Jack of all trades: Anion and transition metal binding by bis-triazole receptors

Article abstract of DOI:10.1080/10610278.2012.688124

Four acyclic phenylene-1,3-bis-triazole receptors were synthesised with the heterocyclic motif covalently attached to the central phenyl ring through either the carbon or nitrogen. ¹H NMR titration experiments reveal that all the receptors bind chloride in d₆-acetone solution with the aryl-substituted systems exhibiting significantly stronger halide association than the alkyl-substituted receptors. Both N-linked systems bind chloride more strongly than their C-linked analogues. Copper(I) and silver(I) cations were also demonstrated to bind to the receptors in solution and in the solid state. Four metal complexes were structurally characterised by X-ray crystallography - in all cases giving interesting polynuclear architectures with a dinuclear silver(I) metallomacrocycle, a trimetallic copper(I) and two tetranuclear silver(I) clusters observed.

Full text of DOI:10.1080/10610278.2012.688124

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Supramolecular Chemistry
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Jack of all trades: anion and transition metal binding
by bis-triazole receptors
Nicholas G. White a & Paul D. Beer a
a Chemistry Research Laboratory, University of Oxford , Mansfield Rd, Oxford , OX1 3TA , UK
Published online: 29 May 2012.
To cite this article: Nicholas G. White & Paul D. Beer (2012) Jack of all trades: anion and transition metal binding by bis-
triazole receptors, Supramolecular Chemistry, 24:7, 473-480, DOI: 10.1080/10610278.2012.688124
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Supramolecular Chemistry
Vol. 24, No. 7, July 2012, 473–480
Jack of all trades: anion and transition metal binding by bis-triazole receptors
Nicholas G. White and Paul D. Beer*
Chemistry Research Laboratory, University of Oxford, Mansfield Rd, Oxford OX1 3TA, UK
(Received 2 March 2012; final version received 30 March 2012)
Four acyclic phenylene-1,3-bis-triazole receptors were synthesised with the heterocyclic motif covalently attached to the
1
central phenyl ring through either the carbon or nitrogen. H NMR titration experiments reveal that all the receptors bind
chloride in d6-acetone solution with the aryl-substituted systems exhibiting significantly stronger halide association than the
alkyl-substituted receptors. Both N-linked systems bind chloride more strongly than their C-linked analogues. Copper(I) and
silver(I) cations were also demonstrated to bind to the receptors in solution and in the solid state. Four metal complexes were
structurally characterised by X-ray crystallography – in all cases giving interesting polynuclear architectures with a
dinuclear silver(I) metallomacrocycle, a trimetallic copper(I) and two tetranuclear silver(I) clusters observed.
Keywords: triazole; anion binding; coordination complexes; chloride; copper; silver
Introduction
versatility for binding both anions and cations in solution
and in the solid state.
Since the development of the copper(I)-catalysed cycload-
dition of azides and alkynes (CuAAC) to give 1,2,3-
triazole groups by Meldal (1) and Fokin and Sharpless (2),
this reaction has found widespread use across numerous
areas of chemistry (3). The large dipole oriented along the
triazole CZH bond as well as its polarisation due to the
electron-withdrawing character of the three nitrogen atoms
generates a potent CZH bond donor. Indeed, several key
studies have shown that hosts incorporating two or more
1,2,3-triazole groups can bind anions in moderately
competitive solvents solely through CZH· · ·anion hydro-
gen bonds (4–11). However, the triazole ring also
possesses Lewis base character and can act as a ligand
for transition metals (12). In the majority of cases, the
triazole is part of a polydentate ligand in conjunction with
a traditional ligand donor such as pyridine or an amine.
For example, the groups of Flood and Hecht have shown
that 2,6-bis(1,2,3-triazol-4-yl)pyridine-based ligands can
act as efficient tridentate donors for complexing FeII, RuII
and EuIII ions (13–15).
Results and discussion
Synthesis
Four acyclic 1,3-phenylbis-triazole receptors were syn-
thesised (Scheme 1), having the triazole rings joined to the
central phenyl group through either the nitrogen or carbon
terminus, and possessing either an alkyl (octyl) or aryl
(4-tbutyl phenyl) substituent. The bis-triazole systems
were prepared under one-pot conditions (24, 25) from
either 5-tert-butyl-1,3-diethynylbenzene or 5-tert-butyl-
1,3-diiodobenzene.
