complexation.15 Special attention has been
drawn to the substituents mimicking the function of the
four amino acids possessing aromatic side chains capable of
complexing alkali metal cations, phenylalanine (benzene),
tyrosine (phenol), tryptophan (indole), as these aromatic
residues are generally regarded as p-donors, and histidine,
(imidazole) as a s-donor.
For decades, the high flexibility of crown ethers (CEs)
has impeded their conformational analysis. However,
nowadays we are witnesses of the growing number of
calculated approaches for analyzing the conformational
mobility of CEs in general and lariat-crown ethers (LCEs) in
particular. Theoretically, different conformers of CEs can be
obtained through a conformational search with molecular
dynamics (MD) or molecular mechanics (MM) techniques,
while the actual conformer(s) may be retrieved from the
Cambridge Structural Database (CSD) when their crystal
structures are known. The latter provides a good starting
point for a conformational search. For example, Reedijk
et al.16 used the computational facilities (MM3, PM3) to
estimate the conformational and electronic properties of
N,S,O-mixed donor CEs in nucleophilic coupling of their
secondary nitrogen atoms to an epoxide. The conformational
analysis of N-tosyl-substituted diaza-crown ethers theoretically
studied by empirical and semi-empirical methods using
MSI/DISCOVER97 (ESFF force field) and MOPAC (PM3)
permitted the authors to estimate the preferred conformations.17
C-pivot LCEs were the subject of the DFT calculations by the
Chinese group to estimate the side arm remote controlling
effect.18 Through the cooperation of the crown ring and the
side arm the LCEs often exhibit different cation-binding
properties when compared with their parent CEs. Because the
functional groups of side arm LCEs are key components in the
formation of metal–CE complexes and in molecular recognition,
detailed information about the conformational energies of LCE
is important for the understanding of the binding affinities of the
crownophanes with guest molecules and for the design of
artificial host molecules. Platas-Iglesias and co-workers have
carried out a systematic investigation of the electronic structure
and changes in conformations on lariat ethers in the complexes,
starting from the X-ray data using DFT facilities.19
Scheme 1 Structure of lariat crown ethers.
(2), N,N0-dimethoxydibenzyldiaza-18C6 (1),20 may enhance the
liphophilicity in two directions—the methyl group will provide
the higher solubility in lipids, while the oxygen atom of the
methoxy group will enhance the water solubility. Furthermore,
the oxygen atom of the methoxy group will provide an
additional acceptor for hydrogen bonding. Apart from the
synthesis20 no data dealing with the complexing ability of 1
are known so far.
Being involved in the host–guest chemistry based on the
CEs and crowncyclophanes,21 we, alongside others, have
studied the complexation of N,N0-dibenzyldiaza-18-crown-6
(2) with neutral molecules.22 In contrast to the well-developed
field of metal complexation by lariat ethers only single examples
of their genuine host–guest complexes are available.23 This gap
is explained by the weakness of the arising hydrogen bonding
with the LCEs bearing the bulky pendant arms. This has
provoked us to study the methoxy-substituted analog of 2,
N,N0-bis(4-methoxybenzyl)-1,7,10,16-tetraoxo-4,13-diazacyclo-
octadecane (1),20 in the host–guest interactions, and compare
this with the data available for 2. For the first time the
bibracchial-crown ether, 7,16-bis(4-methoxybenzyl)-1,4,10,13-
tetraoxa-7,16-diazacyclooctadecane (1), and its molecular
complex 1ꢀ(H2NCS)2 (3) and proton-transfer complexes
(1-H2)ꢀ[ClO4]2ꢀ2H2O (4), (1-H2)ꢀ[NbF6]2ꢀ2H2O (5), (1-H2)ꢀ
[TaF6]2ꢀ2H2O (6), (1-H2)ꢀ[BF4]2 (7) and (2-H2)ꢀ[ClO4]2ꢀ2H2O
(8) were isolated and characterized by X-ray single-crystal
diffraction. We intend to comparatively study the conformations
of these two LCEs by computational methods in order to
obtain a better insight into the conformational behavior of
these kinds of compounds, and we will also try to estimate the
preferable conformations for 1 and 2 depending on the degree
of their protonation and the surrounding environment. We
offer these results as a proof that the computational technique
has now advanced to the point where calculated geometries
and conformational energies of relatively complicated crown–
ethers complexes are in agreement with the experimental
findings (Scheme 1).
Results and discussion
The aza-crown ethers bearing the phenolic side arms are very
attractive targets and their synthesis has been reported.14b For a
wide range of metals, a strong affinity was found for the
mono- and diaza-crown ethers containing a phenolic group.
The advantage of phenol-containing LCEs might refer to the
possibility of forming covalent complexes as well as complexes
with ion-pair binding between the phenoxide oxygen and
metal cation; moreover, the selective cation coordination by
these lariats is pH-dependent. It might be expected that the
replacement of a phenoxy hydrogen by a methyl group, resulting
in the methoxy-substituted analog of N,N0-dibenzyldiaza-18C6
X-Ray crystallography
Free macrocycle
1 crystallizes in the centrosymmetric
monoclinic space group C2/c with the macrocyclic molecule
residing on an inversion center giving half a molecule in the
asymmetric unit. Molecule 1 with the numbering scheme is
shown in Fig. 1. The same numbering is used both for 1 in 3–7
and for 2 (except for the missing methoxy group) in 8.
In 1 the oxygen atoms are arranged in an endo-dentate mode
typical for most crowns, while the nitrogen atoms flip to an
exo-dentate mode to incorporate binding of the methoxybenzyl
ꢁc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2009 New J. Chem., 2009, 33, 1646–1656 | 1647

Fig. 2 Fragment of crystal packing in 1 showing the association of
the molecules in a sheet via CHꢀ ꢀ ꢀO hydrogen bond, Hꢀ ꢀ ꢀO 2.46,
Cꢀ ꢀ ꢀO 3.417(3) A, CHO angle 1691.
Fig. 1 Compound 1: view with the numbering scheme.
groups. The molecule adopts a typical elliptical shape (Fig. 1)
with two inversion-related methylene hydrogens turned inward
toward the center of the ring. The two nitrogen atoms extend
out in a trans-fashion, deviating from the plane of four oxygen
atoms at ꢂ0.884(3) A. The conformation of the asymmetric
part of the crown molecule is described by the sequence of
four consecutive bonds in trans-conformation, followed by
the gauche, gauche, trans, trans, gauche sequence (Table 1).
The comparison with the pure phases of other bibracchial
diaza-18C6 derivatives24 as well as with the 18-membered
crown ethers, 18C6, cis-transoid-cis-dicyclohexano-18C625
shows similarities in the shape of the macrocyclic cavity and
in the pattern of the torsion angles. The methoxybenzyl side
arms in 1 splay out from the crown rather than being below and
above the macrocyclic plane; the dihedral angle between the
planes of the N2O4 macrocyclic heteroatoms and the phenyl
ring of the side arm is equal to 66.35(6)1.
