Hammett correlations 'beyond the molecule'

Article abstract of DOI:10.1039/a802406e

The crown ether dibenzo[24]crown-8 (DB24C8) is interpenetrated by a wide range of disubstituted dibenzylammonium cations to generate [2]pseudorotaxane complexes by virtue of, inter alia, hydrogen bonds. ¹H NMR spectroscopic measurements indicat

Full text of DOI:10.1039/a802406e

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Hammett correlations ‘beyond the molecule’1
Peter R. Ashton,a Matthew C. T. Fyfe,a Sarah K. Hickingbottom,a
J. Fraser Stoddart,*,†,a Andrew J. P. Whiteb and David J. Williams*,b
a School of Chemistry, The University of Birmingham, Edgbaston, Birmingham, UK B15 2TT
b Department of Chemistry, Imperial College, South Kensington, London, UK SW7 2AY
The crown ether dibenzo[24]crown-8 (DB24C8) is interpenetrated by a wide range of disubstituted
dibenzylammonium cations to generate [2]pseudorotaxane complexes by virtue of, inter alia, hydrogen
bonds. 1H NMR spectroscopic measurements indicate that the solution phase binding strengths of the
pseudorotaxane complexes can be controlled accurately via judicious manipulation of the substituents
attached to the dibenzylammonium cations’ aryl rings. A linear free energy relationship (LFER) has been
found to exist between the complexes’ stability constants (Kas) and the Hammett substituent constants (ó).
X-Ray crystallographic analyses of the pseudorotaxanes reveal that each of their discrete supramolecular
units display similar solid state superstructures. However, these analyses also demonstrate that the
pseudorotaxanes associate with one another, via a myriad of intersupramolecular packing motifs, to
generate a wide range of novel superarchitectures.
cyclic polyether dibenzo[24]crown-8 (DB24C8) to produce
Introduction
(Scheme 1) a 1:1 inclusion complex exhibiting a pseudorotax-
ane co-conformation§ in solution, in the ‘gas phase’ and in the
Supramolecular chemistry2 has evolved rapidly over the past
three decades so that the noncovalent syntheses3 of an exten-
sive4 range of intricate superarchitectures—held together by
means of noncovalent bonding interactions—can now be
accomplished with control and precision. Self-assembly5 has
proven to be an especially powerful tool for the construction of
these supramolecular edifices, which are often synthesised non-
covalently with a particular function in mind. However, before
these functions can be realised completely, chemists must first
of all grapple with the fundamentals of molecular recognition,
so that their basic understanding of the intermolecular bond-
ing interactions, that permit the noncovalent synthesis of
ever more complex superarchitectures, is suitably augmented.
Accordingly, in this Keynote Article, we discuss our studies on
supramolecular structure–activity relationships, in relation to
pseudorotaxane‡ formation, with a view to expediting some of
our goals in supramolecular synthesis.
1
solid state, as demonstrated by H NMR spectroscopy, mass
spectrometry and X-ray crystallography, respectively. The non-
covalent synthesis of the [DB24C8ؒ1]ϩ superstructure may be
attributed to the stabilising noncovalent bonding interactions
that arise as a consequence of (1) hydrogen bonds between the
oxygen acceptor atoms of the DB24C8 macroring and the
ϩ
hydrogen donor atoms of the cation’s NH2 and CH2 groups,
ϩ
(2) coulombic interactions involving the NH2 centres and
DB24C8’s ligating atoms, as well as (3) π–π interactions10
between the aromatic moieties of each of the pseudorotaxane’s
components. This simple recognition motif has been11
developed subsequently for the construction of numerous
molecular and supramolecular assemblages with varying
stoichiometries and co-conformations. Next, we decided to
‘fine-tune’ these systems, so that we could control, along with
their compositions and co-conformations, the binding strengths
of the pseudorotaxanes more precisely. As a result, we have
studied pseudorotaxane formation (Scheme 1) between
DB24C8 and the salts 1ؒPF6–13ؒPF6 in various solvents/phases.
The solution phase studies, presented here, demonstrate that
a linear free energy relationship12 (LFER) exists between the
stability constants (Kas) for the formation of the pseudo-
rotaxanes [DB24C8ؒ1]ϩ–[DB24C8ؒ13]ϩ and the Hammett13
substituent constants (σ).14 Moreover, X-ray crystallographic
studies reveal that, while discrete pseudorotaxanes maintain
similar co-conformations in the solid state, there are a large
number of distinct interpseudorotaxane packing motifs that
are associated with these systems.
Thirty years have passed since Pedersen published6 his
seminal paper on the discovery of the crown ethers, which
ϩ
detailed the binding of ammonium (NH4
) and alkyl-
ammonium (RNH3ϩ) ions—in a face-to-face7 manner—by
dibenzo[18]crown-6 (DB18C6). We have recently extended8
ϩ
Pedersen’s investigations so that the NH2 centres of the
sterically more encumbered secondary (R2NH2ϩ) ions can be
accommodated centrally within the cavities of macrocyclic
polyethers to generate multicomponent pseudorotaxane super-
architectures.9 By way of illustration, the dibenzylammonium
ion (1ϩ) interpenetrates the cavity of the suitably-sized macro-
† Present address: Department of Chemistry and Biochemistry,
University of California, Los Angeles, 405 Hilgard Avenue, Los
Angeles, CA 90095, USA. Tel.: ϩ(310) 206-7078. Fax: ϩ(310) 206-
1843. E-Mail: stoddart@chem.ucla.edu
Results and discussion
Synthesis
‡ Pseudorotaxanes have been defined (P. R. Ashton, D. Philp, N.
Spencer and J. F. Stoddart, J. Chem. Soc., Chem. Commun., 1991, 1677)
as the non-interlocked counterparts of rotaxanes (G. Schill, Catenanes,
Rotaxanes and Knots, Academic, New York, 1971, p. 3), in which one or
more thread-like molecules/ions interpenetrate the cavities of one or
more macrocyclic species to generate inclusion complexes. As distinct
from rotaxanes, these supramolecular complexes are free to dissociate
into their independent components as they do not possess bulky
stopper groups. Their analogy in the macroscopic world would consist
of one or more beads being threaded onto one or more strings (that
have no knots at their ends). Pseudorotaxanes are comprised of n
components, as indicated by the prefix [n].
The new disubstituted dibenzylammonium hexafluoro-
phosphate salts 2ؒPF6–9ؒPF6 and 12ؒPF6–13ؒPF6 were readily
synthesised using (Scheme 2) a simple four-step protocol, which
§ The term ‘co-conformation’ has been employed previously (M. C. T.
Fyfe, P. T. Glink, S. Menzer, J. F. Stoddart, A. J. P. White and D. J.
Williams, Angew. Chem., Int. Ed. Engl., 1997, 36, 2068) to characterise
the three-dimensional spatial arrangement of the atoms in molecular
and supramolecular entities that are comprised of two or more distinct
components.
J. Chem. Soc., Perkin Trans. 2, 1998
2117

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H
NH2
O
+
O
O
–
R
R
PF6
(1) PhMe/∆
(3) HCl
+
O
O
O
O
N
(4) NH4PF6
(2) NaBH4 or
NaBH3CN
H2
+
R
R
+
N
1·PF6–13·PF6
–
H2
PF6
O
O
R
R
[DB24C8·Salt]
2·PF6–9·PF6 & 12·PF6–13·PF6
=
Ka
[DB24C8][Salt]
Scheme 2 Synthetic procedure employed for the syntheses of the salts
2ؒPF6–9ؒPF6 and 12ؒPF6–13ؒPF6
DB24C8
O
O
O
O
O
–
PF6
+
N
H2
O
R
O
O
R
[DB24C8·1][PF6]–[DB24C8·13][PF6]
Salt
R
Salt
R
1·PF6
2·PF6
3·PF6
4·PF6
5·PF6
6·PF6
7·PF6
H
8·PF6
p-Br
p-OMe
m-OMe
p-Me
m-Me
p-Cl
9·PF6
m-Br
10·PF6
11·PF6
12·PF6
13·PF6
p-CO2H
m-CO2H
p-NO2
m-NO2
Fig. 1 Representative partial 1H NMR spectrum [400.1 MHz, CDCl3–
CD3CN (1:1), 304 K] of an equimolar solution of DB24C8 and 6ؒPF6
(both 1.0 × 10Ϫ2 ), demonstrating that uncomplexed (uc) and com-
plexed (c) species are equilibrating with one another slowly on the
NMR timescale
m-Cl
1
slowly with one another on the H NMR timescale as a con-
sequence of the large steric barrier encountered when the
cations’ relatively bulky aryl rings attempt to pass through/out
of the cavity of the DB24C8 macroring. This kinetic effect
permits the calculation of the absolute concentrations of the
(1) uncomplexed macrocycle/salt and (2) pseudorotaxane
from the known initial crown ether/salt concentrations of the
Scheme 1 Dibenzylammonium salts thread their way through the
cavity of the DB24C8 macroring to generate [2]pseudorotaxane super-
molecules that are stabilised by numerous noncovalent bonding inter-
actions. The pseudorotaxanes’ stability constants (Kas) are determined
using the relationship Ka = [DB24C8ؒSalt]/[DB24C8][Salt].
1
consisted of condensation of the appropriate amine and alde-
hyde, followed by reduction, acid treatment and counterion
exchange.
crown ether and the salts and H NMR signals’ intensities, so
that the complexes’ Kas, along with their associated free ener-
gies of complexation (Ϫ∆GЊ), may be estimated utilising the
so-called single-point15 method. The Ka values for the com-
plexes [DB24C8ؒ1][PF6]–[DB24C8ؒ13][PF6], in both CD3CN
and CDCl3–CD3CN (1:1), are displayed in Table 3, in addition
to the σ values for the substituents attached to the cations’ aro-
matic rings. Perhaps unsurprisingly, the complexes’ solution-
phase stability constants are decreased by electron-donating
substituents (negative σ values), while they are increased by
their electron-withdrawing counterparts (positive σ values).
