Selection rules for helicate ligand component self-assembly: Steric, pH, charge, and solvent effects

Article abstract of DOI:10.1021/ja046001z

The reaction between 1,10-phenanthroline-2,9-dicarboxaldehyde, copper(I), and certain primary amines was found to give quantitatively a dicopper double-helicate product (two of which were crystallographically characterized) by imine self-assembly around Cu¹ templates. The parameters of this reaction were investigated, and important roles were found to be played by (i) the steric bulk of the amine, (ii) the charge of the amine, (iii) the solvent used, and (iv) the pH of the solution. Water was found to allow the broadest range of structures to form, and ligand-component exchange reactions (involving the substitution of an aromatic for an aliphatic amine) were demonstrated to proceed readily in this solvent.

Full text of DOI:10.1021/ja046001z

Published on Web 11/23/2004
Selection Rules for Helicate Ligand Component
Self-Assembly: Steric, pH, Charge, and Solvent Effects
Jonathan R. Nitschke,*,† David Schultz,† Ge´rald Bernardinelli,‡ and David Ge´rard†
Contribution from the Department of Organic Chemistry, UniVersity of GeneVa,
30 Quai Ernest Ansermet, 1211 Gene`Ve 4, Switzerland, and Laboratory of X-Ray
Crystallography, UniVersity of GeneVa, 24 Quai Ernest Ansermet, 1211 Gene`Ve 4, Switzerland
Received July 5, 2004; E-mail: Jonathan.Nitschke@chiorg.unige.ch
Abstract: The reaction between 1,10-phenanthroline-2,9-dicarboxaldehyde, copper(I), and certain primary
amines was found to give quantitatively a dicopper double-helicate product (two of which were
crystallographically characterized) by imine self-assembly around CuI templates. The parameters of this
reaction were investigated, and important roles were found to be played by (i) the steric bulk of the amine,
(ii) the charge of the amine, (iii) the solvent used, and (iv) the pH of the solution. Water was found to allow
the broadest range of structures to form, and ligand-component exchange reactions (involving the substitution
of an aromatic for an aliphatic amine) were demonstrated to proceed readily in this solvent.
by the metal-templated14 formation of imine bonds, bringing
both ligands and supramolecular complexes into being at the
Introduction
Metalloorganic self-assembly has proven a versatile and
powerful means to construct nanoscale architectures, which are
beginning to approach the necessary degree of complexity to
serve as useful molecular machines.1-7 Building upon the
successes of the programmed self-assembly of preformed ligands
with metals8-13 and Busch’s concept of template synthesis,14
ligand-component self-assembly is emerging as a powerful
means to create such structures. Starting from the fundamental
building blocks of ligand subcomponents and metal ions, such
diverse structures as catenanes15 (including Borromean rings16),
rotaxanes,17 grids,18,19 and helicates20-22 have been generated
same time.
The use of ligand-component assembly reactions not only
reduces the effort required for ligand synthesis23 but also
furnishes a means to create structures capable of dynamic
rearrangement24 in solution through Schiff-base metathesis.25,26
Dynamic reassembly reactions of metalloorganic complexes,
such as have been induced by transmetalation,18,27 redox
processes,28 the presence of guest species,29-34 or interactions
with a different complex,35 constitute means for these complexes
to interact with the environment in well-defined ways, possibly
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† Department of Organic Chemistry.
‡ Laboratory of X-ray Crystallography.
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16538
J. AM. CHEM. SOC. 2004, 126, 16538-16543
10.1021/ja046001z CCC: $27.50 © 2004 American Chemical Society

Helicate Ligand Component Self-Assembly
A R T I C L E S
Scheme 1. Aqueous Template Synthesis of Dicopper(I) Double Helicate 12-, from Copper(I) Oxide or from Conproportionation of Copper(II)
Sulfate and Copper Metal
doing useful work. We have recently explored dynamic ligand-
component assembly and exchange using mononuclear CuI bis-
imine complexes36 and tetranuclear strained grids37 that self-
assemble in aqueous solution.