Interestingly, although the octyl-substituted receptors
could be prepared readily in very good yields (88% and
95%), isolated yields of the corresponding aryl-substituted
receptors were substantially lower (14% and 19%), and
chromatographic purification proved problematic. Recrys-
tallisation from methanol gave pure samples of 3 and 4
together with single crystals suitable for characterisation
by X-ray crystallography (Figure 1).
Unsupported triazole ligands in which metal coordi-
nation occurs exclusively via triazole groups are beginning
to appear in the literature (16–23).1 Notably, Crowley and
co-workers (18, 19) have demonstrated that AgI and PdII
complexes of such ligands can form interesting metallo-
supramolecular architectures (cages and metallomacro-
cycles).
Chloride binding
The binding of chloride anion by the four acyclic receptors
1
was investigated by H NMR titration experiments in d6-
acetone, monitoring the triazole resonance in each case.
Addition of tetrabutylammonium (TBA) Cl caused down-
field shifts of the triazole proton signals, as well as the
phenyl CZH proton resonances between the two triazole
Herein, we describe the synthesis of four new acyclic
triazole ligand systems and demonstrate their coordinative
*Corresponding author. Email: paul.beer@chem.ox.ac.uk
ISSN 1061-0278 print/ISSN 1029-0478 online
q 2012 Taylor & Francis
http://dx.doi.org/10.1080/10610278.2012.688124
http://www.tandfonline.com

474
N.G. White and P.D. Beer
Transition metal binding
Complexation studies of 1–4 were undertaken with the
metal ions AgI and CuI. In solution investigations, the
cations were added as their PF26 salts to eliminate any
significant competition from anion binding by the triazole
groups. The solution behaviour was investigated using 1H
NMR,4 and four complexes were characterised in the solid
state by single crystal X-ray crystallography. The alkyl-
substituted ligands 1 and 2 were used for solution studies
in d6-acetone.
Addition of AgPF6 or [Cu(CH3CN)4](PF6) to either the
N-linked or the C-linked ligands resulted in substantial
movement of the signals corresponding to the phenylene
and triazole protons. Unfortunately, neither the silver nor
copper salts used had sufficient solubility to allow
quantitative titrations to be carried out. Qualitatively, the
data suggest very strong binding (Ka . 104 M21).
Scheme 1. Synthesis of bis-triazole receptors 1–4 used in this
study. Conditions and reagents: (i) bromooctane, ascorbic acid,
sodium carbonate, sodium azide, copper(II) sulfate pentahydrate,
4:1 DMF:H2O, 808C, 95%; (ii) 4-tbutyliodobenzene, L-proline,
sodium ascorbate, sodium carbonate, sodium azide, copper(II)
sulfate pentahydrate, 9:1 DMSO:H2O, 658C, 19%; (iii) decyne,
L-proline, sodium ascorbate, sodium carbonate, sodium azide,
copper(II) sulfate pentahydrate, 9:1 DMSO:H2O, 658C, 79%;
(iv) 4-tbutylphenylacetylene, L-proline, sodium ascorbate, sodium
carbonate, sodium azide, copper(II) sulfate pentahydrate, 9:1
DMSO:H2O, 658C, 14%.
Metal binding in solution – copper(I)
Both the N-linked and the C-linked receptors display 1:1
binding stoichiometries in solution with copper(I) cation
(Figures 3 and 4), which is somewhat surprising given the
metal’s known preference for a tetrahedral binding
geometry, which would result in complexes with ML2
stoichiometric binding. The X-ray crystal structures of the
two uncomplexed receptors (Figure 1) indicate neither
would facilitate a conventional ML2 binding arrangement.
In the case of the N-linked receptors, the N3 nitrogen atoms,
which are the most electron-rich5, are divergent and so do
not allow for bidentate coordination. In the case of the
C-linked receptors, these nitrogen atoms are convergent,
giving the possibility of cooperative bidentate binding;
groups. Job plot analysis indicated the formation of 1:1
stoichiometric complexes in all cases, and association
constants were calculated using WINEQNMR2 (26). As
shown in Table 1 and Figure 2, the aryl-substituted
receptors, 3 and 4, exhibit far stronger binding of chloride
than the alkyl-substituted systems, 1 and 2. Interestingly,
the N-linked receptors both exhibit stronger association
with chloride than the analogous C-linked systems,
possibly due to the N-termini of the triazole groups making
the central phenylene proton more acidic (27).
