Anion-driven conformation control and enhanced sulfate binding utilising aryl linked salicylaldoxime dicopper helicates

Article abstract of DOI:10.1039/c1dt10808e

The synthesis and spectroscopic analysis of both "metal-only" and anion encapsulated dicopper(ii) double helicates utilising a new 1,4-aryl spacer is described. X-Ray crystallographic analysis of the complexes reveal that the aromatic spacer increases rig

Full text of DOI:10.1039/c1dt10808e

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PAPER
Anion-driven conformation control and enhanced sulfate binding utilising aryl
linked salicylaldoxime dicopper helicates†
James R. Stevens and Paul G. Plieger*
Received 1st May 2011, Accepted 26th July 2011
DOI: 10.1039/c1dt10808e
The synthesis and spectroscopic analysis of both “metal-only” and anion encapsulated dicopper(II)
double helicates utilising a new 1,4-aryl spacer is described. X-Ray crystallographic analysis of the
complexes reveal that the aromatic spacer increases rigidity in the complex, yet the complexes are still
able to undergo a dramatic “coiling up” to bind anions. Spectroscopic analysis has shown a clear
enhancement in the binding strength of SO4 over the non-coordinating anions ClO4 , NO3 and Br-
which has been attributed to a combination of enhanced rigidity in the complex and an increased
electrostatic interaction between the complex and the dianion.
2-
-
-
Introduction
The binding and extraction of anions continues to receive intense
attention due to the great importance these molecules play in a
variety of environmental, biological and commercial applications.1
Ditopic receptors designed for simultaneous binding of both
cations and their attendant anions is a challenging task due to
the specific requirements needed to be met by both the metal
coordinating site and the anion binding site/pocket.2 Nevertheless
there continues to be innovative and well designed examples
reported on a regular basis.3
Scheme 1 General form of the ligands used to make the dicopper
helicates.
In the last few years we have devoted some time to exploring
anion binding complexes that have been designed to specifically
encapsulate anions within dicopper helicates. These complexes
contain metal complexation sites utilising salicylaldimine4,5 or
salicylaldoxime6,7 units which are linked to one another via spacers
of alkyl tertiary amines (L2 in Scheme 1). Upon complexation
the complexes self assemble and form neutral di-metallic helicates.
When these groups of anion receptors are further protonated, they
are able to exist in a zwitterionic state and form both hydrogen
bonds and (in some cases) metal covalent bonds with encapsulated
anions.4–7 We have shown that dramatic conformational changes
can occur within these complexes upon binding an anion; the
complexes coil up and there is a substantial contraction of the
central cavity within the complex, bringing the Cu(II) centres closer
together with a corresponding increase in the helix twist angle of
the complex. Anion binding studies with this complex however
showed only minor changes in anion binding strength in non-
aqueous media6 yet were shown to be selective for both sulfate and
dihydrogen phosphate in aqueous media.7 Further, deprotonation
of the oxime groups can lead to extended hexanuclear trihelicates.8
In this paper, we demonstrate that a decrease in ligand
conformational flexibility can lead to an enhancement in anion
binding strength. This has been achieved by the substitution of a
six-carbon alkyl spacer (L2 Scheme 1) which is used to link two
salicylaldoxime units together with that of a six carbon aromatic
spacer (L1 Scheme 1). This minor change has led to a clear
enhancement in the binding strength of sulfate over other non-
coordinating anions.
Results and discussion
Synthesis of the ligands
Ligand L1 was prepared from terephthalaldehyde as outlined in
Scheme 2. Condensation of the resulting secondary diamines
with 3-(bromomethyl)-5-tert-butyl-2-hydroxybenzaldehyde9 in
dichloromethane resulted in the formation of the aromatic linked
salicylaldehyde. Subsequent oximation gave the final ligand in an
overall yield of 43%. The ligand was fully characterised including
X-ray structural analysis (see experimental and ESI†).
Institute of Fundamental Sciences, Massey University, Private Bag 11
222, Palmerston North, New Zealand. E-mail: p.g.plieger@massey.ac.nz;
Fax: 0064 6 350 5682; Tel: 0064 6 356 9099, extension 7825
† Electronic supplementary information (ESI) available: X-Ray of the
ligand L1 and further descriptions of the structures of 3 and 4. CCDC
reference numbers 824379–824382. For ESI and crystallographic data in
CIF or other electronic format, see DOI: 10.1039/c1dt10808e
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 12235–12241 | 12235
©

Table 1 Selected bond lengths and angles for the Cu(II) centres of 1
Bond angles (◦)
˚
Atoms
Bond lengths (A) X–Cu–X
Cu1–O11
Cu1–O12
Cu1–N212 1.950(1)
Cu1–N222 1.947(1)
Cu2–O13
Cu2–O14
Cu2–N232 1.946(2)
Cu2–N242 1.953(2)
Cu2–O12b 2.9109(1)
1.852(2)
1.870(2)
O11–Cu1–N212
93.5(1)
87.3(1)
88.6(1)
92.6(1)
92.6(1)
87.8(1)
89.3(1)
92.6(1)
86.9(1)
O11–Cu1–N222
O12–Cu1–N212
O12–Cu1–N222
O13–Cu2–N232
O13–Cu2–N242
O14–Cu2–N232
O14–Cu2–N242
O13–Cu2–O12b
1.865(1)
1.863(1)
O11–Cu1–Cu2–O13 78.3(1)
O12–Cu1–Cu2–O14 79.2(1)
Cu1–Cu2
8.2588(9)
Fig. 1 Perspective views of 1 showing the edge on nature of the aryl linkers
and positioning of the CHCl3 solvent molecule (a) and copper coordination
site with labels (b). Hydrogen atoms not involved in H-bonding have been
omitted for clarity.