The crystal packing for 1 clearly demonstrates the contribution
of the methoxy group to the whole system of intermolecular
interactions (Fig. 2). The molecules via weak CHꢀ ꢀ ꢀO
hydrogen bonds are associated in tetramers giving rise to the
H-bonded sheets. Due to the C2/c crystal symmetry these
sheets interpenetrate in such a way that the methyl group of
the pendant arm is arranged at 2.75 A above (and below) the
macrocyclic cavity of the nearest symmetry-related molecule
of 1. Such an arrangement is very common for the complexes
of 18C6 with the CH3 group containing guests,26 although in
our case the cavity is closed by the cross-cavity interactions
Fig. 3 View of 3 with the partial numbering scheme. Hydrogen
bonding is shown by dotted lines.
and no CH (methyl)ꢀ ꢀ ꢀO (crown) short contacts typical for the
actual host–guest complexes were found.
Fig. 3 depicts the molecular complex 3 in a 1 : 1 ratio that
crystallizes in the centrosymmetric monoclinic space group
C2/c. Both 1 and dithiooxamide (dtox) molecules reside on
inversion centers. They are held together via a single hydrogen
bond, N2ꢀ ꢀ ꢀN1 = 3.096(3) A (Table 2). The planar dtox
molecule is inclined at an angle of 76.46(7)1 to the mean plane
of six N2O4 heteroatoms of 1, N2 atom deviating at 2.254(2) A
from the same plane.
Two dtox molecules are arranged on both sides of the
centrosymmetric macrocyclic cavity. The arising host–guest
interactions essentially influence the conformation of the
macrocyclic molecule, which in 3 has a more flat and a more
circular shape (Table 4) than in the free molecule 1, characterized
by the deviation of nitrogen atoms from the plane of four
macrocyclic oxygens equal to ꢂ0.473(3) A and transition of
two C–C bonds from trans-conformation to the preferable
Table 1 Torsion angles (1) along the macrocyclic framework in 1, 3–5, 7
Angle
1
3
4
5
7A
7B
C(6)–O(1)–C(5)–C(4)
O(1)–C(5)–C(4)–N(1)
C(5)–C(4)–N(1)–C(1)
C(4)–N(1)–C(1)–C(2)
N(1)–C(1)–C(2)–O(2)
C(1)–C(2)–O(2)–C(3)
C(2)–O(2)–C(3)–C(6)a
O(2)–C(3)–C(6)a–O(1)a
C(3)–C(6)a–O(1)a–C(5)a
C(1)–N(1)–C(7)–C(8)
C(4)–N(1)–C(7)–C(8)
ꢃ179.6(2)
ꢃ161.0(2)
168.2(2)
ꢃ81.0(2)
76.7(2)
ꢃ179.8(2)
178.0(2)
ꢃ71.4(2)
ꢃ178.2(2)
ꢃ66.7(2)
169.3(2)
ꢃ173.0(2)
ꢃ67.7(2)
171.8(2)
ꢃ55.3(3)
ꢃ53.8(3)
175.6(2)
173.2(2)
73.8(3)
ꢃ171.6(3)
53.8(3)
56.3(3)
175.6(3)
60.4(3)
ꢃ175.1(3)
ꢃ179.3(3)
63.8(3)
173.8(3)
164.6(3)
40.1(3)
ꢃ179.7(4)
58.4(5)
59.9(4)
ꢃ173.5(1)
43.7(1)
ꢃ171.7(1)
45.5(1)
ꢃ172.5(1)
ꢃ169.2(1)
ꢃ176.0(3)
86.6(1)
55.6(1)
89.8(1)
58.1(1)
53.6(4)
ꢃ178.9(4)
177.3(4)
64.0(5)
170.5(4)
ꢃ163.9(3)
70.2(4)
71.5(1)
163.3(1)
63.5(1)
177.1(1)
67.35(1)
166.31(1)
73.9(1)
158.3(1)
61.2(1)
ꢃ178.6(1)
166.9(1)
ꢃ67.4(1)
172.3(2)
ꢃ65.7(3)
60.6(3)
a
Symmetry transformations used to generate equivalent atoms: a ꢃ x + 1/2, ꢃy + 3/2, ꢃz + 1 (1); ꢃx + 1, ꢃy + 1, ꢃz (3); ꢃx + 1, ꢃy + 1,
ꢃz + 1 (4); ꢃx + 2, ꢃy + 1, ꢃz + 2 (5); ꢃx + 1, ꢃy + 1, ꢃz (7A); ꢃx + 2, ꢃ y + 2, ꢃz + 1 (7B).
ꢁc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2009
1648 | New J. Chem., 2009, 33, 1646–1656

Table 2 Hydrogen bond distances (A) and angles (1) in 3–5, 7, 8
Symmetry transformation
for acceptor
D–Hꢀ ꢀ ꢀA
d(D–H)
d(Hꢀ ꢀ ꢀA)
d(Dꢀ ꢀ ꢀA)
+(DHA)
3
N(2)–H(2N)ꢀ ꢀ ꢀN(1)
0.94(2)
2.16(3)
3.096(3)
179(2)
x, y, z
4
N(1)–H(1N)ꢀ ꢀ ꢀO(1W)
O(1W)–H(1W)ꢀ ꢀ ꢀO(4)
O(1W)–H(1W)ꢀ ꢀ ꢀO(40)
O(1W)–H(2W)ꢀ ꢀ ꢀO(2)
5
0.89(1)
1.00(4)
1.00(4)
0.83(4)
1.92(3)
1.87(4)
2.15(6)
2.17(5)
2.805(3)
2.818(6)
2.84(5)
169(2)
158(3)
125(3)
172(4)
x, y, z
x, y, z
x, y, z
1 ꢃ x, 1 ꢃ y, 1 ꢃ z
2.995(4)
N(1)–H(1N1)ꢀ ꢀ ꢀO(1W)
O(1W)–H(2W)ꢀ ꢀ ꢀO(2)
O(1W)–H(1W)ꢀ ꢀ ꢀF(6)
7
0.88
0.91
1.04
2.00
2.03
2.12
2.874(5)
2.928(5)
3.043(6)
174
170
147
x, y, z
2 ꢃ x, 1 ꢃ y, 2 ꢃ z
1 ꢃ x, 1 ꢃ y, 1 ꢃ z
N(1A)–H(1A)ꢀ ꢀ ꢀO(2A)
N(1B)–H(1B)ꢀ ꢀ ꢀO(2B)
8
0.91(2)
0.92(2)
2.35(1)
2.40(1)
2.864(1)
2.889(1)
116(1)
114(1)
x, y, z
x, y, z
N(1)–H(1N)ꢀ ꢀ ꢀO(1W)
O(1W)–H(1W)ꢀ ꢀ ꢀO(1)
O(1W)–H(2W)ꢀ ꢀ ꢀO(60)
O(1W)–H(2W)ꢀ ꢀ ꢀO(6)
0.90(3)
0.73(5)
0.89(5)
0.89(5)
1.90(3)
2.27(5)
2.01(5)
2.02(5)
2.792(3)
2.989(3)
2.90(1)
171(3)
173(5)
173(4)
167(4)
ꢃx, ꢃy, 1 ꢃ z
x, y, z
x, y, z
2.893(7)
x, y, z
Table 3 Comparison of calculated structures of neutral 1 and 2 with experimental solid-state structuresa
1
Calculated structure 1
Calculated structure 2
Experimental structure
Vacuum
Methanol
Experimental structure, XESSUJ01
Vacuum
Methanol
Nꢀ ꢀ ꢀN0
7.696
4.565
6.124
7.925
4.690
6.388
7.926
4.754
6.403
7.298
4.578
6.809
7.925
4.678
6.386
7.920
4.747
6.412
O1ꢀ ꢀ ꢀO10
O2ꢀ ꢀ ꢀO20
i-Cꢀ ꢀ ꢀi-C0
12.518
ꢃ66.65
169.31
12.727
ꢃ68.66
160.01
12.729
ꢃ70.43
159.42
12.207
ꢃ74.40
167.84
12.715
ꢃ69.21
159.06
12.719
ꢃ70.09
159.46
C1–N1–CH2–Cipso
C4–N1–CH2–Cipso
a
The coordinates for 2 were taken from CSD (ref. code XESSUJ01).