Hammett-type plots13 were then constructed (Fig. 2) by
plotting the log [Ka(R)/Ka(H)] values—where Ka(R) and Ka(H)
Solution phase binding studies
The 1H NMR spectra [400.1 MHz, CD3CN or CDCl3–CD3CN
(1:1), 304 K] of equimolar mixtures of DB24C8 and the
dibenzylammonium salts 1ؒPF6–13ؒPF6 exhibit (Fig. 1) three
different sets of resonances (Tables 1 and 2) for (1) free DB24C8,
(2) the uncomplexed salt, together with (3) the 1:1 complex
formed between both components. This phenomenon has been
observed previously8 for the [DB24C8ؒ1]ϩ complex and
indicates that the free and complexed species are equilibrating
2118
J. Chem. Soc., Perkin Trans. 2, 1998

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Table 1 1H NMR dataa (δ values) for the pseudorotaxanes [DB24C8ؒ1][PF6]–[DB24C8ؒ13][PF6] and their uncomplexed constituents (400.1 MHz,
CD3CN, 304 K)b
Crown ether
Dibenzylammonium salt
c
c
c
Compound/complex
o-O2C6H4
α-OCH2
β-OCH2
γ-OCH2
NH2ϩCH2
C6H4
CH3
DB24C8
1ؒPF6
[DB24C8ؒ1][PF6]
2ؒPF6
[DB24C8ؒ2][PF6]
3ؒPF6
[DB24C8ؒ3][PF6]
4ؒPF6
[DB24C8ؒ4][PF6]
5ؒPF6
[DB24C8ؒ5][PF6]
6ؒPF6
[DB24C8ؒ6][PF6]
7ؒPF6
[DB24C8ؒ7][PF6]
8ؒPF6
[DB24C8ؒ8][PF6]
9ؒPF6
[DB24C8ؒ9][PF6]
10ؒPF6
[DB24C8ؒ10][PF6]
11ؒPF6
[DB24C8ؒ11][PF6]
12ؒPF6
[DB24C8ؒ12][PF6]
13ؒPF6
[DB24C8ؒ13][PF6]
6.89–6.97
—
6.76–6.88
—
6.75–6.80, 6.82–6.87
—
6.78–6.82, 6.83–6.87
—
6.75–6.81, 6.82–6.88
—
6.82–6.87, 6.88–6.92
—
6.73–6.79, 6.81–6.87
—
6.78–6.87
—
6.74–6.80, 6.83–6.89
—
6.79–6.86
—
6.69–6.81
—
6.71–6.75, 6.76–6.80
—
4.10
—
4.03
—
4.04
—
4.06
—
4.04
—
4.05
—
4.03
—
4.06
—
4.03
—
4.06
—
4.01
—
4.01
—
3.80
—
3.75
—
3.75
—
3.76
—
3.75
—
3.75
—
3.76
—
3.78
—
3.77
—
3.78
—
3.77
—
3.78
—
3.68
—
3.51
—
3.67
—
3.55
—
3.57
—
3.52
—
3.58
—
3.58
—
3.59
—
3.58
—
3.58
—
3.62
—
—
—
7.44
7.08–7.15, 7.30
6.92, 7.33
6.64, 7.20
6.78–6.94, 7.35–7.39
6.70–6.73, 6.99–7.08
7.26, 7.33
6.96, 7.20
7.22–7.35
6.99–7.16
7.41–7.53
7.14, 7.31
7.38–7.51
7.12–7.20, 7.25–7.29
7.37, 7.62
7.24, 7.30
7.34–7.47, 7.64–7.72
7.08, 7.28–7.32, 7.57, 7.60
7.56, 8.06
—
—
—
4.20
4.60
4.08
4.51
4.18
4.66
4.15
4.61
4.14
4.62
4.15
4.65
4.19
4.67
4.16
4.65
4.17
4.65
4.31
4.78
4.31
4.76
4.32
4.88
4.34
4.88
3.79
3.50
3.80
3.61
2.35
2.19
2.35
2.13
—
—
—
—
—
—
—
—
—
—
—
—
—
7.44, 7.75
7.59, 7.69, 8.07, 8.13
7.25–7.30, 7.59, 7.74–7.78, 8.05
7.72, 8.26
7.57, 7.96
7.66–7.72, 7.85, 8.35, 8.40
7.38–7.43, 7.72–7.76, 7.94–7.98, 8.28
6.69–6.77
—
6.64–6.67, 6.68–6.71
4.02
—
4.00
3.79
—
3.80
3.65
—
3.67
—
—
—
a The spectra were recorded on a Bruker AMX400 Spectrometer employing the peak observed for the residual protons in CD3CN, at δ 1.93, as the
internal reference. b The concentrations of the crown ether and dibenzylammonium salt were both 1.0 × 10Ϫ2  initially. c The descriptors α, β and γ
are defined in Fig. 1.
Table 2 1H NMR dataa (δ values) for the pseudorotaxanes [DB24C8ؒ1][PF6]–[DB24C8ؒ13][PF6] and their free constituents (400.1 MHz, CDCl3–
CD3CN (1:1), 304 K)b
Crown ether
Dibenzylammonium salt
c
c
c
Compound/complex
o-O2C6H4
α-OCH2
β-OCH2
γ-OCH2
NH2ϩCH2
C6H4
CH3
DB24C8
1ؒPF6
[DB24C8ؒ1][PF6]
2ؒPF6
[DB24C8ؒ2][PF6]
3ؒPF6
[DB24C8ؒ3][PF6]
4ؒPF6
[DB24C8ؒ4][PF6]
5ؒPF6
[DB24C8ؒ5][PF6]
6ؒPF6
[DB24C8ؒ6][PF6]
7ؒPF6
[DB24C8ؒ7][PF6]
8ؒPF6
[DB24C8ؒ8][PF6]
9ؒPF6
[DB24C8ؒ9][PF6]
10ؒPF6
[DB24C8ؒ10][PF6]
11ؒPF6
[DB24C8ؒ11][PF6]
12ؒPF6
[DB24C8ؒ12][PF6]
13ؒPF6
[DB24C8ؒ13][PF6]
6.86
—
4.09
—
4.05
—
4.05
—
4.05
—
4.04
—
4.05
—
4.03
—
4.07
—
4.02
—
4.07
—
4.04
—
4.03
—
3.81
—
3.72
—
3.74
—
3.75
—
3.73
—
3.73
—
3.75
—
3.76
—
3.75
—
3.77
—
3.76
—
3.76
—
3.70
—
3.45
—
3.68
—
3.50
—
3.50
—
3.46
—
3.54
—
3.52
—
3.53
—
3.52
—
3.55
—
3.54
—
—
—
—
—
—
4.16
4.62
4.06
4.52
4.12
4.61
4.09
4.56
4.10
4.57
4.13
4.63
4.14
4.61
4.12
4.60
4.13
4.59
4.26
4.70
4.23
4.68
4.26
4.84
4.29
4.83
7.28–7.31, 7.42
7.16–7.20
6.92, 7.33
6.66, 7.20
7.18–7.32
6.99–7.12
7.22, 7.29
6.94, 7.17
7.18–7.32
6.98–7.13
7.39, 7.41
7.14, 7.28
7.34–7.44
7.10–7.22
7.32, 7.57
7.19, 7.28
6.76–6.81, 6.82–6.87
—
6.77–6.81, 6.83–6.87
—
6.75–6.80, 6.82–6.87
—
6.74–6.79, 6.81–6.86
—
6.77–6.82, 6.84–6.89
—
6.73–6.77, 6.82–6.86
—
6.75–6.80, 6.82–6.88
—
6.72–6.78, 6.84–6.90
—
6.76–6.81, 6.82–6.87
—
6.70–6.75, 6.76–6.81
—
6.70–6.75, 6.77–6.81
—
6.66–6.71, 6.74–6.79
—
6.64–6.69, 6.73–6.78
3.79
3.51
3.79
3.60
2.35
2.19
2.35
2.13
—
—
—
—
—
—
—
—
—
—
—
—
—
7.40–7.44, 7.50–7.65
7.05–7.10, 7.21–7.26, 7.30–7.36
7.48, 8.08
7.27, 7.80
7.52, 7.64, 8.04, 8.11
7.26, 7.45, 7.80, 8.07
7.70, 8.21
7.52, 7.96
7.48, 7.64, 7.82, 8.35
7.39, 7.69, 7.95, 8.26
4.01
—
4.01
3.78
—
3.80
3.60
—
3.65
—
—
—
a The spectra were recorded on a Bruker AMX400 Spectrometer employing the peak observed for the residual protons in CD3CN, at δ 1.93, as the
internal reference. b The concentrations of the crown ether and dibenzylammonium salt were both 1.0 × 10Ϫ2  initially. c The descriptors α, β and γ
are outlined in Fig. 1.