Formation of metal salt complexes
Scheme
2
Ligand synthesis of L1. Reagents and conditions: (i)
-
Examples of Cu(II) salt complexes containing the anions ClO4 ,
MeNH2·HCl/KOH, MeOH, rt, 2 h; (ii) NaBH4/MeOH, rt, 1 h; (iii) Et3N,
NO3 , SO42-, BF4 , and Br- were readily prepared by direct
combination of L1 and the appropriate Cu(II) salt in methanol.
Crystals suitable for X-ray structure determination were obtained
for [ClO4ÃCu2L1 ](ClO4)3 (3) (Fig. 2) and [BF4ÃCu2L1 ](BF4)3
-
-
CH2Cl2, rt, 15 h; (iv) NH2OH·HCl/KOH, EtOH, rt, 15 h.
Formation of “metal only” complexes
2
2
The anion-free charge-neutral dinuclear Cu(II) complex [Cu2(L1-
2H)2] (1), was readily isolated from the reaction of the ligands with
copper acetate in a manner akin to that used to prepare complexes
of L2 previously.6 Microanalysis, ESMS and X-ray structure
determination (see below) all confirmed the general formula of the
complex. The complex consists of two Cu(II) atoms coordinated
to two ligand molecules with each copper centre sharing both
ligands via coordination to the N-oximate and phenolate positions
(N2O22-). Head-to-tail hydrogen-bonding of the salicylaldoxime
ligand dominate the coordination site providing a near square
planar coordination geometry for Cu1 and a square pyramidal
geometry for Cu2 which possess a weak fifth phenolate oxygen
donor from an adjacent complex (Fig. 1 and Table 1). In 1
each 1,4-aryl linker (one from each ligand) is wound around one
another in a helical fashion with each salicylaldoxime ring sitting
above a corresponding ring from the opposing ligand and the aryl
groups in the spacers sit edge-on to one another. There is a CHCl3
molecule encapsulated within the complex making a weak H-bond
(4) to determine the extent to which a restrictive spacer might
influence both anion binding and cavity geometries. Comparisons
have also been made with metal salt complexes of L2 which have
been communicated previously.6,7
˚
to p interaction to one of the phenolate rings of 3.50(1) A. The
rigid nature of the spacer has resulted in a copper–copper distance
◦
˚
for 1 of 8.2588(9) A and a helix twist angle of 78.7(2) (the mean
of the two O–Cu–Cu–O angles), which is considerably shorter
and less twisted than the corresponding distance and angle for the
Fig. 2 Perspective view of [ClO4ÃCu2L1 ]3+, showing the atom labelling
2
scheme and the weakly coordinated axial O–N–Cu atoms of an adjacent
complex. Hydrogen atoms, disorder around the central perchlorate (50 : 50)
and the three counter perchlorate anions have been omitted for clarity.
◦
2
˚
more floppy complex [Cu2(L -2H)2] at 10.191(3) A and 85.9(3)
respectively.6
12236 | Dalton Trans., 2011, 40, 12235–12241
This journal is
The Royal Society of Chemistry 2011
©

Table 2 Selected bond lengths and angles at the Cu(II) centres of 3
of similar distance (Cu1–O11 2.4857(3) and Cu2–O12 2.6062(2)
˚
A) between two of the oxygen atoms from the central anion and
each copper atom. Secondly, there exists three moderate to weak
˚
Atoms
Bond lengths (A) X–Cu–X
Bond angles (◦)
˚
hydrogen bonds (range = 2.839–3.295 A for N ◊ ◊ ◊ F distances) for
Cu1–O1
Cu1–O3
Cu1–N212
Cu1–N232
Cu1–O11
Cu1–O213b 2.853(3)
Cu2–O2
Cu2–O4
1.900(4)
1.907(4)
1.942 (6)
1.952(6)
2.487(11)
O1–Cu1–N212
92.7(2)
90.8(2)
87.4(2)
91.7(2)
89.9(4)
84.5(2)
91.6(2)
89.6(2)
88.4(2)
91.9(2)
76.5(3)
129.8(2)
128.3(2)
each disordered orientation of the anion, originating from the
four protonated tertiary amines on the two spacers which all point
inwards towards the central cavity (see Fig. 3 and Table 3 for
hydrogen bond distances and angles). Finally, in contrast to the
“metal-only” complex 1, the aryl groups are now rotated so the aryl
rings face towards the anion forming an anion–p interaction10,11 at
O1–Cu1–N232
O3–Cu1–N212
O3–Cu1–N232
O11–Cu1–O1
O213b–Cu1–O1
O2–Cu2–N222
O2–Cu2–N242
O4–Cu2–N222
O4–Cu2–N242
O12–Cu2–O2
1.931(5)
1.907(4)
1.953(6)
1.933(6)
2.606(11)
Cu2–N222
Cu2–N242
Cu2–O12
˚
a distance of 3.02 and 3.04 A for each of the positionally disordered
sites of the anion. These two anion–p distances are relatively strong
compared to other perchlorate oxygen–p interactions of this type,
possibly as a consequence of the restricted movement this anion
possesses within the cavity.10
O1–Cu1–Cu2–O2
O3–Cu1–Cu2–O4
Cu1–Cu2
7.135(2)
The coordination environment for each copper atom in 3 is
similar to 1 above with both Cu(II) atoms coordinated to two L1
ligands through N-oximate and phenolate donors (N2O22-). Both
copper atoms coordinate to oxygen atoms of the encapsulated
perchlorate anion and Cu1 has an additional weak interaction to
an oximate O atom on an adjacent complex situated directly above
it. The coordination environments for Cu1 and Cu2 are therefore
best described as distorted octahedral and distorted square
pyramidal respectively (see Table 2 for selected bond lengths and
angles around the metal centres). The pseudo macrocyclic cavity
surrounding each metal centre is completed by an oxime hydrogen
bonded towards the opposing phenolate oxygen with an average
˚
distance of ~2.72 A which is buttressed with a secondary H-bond
from each protonated tertiary amine on the spacer to the phenolate
˚
oxygen atoms with an average distance of ~2.90 A (refer to Table 3
for H-bond distances and angles). Each tertiary amine in the aryl
containing spacer of L1 is protonated and located around the
periphery are three perchlorate anions giving rise to an overall
neutral complex.