gauche-conformation (Table 1). In spite of these pronounced
changes, the macrocycle in 3 retains its extended conformation
with the twisting angle between the planes of the macrocyclic
are held together via conventional NH(CH)ꢀ ꢀ ꢀO(N)crown
hydrogen bonds.
Compounds 4–8 represent the proton-transfer complexes
built up of doubly protonated macrocyclic cations, (1-H2)2+
in 4–7 or (2-H2)2+ in 8 and inorganic anions. The N-bound
H-atoms were objectively localized in the difference Fourier
maps. All except 7 represent the crystal hydrates with the
water molecules incorporated between the charged species;
complexes 4 and 8, which differ by the LCE used, have a
similar composition and structure and will be discussed in a
sequential order, while complexes 5 and 6 are isomorphous,
and so only 5 will be discussed in detail. All compounds
crystallize in centrosymmetric space groups, and the macro-
cyclic cations (1-H2)2+ and (2-H2) exhibit a crystallographically
imposed Ci symmetry. The protonation of the macrocyclic
nitrogen atoms causes dramatic changes in the macrocyclic
shape and in the arrangement of the pendant arms in
comparison with the neutral molecules (Table 5). Complexes
N2O4 heteroatoms and phenyl ring of the side arm equal
22
to 33.78(7)1. The recently described complex 2ꢀ(H2NCS)2
,
similarly to 3, crystallizes as a 1 : 1 tape where the components
alternate. Similar to all previously reported dtox complexes
with CEs including complex 2ꢀ(H2NCS)2 no short contact
dtoxꢀ ꢀ ꢀdtox were found in 3. Similar to 1, the contribution
of the methoxy oxygen atom to the intermolecular CHꢀ ꢀ ꢀO
interactions is essential although the Hꢀ ꢀ ꢀO distance slightly
exceeds the parameter typical for the conventional hydrogen
bond. Due to these interactions, the tapes are packed in a
zipper-like mode providing their partial interpenetration and
giving rise to the layer. Following the recent investigation by
Gdaniec and co-workers,27 we can also mention here the
multiple CHꢀ ꢀ ꢀS interactions, which contribute to the stability
of the layer in 3 (Fig. 4).
A search of the CSD28 and our own efforts to expand this
family of complexes led us to conclude that the genuine
molecular host–guest complexes are rather rare for LCEs.
The most preferable guest for them is a water molecule that,
due to its small size, is easily accommodated on both sides
of the macrocyclic cavity.23 In the complexes with dtox,
4-nitrophenylsulfonamide,22 and malononitrile,23a the components
4 (Fig. 5) and 8 (Fig. 6) crystallize in triclinic space group P1,
ꢀ
with similar unit cell dimensions (Table 6). The macrocyclic
cations reside on an inversion center. The water molecule
and the [ClO4]ꢃ anion occupy general positions, with the
latter being disordered over two sites; hence, only its major
component is shown in Fig. 5 and 6. Two water molecules are
located on either side of the macrocyclic cavity and reside at
ꢁc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2009 New J. Chem., 2009, 33, 1646–1656 | 1649

Fig. 4 Fragment of crystal packing in 3 showing the association of
molecular complexes in the layer via NHꢀ ꢀ ꢀN hydrogen bond and
weak CHꢀ ꢀ ꢀO and CHꢀ ꢀ ꢀS interactions, Hꢀ ꢀ ꢀO 2.65, Cꢀ ꢀ ꢀO 3.533(3) A,
CHO angle 1591, Hꢀ ꢀ ꢀS 2.93 and 2.98, Cꢀ ꢀ ꢀS 3.551(3) and 3.684(3) A,
CHS angles 1201 and 1351.
1.805(3) A (4) and 1.678(3) A (8), respectively, above the
macrocyclic plane in a twin pseudo-perched orientation. In
both complexes, the nitrogen atom adopts an endo-orientation,
with their hydrogen atom being involved in NHꢀ ꢀ ꢀO hydrogen
bonding with the lone pair of the water molecule. In turn, the
water molecule, acting as a H-donor, provides both of its
hydrogens for the OHꢀ ꢀ ꢀO interactions with one oxygen atom
of the crown molecule and one oxygen atom of the [ClO4]ꢃ
anion (Table 2). Thus, the water molecule exhibits its traditional
mediating function between the charged species.29 A very
similar example gives N,N0-dibenzyl-4,13-diazonia-18-crown-6
tetrachloro-dioxo-uranium dihydrate (2-H2)(UCl4O2)ꢀ2H2O,8
where two water molecules bind to the inner cavity of the
crown ether in a symmetry-related mode. For both protonated
macrocycles, we observe the further tendency toward more
circular (Tables 4 and 5) and more planar shapes in comparison
with the neutral molecules; the deviation of the nitrogen atoms
from the plane through the macrocyclic oxygens is equal to
ꢂ0.606(4) A and ꢂ0.629(3) A in (1-H2)2+ and (2-H2)2+
,
respectively. The twisting angle between the N2O4 and
C8–ꢀ ꢀ ꢀ–C13 planes is equal to 62.76(9) in 4 and 77.45(8) in 8,
respectively.
The distinction in the twisting angle values is most probably
dictated by the involvement of the methoxy group in
the intermolecular interactions with the inversion-related
2
macrocyclic cations with the formation of R2 (8) planar
supramolecular synthon (Fig. 7a), while in 8 the aryl
substituents are displayed in parallel planes with an interplane
distance of 3.330 A (Fig. 7b).
Recently,30a we have succeeded in using aza-CEs, namely
aza-15C5 and aza-18C6, under synthetic conditions identical
to those described in the Experimental part of this article to
elicit the rather unusual anionic forms for Nb and Ta,
[(H2O)NbF4ONbF5]ꢃ and [(TaF5)2O]2ꢃ, respectively. How-
ever, the use of 1 yielded two isomorphous complexes 5 and 6
(Table 3), with the [NbF6]ꢃ and [TaF6]ꢃ hexafluorometallate
anions as the counter-ions being typical for the oxonium
complexes of O-containing CEs.30b In 5 and 6 both [NbF6]ꢃ
and [TaF6]ꢃ have an octahedral geometry, with the Nb–F and
Ta–F distances being in the range 1.852(4)–1.879(2) and
1.856(8)–1.885(8) A, respectively. In 5 the (1-H2)2+ cation
and the two crystallographically unique [NbF6]ꢃ anions reside
on inversion centers, while the water molecule occupies the
general position (Fig. 8). Similar to 4 and 8, the water molecule
ꢁc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2009
1650 | New J. Chem., 2009, 33, 1646–1656

Fig. 5 View of 4 with the partial numbering scheme. Only the major
position for the disordered anion is shown. Hydrogen bonding is
shown by dotted lines. The atom with the suffix A is at the symmetry
position (1 ꢃ x, 1 ꢃ y, 1 ꢃ z).