A deliberate comparison of anion binding strength for
the C-linked versus the N-linked triazole receptors has not,
to the best of our knowledge, been described previously
despite the considerable interest in triazole-based anion
receptors.2 Craig has reported a closely related phenylene-
1,3-bis-triazole receptor that has an ester substituent
instead of the tertiary butyl group, which displays even
stronger chloride association in d6-acetone [Ka for
˚
however, the distance between them is 5.4 A, presumably
too far apart for a small-sized first-row transition metal
cation such as copper(I).
When copper(I) is added to the N-linked receptor,
downfield shifts are observed in the signals of the interior
and the exterior phenyl protons as well as the triazole
protons and the alkyl protons on the CH2 groups adjacent
to the triazole rings (Figure 3). In the case of the C-linked
receptor, the situation is more complex: addition of a small
amount of copper results in the appearance of five new
peaks in the aromatic region, as well as two new triplet
4 ¼ 380(18) M21, Ka for Craig’s host ¼ 1260(30) M21
]
(5), demonstrating the substantial effect that electron-
donating or electron-withdrawing groups have on the
chloride anion binding strength of these systems.3
Figure 1. Solid state structures of 3 and 4. Ellipsoids shown at 50% probability. Hydrogen atoms and methanol solvates omitted for clarity.

Supramolecular Chemistry
475
Table 1. Association constants, Ka (M21) for receptors 1–4
with chloride aniona in d6-acetone.
b
Host
Ka
1
2
3
4
32 (3)
55 (5)
309 (29)
380 (18)
Note: Estimated standard errors are given in parentheses.
a
Added as TBA salt.
b
At 293 K, calculated using WINEQNMR2 (26).
signals at 4.62 and 4.75 ppm (Figure 4). Continuing to add
copper results in the new peaks growing at the expense of
the signals from uncomplexed ligand. When 1 equivalent
of copper has been added, only five aromatic signals and
two signals at 4.62 and 4.75 ppm remain.
Figure 3. 1H NMR spectra of a d6-acetone solution of 2 upon
addition of [Cu(CH3CN)4](PF6) (293 K).
These results suggest that copper(I) binding to ligand
1
1 is slow on the H NMR timescale. The new signals of
the copper(I)–ligand complex imply a desymmetrisation
of the ligand, such that the two alkyl groups adjacent to
the triazole motifs are inequivalent, as are all five
aromatic protons (two each from the triazole groups and
three phenylene protons). Interestingly, proton c splits
into two new resonances, both of which are shifted upfield
relative to the free ligand. This is in contrast to the
N-linked ligand, in which all peaks move downfield upon
complexation to copper, and binding is fast on the NMR
timescale.
is observed after the addition of 1.0 equivalent of metal,
implying a 1:1 binding stoichiometry. When the C-linked
ligand, 1, is used, no movement is observed after addition
of 0.5 equivalents of Ag(I), implying a ML2 stoichiometric
complex in solution. As observed in the copper(I) complex
of this ligand, proton c shifts upfield, while all other
protons move downfield.
Solid-state metal complexes
For three of the four metal complexes (the Cu3 and Ag4
clusters) characterised by X-ray crystallography, crystals
were small and poorly diffracting. Attempts to use
synchrotron radiation were unfortunately unsuccessful,
with the crystals appearing to suffer significant radiation
damage. Instead, Cu Ka radiation and very long collection
times (3 days to collect all unique reflections with a
redundancy of one) were used. Despite these difficulties,
Metal binding in solution – silver(I)
Addition of AgPF6 to either the C-linked or the N-linked
receptors causes downfield shifts in the signals arising
from the aromatic protons, as well as the CH2 protons
adjacent to the triazole groups (Figures 5 and 6). Only one
set of peaks is visible in both cases, implying fast
exchange on the NMR timescale. In the case of the N-
linked ligand, 2, no further movement of the ligand peaks
4
1.60
1.40
120
3
1.00
0.80
0.60
0.40
0.20
0.00
2
1
0
1
2
3
4
5
6
7
8
9
10
Equivalents added
Figure 2. Experimental titration data (solid points) and fitted
binding isotherms (lines) for addition of TBA·Cl to d6-acetone
solutions of 1–4 (293 K).