Fig. 3 Perspective view of [ClO4ÃCu2L1 ]3+ showing one disordered
position of the ClO4 anion and both the H-bonding of the anion to
Located at the centre of the complex, flanked by both the metal
2
-
-
centres and the aryl rings of the spacer, is a ClO4 anion. It sits
the ammonium groups and the anion–p interaction to the aryl ring of the
linker. Hydrogen atoms not involved in hydrogen bonding, the tert-butyl
groups and counter anions have been omitted for clarity.
comfortably inside the cavity created by the complex and the
complex has contracted significantly in the process so that both of
the copper(II) centres are able to make weak interactions with this
traditionally non-coordinating anion. This encapsulated anion is
stabilised by three distinct interactions; there are two Cu–O bonds
The distance between the two copper(II) centres in 3 has reduced
˚
˚
markedly from 8.2588(9) to 7.135(2) A (D ª 1.12 A or 14%)
upon encapsulating the perchlorate anion, in addition, the average
helix twist angle (O–Cu–Cu–O) of 3 has increased substantially
by over 50◦ to 129.0 (4)◦. This indicates that this more rigid
aromatic spacer still imparts sufficient flexibility to allow the
Table 3 Selected H-bond and anion–p distances and angles for 3
˚
Atoms
D–H–A distance (A)
D–H–A angle (◦)
N622–H62j ◊ ◊ ◊ O12
N612–H61j ◊ ◊ ◊ O13
N642–H64j ◊ ◊ ◊ O14
N632–H63j ◊ ◊ ◊ O11A
N612–H61j ◊ ◊ ◊ O13A
N642–H64j ◊ ◊ ◊ O14A
O213–H213 ◊ ◊ ◊ O3
O223–H223 ◊ ◊ ◊ O4
O233–H233 ◊ ◊ ◊ O1
O243–H243 ◊ ◊ ◊ O2
N612–H61j ◊ ◊ ◊ O1
N622–H62j ◊ ◊ ◊ O2
N632–H63j ◊ ◊ ◊ O3
N642–H64j ◊ ◊ ◊ O4
Cl1–O14 ◊ ◊ ◊ Ring 1
Cl1–O13a ◊ ◊ ◊ Ring 2
3.08(1)
2.99(2)
3.30(2)
2.84(2)
3.29 (2)
2.95(1)
2.63(1)
2.66(1)
2.85(1)
2.73(1)
2.81(1)
2.88(1)
2.94(1)
2.96(1)
3.02
143.6
115.9
147.7
145.4
135.0
128.6
132.8
132.4
125.8
130.7
130.0
128.0
126.0
124.0
151.9
157.8
-
complex to coil up to accommodate the encapsulated ClO4
anion. The coordination geometry around the copper metals has
been influenced slightly with the incorporation of the anion. The
˚
average Cu–O bond distance has increased slightly (0.05 A) and the
average O–Cu–O bond angle is now slightly more linear (173.5◦).
Conversely, the Cu–N bond distance has remained unchanged and
the average N–Cu–N bond angle is now more bent (161.6◦). The
weak intermolecular bond to the copper seen in 1 is retained in 3.