Fig. 6 View of 8 with the partial numbering scheme. Only the major
position for the disordered anion is shown. Hydrogen bonding is
shown by dotted lines. Atoms with the suffix A are at the symmetry
position (ꢃx, ꢃy, 1 ꢃ z).
mediates charged species as a single acceptor with the crown’s
NH+ group via an NH+ꢀ ꢀ ꢀO (water) hydrogen bond and
as a double donor via OH (water)ꢀ ꢀ ꢀO and OH (water)ꢀ ꢀ ꢀF
hydrogen bonds with one oxygen atom of the macrocycle and
one fluorine atom of the anion (Table 2). It is located at
1.577(5) A (1.678(3) A in 6) above the mean plane of the
N2O4 set of heteroatoms. Only one anion, [Nb(2)F6]ꢃ, makes
contact with the intermediate water molecule, while the other,
[Nb(1)F6]ꢃ, is involved in the CHꢀ ꢀ ꢀF intermolecular inter-
actions, thus being interspersed between a network of crown
molecules (Fig. 9). The trans-annular Nꢀ ꢀ ꢀN and Oꢀ ꢀ ꢀO
distances across the cavity and the sequence of torsion angles
along the macrocyclic framework in the (1-H2)2+ cation are
very close to those of 4, while the orientation of the side arms
differs as indicated by the twisting angle of 75.03(9)1 between
the planes through the N2O4 set and the phenyl ring.
The explanation for the different turn of the pendant arms
in 4 and 5 may follow from slightly different interactions
between the pendant arms of neighboring complexes, since
the lone pair of the methoxy-group oxygen atom in 5(6) is
not involved in the H-bonding self-assembling interactions,
and the pendant arms of inversion-related macrocycles are
ꢁc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2009 New J. Chem., 2009, 33, 1646–1656 | 1651

Table 6 Crystal data and structure refinement parameters for 1, 3–8
1
3
4
5
6
7
8
Formula
C28H42N2O6
C28H42N2O6ꢀ
C2H4N2S2
622.83
Monoclinic
C2/c
C28H44N2O6ꢀ
C
28H44N2O6ꢀ
C
28H44N2O6ꢀ
C
28H44N2O6ꢀ[BF4]2 C26H40N2O4ꢀ
[ClO4]2ꢀ2H2O
[ClO4]2ꢀ2H2O [NbF6]2ꢀ2H2O [TaF6]2ꢀ2H2O
Formula weight
Crystal system
Space group
502.64
Monoclinic
C2/c
739.58
Triclinic
ꢀ
P1
954.50
Triclinic
1130.58
Triclinic
ꢀ
P1
678.27
Triclinic
ꢀ
P1
679.53
Triclinic
ꢀ
P1
ꢀ
P1
a/A
b/A
c/A
a/1
21.436(4)
11.050(2)
12.701(3)
90.0
108.86(3)
90.0
2846.9(10)
4
1.173
0.082
1088
17.2050(5)
8.4590(3)
23.3120(9)
90.0
104.260(12)
90.0
3288.2(2)
4
1.258
0.208
1336
8339/2905
7.322(1)
10.757(2)
12.450(2)
91.67(2)
104.92(3)
109.41(3)
886.6(2)
1
1.385
0.256
392
9404/3296
6.8821(3)
11.3041(5)
14.0931(5)
106.232(2)
101.770(2)
106.118(2)
963.03(7)
1
1.646
0.699
484
6316/3763
6.8062(11)
11.3381(18)
14.098(2)
105.873(9)
101.336(9)
106.175(6)
960.2(3)
1
1.955
5.797
548
5444/3640
11.933(2)
12.120(2)
12.404(2)
94.820(1)
111.714(1)
100.392(1)
1616.86(5)
2
1.393
0.125
712
11815/6275
7.592(2)
10.458(2)
10.976(2)
98.11(3)
94.67(2)
108.51(3)
810.7(3)
1
b/1
g/1
V/A3
Z
r
calc/g cmꢃ3
1.392
0.268
m/mmꢃ1
F(000)
Reflections collected/ 10373/2525
unique
3162/3162
Reflections with
1661
1947
2039
2854
2021
5547
2361
[Rint = 0.031]
1.030
I 4 2s(I)(Rint
Goodness-of-fit
)
[Rint = 0.042] [Rint = 0.0655] [Rint = 0.041] [Rint = 0.0212] [Rint = 0.0371] [Rint = 0.0139]
1.055 0.953 1.106 1.068 0.924 1.046
R1, wR2 [I 4 2s(I)]
R1, wR2 (all data)
0.0456, 0.1210 0.0568, 0.1474 0.0574, 0.1599 0.0550, 0.1658 0.0546, 0.1571 0.0338, 0.0914
0.0784, 0.1331 0.0838, 0.1595 0.1009, 0.1747 0.0688, 0.1788 0.0971, 0.1870 0.0387, 0.0943
0.0585, 0.1668
0.0793, 0.1781
Fig. 8 View of 5 with the partial numbering scheme. Hydrogen
bonding is shown by dotted lines. Atoms with the suffixes A and B are
at the symmetry positions (1 ꢃ x, 1 ꢃ y, 1 ꢃ z) and (2 ꢃ x, 1 ꢃ y, 2 ꢃ z),
respectively.
Fig. 7 (a) Self-assembling of adjacent macrocycles in 4 via C–Hꢀ ꢀ ꢀO
hydrogen bonds, Hꢀ ꢀ ꢀO 2.56, Cꢀ ꢀ ꢀO 3.491(4) A, CHO angle 1791. (b)
An arrangement of adjacent macrocycles in 8 with the interplane
distance of 3.330 A. The shortest intermolecular contacts are shown by
dotted lines.
arranged in parallel planes with a partial overlap typical for
the p–p interactions (Fig. 9).
Compound 7 of the 1 : 2 ratio crystallizes in the triclinic
ꢀ
space group P1. The asymmetric unit contains two halves of
two macrocyclic cations (labeled A and B) that reside on two
different inversion centers and two [BF4]ꢃ anions (also labeled
A and B) in general positions. The conformations of the two
macrocycles (Tables 1 and 5) and the geometry of the two
[BF4]ꢃ anions are very similar, and so only the components
labeled A are shown in Fig. 10.
Of the proton-transfer complexes discussed herein, only 7
represents a water-free compound. The protonated macro-
cyclic nitrogen atoms adopt an endo-orientation that is stabilized
by the short-cut intramolecular N–Hꢀ ꢀ ꢀO distance (Table 2).