Figure 4. 1H NMR spectra of a d6-acetone solution of 1 upon
addition of [Cu(CH3CN)4](PF6) (293 K).

476
N.G. White and P.D. Beer
Figure 7. Solid-state structure of ½CuI3ð3Þ4ꢀðPF6Þ. Only one of
the two independent Cu3 complexes in the asymmetric unit is
shown. Counteranions and hydrogen atoms are omitted for
clarity.
Figure 5. 1H NMR spectra of a d6-acetone solution of 2 upon
addition of AgPF6 (293 K).
central metal binds to four bridging triazole groups, while
the two outer copper ions each bind two monodentate and
two bridging rings (Figure 8). Surprisingly, there are only
slight differences in coordination bond lengths between
the bridging and monodentate triazole donors or between
the different donors on the bridging atoms (monodentate,
the data allow unambiguous determination of the gross
structure of the metal complexes and the coordination
environments of the metal ions.
˚
˚
meanCuZN ¼ 2.03 A, bridging N3: meanCuZN ¼ 2.05 A;
˚
bridging N2: meanCuZN ¼ 2.08 A). This bridging/mono-
Solid-state metal complexes – copper(I)
dentate arrangement may explain the observed asymmetry
of 1 observed in solution in the presence of CuI, as one side
of each ligand is coordinated to two copper ions, making it
more electron poor than the other side of the ligand, which
binds only one metal ion (29).7
Single crystals were obtained by diffusing diethyl ether
vapour into a d6-acetone solution of a 1:1 mixture of the C-
linked aryl-substituted ligand 3 and [CuI(CH3CN)4](PF6).
In the solid state, the structure forms the complex
½CuI3ð3Þ4ꢀðPF6Þ3 with two complete complexes in the
asymmetric unit. Each copper ion has a distorted
tetrahedral geometry and coordinates to four triazole
nitrogen atoms (Figure 7). Copper–copper distances range
Solid-state metal complexes – silver
˚
between 3.3 and 3.4 A. In each of the four ligands, one
Diffusion of diethyl ether vapour into a d6-acetone solution
of a 1:1 mixture of 4 and AgI(CF3SO3) gave colourless
crystals of [Ag2(4)2(CF3SO3)2] [unfortunately no crystals
were obtained when AgPF6 was used instead of Ag(CF3-
SO3)]. In the solid state, the complex forms a [2 þ 2]
metallomacrocycle (Figure 9). The AgI ions in the
metallomacrocycle each forms two short AgZN bonds
triazole ring binds to one copper ion, while the other acts
as a bridge between two coppers (28),6 such that the
˚
[2.1581(18)–2.1729(19) A] to N3 atoms on the triazole
Figure 8. Truncated crystal structure of ½CuI3ð3Þ4ꢀðPF6Þ3
showing only one ligand strand and the bridging and
monodentate coordination modes present. This binding
arrangement also occurs in silver complexes of 3.
Figure 6. 1H NMR spectra of a d6-acetone solution of 1 upon
addition of AgPF6 (293 K).

Supramolecular Chemistry
477
Figure 11. Solid-state structure of [Ag4(3)4(PO2F2)2]
(PO2F2)(PF6). Hydrogen atoms are omitted for clarity.
Figure 9. Solid-state structure of [Ag2(4)2(CF3SO3)]. Only one
of the two crystallographically independent metal complexes in
the asymmetric unit is shown. Hydrogen atoms and solvent
molecule are omitted for clarity.
binds to three of the four silver ions, with one triazole ring
binding in a monodentate fashion and the other triazole
bridging two further silver ions, as seen with the copper
complex of 3. In this structure, however, each silver forms
only three bonds to triazole donors, with an additional
weaker bond being formed to a solvent molecule (either
water or acetone). The change in bond lengths between the
three types of donors in the ligand is more pronounced than
in the copper complex of this ligand (monodentate,
ligands, such that there is a close to linear NZAgZN
arrangement [, N· · ·Ag· · ·N ¼ 158.32(7), 160.43(7)8].