The overall structural features of 4 are similar to 3. Both Cu(II)
centres in 4 have the same trans arrangement as the four in-
plane donors of 3. The pseudo macrocyclic cavity surrounding
each metal centre is retained with oxime to phenolate hydro-
gen bonds again buttressed with secondary H-bonds to each
3.04
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 12235–12241 | 12237
©

Table 4 Selected bond lengths and angles for 4
Bond angles (◦)
˚
Atoms
Bond lengths (A) X–Cu–X
Cu1–O11
Cu1–O14
Cu1–N212
Cu1–N242
Cu2–O13
Cu2–O12
Cu2–N222
Cu2–N232
Cu2–F11b
Cu1–Cu2
1.881(4)
1.903(4)
1.955(5)
1.952(5)
1.894(3)
1.896(3)
1.951(4)
1.932(5)
2.538(2)
7.212(1)
O11–Cu1–N212
92.1(2)
89.1(2)
88.9(2)
91.2(2)
92.3(2)
89.7(2)
88.0(2)
92.1(2)
76.5(4)
O11–Cu1–N242
O14–Cu1–N212
O14–Cu1–N242
O12–Cu2–N222
O12–Cu2–N232
O13–Cu2–N222
O13–Cu2–N232
F11b–Cu2–O12
O11–Cu1–Cu2–O12 130.7(2)
O14–Cu1–Cu2–O13 130.4(2)
F11 ◊ ◊ ◊ Cu2
2.84(2)
O12–Cu2–F11
O12–Cu2–F11b
O14–Cu1–F14
O14–Cu1–F14b
74.3(4)
76.4(3)
73.2(3)
69.2(2)
Bond lengths (A)
2.981(6)
2.818(5)
3.003(5)
2.877(6)
F11b ◊ ◊ ◊ Cu2 2.54(1)
F14 ◊ ◊ ◊ Cu1
F14b ◊ ◊ ◊ Cu1 3.10(1)
Atoms
O213 ◊ ◊ ◊ O14 2.693(5)
O223 ◊ ◊ ◊ O13 2.649(5)
O233 ◊ ◊ ◊ O12 2.756(5)
O243 ◊ ◊ ◊ O11 2.707(5)
2.63(1)
˚
˚
Bond lengths (A) Atoms
N612 ◊ ◊ ◊ O11
N622 ◊ ◊ ◊ O12
N632 ◊ ◊ ◊ O13
N642 ◊ ◊ ◊ O14
Fig. 4 Perspective view of [BF4ÃCu2L1 ]3+ showing the major component
2
-
(60%) of the disordered BF4 with H-bonding to the ammonium groups
phenolate oxygen from the protonated tertiary amines. The
occluded tetrafluoroborate anion is positionally disordered over
two sites in a 60 : 40 ratio. Each disordered position has one
weak bonding interaction between one fluorine atom and one
of the copper atoms but in opposing directions, therefore, the
coordination environments for the Cu(II) centres in 4 are described
as distorted square planar (Cu1) and distorted square pyramidal
(Cu2) for the major component of the disorder and the reverse
description for the minor component (refer to Table 4 for selected
bond distances and angles).
and the anion–p interaction to the aryl ring on the spacer. Hydrogen
atoms not involved in hydrogen bonding, the tert-butyl groups, the minor
component of the anion disorder (40%) and the peripheral counter anions
have been omitted for clarity.
Table 5 Selected H-bond distances, angles and anion–p interactions
-
between the encapsulated BF4 anion and the complex 4
˚
Atoms
H-bond distances (A)
D–H–A angles (◦)
N622–H62j ◊ ◊ ◊ F11
N612–H61j ◊ ◊ ◊ F12
N632–H63j ◊ ◊ ◊ F13
N642–H64j ◊ ◊ ◊ F14
N622–H62j ◊ ◊ ◊ F11b
N612–H61j ◊ ◊ ◊ F12b
N632–H63j ◊ ◊ ◊ F13b
N642–H64j ◊ ◊ ◊ F14b
B1–F13 ◊ ◊ ◊ Ring 2
B1b–F12b ◊ ◊ ◊ Ring 1
3.01(2)
2.92(1)
3.00(1)
3.12(1)
3.17(1)
3.08(1)
2.92(1)
2.81(1)
3.10
137.7
126.3
150.2
146.0
144.1
149.8
131.2
135.0
133.5
124.0
The distance between the two Cu(II) centres in 4 at 7.212(1)
A has decreased significantly from that of 1, but is only slightly
˚
larger than that of 3. The average helical twist angle has again
increased significantly over 1 but is comparable to 3 at 130.6◦.
Therefore it appears that while the complex has again coiled up
to accommodate this anion it may now have reached its limit
of conformational flexibility and may not be able to further
contract for this slightly smaller anion. An inspection of the H-
bonds around the entrapped BF4- anion reveals hydrogen bonding
now plays a more dominant role in stabilising the anion with
each disordered tetrafluoroborate now stabilised by four moderate
hydrogen bonds.
3.31
Table 6 Formation constants of [Xn-ÃCu2L1 ](4-n)+ obtained from spec-
2
trophotometric titrationsa of 1 with H2SO4, HClO4, HBr, and HNO3 in
THF at 294 K
Acid/anion
log K
Similarly to 3, the anion–p interaction is again present but is
˚
weaker at distances of 3.31 and 3.10 A, for the major and minor
H2SO4
HClO4
HNO3
HBr
5.53 0.32
3.86 0.22
3.72 0.08
3.69 0.17
components of the disordered BF4- anion respectively (Fig. 4 and
Table 5). Overall there appears to be a subtle shift away from
stabilisation utilising metal–anion bonds towards an increased role
in stabilisation by hydrogen bonding as a consequence of both
reduced anion volume and restrictive conformational flexibility of
the receptor.
a For the reaction [Cu2L1 ]4+ + Xn- ꢀ [Xn-ÃCu2L1 ](4-n)+ involving com-
2
2
plexes with L1 in its zwitterionic form with both aminomethyl substituents
protonated.