The macrocyclic cavity adopts a chair conformation with the
deviation of nitrogen atoms at ꢂ1.507(1) A (ꢂ1.511(1) A in
Fig. 9 Fragment of crystal packing in 5 showing the association of
the adjacent macrocycles. The interplane separation between the
aromatic units is equal to 3.389 A. The shortest CHꢀ ꢀ ꢀF inter-
molecular contacts Hꢀ ꢀ ꢀF 2.52–2.64, Cꢀ ꢀ ꢀF 3.308(3)–3.461(3) A,
CHF angle 1361–1541 are shown by dotted lines.
ꢁc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2009
1652 | New J. Chem., 2009, 33, 1646–1656

The reported data represent three types of complexes: the
genuine host–guest complex 3 with the conventional hydrogen
bonds as the main interactions between the components, the
proton-transfer ternary complexes 4–6, 8 with the water
molecule incorporated between the charged species, and the
binary water-free complex 7. Our own results and recent
literature data providing the structural information make it
possible to compare the conformations of 1 and 2 with the
related structure complexes and to estimate the influence
of minor changes in the macrocycle (the methoxy group
incorporated into the pendant arm) on the conformation of
the macrocycle and the overall system of interactions.
Quantum chemical calculations
Herein we have completed the X-ray data by quantum
chemical calculations on the DFT level of theory that provide
in-depth details on the conformations of 1 and 2 macrocycles,
and especially on the positions of the pendant arms. Calculations
were performed in the gas phase and in methanol to simulate
the solvation effects. Since the relevant experimental structures
exhibited crystallographically imposed inversion symmetry, all
quantum chemical calculations were also performed with that
symmetry restriction. For all structures, the optimization of
the geometry of the macrocycle in vacuum and in methanol
solution has been carried out and the results are summarized
in Tables 3–5. All the calculated conformers are very close to
the parent X-ray structures. In general, for all optimized
structures, the shape of the macrocycle (measured by the
distances of opposite facing heteroatoms) and the position of
the pendant arms measured by the distance of two ipso-C
atoms (atom C7 and its symmetry-related counterpart in
Fig. 1) are close to the experimental solid-state structures
(see Tables 3–5). The comparison of two sets of optimization
carried out in vacuum and in methanol reveals the best fit of
crystalline data with the vacuum structure for free 1, while
for the complexed macrocycle the best fit was obtained when
the solvation effects were taken into consideration, i.e. for the
optimization made in methanol. Fig. 12 summarizes the
equilibrium structures for 1 and (1-H2)2+ in 1, 3–7.
Fig. 10 Top (a) and side (b) views of complex 7A with the partial
numbering scheme. The shortest CHꢀ ꢀ ꢀF intermolecular contacts
Hꢀ ꢀ ꢀF 2.54 and 2.59, Cꢀ ꢀ ꢀF 3.485(4) and 3.130(4) A, CHF angle
1641 and 1151 are shown by dotted lines. (b) C–Hꢀ ꢀ ꢀp interaction is
shown by a dotted line.
cation B) from the plane of four oxygen atoms, the value being
maximal among all the complexes described here. The
C–Hꢀ ꢀ ꢀp interactions between two methylene hydrogens and
aromatic subunits effectively turn the phenyl groups of the side
arms above and below the macrocycle (Fig. 10b) in such a way
that the dihedral angle between the plane of the aromatic ring
and the plane of the crown oxygen atoms is 43.17(4)1
(45.46(4)1 for cation B). Both of these types of intramolecular
interactions were previously noted in the parent (2-H2)2+ in
the series of lanthanoid complexes,8 in (2-H2)I8,12 and in
(2-H2)[BF4]2ꢀH2O.11 Inspection of torsion angles (Table 1)
reveals that the macrocycle is characterized by the energetically
preferable gauche- and trans-conformations along the C–C
and C–O bonds, while N–C bonds are equally distributed
between gauche- and trans-conformations. The pendant arms
of the symmetry-related macrocycles demonstrate the same
type of self-association as in 5 (Fig. 11).
Ab initio HF/6-31+G quantum chemical calculations
have been performed for the complexation energy for
pairs of compounds 1ꢀ(H2NCS)2, (3) and 2ꢀ(H2NCS)2, and
Fig. 12 Calculated equilibrium structures for neutral 1 and (1-H2)2+
cation from 1, 3–7. All C-bound H-atoms are omitted for clarity. (a)
free 1 (vacuum); (b) neutral 1 from 3 (methanol); (c) (1-H2)2+ from 4
(methanol); (d) (1-H2)2+ from 5 (vacuum); (e) (L1H2)2+ from 7
(methanol).
Fig. 11 Fragment of crystal packing in 7. Self-assembling of adjacent
macrocycles (labeled A) via C–HꢀꢀꢀO hydrogen bond, Hꢀ ꢀ ꢀO 2.57,
Cꢀ ꢀ ꢀO 3.452(4) A, CHO angle 1601. The shortest intermolecular
contacts are shown by dotted lines.
ꢁc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2009 New J. Chem., 2009, 33, 1646–1656 | 1653

(1-H2)ꢀ[BF4]2 (7) and (2-H2)ꢀ[BF4]2ꢀH2O, where the water
molecules are not incorporated between the host and guest
molecules. The complexation energy was estimated as
transparent crystals were obtained, mp 108–110 1C. Analysis:
found: C, 57.81, H, 7.49, N, 9.06, S, 10.33%; C30H46N4O6S2:
calc.: C, 57.85, H, 7.44, N, 9.00, S, 10.30%.
DE
=
EComplex
ꢃ
EHost
ꢃ
EGuest. The complexation
energies of ꢃ724.844 kcal molꢃ1 for complex
7 and
(1-H2)ꢀ[ClO4]2ꢀ2H2O (4). To 1 (50 mg, 0.1 mmol) dissolved
in methanol (5 ml) was added 70% perchloric acid (0.7 ml)
dissolved in methanol (2 ml) at 64 1C, followed by the addition
of ethyl acetate (4 ml). The resulting clear solution was slowly
reduced in volume by evaporating the solvents at room
temperature. Colorless transparent crystals were obtained,
mp 132–134 1C. C28H48Cl2N2O16: calc.: C, 45.47; H, 6.54;
N, 3.79%. Found: C, 45.43; H, 6.57; N, 3.82%.
ꢃ762.558 kcal molꢃ1 for (2-H2)ꢀ[BF4]2ꢀH2O show a better
complexation efficiency for the proton-transfer complexes
than for the molecular complexes, ꢃ16.996 kcal molꢃ1 for
1ꢀ(H2NCS)2, (3), and ꢃ12.408 kcal molꢃ1 for 2ꢀ(H2NCS)2.
Conclusion
We have reported the synthesis, and X-ray and DFT studies
for the molecular and proton-transfer complexes based on
unexplored bibracchial-crown ether, N,N0-dimethoxydibenzyl-
1,7,10,16-tetraoxo-4,13-diazacyclooctadecane (1). The available
data demonstrate the pronounced conformational mobility of
macrocyclic cavity and distinctions in the orientation of
pendant arms. Moreover, the nature of the anion strongly
influences the twisting of the pendant group, making it orient
in opposite directions. To rationalize different conformations
of 1 in comparison with the parent N,N0-bis(4-methoxybenzyl)-
1,7,10,16-tetraoxo-4,13-diazacyclooctadecane (2), theoretical
quantum chemical calculations on the DFT (B3LYP) level
were performed. All calculated conformers are close to the
initial X-ray structures. The investigation shows that
the computational approach correlates with the structural
findings. We can conclude that we can emulate in the
calculations the weak force interactions that we observe in
the solid-state structures. The methoxy group that contributes
by the C–Hꢀ ꢀ ꢀO(OCH3) hydrogen bonding to the overall
system of intermolecular interactions imposes distinctions
both in the orientation of pendant arms in particular and in
the crystal packing as a whole.