correspond, respectively, to the stability constants for the com-
plexes [DB24C8ؒ1][PF6]–[DB24C8ؒ13][PF6] and [DB24C8ؒ1]-
[PF6]—against the σ values. For both solvent systems, a clear
straight-line correlation can be observed immediately, suggest-
ing that an LFER exists between the stability constants for the
DB24C8–dibenzylammonium salt complexes in solution and
J. Chem. Soc., Perkin Trans. 2, 1998
2119

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Table 3 Stability constants (Ka) and related free energies of complexation (Ϫ∆GЊ) for the [2]pseudorotaxane complexes formed between DB24C8
and the disubstituted dibenzylammonium salts 1ؒPF6 –13ؒPF6 a in (a) CD3CN and (b) a CDCl3–CD3CN (1:1) solvent system at 304 K
CD3CN
CDCl3–CD3CN (1:1)
Substituent
(R)
log[Ka(R)/
Ka(H)]d
Ϫ∆GЊ/
Ka(R)/
log[Ka(R)/
Ka(H)]d
Ϫ∆GЊ/
Complex
σb
Ka(R)/Ϫ1 c
kcal molϪ1 e
Ϫ1 c
kcal molϪ1 e
[DB24C8ؒ2][PF6]
[DB24C8ؒ4][PF6]
[DB24C8ؒ5][PF6]
[DB24C8ؒ1][PF6]
[DB24C8ؒ3][PF6]
[DB24C8ؒ6][PF6]
[DB24C8ؒ8][PF6]
[DB24C8ؒ11][PF6]
[DB24C8ؒ9][PF6]
[DB24C8ؒ7][PF6]
[DB24C8ؒ10][PF6]
[DB24C8ؒ13][PF6]
[DB24C8ؒ12][PF6]
p-OMe
p-Me
m-Me
H
m-OMe
p-Cl
p-Br
m-CO2H
m-Br
m-Cl
p-CO2H
m-NO2
p-NO2
Ϫ0.27
Ϫ0.14
Ϫ0.06
0
0.12
0.24
0.26
0.35
0.37
0.37
0.44
0.71
0.78
130
170
180
200
280
470
460
660
570
580
510
1350
1300
Ϫ0.19
2.94
3.10
3.14
3.20
3.40
3.72
3.70
3.92
3.83
3.84
3.77
4.35
4.33
990
960
Ϫ0.05
4.17
4.15
4.23
4.24
4.35
4.56
4.59
4.84
4.79
4.80
4.73
5.30
5.25
Ϫ0.07
Ϫ0.05
0.00
0.15
0.37
0.36
0.52
0.46
0.46
0.41
0.83
0.81
Ϫ0.06
0.00
0.00
0.09
0.23
0.26
0.41
0.40
0.40
0.36
0.77
0.73
1100
1110
1350
1890
2010
2850
2760
2810
2520
6460
5940
a The initial concentration of both components was 1 × 10Ϫ2 . b The Hammett substituent constants (σ) were acquired from O. Exner, Correlation
Analysis in Chemistry, Plenum, London, 1978. c Stability constants (Ka) were obtained as outlined in ref. 8 (percentage error р 15%). d The descrip-
tors Ka(R) and Ka(H) denote the stability constants for the formation of the complexes [DB24C8ؒ1][PF6]–[DB24C8ؒ13][PF6] and [DB24C8ؒ1][PF6],
respectively. e The free energies of complexation (Ϫ∆GЊ) were calculated from the Ka values using the equation Ϫ∆GЊ = RT ln Ka.
the electronic nature of the substituents (as defined13a,b by the
ionisation of substituted benzoic acids at 298 K, i.e. Hammett’s
original system). This correlation may be ascribed to the influ-
ence of the substituents attached to the cations’ aromatic rings,
since they undoubtedly modify the hydrogen bond donor abil-
ity of the NH2ϩ centres and benzylic CH2 groups, in addition to
changing the propensity of the substituted aromatic units to
become involved in π–π stacking interactions with the catechol
units of the DB24C8 macrocycle. The slopes of the graphs por-
trayed in Fig. 2 are equivalent to the supramolecular reaction
constants (ρ) and have values of ϩ1.03 and ϩ0.86 for the
CD3CN and CDCl3–CD3CN (1:1) solvent systems, respect-
ively. The positive values, similar to those acquired13a,b for
Hammett’s original system, obtained for ρ indicate¶ that the
cations’ positive charge effectively becomes spread out over the
macroring’s oxygen atoms upon complexation. Moreover, the
fact that Hammett-type correlations are observed|| with two dif-
ferent solvent systems implies that the cations’ aromatic sub-
stituents will alter the stability constants of the complexes
formed between DB24C8 and the salts 1ؒPF6–13ؒPF6 regardless
of the nature of the solvent present. Nevertheless, the slightly
smaller ρ value calculated for the studies carried out in the
CDCl3–CD3CN (1:1) solvent system demonstrates that the
polar effect exerted by the cations’ aromatic substituents has
less bearing on pseudorotaxane formation in solvents of
reduced polarity. This observation is hardly surprising, inas-
much as these particular pseudorotaxane supermolecules are
stabilised8 to a greater extent in CDCl3 as compared to more
polar solvents such as CD3CN. In other words, the relative
¶ This assertion can be made since the ρ value may be regarded as a
measure of the change in the charge density at the (supramolecular)
ϩ
reaction centre, which is, in this instance, the NH2 centre. A positive
ρ value indicates (P. Sykes, A Guidebook to Mechanism in Organic
Chemistry, Longman, Harlow, 6th edn., 1986, p. 368) the effective
disappearance of the positive charge at this centre.
|| The formation of all of the complexes was demonstrated additionally
in the ‘gas phase’ by liquid secondary ion (LSI) mass spectrometry. All
of the LSI mass spectra displayed strong peaks for the 1:1 complexes
Fig. 2 Hammett correlations between log [Ka(R)/Ka(H)] and σ in
(a) CD3CN and (b) CDCl3–CD3CN (1:1) at 304 K. The slopes of
the straight lines obtained correspond to the supramolecular reaction
constants (ρ)
Ϫ
with the loss of their PF6 anions, i.e. [DB24C8ؒ1]ϩ–[DB24C8ؒ13]ϩ.
However, when these mass peaks were calibrated against peaks
associated with the bis(4-tert-butylbenzyl)ammonium ion—a cation
that does not (P. R. Ashton, I. Baxter, M. C. T. Fyfe, F. M. Raymo,
N. Spencer, J. F. Stoddart, A. J. P. White and D. J. Williams, J. Am.
Chem. Soc., 1998, 120, 2297) complex with DB24C8—there appeared
to be no clear relationship between their relative intensities and the Ka
values obtained in solution. In other words, we could not find any
evidence for a Hammett correlation in the ‘gas phase’.
importance of the effect that the substituents have on the over-
all stabilisation of the pseudorotaxanes [DB24C8ؒ1][PF6]–
[DB24C8ؒ13][PF6] decreases as the solvent’s polarity decreases.
X-Ray crystallography
The solid state structures of 11 of the 12 substituted [2]pseudo-
2120
J. Chem. Soc., Perkin Trans. 2, 1998

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Table 4 Intrapseudorotaxane hydrogen bonding and π–π interactionsa
[Nϩ ؒ ؒ ؒ O]/ [H ؒ ؒ ؒ O]/ [Nϩ᎐
[H ؒ ؒ ؒ O]/ [C᎐
H ؒ ؒ ؒ O]/Њ
[A ؒ ؒ ؒ C]
interplanar/Å
[A ؒ ؒ ؒ C]/ A/C
[B ؒ ؒ ؒ D]/
Å
Å
Å
H ؒ ؒ ؒ O]/Њ [C ؒ ؒ ؒ O]/Å
Å
Å
tilt/Њ
[DB24C8ؒ1][PF6]b 2.99, O(2) 2.14
157
155
161
170
153
166
166
167
3.27, CD ؒ ؒ ؒ O(7) 2.45
3.24, CD ؒ ؒ ؒ O(7) 2.49
3.29, CD ؒ ؒ ؒ O(7) 2.42
143
134
152
3.48
3.55
3.54
3.50
3.79
3.82
3.72
3.75
11
9
6.74
6.16
5.97
5.89
3.12, O(8) 2.28
[DB24C8ؒ2][PF6]
[DB24C8ؒ3][PF6]
[DB24C8ؒ4][PF6]
3.05, O(2) 2.18
3.17, O(8) 2.28
3.11, O(2) 2.28
3.17, O(8) 2.29
3.05, O(2) 2.17
3.19, O(8) 2.31
10
7
3.28, CC ؒ ؒ ؒ O(6) 2.34
3.47, CD ؒ ؒ ؒ O(4) 2.51
3.20, CD ؒ ؒ ؒ O(7) 2.47
3.33, CC ؒ ؒ ؒ O(6) 2.45
3.47, CD ؒ ؒ ؒ O(4) 2.49
3.14, CD ؒ ؒ ؒ O(7) 2.34
3.31, CC ؒ ؒ ؒ O(6) 2.40
3.16, CD ؒ ؒ ؒ O(7) 2.43
3.32, CC ؒ ؒ ؒ O(6) 2.52
3.23, CD ؒ ؒ ؒ O(7) 2.40
3.20, CD ؒ ؒ ؒ O(7) 2.45
165
178
134
151
176
141
158
133
141
144
135
[DB24C8ؒ5][PF6]
3.10, O(2) 2.23
3.08, O(8) 2.24
164
157
3.63
3.87
13
6.04
[DB24C8ؒ6][PF6]
[DB24C8ؒ7][PF6]
[DB24C8ؒ8][PF6]
3.11, O(2) 2.28
3.15, O(8) 2.25
3.09, O(1) 2.38
2.93, O(2) 2.07
3.08, O(2) 2.24
3.04, O(3) 2.35
3.19, O(8) 2.31
3.10, O(1) 2.37
2.93, O(2) 2.09
152
179
135
157
154c
133c
165
138
156
165
158
133d
157d
151e
136e
171
169
3.48
3.55
3.47
3.74
4.18
3.73
6
13
7
5.92
6.42
6.05
[DB24C8ؒ9][PF6]
3.28, CC ؒ ؒ ؒ O(6) 2.50
3.23, CD ؒ ؒ ؒ O(7) 2.38
3.21, CD ؒ ؒ ؒ O(7) 2.37
139
147
145
3.59
3.74
3.66
4.23
3.91
3.95
15
13
13
6.37
5.87
6.02
[DB24C8ؒ10][PF6] 3.02, O(2) 2.14
3.11, O(8) 2.26
[DB24C8ؒ11][PF6] 3.01, O(1) 2.32
3.12, O(8) 2.28
3.02, O(2) 2.20
3.05, O(3) 2.34
[DB24C8ؒ13][PF6] 2.86, O(2) 1.97
3.32, CC ؒ ؒ ؒ O(6) 2.49
3.16, CD ؒ ؒ ؒ O(7) 2.52
145
157
3.24, CC ؒ ؒ ؒ O(6) 2.30
3.37, CD ؒ ؒ ؒ O(4) 2.42
167
168
3.46
3.65
5
5.96
3.21, O(8) 2.32
a All cations have been normalised to a common equivalent ‘chirality’. Atom and ring designations correspond to those given in Fig. 3. The Nϩ᎐H and
C᎐H distances have been normalised to 0.90 and 0.96 Å, respectively. b Though this complex crystallises with two independent supermolecules in the
asymmetric unit, only one of these adopts a conformation analogous to that seen in the other structures. Consequently, only this supermolecule has
been analysed here. c–e Bifurcated hydrogen bonds.