The binding constants given in Table 4 vary in the order
Anion binding studies
-
-
-
Br- ª NO3 ª ClO4 ꢀ SO4 . This order is consistent with the
The “copper only” complex was subjected to UV-Vis titration
experiments in THF to quantify the effect that a more rigid spacer
has with regards to anion affinity. Preliminary stability constants
have been calculated for SO42-, NO3 , ClO4 and Br- anions and
are shown in Table 6.
stability of the [Xn-ÃCu2L1 ](4-n)+ complexes being dependent on a
2
combination of anion charge, size, shape, coordination ability to
the copper atoms and ability to form hydrogen bonds to the N–H in
the alkylammonium groups. These factors favour the inclusion of
the dianion sulfate, yet there appears to be an added enhancement
-
-
12238 | Dalton Trans., 2011, 40, 12235–12241
This journal is
The Royal Society of Chemistry 2011
©

in binding strength towards sulfate for the more conformationally
restricted L1 (+1.7 log units) when the data is compared against
that for the L2 inclusion complexes (~0.1 log units).6 For the weakly
dichloromethane (50 ml) were added simultaneously and
slowly (over 1 h) solutions of 3-(bromomethyl)-5-tert-butyl-2-
hydroxybenzaldehyde (3.345 g, 12.3 mmol) in dichloromethane
(50 ml) and N,N¢-dimethyl-p-xylylenediamine (1.013 g, 6.5 mmol)
in methanol/dichloromethane (1 : 20, 50 ml). The resulting
mixture was left to stir at rt overnight. The reaction was
monitored for completion via 1H-NMR. The solvent was
evaporated to dryness and the yellow solid was redissolved in
chloroform (80 ml) then filtered. The organic layer was washed
with water (3 ¥ 30 ml), separated and dried over anhydrous
MgSO4. The solvent was removed under reduced pressure and
dried in vacuo to give a bright yellow solid (3.262 g, 97%). dH
(500 MHz; CDCl3; Me4Si): 10.32 (2H, S, CHO), 7.62 (2H, d,
J = 2.3 Hz, ArH), 7.38 (2H, d, J = 1.8 Hz, ArH), 7.31 (4H, s,
ArH), 3.74 (4H, s, CH2), 3.61 (4H, s, CH2), 2.26 (6H, s, NCH3),
1.28 (18H, s, C(CH3)3). dC (125 MHz; CDCl3; Me4Si): 192.4
(CHO), 159.3 (COH), 142.1 (ArC), 136.7 (ArC), 133.1 (ArCH),
129.6 (ArCH), 125.1 (ArCH), 124.0 (ArC), 122.1 (ArC), 61.5
(CH2), 59.1 (CH2), 41.8 (NCH3), 34.3 (C(CH3)3), 31.5 (C(CH3)3).
Found: C, 74.21; H, 8.31; N, 4.78%. C34H44N2O4·0.3H2O requires
C, 74.23; H, 8.17; N, 5.09%. m/z (ESI) 545.71 (1b)+. vmax/cm-1
2962br (C–H), 1676s (C O), 1216s (C–O), 825s (Ar–H). Mp
129.2–131.1 ◦C.
coordinating anions, ClO4 , NO3 and Br- there appears to be no
discernible difference in binding strength. The inclusion of the
aryl ring in the spacer may have reduced the dependency on anion
shape for the binding of these anions.
-
-
Conclusion
The inclusion of aromatic spacers in the salicylaldoxime ligand
spacers of these complexes has led to a number of changes in
the anion binding characteristics of complexes of this type. The
increase in rigidity has played a major role in the clear enhance-
ment in strength of binding sulfate over the non-coordinating
anions. Less of an effect, if at all any, has been noticed with the
introduction of groups capable of anion–p interactions. In fact, the
addition of these aromatic spacers appears to minimise differences
in binding strength attributed to the shape of the anions. Work
continues with us to further probe this theory.
Experimental
Unless specified, commercial regents and solvents were used
without purification. 1H and 13C NMR spectra were recorded
on Bruker Avance 400 MHz and 500 MHz spectrometers; d
values are relative to TMS or the corresponding solvent. Mass
spectra were obtained using a Micromass ZMD 400 electrospray
spectrometer. IR spectra were recorded on a Nicolet 5700 FT-IR
spectrometer from Thermo Electron Corporation using an ATR
sampling accessory. UV-Vis spectra were recorded in THF using
a CARY 100Bio UV-Vis spectrometer. Elemental analyses were
determined by the Campbell Microanalytical Laboratory at the
University of Otago.
(1E,1¢E)-5-tert-Butyl-3-(((4-(((5-tert-butyl-2-hydroxy-3-((E)-
( hydroxyimino ) methyl ) benzyl ) ( methyl ) amino ) methyl ) benzyl )-
(methyl)amino)methyl)-2-hydroxybenzaldehyde oxime (L1). A so-
lution of hydroxylamine hydrochloride (0.400 g, 5.76 mmol) in
ethanol (60 ml) was added to a solution of potassium hydroxide
(0.324 g, 5.77 mmol) in ethanol (60 ml). The resulting white
precipitate was removed by filtration. The filtered solution was
slowly dripped into a solution of 1b (1.032 g, 1.90 mmol) in a
chloroform/ethanol mix (1 : 20, 100 ml) over 2 h. The pale yellow
solution was then allowed to stir at rt overnight. The solution
was removed under reduced pressure, dissolved in chloroform
(50 ml) and washed with water (2 ¥ 20 ml). The organic layer was
separated and dried over anhydrous MgSO4, filtered and dried to
give a pale yellow solid. The product could be further purified by
crystallisation from hot toluene to give colourless block shaped
crystals (0.580 g, 53%). dH (400 MHz; CDCl3; Me4Si): 10.09 (2H,
br s, NOH), 8.46 (2H, s, CHNOH), 7.44 (2H, d, J = 2.1 Hz, ArH),
7.32 (4H, s, ArH), 7.15 (2H, d, J = 2.1 Hz, ArH), 3.75 (4H, s, CH2),
3.63 (4H, s, CH2), 2.27 (6H, s, NCH3), 1.30 (18H, s, C(CH3)3).