The generality of this double-helicate-forming reaction was
demonstrated by the synthesis of 22+ (eq 1), employing
2-aminoethanol and copper(I) tetrakis(acetonitrile) tetrafluo-
roborate in place of sulfanilic acid and copper(I) oxide.
To extend the chemistry of ligand-component self-assembly,
knowledge must be gained as to which building blocks will be
incorporated into a given structure under a given set of
conditions. The development of such “selection rules” is
necessary for the construction of complex, functional architec-
tures: specific components must be guided to specific sites of
incorporation based upon steric and electronic factors. Comple-
menting such guidelines would be reassembly guidelines
detailing under what conditions a structure reconfigures itself,
and into what products. Herein we describe the results of
investigations into the rules governing the synthesis and
reassembly of a class of dicopper(I) double-helicate complexes,
which were generated by ligand-component self-assembly in
aqueous and acetonitrile solutions.
The crystal structure of 22+ is shown in Figure 3. The helical
core of this molecule is nearly isostructural with that of 12-
,
showing no statistically significant deviations in bond lengths
and angles despite the substitution of alkyl chains for aryl rings.
Copper(I) helicate complexes have been used as a platform
to develop much fundamental supramolecular chemistry,20,22,39-57
and dicopper double helicates structurally similar to these have
been reported by Ziessel58 and Henkel.59 This led us to develop
our aqueous Cu(I)-templated ligand-component assembly36,37 in
this direction, using these helicate complexes to explore the
Results and Discussion
A mixture of 1,10-phenanthroline-2,9-dicarboxaldehyde38 (2
equiv), sulfanilic acid (4-aminobenzenesulfonic acid, 4 equiv),
copper(I) oxide (1 equiv), and sodium bicarbonate (2 equiv)
dissolved over several hours in deuterium oxide under an argon
atmosphere to give a dark green solution. Despite this color,
which is often associated with copper(II), NMR spectra showed
that the unique product was diamagnetic and were consistent
with the double-helical structure 12- shown in Scheme 1. The
complex is inert to both imine hydrolysis and CuI dispropor-
tionation in solution, with the ligands and metals being mutually
stabilized in aqueous solution by complex formation.36 The
thermodynamic stability of this complex is demonstrated by the
fact that it may also be prepared by the conproportionation of
copper(II) sulfate and copper(0) metal in place of copper(I) oxide
(Scheme 1).
The identity of this complex was confirmed by X-ray
crystallography; an ORTEP diagram of 12- is shown in Figure
1. The helicate consists of two ligand strands wrapped around
two CuI ions of flattened tetrahedral coordination geometry
(Figure 1).
The crystal, obtained through the diffusion of an aqueous
solution of Na21 into an aqueous solution of Ba(ClO4)2, is
composed of layers of helicate dianions separated and bridged
by layers of barium cations and water molecules. A network of
hydrogen bonds serves to order and orient the water molecules
within the layers (Figure 2).
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A R T I C L E S
Nitschke et al.
Figure 1. ORTEP view of 12-. Ellipsoids are represented at the 50%
probability level. Selected mean bond distances [Å] and angles [°]: Cu1‚
‚‚Cu2 2.730(1), Cu-Nimine(N3,N4) 2.026(9), Cu-Nphen(N1,N2) 2.089(8); Nimine
-
Cu-Nimine 142(1), Nphen-Cu-Nphen 148.8(2), Nimine-Cu-Nphen(intra)
79.9(4), Nimine-Cu-Nphen(inter) 111(2).
Figure 3. ORTEP diagram of 22+. Ellipsoids are represented at the 50%
probability level. Selected mean bond distances [Å] and angles [°]: Cu1‚
‚‚Cu2 2.7321(6), Cu-Nimine(N3,N4) 2.011(12), Cu-Nphen(N1,N2) 2.087(17);
Nimine-Cu-Nimine 133(7), Nphen-Cu-Nphen 152(3), Nimine-Cu-Nphen(intra)
81.1(5), Nimine-Cu-Nphen(inter) 110(2).