All of the [2]pseudorotaxanes are stabilised by a combination
of [Nϩ᎐H ؒ ؒ ؒ O] and [C᎐H ؒ ؒ ؒ O]17 hydrogen bonds, as well as
by π–π stacking interactions. Table 4 gives a summary of both
the hydrogen bonding and π–π stacking interactions in the 11
complexes studied, together with, for comparison purposes, the
data for the ‘unsubstituted’ complex [DB24C8ؒ1]ϩ that has
been reported previously.8 The identities of the interacting sites,
listed in this Table, are identified in Fig. 3, which illustrates the
solid state structure of the complex [DB24C8ؒ1]ϩ. There is a
high degree of consistency in the hydrogen bonding patterns,
which appear to be independent of the nature of the substituent
present on rings C and D. The geometries associated with the
π–π stacking interactions between rings A and C are also very
similar, the largest deviations being associated with those cat-
ions endowed with more sterically demanding substituents,
Fig. 3 Crystal structure of one of the two crystallographically-
e.g. in the [DB24C8ؒ9]ϩ complex. Table 5 summarises the con-
formational details of the cations in the 12 structures studied.
The conformations of the cations are also very similar, their
C᎐CH2᎐NH2ϩ᎐CH2᎐C backbones adopting a near-planar all-
anti geometry. Ring C is usually inclined fairly steeply to this
backbone, tilt angles ranging between 58 and 78Њ (average 73Њ),
whereas ring D has a shallower angle of incline in all of the
structures, except in the complex [DB24C8ؒ13]ϩ, where the
orientation is almost orthogonal.
independent [DB24C8ؒ1]ϩ pseudorotaxanes. The aromatic rings’
descriptors A–D are explained in the text.
rotaxanes described in this paper have been elucidated by single
crystal X-ray crystallography. As expected, they all possess co-
conformations that are very similar, and which are comparable
to one of the two independent co-conformations observed8 for
the 1:1 complex formed (Fig. 3) between DB24C8 and the
dibenzylammonium cation (1ϩ). In all of the crystal structures,
the macrocyclic polyether DB24C8 has an extended, approxi-
mately Ci-symmetric conformation, with its phenoxyethylene
units approximately coplanar with their associated catechol
rings, thus maintaining a conformation comparable16 to that
adopted in its uncomplexed state. The different disubstituted
dibenzylammonium cations are threaded asymmetrically
through the centre of the polyether macroring and have, in each
case, one of their aryl rings (C) oriented approximately parallel
to, and overlaying, one (A) of the catechol rings on the DB24C8
macrocycle. The cation’s second aryl ring (D) is orientated
approximately axially with respect to the DB24C8 macrocycle.
Although there are no major differences in the crystal
structures of the individual [2]pseudorotaxane units, there
are marked contrasts in their packing structures. The 1:1
pseudorotaxane complexes [DB24C8ؒ2]ϩ, [DB24C8ؒ4]ϩ and
[DB24C8ؒ6]ϩ stack to form ‘dimer pairs’, as illustrated in Fig. 4,
with the substituted aryl ring C of the cation of one [2]pseudo-
rotaxane unit being π-stacked with its Ci-related counterpart.
The mean interplanar separations between the aryl rings C of
the cations are 3.55, 3.53 and 3.50 Å, respectively, with associ-
ated centroid–centroid separations of 4.26, 3.86 and 3.82 Å.
In the [DB24C8ؒ3]ϩ complex, the aryl ring D of the cation—
J. Chem. Soc., Perkin Trans. 2, 1998
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Table 5 Comparison of the cations’ torsion angles in their DB24C8
complexesa
CC᎐Ar/Њb
Ϫ67
CC᎐N/Њ
Ϫ180
N᎐CD/Њ
Ϫ172
CD᎐Ar/Њb
Ϫ52
[DB24C8ؒ1]ϩ c
[DB24C8ؒ2]ϩ
[DB24C8ؒ3]ϩ
[DB24C8ؒ4]ϩ
[DB24C8ؒ5]ϩ
[DB24C8ؒ6]ϩ
[DB24C8ؒ7]ϩ
[DB24C8ؒ8]ϩ
[DB24C8ؒ9]ϩ
[DB24C8ؒ10]ϩ
[DB24C8ؒ11]ϩ
[DB24C8ؒ13]ϩ
Ϫ75
Ϫ58
Ϫ75
Ϫ75
Ϫ76
Ϫ78
Ϫ73
Ϫ78
Ϫ73
Ϫ71
Ϫ78
Ϫ175
Ϫ169
Ϫ172
Ϫ175
Ϫ172
Ϫ183
Ϫ170
Ϫ183
Ϫ178
Ϫ176
Ϫ167
Ϫ173
Ϫ169
Ϫ171
Ϫ176
Ϫ169
Ϫ170
Ϫ170
Ϫ171
Ϫ175
Ϫ171
Ϫ163
Ϫ40
Ϫ55
Ϫ41
Ϫ42
Ϫ40
Ϫ61
Ϫ44
Ϫ61
Ϫ49
Ϫ58
Ϫ82
a All cations have been normalised to a common equivalent ‘chirality’.
Atom designations correspond to those given in Fig. 3. b The out-of-
plane tilts of each ring are those looking down the CC᎐Ar and CD᎐Ar
bonds, respectively. c Though this complex crystallises with two
independent supermolecules in the asymmetric unit, only one of these
adopts a conformation analogous to that seen in the other structures.
Accordingly, only this supermolecule has been analysed here.
Fig. 5 View of the pseudopolyrotaxane ([DB24C8ؒ3]ϩ)n that is gener-
ated by means of aryl–aryl stacking interactions in the solid state
Fig. 4 The ‘dimer pair’ generated through π–π stacking of the
aromatic rings C of two units of the pseudorotaxane [DB24C8ؒ2]ϩ in
the solid state. Similar packing motifs are observed for the pseudo-
rotaxanes [DB24C8ؒ4]ϩ and [DB24C8ؒ6]ϩ.
which is not involved in intrapseudorotaxane stacking inter-
actions—in one pseudorotaxane supermolecule is π-stacked
with ring C of the cation of the next, via a glide plane, to
produce a pseudopolyrotaxane18 superstructure (Fig. 5). Rings
C and D of glide-related [2]pseudorotaxane supermolecules are
inclined by ca. 13Њ to each other, with centroid–centroid and
mean interplanar separations of 4.12 and 3.57 Å, respectively.
The angle subtended by the vectors linking the centroids of
rings A and C of one pseudorotaxane and D of the next is 152Њ.
The crystals of the [DB24C8ؒ5]ϩ complex contain two pseu-
dorotaxanes of only one ‘chirality’—spontaneous resolution
having occurred upon crystallisation. The 1:1 complexes pack
to give (Fig. 6) helical4e pseudopolyrotaxane chains that are
held together by edge-to-face interactions19 between rings B
and D. Ring B of one supermolecule is inclined by ca. 89Њ
to ring D of the next with a centroid–centroid separation of
5.08 Å.
Fig. 6 Portrayal of the helical pseudopolyrotaxane supramolecular
array that is produced via the noncovalent polymerisation of the
pseudorotaxane [DB24C8ؒ5]ϩ in the solid state
The crystal structure of the [DB24C8ؒ8]ϩ complex reveals
that the π-stacked ‘dimer pairs’, of the type observed for the
complexes [DB24C8ؒ2]ϩ, [DB24C8ؒ4]ϩ and [DB24C8ؒ6]ϩ,
extend via parallel π-stacking, involving rings D of adjacent
Ci-related pseudorotaxane supermolecules, to form (Fig. 7) a
π-stacked pseudopolyrotaxane supramolecular array. In this
case, the centroid–centroid and interplanar separations between
rings D of adjacent supermolecules are 3.92 and 3.56 Å,
respectively, while those between rings C are 3.86 and 3.51 Å.
Accompanying this extended aryl–aryl stacking mode is a
short20 contact (3.26 Å) between the bromine atom attached to
ring D of one pseudorotaxane and one of the polyether oxygen
atoms of an adjacent pseudorotaxane within the same chain.
In the structures of the [DB24C8ؒ7]ϩ and [DB24C8ؒ9]ϩ com-
plexes, there is ‘dimer pair’ formation analogous to that seen in,
for example, the complex [DB24C8ؒ2]ϩ (Fig. 4), but involving
(Fig. 8) ring D of Ci-related supermolecules (as opposed to ring
C)—the centroid–centroid and mean interplanar separations
2122
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Fig. 9 View of the crystal structure of the ([DB24C8ؒ10ؒMe2CO]ϩ)2
supermolecule
Fig. 7 Pseudopolyrotaxane superarchitecture ([DB24C8ؒ8]ϩ)n that is
created as a result of π–π and [Br ؒ ؒ ؒ O] interactions in the solid state
Fig. 10 Pseudopolyrotaxane ([DB24C8ؒ11]ϩ)n that is formed by
combining two hydrogen bonding motifs—viz., the threading of
dibenzylammonium ions through the DB24C8 macroring and the
carboxyl dimer—in the solid state
[2]pseudorotaxane and vice versa. The respective [O ؒ ؒ ؒ O] and
[H ؒ ؒ ؒ O] distances are 2.73 and 1.85 Å, while the [O᎐H ؒ ؒ ؒ O]
angle is 165Њ. Further propagation of this recognition motif is
halted by the intervention of an Me2CO solvent molecule,
which is hydrogen bonded to the vacant carboxy donor site
attached to ring C of each cation. The associated hydrogen
bonding geometries are 2.78, 1.88 Å and 173Њ, respectively.