(1-H2)ꢀ[NbF6]2ꢀ2H2O (5). To niobium oxide (V) (133 mg,
0.5 mmol) was added 45% hydrofluoric acid (10 ml). The
resulting solution was boiled till the volume of 4–5 ml was
reached. To the obtained acidic solution was added a solution
of 1 (251 mg, 0.5 mmol) in methanol (10 ml). The resulting
crystals were removed from the solution before the solvent had
completely evaporated. Colorless transparent crystals of the
complex were obtained, mp 185–187 1C (dec.). The yield is
almost quantitative. C28H48F12N2Nb2O8: calc.: C, 35.23; H,
5.07%; F, 23.89; N, 2.93%. Found: C, 35.28; H, 5.02; F, 23.86;
N, 2.96%.
(1-H2)ꢀ[TaF6]2ꢀ2H2O (6). To tantalum oxide (V) (221 mg,
0.5 mmol) was added 45% hydrofluoric acid (10 ml). The
resulting solution was boiled till the volume of 4–5 ml was
reached. To the obtained acidic solution was added a solution
of L1 (251 mg, 0.5 mmol) in methanol (10 ml). The resulting
crystals were removed from the solution before the solvent had
completely evaporated. Colorless transparent crystals of the
complex were obtained, mp 185–187 1C (dec.). The yield was
almost quantitative. C28H48F12N2O8Ta2: calc.: C, 29.75; H,
4.28; F, 20.17; N, 2.48%. Found: C, 29.71; H, 4.25; F, 20.21;
N, 2.44%.
(1-H2)ꢀ[BF4]2 (7). To L1 (50 mg, 0.1 mmol) dissolved in
methanol (5 ml) boron trifluoride etherate (0.35 ml) was
added. The resulting clear solution was slowly reduced in
volume by evaporating the solvents at room temperature.
Colorless transparent crystals were obtained by recrystallization
from a methanol–ethyl acetate mixture (1 : 2), mp 132–134 1C.
C28H44B2F8N2O6: calc.: C, 49.58; H, 6.54; F, 22.41; N, 4.13%.
Found: C, 49.54; H, 6.59; F, 22.47; N, 4.15%.
Experimental
General
Caution! Although we have experienced no difficulties with the
perchloric and hydrofluoric acids, these should be regarded as
potentially dangerous substances and handled with care.
Commercially available reagents were used as received.
Compounds 3–8 were analyzed for C, H, and N in a Perkin
Elmer 240C. The thin layer chromatographic control of the
purity of substances was performed on Silufol UV-254 plates.
All compounds were synthesized by an addition of the
corresponding ‘guest’ species directly to a stirred solution of
the LCE. Moderate heating was required to complete full
dissolution. The composition of all compounds was confirmed
by routine elemental analysis.
(2-H2)ꢀ[ClO4]2ꢀ2H2O (8). To 2 (44 mg, 0.1 mmol) dissolved
in a mixture of methanol (5 ml) and n-BuOH (0.5 ml) was
added 70% perchloric acid (0.3 ml). The resulting clear
solution was slowly reduced in volume by evaporating the
solvents at room temperature. Colorless transparent crystals
were obtained, mp 154–155 1C. C26H44Cl2N2O14: calc.: C,
45.95; H, 6.53; N, 4.12%. Found: C, 45.92; H, 6.57; N, 4.10%.
(1). The initial ligand was synthesized following the
procedure described earlier.20
X-Ray crystallographic data for 1, 3–8. The X-ray data and
the details of the refinement for 1, 3–8 are given in Table 6; the
torsion angles and H-bonding data are summarized in
Tables 1 and 2, respectively. Tables 3–5 contain the geometric
parameters for 1, 2 and their protonated forms for the
experimental solid-state and calculated structures. The
X-ray intensity data for 1, 3–5 and 8 were collected at
1ꢀ(H2NCS)2 (3). 1 (125 mg, 0.25 mmol) and ethanedithioamide
(30 mg, 0.25 mmol) were dissolved in methanol (3 ml) at 64 1C,
followed by the addition of ethyl acetate (3 ml) and n-butanol
(1 ml). The resulting clear solution was slowly reduced in
volume by evaporating the solvents at room temperature. Red
ꢁc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2009
1654 | New J. Chem., 2009, 33, 1646–1656

room temperature on a Nonius Kappa CCD diffractometer31
while for 6 and 7 they were collected on a Bruker CCD
diffractometer—both diffractometers were equipped with
graphite monochromated Mo-Ka radiation. Unit cell
parameters were obtained and refined using the whole data
set. Frames were integrated and corrected for Lorentz and
polarization effects using DENZO.32 The scaling and the
global refinement of the crystal parameters were performed
by SCALEPACK.32 For 5 and 6, the absorption correction
using SADABS was applied.33 The structure solution and
refinement proceeded similarly for all structures using the
SHELX-97 program package.34 Direct methods yielded all
non-hydrogen atoms of the asymmetric unit. These atoms
were treated anisotropically (full-matrix least squares method
on F2). In 4 the oxygen atoms of the [ClO4]ꢃ anion are
disordered over two positions with occupancies of 0.86(1)
and 0.14(1), respectively, and only the major component was
treated anisotropically. In 7 the oxygen atom of the water
molecule was refined with the partial occupancy of 0.17(2) in
an isotropic approximation. Hydrogen atoms in the water
molecule were not localized. In 8 three oxygen atoms O4, O5,
and O6 of the [ClO4]ꢃ anion are disordered over two positions
with occupancies of 0.75(1) and 0.25(1), respectively; the
major component was treated anisotropically and the minor
position was treated in an isotropic approximation. In all
structures, C-bound H atoms were placed in the calculated
positions and were treated using a riding-model approximation,
with Uiso(H) = 1.2 Ueq(C) for methylene and Uiso(H) = 1.5
Ueq(C) for methyl groups, respectively, while the N- and
O-bound H-atoms were found from differential Fourier maps
at an intermediate stage of the refinement and were treated
isotropically. All images were produced using Mercury.35
4 V. J. Gatto and G. W. Gokel, J. Am. Chem. Soc., 1984, 106, 8240.
5 K. A. Arnold, A. M. Viscariello, M. Kim, R. D. Gandour,
F. R. Fronczek and G. W. Gokel, Tetrahedron Lett., 1988, 29,
3025.
6 (a) G. W. Gokel, W. M. Leevy and M. E. Weber, Chem. Rev.,
2004, 104, 2723; (b) G. W. Gokel, Chem. Soc. Rev., 1992, 21, 39.
7 K. R. Fewings and P. C. Junk, Aust. J. Chem., 1999, 52, 1109.
8 D. J. Evans, P. C. Junk and M. K. Smith, New J. Chem., 2002, 26,
1043.