Chart 1. Helicate Formation Selection Rules in Water and
Acetonitrile
-
Figure 2. View parallel to the c-axis of Ba2+12-‚Ba2+(ClO4
) in the
2
crystal, showing the layered structure. The purple spheres represent Ba2+
ions; hydrogen bonds are indicated by dashed lines.
parameters and limits of our methodology. Noting the aqueous
stability and quantitative formation of the double-helical motif
of 12- and 22+, we sought to investigate what other amines might
be similarly incorporated, as shown in Chart 1. The general
procedure consisted of mixing amines a-h (4 equiv), 1,10-
phenanthroline-2,9-dicarboxaldehyde (2 equiv), and copper(I)
tetrakis(acetonitrile) tetrafluoroborate (2 equiv) in deuterium
oxide or acetonitrile-d3. In all cases where helicate formation
was noted to have occurred, all solids dissolved within 2 h of
as the cationic amines g and h, appeared to be excluded by the
self-assembly process. Models suggest that steric encumbrance
would prevent the incorporation of f and might hinder the
incorporation of g. Mutual repulsion between the positive
charges of g and h and the cationic helicate backbone appear
to disfavor helicate formation. The low nucleophilicity of h, a
result of the partial positive charge on its NH2 group, also could
help to explain its nonincorporation.
The use of acetonitrile as a reaction solvent brought to bear
a more restricted set of selection rules upon the helicate self-
assembly process. In addition to the cationic amines, the anionic
amines d and e did not give helicates. This could be a result of
the negligible solubility of sodium sulfonates in acetonitrile,
which is a poor hydrogen bond donor.
1
ultrasonication to give a dark solution, the H and 13C NMR
spectra of which were consistent with quantitative double-
helicate formation. In cases where helicate formation is listed
as not having occurred, ultrasonication for 12 h failed to give
a green solution, and NMR spectra indicated mixtures of
products.
Certain patterns were noted through this series of experiments
(Chart 1). In aqueous solution, amines bearing a methoxy-
(ethanol) group or one or two hydroxymethyl groups on the
R-carbon were thus “allowed” as shown by entries a-c.
Sulfonated aryl and primary amines d and e were likewise
readily incorporated into these helicates. Amines such as f
bearing three alkyl groups on the R-carbon, however, as well
Serinol (2-aminopropane-1,3-diol) (c) likewise did not give
a helicate in acetonitrile, although it is soluble in this solvent.
9
16540 J. AM. CHEM. SOC. VOL. 126, NO. 50, 2004

Helicate Ligand Component Self-Assembly
A R T I C L E S
Figure 4. Disassembly of helicates 12- and 32- as a function of acidity.
The serinol-derived helicate formed in D2O is sterically
hindered, as was revealed by its 1H spectrum at 298 K. Although
the phenanthroline and imine resonances were sharp, the peaks
resulting from the serinol-derived diastereotopic protons were
broad. This is ascribed to rapid racemization between (P) and
(M) helicates on the NMR time scale, which suggests a ground-
state steric destabilization of the helical structure. Although
NMR and mass spectra are consistent with helicate formation,
the color of the serinol-containing helicate is dark brown,
contrasting with the dark green color of all of the other helicates
observed. This might indicate a structural perturbation to the
di-copper(I) chromophore.
phenanthroline-2,9-dicarboxaldehyde. One may nonetheless
consider the amplification effect of the copper(I) template14 upon
its chosen ligand, taking into account the fact that not only the
equilibria between solution species, but also the partitioning of
species between solution and the solid state, are perturbed. In
1
acetonitrile, H NMR showed that the hydroxyamines a and b
reacted to form bis-imines quantitatively with 1,10-phenanthro-
line-2,9-dicarboxaldehyde, thus allowing for no amplification
effect. In D2O amines a, b, and c gave respectively 57%, 44%,
1
and 63% imine (by H integration), corresponding to modest
amplification factors of 1.7, 2.3, and 1.6 upon quantitative
templating of the imines by copper. More remarkably, no imine
at all was observed by NMR with sulfonated amines d and e in
the absence of copper. The quantitative formation of helicates
(having a ligand concentration of 50 mM) from these compo-
nents thus implies an amplification of the bis-imine ligands by
a factor of more than 500, conservatively assuming an 1H NMR
detection limit of 0.1 mM.