Although there were small amounts of Me2CO solvent in the
crystals of [DB24C8ؒ11]ϩ, they did not interfere with the
‘expected’ hydrogen bonding pattern—supramolecular poly-
merisation, employing the conventional hydrogen bonds of
the carboxy dimer ([O ؒ ؒ ؒ O] = 2.63 Å) generates21 the hydro-
gen bonded pseudopolyrotaxane superstructure illustrated in
Fig. 10.
Fig. 8 ‘Dimer pair’ formed by means of π–π stacking interactions
between the aromatic rings D of two units of the pseudorotaxane
[DB24C8ؒ9]ϩ in the solid state. A similar packing motif is observed for
the pseudorotaxane [DB24C8ؒ7]ϩ.
are 3.94 and 3.51 Å for [DB24C8ؒ7]ϩ and 4.11 and 3.58 Å for
[DB24C8ؒ9]ϩ, respectively.
The packing motif observed21 for the [DB24C8ؒ10]ϩ complex
is identical to that observed for the [DB24CBؒ7]ϩ and
[DB24C8ؒ9]ϩ complexes, with respective centroid–centroid and
interplanar separations of 4.19 and 3.79 Å between rings D of
Ci-related [2]pseudorotaxanes. This pseudorotaxane dimer is
further stabilised (Fig. 9) via pairs of [O᎐H ؒ ؒ ؒ O] hydrogen
bonds between the carboxy moiety of one 10ϩ cation and
an oxygen atom—specifically, O(6)—in one of the polyether
linkages of the DB24C8 macroring of a symmetry-related
In the final structure examined—viz., [DB24C8ؒ13]ϩ—
spontaneous resolution occurs once again in the crystals and a
face-to-face helical4e π-stacked pseudopolyrotaxane super-
structure is formed, as portrayed in Fig. 11. Rings C and D of
adjacent screw-related cations are inclined by ca. 2Њ with respect
to one another and have centroid–centroid and interplanar sep-
arations of 3.91 and 3.60 Å, respectively. The angle subtended
J. Chem. Soc., Perkin Trans. 2, 1998
2123

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Scheme 3 Schematic diagram illustrating how the stabilities of
the DB24C8–dibenzylammonium ion-based pseudorotaxanes are
dependent on the nature of the substituent attached to the cations’
aromatic rings. Dibenzylammonium ions bearing electron donating
groups generate pseudorotaxanes with low stabilities, while those
endowed with electron withdrawing substituents form highly stable
pseudorotaxanes.
between substitution and activity has been accepted in the con-
text of the covalent bond for decades13—the work presented
here shows, along with results from other research laborator-
ies,14 that this phenomenon can be extended to include the
realm of the noncovalent bond. Conceptually, supramolecular
design is thus evolving one step further so that the strength of
complexation, i.e. the Ka value, can be ‘fine-tuned’ in a manner
of which an engineer would be proud. We envisage that this
kind of ‘supramolecular engineering’ will form the basis for the
fabrication of device-like materials23—based upon molecular
components—which will surely become a part of everyday life
in the new millennium. Nevertheless, such engineering may
require the exact positioning of individual device-like (super)-
molecules, a feat which we have not, as yet, been able to achieve
predictably, in the solid state, with the pseudorotaxanes
described in this Keynote Article. Indeed, it seems that, in
general,24 crystallisation processes are difficult to manipulate
in a predictable manner as they are kinetically-controlled.25 In
other words, the solid state may be too restrictive for formu-
lating device-like materials from molecular/supramolecular
components—the synthetic supramolecular chemist must
explore alternative ways of structurally organising and func-
tionally integrating chemical architectures (e.g. on surfaces,26 at
air–water interfaces27 or on the peripheries of dendrimers28).
Fig. 11 Helical supramolecular array ([DB24C8ؒ13]ϩ)n that is pro-
duced via the π–π-facilitated noncovalent polymerisation of the
pseudorotaxane [DB24C8ؒ13]ϩ
Ϫ
Fig. 12 Solid state association of a PF6 anion with the pseudo-
Experimental
rotaxane [DB24C8ؒ6]ϩ via [Cl ؒ ؒ ؒ F] and [C᎐H ؒ ؒ ؒ F] interactions. The
pseudorotaxane [DB24C8ؒ8]ϩ associates with a PF6 anion through a
Ϫ
Previously published procedures were used to prepare the salts
1ؒPF6,8 10ؒPF6 and 11ؒPF6,21 while the crown ether DB24C8 is
commercially available from Aldrich. Anhydrous MeOH and
THF were obtained from Aldrich in Sure/Seal containers and
were stored under dry N2. Melting points were determined
employing an Electrothermal 9200 melting point apparatus and
similar recognition motif.
by the vector linking the centres of rings A–C and C–D within
this chain is 141Њ.
Other supramolecular features worthy of note are the close
approaches involving (Fig. 12) one of the halogen atoms of the
[2]pseudorotaxanes [DB24C8ؒ6]ϩ and [DB24C8ؒ8]ϩ with one of
1
are uncorrected. Routine H NMR spectra were recorded on
either Bruker AC300 or AMX400 spectrometers (at 300.1 or
400.1 MHz, respectively) using the deuterated solvent as the
lock and the residual solvent as internal reference. Coupling
constants (J) are reported in Hz. Routine 13C NMR spectra
were recorded on the Bruker AC300 spectrometer (75.5 MHz)
employing the PENDANT pulse sequence. Liquid secondary
ion (LSI) mass spectra were obtained from a VG Zabspec mass
spectrometer equipped with a caesium ion source and utilising
an m-nitrobenzyl alcohol matrix. Microanalyses were per-
formed by the University of North London Microanalytical
Services.
the fluorine atoms of their associated PF6 anions.22 The rele-
Ϫ
vant [Cl ؒ ؒ ؒ F] and [Br ؒ ؒ ؒ F] distances are both 3.22 Å. In both
cases, there is a secondary approach of one of the hydrogen
atoms—at the 3-position on catechol ring A—and one of the
anion’s other fluorine atoms. The respective [C ؒ ؒ ؒ F]/[H ؒ ؒ ؒ F]
distances and [C–H ؒ ؒ ؒ F] angles are 3.54, 2.65 Å and 160Њ in
the pseudorotaxane [DB24C8ؒ6]ϩ, while they are 3.54, 2.66 Å
and 158Њ in its bromine-containing congener [DB24C8ؒ8]ϩ.
Conclusions
We have designed, synthesised and evaluated a supramolecular
system in which the solution phase binding strengths of pseudo-
rotaxane complexes can be controlled precisely by the judicious
General Synthetic Procedure A—bis(4-methoxybenzyl)-
ammonium hexafluorophosphate 2ؒPF6
A solution of 4-methoxybenzylamine (1.01 g, 7.4 mmol) and 4-
anisaldehyde (1.00 g, 7.4 mmol) in PhMe (150 ml) was heated
manipulation of substituents (Scheme 3).
A correlation
2124
J. Chem. Soc., Perkin Trans. 2, 1998

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Table 6 Solvent systems employed for the crystallisation of the pseudo-
under reflux with stirring for 24 h—the H2O produced was col-
lected in a Dean–Stark separator. The solution was filtered
while hot and the solvent evaporated off under reduced
pressure to furnish 4-methoxybenzylidene-4-methoxybenzyl-
amine29 (1.79 g, 95%) as a yellow oil [δH(CDCl3) 3.82 (3H, s),
3.84 (3H, s), 4.77 (2H, s), 6.95 (4H, m), 7.32 (2H, d, J 9), 7.77
(2H, d, J 9), 8.32 (1H, s)], which was dissolved in a THF–
MeOH solution (1:1, 100 ml), before being treated with NaBH4
(0.28 g, 7.4 mmol) with stirring at 20 ЊC. After an additional
2 h, a further portion of NaBH4 (0.28 g, 7.4 mmol) was added
to the reaction mixture. Thereupon, the solution was stirred for
16 h, before being treated with 6  HCl (50 ml). The solvents
were evaporated off and the residue was partitioned between
5  KOH (100 ml) and CH2Cl2 (100 ml), the aqueous phase
being extracted further with CH2Cl2 (3 × 75 ml). The combined
organic extracts were washed with H2O (75 ml), dried (MgSO4),
filtered and concentrated to afford bis(4-methoxybenzyl)-
amine29 (1.20 g, 60%) as a yellow oil [δH(CDCl3) 3.74 (4H, s),
3.79 (6H, s), 6.92 (4H, d, J 8), 7.29 (4H, d, J 8)]. An aliquot of
this amine (0.50 g, 1.95 mmol) was dissolved in CHCl3 (10 ml)
and HCl gas bubbled through the stirred reaction mixture for
30 min. The chloride salt, that had precipitated out of solution,
was collected, washed with Et2O (10 ml) and dried under high
vacuum. The solid was suspended in Me2CO (90 ml) and then
treated with an aqueous NH4PF6 solution (0.2 , 60 ml) to
effect dissolution. After stirring for 30 min, the Me2CO was
removed in vacuo so that the hexafluorophosphate salt precip-
itated out of solution. The remainder was treated with H2O (50
ml) and the residual white solid collected, before being washed
with more H2O (30 ml). Drying provided 2ؒPF6 as a white solid
(0.68 g, 87%), mp 126 ЊC with decomp. (Found: C, 47.8; H, 5.1;
N, 3.4. C16H20F6NO2P requires C, 47.7; H, 5.0; N, 3.5%);
δH(CD3CN) 3.79 (6H, s), 4.08 (4H, s), 6.92 (4H, d, J 8), 7.33
(4H, d, J 8); δC(CD3CN) 51.5, 56.0, 115.2, 123.4, 132.6, 161.5;
m/z 258 (M Ϫ PF6)ϩ.
