Metal-directed assembly of large dinuclear copper(II) dithiocarbamate macrocyclic complexes

Article abstract of DOI:10.1016/j.ica.2009.09.052

The synthesis of a range of dinuclear Cu(II) dithiocarbamate (dtc)-based macrocycles and their characterisation are described. By carefully tuning the size of the aromatic spacer, cavities of different dimensions can be designed. The length and flexibility of the chosen spacer group dictates the intermetallic distance and hence the degree of communication between the two metal centres as evidenced by electrochemical and EPR experiments. This is illustrated by crystallographic evidence that show the macrocycles can host guests (such as CH₂Cl₂) or can fold and form unexpected Cu(I) dtc clusters.

Full text of DOI:10.1016/j.ica.2009.09.052

Inorganica Chimica Acta 363 (2010) 1195–1203
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Metal-directed assembly of large dinuclear copper(II) dithiocarbamate
macrocyclic complexes
James Cookson a,b, Emma A.L. Evans a, John P. Maher c, Christopher J. Serpell a, Rowena L. Paul a,
Andrew R. Cowley a, Michael G.B. Drew d, Paul D. Beer a,
*
a Department of Chemistry, Chemistry Research Laboratory, University of Oxford, Mansfield Road, Oxford, OX1 3TA, UK
b Johnson Matthey Technology Centre, Blount’s Court, Sonning Common, Reading, RG4 9NH, UK
c The School of Chemistry, University of Bristol, Bristol, BS8 1TS, UK
d School of Chemistry, The University of Reading, Whiteknights, P.O. Box 217, Reading, Berkshire, RG6 6AH, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 3 June 2009
Received in revised form 28 August 2009
Accepted 14 September 2009
Available online 13 October 2009
The synthesis of a range of dinuclear Cu(II) dithiocarbamate (dtc)-based macrocycles and their character-
isation are described. By carefully tuning the size of the aromatic spacer, cavities of different dimensions
can be designed. The length and flexibility of the chosen spacer group dictates the intermetallic distance
and hence the degree of communication between the two metal centres as evidenced by electrochemical
and EPR experiments. This is illustrated by crystallographic evidence that show the macrocycles can host
guests (such as CH2Cl2) or can fold and form unexpected Cu(I) dtc clusters.
Dedicated to Prof. Jonathan R. Dilworth
Ó 2009 Elsevier B.V. All rights reserved.
Keywords:
Dithiocarbamate
Copper
Macrocycle
X-ray crystal structures
Conformational flexibility
1. Introduction
carbamate (dtc) ligand as a self-assembling structural motif, we
have synthesised novel nano-sized resorcarene-based transition
The synthesis of two- and three-dimensional macrocyclic and
cage-like host molecules using metal-directed self-assembly is a
current area of intense research activity [1]. Metal-directed self-
assembly has numerous advantages over conventional covalent
synthesis. For example, only a few basic subunits are required to
generate complex architectures, in just a single or a few steps.
The construction process proceeds via reversible bond formation,
allowing error recovery and structural changes, according to its
environment. Furthermore, through prudent choice of metal ion
and multidentate ligand components, the resulting self-assembled
polymetallic array can be designed to exhibit unique structural
and/or electronic and magnetic properties, and have the potential
to bind and sense guest substrates [1,2]. At present, the field is
dominated by square planar Pt(II) metals in combination with var-
ious oligopyridine ligands [1c,3], Cu(I), Ni(II), Ag(I), Fe(II) helical
structures of oligobipyridyls [3] and pseudo-octahedral Ti(IV),
Al(III), Fe(III), Ga(III) complexes of oligocatecholate ligands leading
to triple helicates [3] and tetrahedral clusters [4]. Using the dithio-
metal polymetallic assemblies [5,6] which bind C60 [7] and Cu(II)
dtc macrocycles capable of selectively sensing anionic guest spe-
cies, using electrochemical techniques [8] or forming interlocked
[2] catenane structures [9].
This paper describes the synthesis of dinuclear macrocyclic
complexes based upon the Cu-dtc motif. Whilst the coordination
chemistry of the dtc ligand is well established [10], it is only re-
cently this ligand has begun to be exploited much more widely
[11], such as in the field of metal directed self-assembly [12],
and nanoparticle stabilisation [13] and their functionalisation
[14]. We report here the use of the dtc linkage separated by a range
of large aromatic spacer groups. The manipulation of the aromatic
group enables the control of the cavity size of the resultant macro-
cycle and hence allowing the incorporation of guest molecules.
Previously, Zn(II) dtc-based macrocyclic complexes with large cav-
ity dimensions have demonstrated the ability to bind various neu-
tral and anionic bidentate guests species by 1H NMR spectroscopy
[15,16]. The advantage of using analogous Cu(II)-based systems is
that the intrinsic electrochemical properties of the Cu-dtc linkage
enables further analysis of the structures adopted in solution in
addition to subsequent host guest association processes.
* Corresponding author. Tel.: +44 (0)1865 285142; fax: +44 (0)1865 272690.
E-mail address: paul.beer@chem.ox.ac.uk (P.D. Beer).
0020-1693/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2009.09.052