We were also able to utilize pH as a means to control the
self-assembly reaction. Figure 4 shows the disassembly of
helicates 12- and 32- (formed from amines d and e) during
titration with D2SO4 in D2O, as followed by 1H NMR integration
of peaks corresponding to free and incorporated amine. The
liberated dialdehyde precipitated during the course of titration,
but the process was nonetheless reversible. Upon the addition
of excess hydroxide, helicates reassembled from the ligand
components as the dialdehyde redissolved.
In contrast to the serinol-derived helicate, the helicates formed
from the less sterically demanding amines a and b have
1
diastereotopic protons that gave sharp and distinct H signals
at 298 K in D2O. The diastereotopic protons of the helicate
derived from amine b were broadened nearly to coalescence at
363 K in D2O, which indicates a barrier to racemization above
67.5 kJ mol-1 60
In acetonitrile, however, these protons gave
.
broad resonances at room temperature, and decoalesce only
below 273 K, which indicates a barrier to racemization of 50
.
kJ mol-1 60 This solvent effect thus gives a ∆∆Gq greater than
17.5 kJ mol-1 between water and acetonitrile, presumably
because acetonitrile stabilizes the racemization transition state
by coordinating to CuI. In the case of serinol in acetonitrile,
the ground-state destabilizing steric effects and the transition-
state stabilizing solvent effects, acting in concert, appear to lower
the energy of the “transition state” below that of the “ground
state,” which made helicate formation energetically disfavorable.
Although capable of dynamic exchange, these systems are
not readily treated using the techniques of dynamic combina-
torial chemistry19,61-65 due to the low solubility of the 1,10-
The difference in pH stability between the two helicates
reflects the difference between the pKa’s of the corresponding
protonated amines. Taurine (e) is less acidic (pKa ) 9.1)66 than
sulfanilic acid (d) (pKa ) 3.2),67 indicating that taurine should
be more readily displaced from a helicate than sulfanilic acid
by proteolysis, as observed.
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9
J. AM. CHEM. SOC. VOL. 126, NO. 50, 2004 16541

A R T I C L E S
Nitschke et al.
Preparative Synthesis of Na+212-. To a 100 mL Schlenk flask was
added 1,10-phenanthroline-2,9-dicarboxaldehyde (0.0197 g, 0.0834
mmol), sulfanilic acid (0.0288 g, 0.166 mmol), copper(I) oxide (0.0059
g, 0.041 mmol), and sodium bicarbonate (0.0069 g, 0.082 mmol). A
magnetic stir bar was added and the flask was sealed. The atmosphere
was purified of dioxygen by three evacuation/argon fill cycles. Water
(16 mL) was then added, causing gas evolution and development of a
green color. Once gas evolution had ceased, the flask was sealed and
the reaction was allowed to stir overnight at room temperature. Volatiles
were then removed under dynamic vacuum, giving an isolated yield
of 0.051 g (98%) of green microcrystalline product, which was pure
In addition to controlling the extent of self-assembly, this
difference in pKa’s may also be used to drive ligand-component
substitution reactions, in fashion similar to what we have shown
in mononuclear systems.36 When sulfanilic acid (1.2 equiv per
incorporated amine) was added to a solution of helicate
incorporating amine a, b, c, or e, the aliphatic amine was
quantitatively displaced within 2 h, as shown in eq 2. The
1
by NMR. H NMR (500 MHz, 300 K, D2O, referenced to 2-methyl-
2-propanol at 1.24 ppm as internal standard): δ ) 8.98 (s, 4 H, imine),
8.46 (d, J ) 8.2 Hz, 4 H, 4,7-phenanthroline), 8.20 (d, J ) 8.2 Hz, 4
H, 3,8-phenanthroline), 7.69 (s, 4 H, 5,6-phenanthroline), 6.92 (d, J )
8.3 Hz, 8 H, phenylene), 6.13 (d, J ) 8.3 Hz, 8 H, phenylene). 13C
NMR (125.77 MHz, 300 K, D2O, referenced to 2-methyl-2-propanol
at 30.29 ppm as internal standard): δ ) 159.5, 148.6, 146.7, 142.8,
140.8, 138.4, 133.1, 129.2, 127.5, 126.6, 121.8. ESI-MS: m/z ) -608.1
(12-), -384.7 (12- lacking one Cu+), -272.4 (metal-free imine ligand
of 12-).