The coordination sphere on each silver ion is completed
by a much weaker bond to an oxygen donor from a
trifluoromethylsulfonate anion [AgZO ¼ 2.4675(19),
˚
˚
meanAgZN ¼ 2.23 A, bridging N3: meanAgZN ¼ 2.28 A;
˚
˚
bridging N2: meanAgZN ¼ 2.34 A).
2.603(2) A], which is approximately at right angles to the
Diethyl ether vapour was also diffused into a 1:2
AgZN bonds. The structure is very similar to that obtained
by Gower and Crowley, who reacted AgSbF6 with the bis-
triazole ligand, 4,40-benzene-1,3-diylbis[1-(pentafluoro-
benzyl)-1,2,3-triazole], although in this case, a solvent
molecule provided the third donor for each silver ion (19).
Diffusion of diethyl ether vapour into an acetone
solution of a 1:1 mixture of AgPF6 and 3 gave crystals of
a tetranuclear cluster, having the formula [Ag4(3)4(OH2)3
(C3H6O)](PF6)4 (Figure 10). Each of the four ligand strands
mixture of AgIPF6 and 3, as this is the stoichiometry of
1
binding indicated by solution H NMR studies with the
closely related ligand, 1 (Figure 6). Over a long period
(several months), small crystals formed, which were
analysed by X-ray crystallography. These have the formula
[Ag4(3)4(PO2F2)2](PO2F2)(PF6) and the overall structure is
almost the same as that of [Ag4(3)4(OH2)3(C3H6O)](PF6)4,
but with the four coordinated solvent molecules replaced
by bridging PO2F2 anions (Figure 11). The hydrolysis of
PF6 anions to PO2F22 is well known and has been
thoroughly investigated by Monzano, Otero and co-
workers who have shown that AgI catalyses this reaction
in organic solvents containing trace amounts of water (30).
To the best of our knowledge, there is only one other
structure (31) in the Cambridge Structure Database in
which PO2F22 coordinates to a metal centre – in the other
30 structures containing this anion, it does not coordinate.
Interestingly, even when two equivalents of ligand are
used for each metal centre, a ML2 complex is not formed,
despite this appearing to be the stoichiometry present in
solution.
Conclusions
Figure 10. Solid-state structure of [Ag4(3)4(OH2)3
(C3H6O)](PF6)4. Hydrogen atoms and counteranions are omitted
for clarity.
We have demonstrated the coordinative versatility of the
1,2,3-triazole motif by using substituted phenylene-1,3-bis-

478
N.G. White and P.D. Beer
triazole receptors to bind anions and cations in solution. For
both alkyl- and aryl-substituted hosts, the N-linked
receptors display stronger chloride anion binding than the
C-linked analogues. The nature of the substituent has a
major effect on association strength, with aryl-substituted
hosts 3 and 4 binding approximately an order of magnitude
more strongly than the alkyl-substituted species 1 and 2.
The systems also bind AgI and CuI transition metal
(50 ml) and diethyl ether (50 ml). The aqueous layer was
extracted further with diethyl ether (50 ml), and the
combined organic fractions were washed with water
(50 ml), saturated brine (50 ml) and then dried (magnesium
sulfate). Purification by column chromatography (silica,
4% methanol in chloroform) gave 1 as a yellow oil. Yield:
0.470 g (95%).
1H NMR (CDCl3): 8.06 (s, 1H, interior phenyl C–H),
7.89 (s, 2H, trz-H), 7.85 (s, 2H, exterior phenyl C–H), 4.41
(t, 3J ¼ 7.2 Hz, 4H, trz-CH2), 1.91–2.00 (m, 4H, trz-
CH2ZCH2), 1.41 (s, 9H, tBu-H), 1.22–1.38 (m, 20H, alkyl
CH2s), 0.87 (t, 3J ¼ 6.9 Hz, 6H, CH3). 13C NMR (CDCl3):
152.6, 147.9, 131.0, 122.5, 120.4, 119.8, 50.5, 40.4, 31.8,
31.4, 30.4, 29.1, 29.0, 26.5, 22.7, 14.1. HR-ESI-MS (pos.):
515.3816, calcd for [C30H48N6·Na]þ ¼ 515.3833.