dC (100 MHz; CDCl3; Me4Si): 154.3 (COH), 148.7 (CHNOH),
141.8 (ArC), 136.3 (ArC), 129.7 (ArCH), 128.2 (ArCH), 123.9
(ArCH), 122.5 (ArC), 117.7 (ArC), 61.2 (CH2), 59.3 (CH2), 41.6
(NCH3), 34.1 (C(CH3)3), 31.5 (C(CH3)3). Found: C, 72.21; H,
8.11; N, 9.22%. C34H46N4O4·0.5C7H8 requires C, 72.55; H, 8.12;
N, 9.02%. m/z (ESI) 575.85 (L1)+. vmax/cm-1 2955br (C–H), 1615m
(C N), 1268s (C–O), 824s (Ar–H). Mp 126 ◦C.
Synthesis of ligands
N,N¢-Dimethyl-p-xylylenediamine (1a). A solution of methy-
lamine hydrochloride (3.115 g, 46.1 mmol) in methanol (60 ml) was
allowed to mix with a solution of potassium hydroxide (2.788 g,
49.7 mmol) in methanol (60 ml). The filtered solution was slowly
dripped into a second solution of terephthalaldehyde (2.106 g,
15.7 mmol) in methanol (80 ml) over 1 h. The pale yellow solution
was stirred at rt for 2 h. Sodium borohydride (1.256 g, 33.2 mmol)
was added portion wise to the stirred solution over 10 min, which
was then left to stir for 1 h. The solvent was removed under reduced
pressure and the resulting white solid was dissolved in chloroform
(70 ml) and washed with water (50 ml). The organic layer was
separated and dried over anhydrous MgSO4. The solvent was
removed under reduced pressure, leaving a pale yellow oil, which
upon standing, solidified into a white solid (2.128 g, 83%). dH
(500 MHz; CDCl3; Me4Si): 7.27 (4H, s, ArH), 3.73 (4H, s, CH2),
2.45 (6H, s, CH3), 1.33 (2H, br s, NH). dC (125 MHz; CDCl3;
Me4Si): 139.1 (ArCHCArCH), 128.4 (ArCH), 56.0 (CH2), 36.2
(CH3). m/z (ESI) 165.45 (1a)+. nmax/cm-1 3259br (N–H), 810s
(Ar–H).
General Cu(II) complex synthesis with L1
To a stirred pale yellow solution of L1 (9.00 mmol L-1) in
methanol/chloroform (10 : 1) was slowly added dropwise 1 mole
equivalent of the copper(II) salt (12.00 mmol L-1) in methanol over
30 min. The resulting coloured solution was stirred for 20 h. The
solvent was evaporated to dryness. The crude product was then
purified by recrystallisation.
3,3¢-(1,4-Phenylenebis(methylene))bis(methylazanediyl)bis(me-
thylene)bis(5-tert-butyl-2-hydroxybenzaldehyde)
(1b). To
a
stirred solution of triethylamine (1.316 g, 13.0 mmol) in
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 12235–12241 | 12239
©

“Copper only” complex, [Cu2(L1-2H)2] (1). The general
method outlined above was followed using copper(II) acetate
monohydrate. The crude brown product was purified by recrys-
tallisation with diisopropyl ether diffusion from chloroform to
afford brown platelet crystals. The crystals were collected and
washed with diisopropyl ether (0.1134 g, 15%). Found: C, 56.49;
H, 6.38; N, 7.05%. C68H88N8O8Cu2·2CHCl3·0.5DIPE requires C,
56.12; H, 6.26; N, 7.17%. m/z (ESI) 636.79 [(L1-H)Cu]+. UV-
Vis (THF, 1.5 ¥ 10-5 mol L-1) lmax/nm (e/L mol-1 cm-1): 350
(21 000), 273 (60 700), 256 (72 800). vmax/cm-1 3137brw (O–H),
1625m (C N), 1216s (C–O), 836s (Ar–H).
acetonitrile. The dark brown precipitate was collected and washed
with diethyl ether (0.082 g, 28%). Found: C, 42.81; H, 4.97; N,
6.10%. C68H92N8O8Br4Cu2·4HBr requires C, 42.54; H, 5.04; N,
5.84%; m/z (ESI) 718.61 ([BrL1Cu])+; UV-Vis (THF/0.1% MeOH,
2.0 ¥ 10-5 mol L-1) lmax/nm (e/L mol-1 cm-1): 670 (825), 386 (7300),
333 (19 300), 311 (23 100); vmax/cm-1 1621m (C N), 834s (Ar–H).