difference in pKa values thus favored the displacement of the
protonated form of the weaker acid (aliphatic ammonium ion)
and the incorporation of the deprotonated form of the stronger
acid (sulfanilic acid) to form 12-
.
Conclusion
Synthesis of 22+(BF4-)2. Into an NMR tube with a Teflon screw
cap was added 1,10-phenanthroline-2,9-dicarboxaldehyde (0.0105 g,
0.0444 mmol), 2-aminoethanol (0.0054 g, 0.0884 mmol), copper(I)
tetrakis(acetonitrile) tetrafluoroborate (0.0139 g, 0.0442 mmol), and
deuterium oxide (0.5 mL). The tube’s atmosphere was purged of
dioxygen with three evacuation/argon purge cycles. Crystals began to
form spontaneously from the dark green solution after 1 h. No side
products were observed in the NMR spectra of this compound. 1H NMR
(400 MHz, 300 K, D2O, referenced to 2-methyl-2-propanol at 1.24 ppm
as internal standard; peak assignments are consistent with COSY and
NOESY spectra): δ ) 8.81 (d, J ) 8.2 Hz, 4 H, 4,7-phenanthroline),
8.66 (s, 4 H, imine), 8.24 (s, 4 H, 5,6-phenanthroline), 8.19 (d, J ) 8.2
Hz, 4 H, 3,8-phenanthroline), 3.19 (m, 4 H, NCH2CH2OH), 2.85 (m,
4 H, NCH2CH2OH), 2.52 (m, 4 H, NCH2CH2OH), 2.03 (m, 4 H, NCH2-
CH2OH). 13C NMR (100.62 MHz, 300 K, D2O, referenced to 2-methyl-
2-propanol at 30.29 ppm as internal standard): δ ) 163.4, 149.9, 141.8,
138.8, 133.2, 129.2, 126.7, 60.6, 60.5. ESI-MS: m/z ) 385.3 (22+),
707.2 (22+ lacking one Cu+).
In summary, we have developed a set of “selection rules”
granting a degree of control over the self-assembly and ligand-
component exchange of a set of bis-CuI double-helicate
complexes. These rules are based upon steric, charge, and
solvent effects, as well as upon pH. The use of water as a
reaction solvent has also been shown to be particularly advanta-
geous, which could be seen as counterintuitive for copper(I)/
imine based structures. In the present study water has allowed
for the synthesis of a wider range of structures, and elsewhere
it has been shown that more highly charged assemblies13,68 may
be generated in water than in other solvents. Water is also the
necessary solvent for interfacing metalloorganic species with
biological systems.69,70 The exploration and development of the
assembly and reassembly rules detailed herein are currently
allowing us to build up larger and more complex structures, as
well as to transform these structures using ligand-component
exchange.
Preparative Synthesis of Na+232-. The helicate complex Na+232-
Experimental Section
was obtained in 97% yield by the same procedure as used in the case
1
of 12-, using taurine in place of sulfanilic acid. H NMR (500 MHz,
All manipulations were carried out under argon or dinitrogen using
degassed solvents. Starting materials of the highest commercially
available purity were used as received; 1,10-phenanthroline-2,9-
dicarboxaldehyde38 and 1-methyl-4-aminopyridinium triflate (amine h
in Chart 1)71 were prepared according to literature procedures.