1
cations as evidenced in solution by H NMR and in the
solid state by single crystal X-ray crystallography. The N-
linked receptor, 4, forms a metallomacrocycle in the solid
state when complexed with silver, while the C-linked
receptor, 3, forms interesting trinuclear and tetranuclear
complexes with copper and silver. One of these tetra-
nuclear clusters includes PO2F22 anions formed from the
hydrolysis of hexafluorophosphate. Unusually, these
PO2F2 anions are observed to coordinate to the silver(I)
cations, only the second time a coordinated PO2F22 motif
has been structurally characterised.
Alkyl-substituted N-linked receptor 2
5-tButyl-1,3-diiodobenzene (0.193 g, 0.500 mmol) and 1-
decyne (0.190 ml, 0.145 g, 1.05 mmol) were placed in a
small vial. L-Proline (0.023 g, 0.20 mmol), sodium
carbonate (0.021 g, 0.20 mmol), sodium ascorbate
(0.040 g, 0.20 mmol), sodium azide (0.078 g, 1.2 mmol),
copper(II) sulfate pentahydrate (0.025 g, 0.10 mmol) and
9:1 DMSO:water (2 ml) were added, and the suspension
was deoxygenated with nitrogen, sealed and heated to
658C overnight. It was cooled to room temperature and
poured into aqueous ammonia (1 mol l21, 30 ml) and then
extracted with ethyl acetate (3 £ 20 ml). The combined
organic fractions were washed with saturated brine
(2 £ 20 ml), dried (magnesium sulfate) and then dried
under reduced pressure. Purification by column chroma-
tography (silica, gradient: 15:1 to 10:1 dichlorometha-
ne:acetone) gave 2 as a golden oil. Yield: 0.195 g (79%).
Experimental
General remarks
Warning
Sodium azide and organic azides are potentially explosive
and should be handled with caution and in small
quantities.
Water was de-ionised and microfiltered using a Milli-
Qw Millipore machine. TBA salts, AgPF6 and [CuI(CH3-
CN)4](PF6) were stored in a vacuum dessicator under
reduced pressure. The precursors 5-tbutyl-1,3-diiodoben-
zene (32) and 5-tbutyl-1,3-diethynylbenzene (33, 34) were
synthesised in two and four steps, respectively, from
4-tbutyl-aniline by slight modifications of literature
procedures. All other compounds were bought commer-
cially and used as received. Routine NMR spectra were
4
1H NMR (CDCl3): 7.89 (t, J ¼ 2.0 Hz, 1H, interior
phenyl C–H), 7.80–7.82 (m, 4H, trz-H, exterior phenyl
1
3
recorded on a Varian Mercury 300 spectrometer with H
C–H), 2.80 (t, J ¼ 7.7 Hz, 4H, trz-CH2), 1.68–1.78 (m,
t
4H, trz-CH2ZCH2), 1.22–1.44 (m, 29H, alkyl CH2, Bu-
NMR operating at 300 MHz, 13C NMR at 75.5 MHz.
Spectra for anion binding titrations were recorded on a
Varian Unity Plus 500 spectrometer with 1H NMR
operating at 500 MHz. Mass spectra were recorded on a
Bruker microTOF spectrometer.
3
H), 0.87 (t, J ¼ 6.9 Hz, 6H, CH3). 13C NMR (CDCl3):
155.6, 149.7, 138.1, 119.0, 117.3, 109.7, 35.6, 32.0, 31.3,
29.5, 29.5, 29.4, 29.3, 25.8, 22.8, 14.2. HR-ESI-MS (pos.):
515.3833, calcd for [C30H48N6·Na]þ ¼ 515.3833.