rotaxanes [DB24C8ؒ1][PF6]–[DB24C8ؒ11][PF6] and [DB24C8ؒ13][PF6]
using the liquid diffusiona technique
Pseudorotaxane
Solvent
Precipitant
[DB24C8ؒ1][PF6]
[DB24C8ؒ2][PF6]
[DB24C8ؒ3][PF6]
[DB24C8ؒ4][PF6]
[DB24C8ؒ5][PF6]
[DB24C8ؒ6][PF6]
[DB24C8ؒ7][PF6]
[DB24C8ؒ8][PF6]
[DB24C8ؒ9][PF6]
[DB24C8ؒ10][PF6]
[DB24C8ؒ11][PF6]
[DB24C8ؒ13][PF6]
CHCl3
n-C6H14
Et2O
CH2Cl2
MeCN
Me2CO
Me2CO
Me2CO
Me2CO
(ClCH2)2
Me2CO
Me2CO
Me2CO
Me2CO
Pri2O
Et2O
Pri2O
Pri2O
Pri2O
n-C6H14
Pri2O
Pri2O
Pri2O
Et2O
a Equimolar quantities of the pseudorotaxanes’ constituents were dis-
solved in a small amount of the solvent (in which all species are totally
soluble), then the precipitant was layered on top of the resulting solu-
tion carefully. X-ray quality crystals were obtained after several days,
when the precipitant had diffused into the solution completely.
7.26 (4H, d, J 8), 7.33 (4H, d, J 8); δC(CD3CN) 21.1, 52.0, 128.3,
130.5, 131.0, 140.8; m/z 226 (M Ϫ PF6)ϩ.
Bis(3-methylbenzyl)ammonium hexafluorophosphate 5ؒPF6
Employing Procedure B, 3-methylbenzylamine (1.01 g, 8.3
mmol) was condensed with 3-tolualdehyde (1.00 g, 8.3 mmol)
to furnish 3-methylbenzylidene-3-methylbenzylamine (1.49 g,
80%) as a yellow liquid [δH(CDCl3) 2.34 (3H, s), 2.36 (3H, s),
4.84 (2H, s), 7.04–7.41 (6H, m), 7.59 (1H, d, J 8), 7.69 (1H, s),
8.36 (1H, s)], which was reduced to afford bis(3-methylbenzyl)-
amine (1.12 g, 75%) as a yellow solid [δH(CDCl3) 2.45 (6H, s),
3.84 (4H, s), 7.13–7.38 (8H, m)]. An aliquot of this amine (1.00
g, 4.4 mmol) was converted into the title compound 5ؒPF6,
which was a white solid (1.23 g, 75%), mp 206 ЊC with decomp.
(Found: C, 51.9; H, 5.3; N, 3.7. C16H20F6NP requires C, 51.8; H,
5.4; N, 3.8%); δH(CD3CN) 2.35 (6H, s), 4.14 (4H, s), 7.22–7.35
(8H, m); δC(CD3CN) 21.3, 52.4, 128.1, 130.0, 131.3, 131.4,
131.7, 140.0; m/z 226 (M Ϫ PF6)ϩ.
Bis(3-methoxybenzyl)ammonium hexafluorophosphate 3ؒPF6
Using Procedure A, 3-methoxybenzylamine (1.01 g, 7.4 mmol)
was condensed with 3-anisaldehyde (1.00 g, 7.4 mmol) to afford
3-methoxybenzylidene-3-methoxybenzylamine (1.80 g, 96%) as
a yellow oil [δH(CDCl3) 3.83 (3H, s), 3.88 (3H, s), 4.84 (2H, s),
6.86–6.91 (1H, m), 6.98–7.10 (1H, m), 7.26–7.49 (6H, m), 8.40
(1H, s)]. The imine was then reduced to afford bis(3-methoxy-
benzyl)amine (1.50 g, 83%) as a pale yellow oil [δH(CDCl3) 3.72
(4H, s), 3.79 (6H, s), 6.79 (2H, dd, J 9, 1), 6.90–6.96 (4H, m),
7.20–7.28 (2H, m)], the entirety of which was transformed into
the white solid 3ؒPF6 (1.80 g, 77%), mp 125 ЊC with decomp.
(Found: C, 47.8; H, 5.0; N, 3.4. C16H20F6NO2P requires C, 47.7;
H, 5.0; N, 3.5%); δH(CD3CN) 3.80 (6H, s), 4.18 (4H, s), 6.78–
6.94 (6H, m), 7.35–7.39 (2H, m); δC(CD3CN) 52.2, 55.9, 116.1,
116.3, 123.0, 131.1, 132.6, 160.8; m/z 258 (M Ϫ PF6)ϩ.
Bis(4-chlorobenzyl)ammonium hexafluorophosphate 6ؒPF6
Following Procedure B, 4-chlorobenzylamine (1.01 g, 7.1
mmol) was condensed with 4-chlorobenzaldehyde (1.00 g, 7.1
mmol) to obtain crude 4-chlorobenzylidene-4-chlorobenzyl-
amine31 as a yellow solid. Recrystallisation from MeOH
furnished the pure imine (1.05 g, 56%) as yellow crystals
[δH(CDCl3) 4.76 (2H, s), 7.22–7.35 (4H, m), 7.41 (2H, d, J 8),
7.72 (2H, d, J 8), 8.32 (1H, s)], which were reduced to yield
bis(4-chlorobenzyl)amine32 (0.71 g, 70%) as a colourless liquid
[δH(CDCl3) 3.75 (4H, s), 7.22–7.37 (8H, m)]. Protonation and
anion exchange provided 6ؒPF6 as a white solid (0.83 g, 79%),
mp 215 ЊC with decomp. (Found: C, 41.2; H, 3.9; N, 3.6.
C14H14Cl2F6NP requires C, 40.8; H, 3.4; N, 3.4%); δH(CD3CN)
4.15 (4H, s), 7.41–7.53 (8H, m); δC(CD3CN) 51.5, 129.7, 130.0,
132.9, 136.1; m/z 266 (M Ϫ PF6)ϩ.
General Synthetic Procedure B—bis(4-methylbenzyl)ammonium
hexafluorophosphate 4ؒPF6
The Procedure was exactly the same as Procedure A, except that
different conditions were utilised for the protonation step.
4-Methylbenzylamine (1.01 g, 8.3 mmol) was condensed with
4-tolualdehyde (1.00 g, 8.3 mmol) to yield 4-methylbenzylidene-
4-methylbenzylamine30 (1.85 g, 100%) as a pale yellow oil
[δH(CDCl3) 2.34 (3H, s), 2.41 (3H, s), 4.78 (2H, s), 7.10–7.30
(6H, m), 7.68 (2H, d, J 8), 8.36 (1H, s)]. Reduction provided
bis(4-methylbenzyl)amine30 (1.01 g, 56%) [δH(CDCl3) 2.43 (6H,
s), 3.88 (4H, s), 7.22 (4H, d, J 8), 7.33 (4H, d, J 8)], which was
boiled with 6  HCl (150 ml) for 24 h with stirring. Upon
cooling, the solvent was evaporated off under reduced pressure,
then the residual white solid was washed with H2O (20 ml),
Me2CO (20 ml) and Et2O (20 ml). Anion exchange yielded the
title compound 4ؒPF6 (1.48 g, 92%), mp 205–207 ЊC with
decomp. (Found: C, 51.7; H, 5.4; N, 3.8. C16H20F6NP requires
C, 51.8; H, 5.4; N, 3.8%); δH(CD3CN) 2.35 (6H, s), 4.15 (4H, s),
Bis(3-chlorobenzyl)ammonium hexafluorophosphate 7ؒPF6
Using Procedure B, 3-chlorobenzylamine (1.01 g, 7.1 mmol)
was condensed with 3-chlorobenzaldehyde (1.00 g, 7.1 mmol)
to furnish 3-chlorobenzylidene-3-chlorobenzylamine31 (1.78 g,
95%) as a yellow oil [δH(CDCl3) 4.79 (2H, s), 7.16–7.57 (6H, m),
7.64 (1H, d, J 9), 7.87 (1H, s), 8.33 (1H, s)], which was reduced
to afford bis(3-chlorobenzyl)amine33 (1.60 g, 90%) as a yellow
oil [δH(CDCl3) 3.76 (4H, s), 7.17–7.27 (6H, m), 7.38 (2H, s)].
Treatment with acid followed by counterion exchange gave
7ؒPF6 as a white solid (2.21 g, 89%), mp 199–200 ЊC with
decomp. (Found: C, 40.7; H, 3.5; N, 3.3. C14H14Cl2F6NP
requires C, 40.8; H, 3.4; N, 3.4%); δH(CD3CN) 4.19 (4H, s),
7.38–7.51 (8H, m); δC(CD3CN) 51.7, 129.7, 130.7, 131.1, 131.7,
133.4, 135.1; m/z 266 (M Ϫ PF6)ϩ.