NMR Studies of Helicate and Ligand Formation. For each of the
amines listed in Chart 1, amine a-h (0.050 mmol), 1,10-phenanthroline-
2,9-dicarboxaldehyde (0.025 mmol, 0.0066 g), and Cu(NCMe)4BF4
(0.025 mmol, 0.0079 g,) were loaded into an NMR tube with a Teflon
screw cap. Deuterium oxide or acetonitrile-d3 (0.5 mL) was then added,
and the tube’s atmosphere was purged of dioxygen with three
evacuation/argon purge cycles. The mixture was then sonicated until
all reagents dissolved, or for 12 h if dissolution was incomplete.
Experiments in which helicate formation was observed were repeated
without copper to determine the extent of ligand formation in its
absence.
300 K, D2O, referenced to 2-methyl-2-propanol at 1.24 ppm as internal
standard; peak assignments are consistent with COSY and NOESY
spectra): δ ) 8.84 (d, J ) 8.2 Hz, 4 H, 4,7-phenanthroline), 8.74 (s,
4 H, imine), 8.24 (s, 4 H, 5,6-phenanthroline), 8.22 (d, J ) 8.2 Hz, 4
H, 3,8-phenanthroline), 3.45 (m, 4 H, NCH2CH2S), 2.29 (m, 4 H, NCH2-
CH2S), 2.18 (m, 4 H, NCH2CH2S), 1.67 (m, 4 H, NCH2CH2S). 13C
NMR (125.77 MHz, 300 K, D2O, referenced to 2-methyl-2-propanol
at 30.29 ppm as internal standard): δ ) 163.5, 149.7, 141.6, 139.2,
133.8, 129.7, 127.1, 54.2, 50.6. ESI-MS: m/z ) -511.2 (32-), -224.4
(imine ligand of 32-).
X-ray Crystal Structure of 12-. Single crystals suitable for X-ray
diffraction were obtained through diffusion of an aqueous solution of
Na+212- into an aqueous solution of Ba(ClO4)2. [Cu2(C26H12N4O6S2)2]2-
‚
(ClO4-)2‚Ba2+2‚(H2O)13; Mr ) 1924.1; µ ) 2.062 mm-1, dx ) 1.882
g‚cm-3, monoclinic, P21/c, Z ) 4, a ) 18.6339(16), b ) 25.6027(14),
c ) 14.4414(11) Å, â ) 99.762(10)°, U ) 6798.9(9) Å3. Cell
dimensions and intensities were measured at 200 K on a Stoe IPDS
diffractometer with graphite-monochromated Mo KR radiation (λ )
0.710 73 Å), 48 564 measured reflections, 13 136 unique reflections
of which 8088 were observable (|Fo| > 4 σ (Fo)); Rint for 34 786
equivalent reflections 0.060. Data were corrected for Lorentz and
polarization effects and for absorption (Tmin, Tmax ) 0.5868, 0.8933).
(68) Bennett, M. V.; Beauvais, L. G.; Shores, M. P.; Long, J. R. J. Am. Chem.
Soc. 2001, 123, 8022-8032.
(69) Meistermann, I.; Moreno, V.; Prieto, M. J.; Moldrheim, E.; Sletten, E.;
Khalid, S.; Rodger, P. M.; Peberdy, J. C.; Isaac, C. J.; Rodger, A.; Hannon,
M. J. Proc. Natl. Acad. Sci. U. S. A. 2002, 99, 5069-5074.
(70) Junicke, H.; Hart, J. R.; Kisko, J.; Glebov, O.; Kirsch, I. R.; Barton, J. K.
Proc. Natl. Acad. Sci. U. S. A. 2003, 100, 3737-3742.