9 M. I. Saleh, A. Salhin, B. Saad and H.-K. Fun, J. Mol. Struct.,
1999, 475, 93.
10 T. W. Hambley, L. F. Lindoy, J. R. Reimers, P. Turner, G. Wei
and A. N. Widmer-Cooper, J. Chem. Soc., Dalton Trans., 2001,
614.
11 S. S. Basok, L. Croitoru, M. S. Fonari, E. V. Ganin,
V. O. Gelmboldt, J. Lipkowski and Yu. A. Simonov, Acta Crystal-
logr., Sect. C: Cryst. Struct. Commun., 2005, 61, o188.
12 A. S. Gaballa, S. M. Teleb, E. Rusanov and D. Steinborn, Inorg.
Chim. Acta, 2005, 357, 4144.
13 P. C. Junk and M. K. Smith, Inorg. Chem. Commun., 2002, 5, 1082.
14 (a) E. K. Elliott, J. Hu and G. W. Gokel, Supramol. Chem., 2007,
19, 175; (b) A. V. Bordunov, J. S. Bradshaw, X. X. Zhang,
N. K. Dalley, X. Kou and R. M. Izatt, Inorg. Chem., 1996, 35,
7229; (c) A. Awasthy, M. Bhatnagar, J. Tomar and U. Sharma,
Bioinorg. Chem. Appl., 2006, 2006, 1.
15 (a) J. Hu, L. J. Barbour, R. Ferdani and G. W. Gokel, Chem.
Commun., 2002, 1806; (b) J. Hu, L. J. Barbour and G. W. Gokel,
Chem. Commun., 2002, 1808; (c) J. Hu, L. J. Barbour, R. Ferdani
and G. W. Gokel, Chem. Commun., 2002, 1810.
16 L. G. A. van de Water, W. Buijs, W. L. Driessen and J. Reedijk,
New J. Chem., 2001, 25, 243.
17 M. Grotjahn and E. Kleinpeter, J. Mol. Model, 1999, 5, 296.
18 (a) C.-C. Su and L.-H. Lu, J. Mol. Struct., 2004, 702, 23;
(b) C.-C. Su, L.-H. Lu and T.-J. Hsieh, J. Mol. Struct., 2007,
831, 151.
19 (a) C. Platas-Iglesias, D. Esteban-Go
F. Avecilla, A. de Blas and T. Rodrı
2005, 44, 2224; (b) C. Platas-Iglesias, D. Esteban, V. Ojea,
F. Avecilla, A. de Blas and T. Rodrıguez-Blas, Inorg. Chem.,
2003, 42, 4299; (c) M. Gonzalez-Lorenzo, C. Platas-Iglesias,
F. Avecilla, S. Faulkner, S. J. A. Pope, A. de Blas and
T. Rodrıguez-Blas, Inorg. Chem., 2005, 44, 4254.
´
mez, T. Enrıquez-Perez,
´ ´
´
guez-Blas, Inorg. Chem.,
´
´
´
Computational details. Ab initio calculations were carried
out using density functional theory with the Gaussian03
package at the B3LYP/6-31+G and HF/6-31+G levels of
theory.36 To avoid SCF convergence problems, a quadratic
convergence procedure was applied during the geometry
optimizations. Full geometry optimizations of the studied
compounds were performed both in solution and in the gas
phase. The polarizable continuum model (PCM) was included
in the SCF procedure for the description of the methanol
solutions with the exception of 4. The dielectric constant was
set at 32.63. All calculations were carried out using the
restricted spin formalism (closed-shell).
20 N. G. Lukyanenko, S. S. Basok, E. Yu. Kulygina and
V. I. Vetrogon, Russ. J. Gen. Chem., 2003, 73, 1919.
21 (a) M. S. Fonari, Yu. A. Simonov, Yu. M. Chumakov, G. Bocelli,
E. V. Ganin and A. A. Yavolovskii, Supramol. Chem., 2004, 16, 23;
(b) N. G. Lukyanenko, T. I. Kirichenko, A. Yu. Lyapunov, C.
Yu. Kulygina, Yu. A. Simonov, M. S. Fonari and
M. M. Botoshansky, Tetrahedron Lett., 2004, 45, 2927;
(c) M. S. Fonari, Yu. A. Simonov, G. Bocelli,
M. M. Botoshansky and E. V. Ganin, J. Mol. Struct., 2005, 738,
85; (d) Yu. A. Simonov, M. S. Fonari, Gh. Duca, M. V. Gonta,
E. V. Ganin, A. A. Yavolovskii, M. Gdaniec and J. Lipkowski,
Tetrahedron, 2005, 61, 6596; (e) N. G. Lukyanenko,
T. I. Kirichenko, A. Yu. Lyapunov, A. V. Mazepa, Yu.
A. Simonov, M. S. Fonari and M. M. Botoshansky, Chem.–Eur.
J., 2005, 11, 262; (f) E. V. Ganin, M. S. Fonari, Yu. A. Simonov,
G. Bocelli, S. S. Basok, V. V. Tkachuk, S. A. Kotlyar and
G. L. Kamalov, J. Inclusion Phenom. Macrocyclic Chem., 2005,
52, 63; (g) W.-J. Wang, E. V. Ganin, M. S. Fonari, Yu. A. Simonov
and G. Bocelli, Org. Biomol. Chem., 2005, 3, 3054;
(h) M. S. Fonari, E. V. Ganin, S.-W. Tang, W.-J. Wang and Yu.
A. Simonov, J. Mol. Struct., 2007, 826, 89; (i) B. Moulton,
B. S. Luisi, M. S. Fonari, S. S. Basok, E. V. Ganin and V.
Ch. Kravtsov, New J. Chem., 2007, 31, 561.
Acknowledgements
The diffraction data for 1, 4 and 8 were collected at the
Schulich Faculty of Chemistry, Technion, Haifa, through the
cooperation of Prof. Menahem Kaftory, whom we would like
to acknowledge. The authors thank Prof. A. S. Dimoglo for
the computational facility.
22 M. S. Fonari, Yu. A. Simonov, L. Croitoru, S. S. Basok,
E. V. Ganin and J. Lipkowski, J. Mol. Struct., 2006, 794, 110.
23 For lariat ethers host–guest molecular complexes see: (a) K. von
Deuten, A. Knochel, J. Kopf, J. Oehler and G. Rudolph, J. Chem.
Res., 1979, 358, 4035; (b) Y. Habata and S. Akabori, J. Chem. Soc.,
Dalton Trans., 1996, 3871; (c) R. E. Gawley, S. Pinet,
C. M. Cardona, P. K. Datta, T. Ren, W. C. Guida, J. Nydick
and R. M. Leblanc, J. Am. Chem. Soc., 2002, 124, 13448;
(d) Y. Habata, T. Saeki and S. Akabori, J. Heterocycl. Chem.,
2001, 38, 585; (e) K. A. Arnold, A. M. Viscariello, M. Kim,
References
1 C. J. Pedersen, J. Am. Chem. Soc., 1967, 89, 7017.
2 C. J. Pedersen, J. Am. Chem. Soc., 1967, 89, 2495.
3 M. E. Weber, E. K. Elliott and G. W. Gokel, Org. Biomol. Chem.,
2006, 4, 83.