J. Chem. Soc., Perkin Trans. 2, 1998
2125

View Article Online
Table 7 Crystal data, data collection and refinement parametersa
Data
[DB24C8ؒ1][PF6]
[DB24C8ؒ2][PF6]
[DB24C8ؒ3][PF6]
[DB24C8ؒ4][PF6]
[DB24C8ؒ5][PF6]
[DB24C8ؒ6][PF6]
Formula
Solvent
C38H48NO8ؒPF6
0.25 H2O
C40H52NO10ؒPF6
—
C40H52NO10ؒPF6
—
C40H52NO8ؒPF6
—
C40H52NO8ؒPF6
—
C38H46NO8Cl2ؒPF6
—
Formula weight
Colour, habit
1592.5
851.8
851.8
Clear prisms
819.8
Clear prisms
819.8
Clear prismatic
platy needles
860.6
Clear prisms
Clear platy needles Clear prisms
Crystal size/mm
Lattice type
Space group symbol,
number
0.73 × 0.33 × 0.10
Triclinic
P1, 2
0.27 × 0.20 × 0.17 1.00 × 0.90 × 0.87 0.80 × 0.77 × 0.73 0.83 × 0.60 × 0.13
1.00 × 0.93 × 0.80
Monoclinic
P21/c, 14
Monoclinic
Monoclinic
Monoclinic
Monoclinic
¯
P21/n, 14
P21/c, 14
P21/c, 14
P21, 4
Cell dimensions
a/Å
b/Å
c/Å
α/Њ
14.430(2)
15.788(4)
18.536(5)
73.30(2)
75.79(2)
84.10(2)
3939(2)
4b
10.850(2)
10.788(2)
36.572(7)
—
91.45(2)
—
4280(1)
4
1.322
15.687(1)
15.157(1)
17.980(2)
—
102.61(1)
—
4171.9(6)
4
1.356
10.644(1)
35.887(2)
10.889(1)
—
90.19(1)
—
4159.0(4)
4
1.309
10.632(1)
11.423(1)
17.793(1)
—
104.36(1)
—
2093.4(2)
2
1.301
10.674(1)
35.733(2)
10.798(2)
—
90.08(1)
—
4118(1)
4
1.388
β/Њ
γ/Њ
V/Å3
Z
Dc/g cmϪ3
1.350
F(000)
1674
1792
1792
1728
864
1792
Radiation used
Cu-Kα
1.33
Cu-Kα
1.28
Cu-Kα
1.32
Cu-Kα
1.26
Cu-Kα
1.25
Cu-Kα
2.47
µ/mmϪ1
θ range/Њ
1.5–55.0
2.4–60.0
2.9–62.1
2.5–60.0
2.6–62.0
2.5–60.0
No. of unique reflections
measured
9857
6629
—
6351
4231
—
6543
4591
—
6140
4371
—
3472
2771
—
6085
3669
—
observed, |Fo| > 4σ(|Fo|)
Absorption correction
Maximum, minimum
transmission
No. of variables
R1 (observed data)c
wR2 (observed data)d
Weighting factors a, bg
Largest difference peak,
hole/e ÅϪ3
—
—
—
—
—
—
1027
577
556
526
518
530
0.063
0.057
0.070
0.067
0.060
0.084
0.068e
0.141f
0.176f
0.166f
0.160f
0.201f
0.0005h
0.31, Ϫ0.25
0.065, 1.851
0.27, Ϫ0.20
0.098, 2.854
0.42, Ϫ0.38
0.090, 2.837
0.44, Ϫ0.34
0.112, 0.208
0.48, Ϫ0.25
0.104, 8.483
0.65, Ϫ0.56
Bis(4-bromobenzyl)ammonium hexafluorophosphate 8ؒPF6
Utilising Procedure B, 4-bromobenzylamine (1.19 g, 6.8 mmol)
was condensed with 4-bromobenzaldehyde (1.18 g, 6.8 mmol)
to give 4-bromobenzylidene-4-bromobenzylamine (2.20 g, 92%)
as a colourless oil [δH(CDCl3) 4.75 (2H, s), 7.20 (2H, d, J 8),
7.47 (2H, d, J 8), 7.58 (2H, d, J 8), 7.66 (2H, d, J 8), 8.31 (1H,
s)]. A portion of this imine (2.10 g, 6.0 mmol) was reduced to
provide bis(4-bromobenzyl)amine33 (1.85 g, 90%) as a low
melting white solid [δH(CDCl3) 3.74 (4H, s), 7.22 (4H, d, J 8),
7.45 (4H, d, J 8)]. An aliquot of this amine (1.81 g, 5.1 mmol)
was then converted, using the standard procedures, into the
white solid 8ؒPF6 (1.44 g, 57%), mp 220 ЊC with decomp.
(Found: C, 33.5; H, 3.0; N, 2.8. C14H14Br2F6NP requires C,
33.6; H, 2.8; N, 2.8%); δH(CD3CN) 4.16 (4H, s), 7.37 (4H, d,
J 8), 7.62 (4H, d, J 8); δC(CD3CN) 51.6, 124.4, 130.5, 133.0,
133.1; m/z 356 (M Ϫ PF6)ϩ.
except for the reduction step. 4-Nitrobenzylamine (0.94 g, 6.2
mmol) was condensed with 4-nitrobenzaldehyde (0.93 g, 6.2
mmol) to give 4-nitrobenzylidene-4-nitrobenzylamine34 (1.61 g,
91%) as a yellowish liquid [δH(CDCl3) 4.95 (2H, s), 7.56 (2H, d,
J 9), 7.96 (2H, d, J 8), 8.23 (2H, d, J 9), 8.32 (2H, d, J 8), 8.54
(1H, s)]. A portion of this imine (0.60 g, 2.1 mmol) was dis-
solved in anhydrous THF (13 ml) at 20 ЊC. HCl gas was bubbled
through the stirred reaction mixture, which became hot and
began to reflux. The flask was then cooled in an ice bath, and
NaBH3CN (0.10 g, 1.6 mmol), dissolved in anhydrous MeOH
(3.7 ml), was added to the reaction mixture in one portion. The
whole was then stirred at 20 ЊC for 1 h, the solvent was
removed in vacuo and the residue partitioned between 0.1 
NaOH (10 ml) and CH2Cl2 (15 ml). The aqueous phase was
extracted further with CH2Cl2 (3 × 15 ml) and then the com-
bined organic extracts were dried (K2CO3), filtered and concen-
trated to afford crude bis(4-nitrobenzyl)amine35 as a yellow
solid. The pure amine was obtained as dark yellow crystals after
recrystallisation from EtOH (0.23 g, 38%) [δH(CDCl3) 3.96 (4H,
s), 7.54 (4H, d, J 9), 8.19 (4H, d, J 9)]. Standard protonation
followed by counterion exchange furnished 12ؒPF6 as a yellow
solid (0.30 g, 87%), mp 198 ЊC with decomp. (Found: C, 38.8;
H, 3.3; N, 9.9. C14H14F6N3O4P requires C, 38.8; H, 3.3; N,
9.7%); δH(CD3CN) 4.32 (4H, s), 7.72 (4H, d, J 9), 8.26 (4H,
d, J 9); δC(CD3CN) 51.6, 124.9, 132.5, 137.8, 148.1; m/z 288
(M Ϫ PF6)ϩ.
Bis(3-bromobenzyl)ammonium hexafluorophosphate 9ؒPF6
Employing Procedure B, condensation of 3-bromobenzylamine
(0.80 g, 4.3 mmol) and 3-bromobenzaldehyde (0.80 g, 4.3
mmol) gave 3-bromobenzylidene-3-bromobenzylamine (1.50
g, 99%) as a yellow oil [δH(CDCl3) 4.74 (2H, s), 7.25–7.42 (6H,
m), 7.52 (2H, s), 8.31 (1H, s)], which was reduced to afford
bis(3-bromobenzyl)amine (1.18 g, 78%) as a yellow solid
[δH(CDCl3) 3.77 (4H, s), 7.14–7.52 (6H, m), 7.49 (2H, s)]. This
amine was then transformed into the title compound 9ؒPF6,
which was a white solid (1.21 g, 73%), mp 222 ЊC with decomp.
(Found: C, 33.3; H, 2.8; N, 2.9. C14H14Br2F6NP requires C,
33.6; H, 2.8; N, 2.8%); δH(CD3CN) 4.17 (4H, s), 7.34–7.47 (4H,
m), 7.64–7.72 (4H, m); δC(CD3CN) 51.6, 123.0, 130.0, 131.8,
132.2, 133.6, 134.0; m/z 356 (M Ϫ PF6)ϩ.
Bis(3-nitrobenzyl)ammonium hexafluorophosphate 13ؒPF6
Using Procedure C, 3-nitrobenzylamine (1.01 g, 6.7 mmol) was
condensed with 3-nitrobenzaldehyde (1.01 g, 6.7 mmol) to
afford 3-nitrobenzylidene-3-nitrobenzylamine34 (1.88 g, 98%)
as a tan solid [δH(CDCl3) 4.96 (2H, s), 7.51–7.78 (3H, m), 8.18
(2H, d, J 9), 8.22 (1H, s), 8.34 (1H, d, J 8), 8.53 (1H, s), 8.64
(1H, s)], which was reduced to produce, after recrystallisation
from EtOH, bis(3-nitrobenzyl)amine35 as yellow crystals (1.30
General Synthetic Procedure C—bis(4-nitrobenzyl)ammonium
hexafluorophosphate 12ؒPF6
The protocol used was analogous, in every way, to Procedure B
2126
J. Chem. Soc., Perkin Trans. 2, 1998

View Article Online
Table 7 (Contd.)