Alkyl-substituted C-linked receptor 1
Aryl-substituted C-linked receptor 3
5-tButyl-1,3-diethynyl benzene (0.182 g, 1.00 mmol) was
dissolved in 4:1 DMF:water (15 ml). Sodium azide
(0.156 g, 2.40 mmol), sodium carbonate (0.106 g,
1.00 mmol), copper(II) sulfate pentahydrate (0.050 g,
0.20 mmol), ascorbic acid (0.176 g, 1.00 mmol) and
bromooctane (0.38 ml, 0.43 g, 2.2 mmol) were added, and
the mixturewas heated to 808C under a nitrogen atmosphere
overnight. It was then cooled to room temperature and
partitioned between aqueous ammonium hydroxide/EDTA
5-tButyl-1,3-diiodobenzene (0.193 g, 0.50 mmol), 4-tbu-
tyl-ethynylbenzene (0.20 ml, 0.17 g, 1.1 mmol), L-proline
(0.035 g, 0.30 mmol), sodium carbonate (0.032 g,
0.30 mmol), sodium azide (0.098 g, 1.5 mmol), sodium
ascorbate (0.099 g, 0.50 mmol) and copper(II) sulfate
pentahydrate (0.037 g, 0.15 mmol) were placed in a
microwave vial. DMSO:water (9:1, 2 ml) was added to the
mixture and was deoxygenated with nitrogen. The vial
was sealed and heated at 608C for 4 days. Then was

Supramolecular Chemistry
cooled to room temperature and partitioned between X-ray crystallography
479
aqueous EDTA/ammonium hydroxide (30 ml) and ethyl
acetate (30 ml). The aqueous layer was extracted with
further ethyl acetate (2 £ 30 ml), the combined organic
fractions were washed with brine (60 mL) and dried
(magnesium sulfate). The organic fractions were taken
to dryness under reduced pressure and the resulting
yellow oil was dissolved in hot methanol (5 mL). It was
left to stand in a freezer overnight, resulting in the
precipitation of pale yellow crystals, which were isolated
by filtration and washed with cold methanol (2 ml). Yield:
0.047 g (18%).
Single crystal X-ray diffraction data for 3 and 4 were
collected using graphite monochromated Mo Ka radiation
˚
(l ¼ 0.71073 A) on a Nonius Kappa CCD diffractometer
equipped with a Cryostream N2 open-flow cooling device
(35), and the data were collected at 150(2) K. Series of v-
scans were done in such a way as to collect all unique
˚
reflections to a maximum of 0.80 A. Cell parameters and
intensity data (including inter-frame scaling) were
processed using the DENZO-SMN package (36).
Single crystal X-ray diffraction data for the metal
complexes were collected using graphite monochromated
1H NMR (CDCl3): 8.29 (s, 2H, trz-H), 8.05 (t,
˚
Cu Ka radiation (l ¼ 1.54184 A) on an Oxford Diffrac-
4
4J ¼ 1.4 Hz, 1H, interior phenyl-H), 7.93 (d, J ¼ 1.4 Hz,
tion SuperNova diffractometer. The diffractometer was
equipped with a Cryostream N2 open-flow cooling device
(35), and the data were collected at 150(2) K. Series of v-
scans were done in such a way as to collect all unique
3
2H, exterior phenyl-H), 7.88 (d, J ¼ 8.2 Hz, 4H, phenyl-
3
CH), 7.51 (d, J ¼ 8.2 Hz, 4H, phenyl-CH), 1.47 (s, 9H,
t
tBu-H), 1.37 (s, 18H, Bu-H). 13C NMR (CDCl3): 155.9,
151.9, 148.9, 138.0, 127.2, 126.0, 125.8, 117.7, 117.5,
109.9, 35.8, 34.9, 31.4, 31.3. HR-ESI-MS (pos.):
555.2308, calcd for [C34H40N6·Na]þ ¼ 555.2307.
˚
reflections to a maximum of 0.80 A. Cell parameters and
intensity data (including inter-frame scaling) were
processed using CrysAlis Pro (37).
The structures were solved by charge-flipping
methods using SUPERFLIP (38) and refined using full-
matrix least-squares on F 2 within the CRYSTALS suite
(39). All non-hydrogen atoms were refined with
anisotropic displacement parameters. Hydrogen atoms
were generally visible in the difference map and their
positions and displacement parameters were refined using
restraints prior to inclusion into the model using riding
constraints (40).
Aryl-substituted N-linked receptor 4
Sodium azide (0.098 g, 1.5 mmol), L-proline (0.035 g,
0.30 mmol), sodium carbonate (0.032 g, 0.30 mmol),
sodium ascorbate (0.099 g, 0.50 mmol) and copper(II)
sulfate pentahydrate (0.037 g, 0.15 mmol) were placed in a
microwave vial. 5-tButyl-1,3-diethynylbenzene (0.046 g,
0.25 mmol) and 4-tbutyl-iodobenzene (0.10 ml, 0.15 g,
0.55 mmol) were mixed in 9:1 DMSO:water (2 ml) and the
dry reagents were added to the mixture. The mixture was
deoxygenated with nitrogen, the vial was sealed and the
mixture was heated at 658C overnight. Then was cooled to
room temperature and partitioned between aqueous
EDTA/ammonium hydroxide (30 ml) and ethyl acetate
(30 ml). The aqueous layer was extracted with further
ethyl acetate (2 £ 30 ml), the combined organics was
washed with brine (60 ml) and dried (magnesium sulfate).