ꢁc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2009 New J. Chem., 2009, 33, 1646–1656 | 1655

R. D. Gandour, F. R. Fronczek and G. W. Gokel, Tetrahedron
Lett., 1988, 29, 3025.
28 F. N. Allen, Acta Crystallogr., Sect. B: Struct. Sci., 2002, 58, 380.
29 (a) Y. Levy and J. N. Onuchic, Annu. Rev. Biophys. Biomol. Struct.,
2006, 35, 389; (b) J. B. Pritchard and D. S. Miller, Physiol. Rev.,
1993, 73, 765; (c) P. L. Geissler, C. Dellago and D. Chandler,
J. Phys. Chem. B, 1999, 103, 3706.
30 (a) M. S. Fonari, V. Ch. Kravtsov, Yu. A. Simonov, S. S. Basok,
E. V. Ganin, V. O. Gelmboldt, K. Suwinska, J. Lipkowski,
O. A. Alekseeva and N. G. Furmanova, Polyhedron, 2008, 27,
2049; (b) M. S. Fonari, Yu. A. Simonov, W.-J. Wang, S.-W. Tang,
E. V. Ganin, V. O. Gelmboldt, T. S. Chernaya, O. A. Alekseeva
and N. G. Furmanova, Polyhedron, 2007, 26, 5193.
31 COLLECT, Nonius BV, Delft, The Netherlands, 1998.
32 Z. Otwinowski and W. Minor, in Methods in Enzymology Macro-
molecular Crystallography, Part A, ed. C. W. Carter and
R. M. Sweet, Academic Press, London, 1996, vol. 276, p. 307.
33 G. M. Sheldrick, SADABS, Bruker AXS Inc., Madison, WI-53719,
USA, 1997.
24 (a) S. L. De Wall, E. S. Meadows, L. J. Barbour and G. W. Gokel,
J. Am. Chem. Soc., 1999, 121, 5613; (b) L. Kh. Minacheva,
I. S. Ivanova, E. N. Pyatova, V. S. Sergienko, A. Yu. Tsivadze,
G. A. Artamkina and I. P. Beletskaya, Russ. Proc. Natl. Acad. Sci.
USSR, 2003, 389, 58; (c) L. Kh. Minacheva, I. S. Ivanova,
E. N. Pyatova, V. S. Sergienko, G. A. Artamkina, I. P. Beletskaya
and A. Yu. Tsivadze, Crystallogr. Rep., 2004, 49, 982; (d) K. Kubo,
R. Ishige, N. Kato, E. Yamamoto and T. Sakurai, Heterocycles,
1997, 45, 2365; (e) E. S. Meadows, S. L. De Wall, L. J. Barbour and
G. W. Gokel, J. Am. Chem. Soc., 2001, 123, 3092; (f) E. S. Meadows,
S. L. De Wall, L. J. Barbour, F. R. Fronczek, M.-S. Kim and
G. W. Gokel, J. Am. Chem. Soc., 2000, 122, 3325; (g) S. Suarez,
O. Mamula, R. Scopelliti, B. Donnio, D. Guillon, E. Terazzi,
C. Piguet and J.-C. G. Bunzli, New J. Chem., 2005, 29, 1323;
(h) G. Ulrich, P. Turek, R. Ziessel, A. De Cian and J. Fischer,
Chem. Commun., 1996, 2461; (i) D. Esteban, F. Avecilla, C. Platas-
Iglesias, J. Mahia, A. de Blas and T. Rodriguez-Blas, Inorg. Chem.,
2002, 41, 4337; (j) T. Gunnlaugsson, H. Q. N. Gunaratne,
M. Nieuwenhuyzen and J. P. Leonard, J. Chem. Soc., Perkin
Trans. 1, 2002, 1954; (k) G. McSkimming, J. H. R. Tucker,
H. Bouas-Laurent, J.-P. Desvergne, S. J. Coles, M. B. Hursthouse
and M. E. Light, Chem.–Eur. J., 2002, 8, 3331.
34 G. M. Sheldrick, SHELXS97 and SHELXL97, Programs for
Crystal Structure Solution and Refinement, University of Gottingen,
Germany, 1997.
¨
35 C. F. Macrae, P. R. Edgington, P. McCabe, E. Pidcock,
G. P. Shields, R. Taylor, M. Towler and J. van de Streek,
J. Appl. Crystallogr., 2006, 39, 453.
36 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, J. A. Montgomery, Jr,
T. Vreven, K. N. Kudin, J. C. Burant, J. M. Millam,
S. S. Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi,
G. Scalmani, N. Rega, G. A. Petersson, H. Nakatsuji, M. Hada,
M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida,
T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li,
J. E. Knox, H. P. Hratchian, J. B. Cross, C. Adamo, J. Jaramillo,
R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin,
R. Cammi, C. Pomelli, J. W. Ochterski, P. Y. Ayala,
K. Morokuma, G. A. Voth, P. Salvador, J. J. Dannenberg,
V. G. Zakrzewski, S. Dapprich, A. D. Daniels, M. C. Strain,
O. Farkas, D. K. Malick, D. Rabuck, K. Raghavachari,
J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul, S. Clifford,
J. Cioslowski, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz,
I. Komaromi, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-Laham,
C. Y. Peng, A. Nanayakkara, M. Challacombe, P. M. W. Gill,
B. Johnson, W. Chen, M. W. Wong, C. Gonzalez and J. A. Pople,
GAUSSIAN 03 (Revision B.01), Gaussian, Inc., Pittsburgh, PA,
2003.
25 (a) E. Maverick, P. Seiler, W. B. Schweizer and J. D. Dunitz, Acta
Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem., 1980, 36,
615; (b) V. Ch. Kravtsov, M. S. Fonari, M. J. Zaworotko and
J. Lipkowski, Acta Crystallogr., Sect. C: Cryst. Struct. Commun.,
2002, 58, o683.
26 (a) R. D. Rogers and P. D. Richards, J. Inclusion Phenom., 1987, 5,
631; (b) G. Weber, J. Mol. Struct., 1983, 98, 333; (c) G. Weber,
Acta Crystallogr., Sect. C: Cryst. Struct. Commun., 1983, 39, 896;
(d) B. L. Allwood, S. E. Fuller, P. C. Y. K. Ning, A. M. Z. Slawin,
J. F. Stoddart and D. J. Williams, J. Chem. Soc., Chem. Commun.,
1984, 1356; (e) J. A. Bandy, M. R. Truter and F. Vogtle, Acta
Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem., 1981, 37,
1568; (f) R. D. Rogers, P. D. Richards and E. J. Voss, J. Inclusion
Phenom., 1988, 6, 65; (g) D. Henschel, K. Wijaya, O. Moers,
A. Blaschette and P. G. Jones, Z. Naturforsch., B: Chem. Sci.,
2000, 55, 299; (h) A. Albert and D. Mootz, Z. Naturforsch., B:
Chem. Sci., 1998, 53, 242.
27 B. Piotrkowska, A. Wasilewska, M. Gdaniec and T. Polonski,
CrystEngComm, 2008, 10, 1421.
ꢁc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2009
1656 | New J. Chem., 2009, 33, 1646–1656