(71) Abbotto, A.; Bradamante, S.; Pagani, G. A. J. Org. Chem. 2001, 66, 8883-
8892.
9
16542 J. AM. CHEM. SOC. VOL. 126, NO. 50, 2004

Helicate Ligand Component Self-Assembly
A R T I C L E S
The structure was solved by direct methods (SIR97);72 all other
calculations were performed with the XTAL system73 and ORTEP74
programs. Full-matrix least-squares refinement based on F using weight
programs. Full-matrix least-squares refinement based on F using weight
of 1/(σ2(Fo) + 0.00015(Fo )) gave final values R ) 0.033, ωR ) 0.032,
2
and S ) 1.22(1) for 593 variables and 4351 contributing reflections.
The maximum ∆/σ on the last cycle was 0.56 × 10-2. One of the BF4
anions showed disorder, which was modeled as two sets of four fluorine
atoms (with occupancies of 0.60 and 0.40, respectively) around a single
boron, refined with restrictions on the bond lengths and angles. The
hydrogen atoms present on the hydroxyl groups and water molecules
were observed and refined with restraints on bond lengths and angles
and blocked during the last cycles; other hydrogen atoms were placed
in calculated positions.
Full structural details for 12- and 22+ are included in the Supporting
Information as CIF files, which have also been deposited as CCDC-
238838 and CCDC-242824. These data can be obtained free of charge
via www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: (+44) 1223-336-033; or deposit@ccdc.cam.ac.uk).
2
of 1/(σ2(Fo) + 0.0002(Fo )) gave final values R ) 0.040, ωR ) 0.038,
and S ) 1.12(1) for 928 variables and 8336 contributing reflections.
The maximum ∆/σ on the last cycle was 0.11 × 10-2. Hydrogen atoms
of the complex were placed in calculated positions. Hydrogen atoms
of the water molecules were refined with restraints on bond lengths
and angles and blocked during the last cycles.
X-ray Crystal Structure of 22+. Single crystals suitable for X-ray
diffraction crystallized spontaneously from the reaction solution.
[Cu2(C18H18N4O2)2]2+‚(BF4-)2‚(H2O)4; Mr ) 1017.6; µ ) 1.104 mm-1
,
dx ) 1.602 g‚cm-3, monoclinic, P21/n, Z ) 4, a ) 12.5079(7), b )
18.8569(12), c ) 17.9012(9) Å, â ) 92.200(6)°, U ) 4219.1(4) Å3.
Cell dimensions and intensities were measured at 200 K on a Stoe
IPDS diffractometer with graphite-monochromated Mo KR radiation
(λ ) 0.710 73 Å), 43 005 measured reflections, 8608 unique reflections
of which 3967 were observable (|Fo| > 4σ(Fo)); Rint for 33 718
equivalent reflections 0.083. Data were corrected for Lorentz and
Acknowledgment. This work was supported by the Fonds
Fre´de´ric Firmenich et Philippe Chuit, the Fonds Xavier Givaudan,
and the Swiss National Science Foundation. We thank P.
Perrottet for mass spectrometric analyses and A. Pinto for
NOESY NMR spectra.
polarization effects and for absorption (Tmin, Tmax ) 0.8161, 0.8819).
72
The structure was solved by direct methods (SIR97);
all other
calculations were performed with the XTAL system73 and ORTEP74
(72) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G.; Giacovazzo, C.;
Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna, R. J. Appl.
Crystallogr. 1999, 32, 115-119.
(73) Hall, S. R.; Flack, H. D.; Stewart, J. M. Xtal 3.2 User’s Manual; Universities
of Western Australia at Crawley, and Maryland at College Park: 1992.
(74) Johnson, C. K. ORTEP II; Report ORNL-5138; ORNL: Oak Ridge, TN,
1976.
Supporting Information Available: CIF files for the struc-
tures of 12- and 22+. This material is available free of charge
via the Internet at http://pubs.acs.org.
JA046001Z
9
J. AM. CHEM. SOC. VOL. 126, NO. 50, 2004 16543