The organic fractions were concentrated under reduced
pressure and purified by column chromatography (silica,
1% methanol in dichloromethane) to give a yellow oil, 1H
NMR of which showed to be slightly crude 4. This was
collected in methanol (5 ml) and cooled in a freezer to
yield yellow crystals, which were isolated by filtration and
washed with cold methanol to give pure 4. Yield: 0.019 g
(14%).
In the trinuclear copper cluster, and both tetranuclear
silver clusters, ill-defined solvent was present, which had
to be dealt with using the PLATON-SQUEEZE procedure
(41, 42), and numerous restraints had to be applied to the
t
poorly behaved parts of the molecule (typically butyl
groups and peripheral phenyl rings). Crystallographic
data for the structures have been deposited with the
Cambridge Crystallographic Data Centre, CCDC:
869301–869305 and 869749. Copies of these data can
be obtained free of charge from the Cambridge Crystal-
lographic Data Centre via http://www.ccdc.cam.ac.uk/
data_request/cif.
Acknowledgements
We thank Diamond Light Source for an award of beamtime on
I19. We thank Oxford Chemical Crystallography for use of
instruments, and Dr Amber L. Thompson for assistance with
crystallography. NGW thanks the Clarendon Fund and Trinity
College for financial support.
1H NMR (CDCl3): 8.30 (s, 2H, trz-H), 8.22 (t,
4J ¼ 1.4 Hz, 1H, interior phenyl C–H), 8.00 (d,
4J ¼ 1.4 Hz, 2H, exterior phenyl C–H), 7.75 (d,
3J ¼ 8.6 Hz, 4H, phenyl C–H), 7.58 (d, 3J ¼ 8.6 Hz,
t
4H, phenyl C–H), 1.46 (s, 9H, Bu–H), 1.39 (s, 18H,
Notes
tBu–H). 13C NMR (CDCl3): 152.9, 152.3, 148.4, 134.8,
130.8, 126.8, 123.1, 120.7, 120.4, 118.1, 35.2, 35.0, 31.5,
31.4. HR-ESI-MS (pos.): 555.3209, calcd for
[C34H40N6·Na]þ ¼ 555.3207.
1. While not derived from a CuAAC reaction, Bronisz and co-
workers have shown that iron(II) complexes of 1,4-bis-
(1,2,3-triazolyl)-butane can give hysteretic spin crossover
behaviour.

480
N.G. White and P.D. Beer
2. The increased binding ability of N-linked triazoles relative
to C-linked triazoles has been implied by Li and Flood in
their studies of tetra-triazole macrocycles (6). A compu-
tational study by Flood and co-workers also suggested that
(14) Meudtner, R.M.; Ostermeier, M.; Goddard, R.; Limberg, C.;
Hecht, S. Chem. Eur. J. 2007, 13, 9834–9840.
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a N-linked triazole-phenyl-
triazole receptor was very slightly more favourable
(231.8 kcal mol21) than to a C-linked triazole-phenyl-
triazole receptor (230.4 kcal mol21) (27).
(16) Suijkerbuijk, B.M.J.M.; Aerts, B.N.H.; Dijkstra, H.P.;
Lutz, M.; Spek, A.L.; Koten, G.V.; Gebbink, R.J.M.K.
Dalton Trans. 2007, 1273–1276.
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were repeated in CDCl3 consistent with previous studies on
the halide binding of bis-triazole receptors in chlorinated
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`
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spectrometry gave ambiguous data, which offered little
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5. The N3 nitrogen atoms are observed to preferentially
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6. This bridging behaviour is perhaps not surprising given the
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7. This arrangement where one triazole group in a bis-triazole
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by Eisenberg et al. who prepared complexes of the form
[Cu4L2I4], where L is a ligand derived from the CuAAC
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