X-Ray structure determination
X-Ray data were recorded at low temperature with a Rigaku-
Spider X-ray diffractometer, comprising a Rigaku MM007
microfocus copper rotating-anode generator, high-flux Osmic
monochromating and focusing multilayer mirror optics (Cu K
[SO4Ã(Cu2L1 )](SO4)3 (2). The general method outlined above
2
˚
radiation, l = 1.5418 A), and a curved image-plate detector.
was followed using copper(II) sulfate pentahydrate. The dark green
product was purified by recrystallisation with diisopropyl ether
diffusion from methanol. The green precipitate was collected
and washed with diisopropyl ether (0.040 g, 26%). Found: C,
48.68; H, 6.28; N, 6.42%. C68H92N8O24S4Cu2·2.5 MeOH requires C,
48.64; H, 5.91; N, 6.44%; m/z (ESI) 734.38 ([SO4L1Cu])+. UV-Vis
(THF/0.1% MeOH, 2.0 ¥ 10-5 mol L-1) lmax/nm (e/L mol-1 cm-1):
310 (15 900); nmax/cm-1 1630brm (C N), 1101brs (SO4), 838w
(Ar–H).
CrystalClear12 was utilized for data collection and FSProcess in
PROCESS-AUTO13 for cell refinement and data reduction. All
structures were solved employing direct methods and expanded by
Fourier techniques.14 Non-hydrogen atoms were refined anisotrop-
ically. Hydrogen atoms were placed in calculated positions and
refined using a riding model with fixed isotropic U values. The
encapsulated perchlorate anion within 3 and one of the attendant
perchlorate anions are both disordered over two sites in a 50 : 50
ratio. Likewise the encapsulated tetrafluoroborate anion in 4 is also
disordered (60 : 40). There exists rotational disorder on a number
of tert-butyl groups in 4 (50 : 50). Disordered solvent regions in the
structures 1·CHCl3 and 3 were treated in the manner described by
van der Sluis and Spek,15 resulting in the removal of 47 and 258
e- per cell respectively. These values approximate to C6H14O (58)
and 2C6H14O + 0.5CH3CN (127) per formula unit respectively.
[ClO4Ã(Cu2L1 )](ClO4)3 (3). The general method outlined
2
above was followed using copper(II) perchlorate hexahydrate.
The green/grey product was purified by recrystallisation with
diisopropyl ether diffusion from acetonitrile to afford green
chunky crystals. The crystals were collected and washed with
diisopropyl ether (0.147 g, 50%). Found: C, 47.43; H, 5.61; N,
6.49%. C68H92N8O24Cl4Cu2·3H2O requires C, 47.25; H, 5.71; N,
6.48%; m/z (ESI) 736.67 ([ClO4L1Cu])+; UV-Vis (THF/0.5%
MeCN, 2.0 ¥ 10-5 mol L-1) lmax/nm (e/L mol-1 cm-1): 351 (8600),
270 (26 200); vmax/cm-1 3132brw (O–H), 1631m (C N), 1091brs
(ClO4), 838w (Ar–H).
Crystal
data
for
[Cu2(L1-2H)2]·CHCl3
(1)·CHCl3.
2(C68H84Cu2N8O8), 0.5(C2H2Cl6) Mr = 2656.39, brown platelet,
¯
˚
0.58 ¥ 0.31 ¥ 0.17 mm, triclinic, P1 EQ, a = 11.4781(3) A, b ◦=
◦
˚
˚
˚
14.4375(3) A, ◦c = 25.0402(18) A, a = 93.474(7) , b = 98.589(7) ,
3
-1
g = 113.012(8) , U = 3744.1(4) A , Z = 1, m = 1.620 mm , F(000) =
1398, T = 123(2)K. A total of 48 836 reflections were collected in
the range 6.6◦ < 2q < 62.4◦. The 11 657 independent reflections
[BF4Ã(Cu2L1 )](BF4)3 (4). The general method outlined above
2
was followed using copper(II) tetrafluoroborate monohydrate. The
crude green product was purified by recrystallisation with diethyl
ether diffusion from acetone to afford brown platelet crystals. The
crystals were collected and washed with diethyl ether (0.034 g,
16%). Found: C, 50.35; H, 5.97; N, 6.64%. C68H92N8O8B4F16Cu2
requires C, 50.30; H, 5.71; N, 6.90%. m/z (ESI) 636.16 [(L1-
H)Cu]+; UV-Vis (THF/0.2% MeCN, 2.0 ¥ 10-5 mol L-1) lmax/nm
(e/L mol-1 cm-1): 351 (17 600), 270 (54 400), 256 (63 000); vmax/cm-1
1630w (C N), 1053brs (BF4), 838w (Ar–H).
[R(int) = 0.058] were used after absorption correction (Tmin
=
0.389, Tmax = 1.000). Refinement of 812 parameters converged to
R1 = 0.0761 [for 8137 reflections having I > 2s(I)], wR2 = 0.2462
and goodness-of-fit of 1.10 (for all 11 657 F2 data). Peak/hole
-3
˚
1.15/-0.88 e A .
Crystal
data
for
[ClO4Ã(Cu2L1 )](ClO4)3
(3).
2
C68H92Cu2N8Cl4O24, Mr
=
1674.38, green chunk, 0.24
¥
¯
˚
0.16 ¥ 0.16 mm, triclinic, P1, a = 14.7◦464(8) A, b = 15.6825(8)
[NO3Ã(Cu2L1 )](NO3)3 (5). The general method outlined
◦
˚
˚
2
A, c = 21.3265(15) A, a = 95.308(7) , b = 109.898(8) , g =
◦
3
-1
˚
above was followed using copper(II) nitrate trihydrate. The dark
green product was purified by recrystallisation with diisopropyl
ether diffusion from a methanol/acetonitrile (4 : 1) mix. The
dark green precipitate was collected and washed with diisopropyl
ether (0.122 g, 37%). Found: C, 52.84; H, 6.46; N, 11.07%.