Data
[DB24C8ؒ7][PF6]
[DB24C8ؒ8][PF6]
[DB24C8ؒ9][PF6]
[DB24C8ؒ10][PF6] [DB24C8ؒ11][PF6] [DB24C8ؒ13][PF6]
Formula
Solvent
Formula weight
Colour, habit
C38H46NO8Cl2ؒPF6
—
860.6
Clear prisms
C38H46NO8Br2ؒPF6 C38H46NO8Br2ؒPF6 C40H48NO12ؒPF6
C40H48NO12ؒPF6
0.25 Me2CO
894.3
Clear prismatic
needles
C38H46N3O12ؒPF6
—
881.8
—
—
Me2CO
949.6
949.6
937.8
Clear blocks
Clear prisms
Clear prisms
Yellow rhombs
Crystal size/mm
Lattice type
Space group symbol,
number
1.00 × 0.83 × 0.50
Monoclinic
P21/c, 14
0.50 × 0.40 × 0.33 0.93 × 0.47 × 0.23 0.93 × 0.83 × 0.40 0.50 × 0.30 × 0.13
0.80 × 0.70 × 0.43
Orthorhombic
P212121, 19
Triclinic
Monoclinic
Triclinic
¯
Triclinic
¯
¯
P1, 2
P21/c, 14
P1, 2
P1, 2
Cell dimensions
a/Å
b/Å
c/Å
α/Њ
10.902(1)
11.052(1)
34.930(3)
—
96.29(1)
—
4183.5(6)
4
1.366
10.619(2)
10.941(2)
17.869(2)
94.29(1)
91.48(1)
90.05(1)
2069.5(5)
2
10.839(1)
11.105(1)
35.472(2)
—
96.50(1)
—
4236.6(4)
4
1.489
11.908(1)
12.336(1)
16.627(2)
79.92(1)
83.55(1)
76.17(1)
2328.8(4)
2
11.015(3)
11.022(1)
19.764(2)
78.39(1)
77.94(2)
89.81(1)
2296.6(7)
2
11.687(1)
16.972(1)
21.324(1)
—
—
—
4229.6(5)
4
1.385
1840
β/Њ
γ/Њ
V/Å3
Z
Dc/g cmϪ3
1.524
968
1.337
984
1.293
936
F(000)
1792
1936
Radiation used
Cu-Kα
2.43
Mo-Kα
2.07
Cu-Kα
3.45
Mo-Kα
0.15
Cu-Kα
1.26
Cu-Kα
1.37
µ/mmϪ1
θ range/Њ
2.6–60.0
1.9–25.0
2.5–60.0
2.0–25.0
2.3–63.0
3.3–64.0
No. of unique reflections
measured
6199
3804
Semi-empirical
0.21, 0.08
7212
4001
Semi-empirical
0.36, 0.30
6237
3772
Semi-empirical
0.24, 0.11
8157
4844
—
7400
5257
—
3922
3019
—
observed, |Fo| > 4σ(|Fo|)
Absorption correction
Maximum, minimum
transmission
No. of variables
R1 (observed data)c
wR2 (observed data)d
Weighting factors a, bg
Largest difference peak,
hole/e ÅϪ3
—
—
—
514
514
514
622
586
550
0.068
0.058
0.076
0.079
0.083
0.068
0.174f
0.112f
0.198f
0.217f
0.246f
0.186f
0.094, 2.321
0.43, Ϫ0.35
0.043, 1.744
0.70, Ϫ0.66
0.125, 2.891
0.68, Ϫ0.54
0.126, 1.334
0.50, Ϫ0.42
0.170, 0.713
0.65, Ϫ0.30
0.120, 1.169
0.33, Ϫ0.25
a Details in common: graphite monochromated radiation, ω-scans, Siemens P4 diffractometer, 293 K. b There are two crystallographically independ-
ent supermolecules in the asymmetric unit. c R1 = Σ|Fo| Ϫ |Fc |/Σ|Fo|. d wR2 = √{Σ[w(Fo2 Ϫ Fc2)2]/Σ[w(Fo )2]}. e Refinement based on F using observed
2
|
|
data. The value given is for Rw. f Refinement based on F2 using all data. g wϪ1 = σ2(Fo ) ϩ (aP)2 ϩ bP. h The value given is g in wϪ1 = σ2(F) ϩ gF2.
2
g, 69%) [δH(CDCl3) 3.92 (4H, s), 7.43–7.51 (2H, t, J 9), 7.70
(2H, d, J 9), 8.10 (2H, d, J 9), 8.21 (2H, s)]. The amine (1.23 g,
4.24 mmol) was then converted, via the standard protocol, into
the title compound, which was a pure white solid (1.77 g, 91%),
mp 221–223 ЊC (Found: C, 39.0; H, 3.1; N, 9.8. C14H14F6N3O4P
requires C, 38.8; H, 3.3; N, 9.7%); δH(CD3CN) 4.34 (4H, s),
7.66–7.72 (2H, t, J 8), 7.85 (2H, d, J 8), 8.35 (2H, d, J 8), 8.40
(2H, s); δC(CD3CN) 51.4, 125.5, 126.1, 131.4, 132.9, 137.5,
149.2; m/z 288 (M Ϫ PF6)ϩ.
meters for complexes [DB24C8ؒ1][PF6]–[DB24C8ؒ11][PF6] and
[DB24C8ؒ13][PF6]. Structure solution and refinement details
for [DB24C8ؒ1][PF6], [DB24C8ؒ10][PF6] and [DB24C8ؒ11]-
[PF6] have been published elsewhere,8a,21 and so will not be
repeated here. The rest of the structures were solved by direct
methods and were refined by full matrix least-squares based on
F2. In structures [DB24C8ؒ2][PF6]–[DB24C8ؒ6][PF6], disorder
was found in part of one of the polyether linkages. In each case,
this was resolved into two partial occupancy orientations,
the major occupancy portions of which were refined aniso-
tropically—in [DB24C8ؒ2][PF6] the minor occupancy portions
were also refined anisotropically, but in the others they were
refined isotropically. In [DB24C8ؒ2][PF6] and [DB24C8ؒ3][PF6],
the PF6Ϫ anions were found to be disordered. In each case, this
was resolved into two partial occupancy orientations, the major
occupancy portions of which were refined anisotropically—in
[DB24C8ؒ3][PF6] the minor occupancy atoms were refined iso-
tropically, whereas in [DB24C8ؒ2][PF6] they were refined aniso-
tropically. The remaining non-hydrogen atoms in all of the
structures were refined anisotropically. In each structure the
C᎐H hydrogen atoms were placed in calculated positions,
assigned isotropic thermal parameters, U(H) = 1.2Ueq(C)
[U(H) = 1.5Ueq(C᎐Me)], and allowed to ride on their parent
atoms. The N᎐H hydrogen atoms in all the structures were
located from ∆F maps and refined isotropically subject to a
distance constraint. The absolute structures of [DB24C8ؒ5]-
[PF6] and [DB24C8ؒ13][PF6] were determined by use of the
Flack parameter, which refined to values of 0.07(16) and
0.10(9) respectively. Computations were carried out using the
SHELXTL PC program system.37 The crystallographic data
(excluding structure factors) for the structures reported in Table
Determination of the stability constants (Ka values) and
supramolecular reaction constants (ñ values)
1:1 Mixtures of DB24C8 and the relevant salt (7.0 × 10Ϫ3
mmol for both components) were dissolved in the appropriate
solvent system (0.7 ml) to adjust the concentration of both
species to 1 × 10Ϫ2 . The absolute concentrations of the
free ([DB24C8] and [Salt]) and complexed ([DB24C8ؒSalt])
species in solution were obtained8 from the relative intensities
1
of the H NMR signals (400.1 MHz, 31 ЊC) of each species,
along with each component’s original (known) concentration.
The Ka values were then calculated using the expression
Ka = [DB24C8ؒSalt]/[DB24C8][Salt]. Linear regression analysis
of the log[Ka(R)/Ka(H)] and σ data furnished the best fit line
with a slope equivalent to ρ.
X-Ray crystallographic analyses
Single crystals of the pseudorotaxanes, that were suitable for
X-ray crystallographic analyses, were obtained, utilising (Table
6) the liquid diffusion method,36 from equimolar solutions of
DB24C8 and the appropriate salt. Table 7 provides a sum-
mary of the crystal data, data collection and refinement para-
J. Chem. Soc., Perkin Trans. 2, 1998
2127

View Article Online
12 For
a review dealing with the application of LFERs to
7 have been deposited with the Cambridge Crystallographic
Data Centre and are available on request. Any such request
should be accompanied by a full bibliographic citation for
this work, together with the reference codes/numbers ZELFOL
(for [DB24C8ؒ1][PF6]),8a 100/689 (for [DB24C8ؒ10][PF6] and
[DB24C8ؒ11][PF6])21 and 188/135 (for [DB24C8ؒ2][PF6]–
[DB24C8ؒ9][PF6] and [DB24C8ؒ13][PF6]). For details of the
deposition scheme, see ‘Instructions for Authors’, J. Chem.
Soc., Perkin Trans. 2, available via the RSC Web page (http://
www.rsc.org/authors).
supramolecular chemistry, see: H.-J. Schneider, Chem. Soc. Rev.,
1994, 23, 227.
13 (a) L. P. Hammett and H. L. Pfluger, J. Am. Chem. Soc., 1933,
55, 4079; (b) L. P. Hammett, J. Chem. Educ., 1966, 43, 464; (c)
C. Hansch, A. Leo and R. W. Taft, Chem. Rev., 1991, 91, 165;
(d) C. Hansch, Acc. Chem. Res., 1993, 26, 147.
14 For some other examples of Hammett correlations ‘beyond the
molecule’, i.e., involving supramolecular chemistry, see: (a)
R. Ungaro, B. El Haj and J. Smid, J. Am. Chem. Soc., 1976, 98, 5198;
(b) Y. Hashida and K. Matsui, Bull. Chem. Soc. Jpn., 1980, 53, 551;
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15 For leading references on this method, see: J. C. Adrian, Jr. and C. S.
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Acknowledgements
This research was supported in the UK by the Engineering and
Physical Sciences Research Council.
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Paper 8/02406E
Received 30th March 1998
Accepted 27th May 1998
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