C68H92N12O20Cu2·H2O requires C, 52.94; H, 6.14; N, 10.90%;
m/z (ESI) 699.77 ([NO3L1Cu])+, 668.22 ([L1Cu]2NO3)2+; UV-Vis
(THF/0.5% acetone, 2.0 ¥ 10-5 mol L-1) lmax/nm (e/L mol-1 cm-1):
338 (13 500), 289 (60 100), 260 (75 700); vmax/cm-1 1660s (C N),
1295brs (NO3), 839m (Ar–H).
104.436(7) , U = 4405.1(6) A , Z = 2, m = 2.304 mm , F(000) =
1748, T = 150(2)K. A total of 56 953 reflections were collected in
the range 6.5◦ < 2q < 61.2◦. The 13 304 independent reflections
[R(int) = 0.116] were used after absorption correction (Tmin
=
0.649, Tmax = 1.000). Refinement of 1038 parameters converged to
R1 = 0.0828 [for 3644 reflections having I > 2s(I)], wR2 = 0.2413
and goodness-of-fit of 0.81 (for all 13 304 F2 data). Peak/hole
-3
˚
0.45/-0.55 e A .
Crystal data for [BF4Ã(Cu2L1 )](BF4)3·3C3H6O (4)·3C3H6O.
2
C68H92Cu2B4F12N8O8, 3(C3H6O), Mr = 1798.05, green platelet,
[BrÃ(Cu2L1 )](Br)3 (6). The general method outlined above
0.19 ¥ 0.17 ¥ 0.10 mm, triclinic, P1, a =◦11.7783(3) A, b =
¯
˚
2
◦
˚
˚
was followed using copper(II) bromide. The dark brown product
was purified by recrystallisation with diethyl ether diffusion from
19.0859(5) A, c = 20.9814(15) A, a = 82.675(6) , b = 77.892(5) , g =
75.638(5) , U = 4453.4(4) A , Z = 2, m = 1.383 mm , F(000) = 1876,
◦
3
-1
˚
12240 | Dalton Trans., 2011, 40, 12235–12241
This journal is
The Royal Society of Chemistry 2011
©

T = 123(2)K. A total of 53 358 reflections were collected in the
range 6.6◦ < 2q < 61.2◦. The 13 270 independent reflections
2 P. A. Gale, Coord. Chem. Rev., 2000, 199, 181–233; L. A. J. Chrisstoffels,
F. Jong, D. N. Reinhoudt, S. Sivelli, L. Gazzola, A. Casnati and R.
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[R(int) = 0.075] were used after absorption correction (Tmin
=
3 J. M. Mahoney, K. A. Stucker, H. Jiang, I. Carmichael, N. R.
Brinkmann, A. M. Beatty, B. C. Noll and B. D. Smith, J. Am. Chem.
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K. Schenk and K. Severin, Inorg. Chem., 2010, 49, 9546–9553; S.
Shanmugaraju, A. K. Bar, K. Chi and P. S. Mukherjee, Organometallics,
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4 P. G. Plieger, S. Parsons, A. Parkin and P. A. Tasker, J. Chem. Soc.,
Dalton Trans., 2002, 3928–3930.
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6 M. Wenzel, G. B. Jameson, L. A. Ferguson, Q. W. Knapp, R. S. Forgan,
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0.452, Tmax = 0.760). Refinement of 1166 parameters converged to
R1 = 0.0881 [for 8153 reflections having I > 2s(I)], wR2 = 0.2718
and goodness-of-fit of 1.09 (for all 13 270 F2 data). Peak/hole
-3
˚
0.92/-0.91 e A .
Spectroscopic titrations
Spectrophotometric measurements in the UV-visible region were
performed at 294 K using a CARY 100Bio UV-Vis spectropho-
tometer and 1 cm path length matched quartz cuvettes. Chemicals
and solvents were of AR grade unless otherwise stated and used
as received. The “metal only” complex 1 was dried in vacuo for
two hours prior to the preparation of the titration solutions
and the titrations were prepared immediately. Solutions of 1 in
THF–CHCl3 (CHCl3 less than 0.01%) (2 mL, 1.5 ¥ 10-5 mol L-1)
were titrated with THF solutions of the acid of interest (2.5 ¥
10-4 mol L-1–1.0 ¥ 10-3 mol L-1). Spectra were recorded following
the addition of each aliquot over the wavelength range of 900 to
250 nm. The acid solutions were titrated at 0.25 molar equivalence
increments for H2SO4 and 1.0 molar equivalence increments
for HNO3, HClO4 and HBr. A 1 : 1 anion to 1 binding model
was assumed. Formation constants were calculated using the
SPECFIT program (version 3.0.40, SPECFIT/32TM).16 Titrations
were repeated until three concordant results were obtained.
8 M. Wenzel, R. S. Forgan, A. Faure, K. Mason, P. A. Tasker, S. Piligkos,
E. K. Brechin and P. G. Plieger, Eur. J. Inorg. Chem., 2009, 4613–4617.
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11 B. P. Hay and R. Custelcean, Cryst. Growth Des., 2009, 9, 2539–2545;
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Gamez, O. Roubeau, E. J. Shotton and S. J. Teat, Inorg. Chem., 2008,
47, 5873–5881.
12 Rigaku, CrystalClear, Version 1.4.0, Rigaku Americas Corporation,
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This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 12235–12241 | 12241
©