1196
J. Cookson et al. / Inorganica Chimica Acta 363 (2010) 1195–1203
mediates, whilst slowly precipitating the final product. Preliminary
experiments in EtOH or MeOH-based solvent systems proved only
moderately successful due to nucleophilic attack of the alcoholic
solvent upon carbon disulphide, resulting in the formation of com-
peting xanthate complexes [19].
2. Synthesis of macrocyclic copper(II) dtc complexes
Bimetallic macrocyclic complexes were designed from second-
ary bis-amines separated by an aromatic spacer. This spacer con-
ferred a degree of rigidity upon the ligand, thus preorganising it
for self-assembly. The resulting bis-amines were then reacted with
base, carbon disulphide and copper(II) metal salt to yield the dinu-
clear macrocyclic complex (Scheme 1) [8].
3. Characterisation of macrocyclic Cu(II) dtc complexes
The parent secondary bis-amines (Lx) were synthesised via a
nucleophilic substitution reaction of bis(halomethyl) aromatic syn-
The macrocyclic complexes have been characterised by a vari-
ety of techniques. Electrospray mass spectra (ESIMS) have been ob-
tained for all of the synthesised products, and these confirm the
formation of dinuclear macrocyclic complexes, with no observa-
tion of any higher oligomers. In general, the [M]+ peaks were ob-
served as the base peaks [20], with isotopic patterns in good
agreement with theoretical calculations. Adducts with sodium
and potassium ions were frequently observed, especially at higher
cone voltages. Co-injection of the sample with sodium or potas-
sium hexafluorophosphate resulted in the significant increase in
the intensity of these peaks, such that they often became the base
peaks in the spectra.
The in situ oxidation of the dinuclear Cu(II) macrocycles could
be achieved by the simultaneous addition of NOBF4 [21]. This gen-
erates the doubly-charged Cu(III) systems, with very high ion
counts, which are clearly observable in the spectra due to the char-
acteristic half-integral splitting of its peaks. In addition to the
dicationic [M]2+ peaks, often tetrafluoroborate adducts [M.BF4]+
were also observed.
thons with neat primary amine. a-
a0-Dihalo-derivatives are either
commercially available or were prepared using existing protocols
[15–17]. Formation of the desired secondary bis-amines (L1–L4)
was achieved by the nucleophilic substitution of the bis(halometh-
yl)-aromatic synthons with excess neat n-butylamine [18]. When
bromo-derivatives were used, the reaction proceeded rapidly and
quantitatively at room temperature. In contrast, when bis-chloro
derivatives were used, it was necessary to both heat the reaction
mixture and add sodium iodide, as a nucleophilic catalyst. In the
absence of iodide, significant amounts of oligomeric side products
were formed.
Alkyl chains other than n-butyl (such as longer or branched
derivatives) can also be used; however, this was shown not to have
any significant effect on the resulting complexes therefore these
will not be discussed here.
Metal-directed self-assembly of the desired dinuclear macrocy-
clic Cu(II) dtc complexes was performed via the initial reaction of
the secondary bis-amines (L1–L4) with potassium hydroxide and
carbon disulphide. This generated the potassium bis-dtc salt
(L1a–L4a) that was not usually isolated. Addition of Cu(II) acetate
to the solution resulted in the formation of the desired macrocyclic
dtc complexes. The dinuclear dtc-based macrocyclic complexes 1–
4 were all purified by crystallisation from CH2Cl2/EtOH.
One of the appealing properties of transition metal dtc com-
plexes is their electronic absorption spectral characteristics. This
results in the formation of distinctively black/brown coloured
Cu(II) dtc complexes.
The UV–Vis spectra of all of the synthesised macrocycles were
recorded in CH2Cl2 solution for characterisation purposes. The
wavelengths k (nm) of the peak maxima and corresponding extinc-
Typically, the reactions were carried out in a THF/H2O (2:1) sol-
vent system as this was found to solubilise the reagents and inter-
tion coefficients (
e
, Mꢀ1 cmꢀ1) are displayed in Table 1. The acyclic
Aromatic
Group
R
S
R
S
N
Cu
N
N
Cu
N
Aromatic
Group
S
S
S
S
b
c
Aromatic
Group
a
Aromatic
Group
R
S
R
S
N
N
R
R
S
R
S
R
X
X
NH
HN
S
S
K
K
Aromatic
Group
Lx
Lxa
X
Aromatic
Group
R
R
NH
HN
R
NH
HN
R
L1
L3
L2
L4
R
R
NH
HN
R
R
R
NH
HN R
NH
HN
Scheme 1. Synthesis of dinuclear Cu(II) dtc macrocyclic complexes. Reaction conditions: (a) BuNH2, room temperature, 18 h; (b) KOH, CS2, room temperature 30 min; (c)
Cu(OAc)2, THF/H2O (2:1), room temperature, 2 h.

J. Cookson et al. / Inorganica Chimica Acta 363 (2010) 1195–1203
1197
analogue Cu(II) bis-(N,N0-diethyldithiocarbamate) [22] (5) was also
examined, as a comparison to the dinuclear complexes.
The Cu(II) containing metallomacrocycles typically exhibit
three bands in their UV–Vis spectra. These can be assigned to a li-
gand to metal charge transfer (LMCT) band [23] at ꢁ430 nm, and
two ligand centred (LC)
ꢁ290 nm (Table 1) [25].
p–
p* transitions [24] at ꢁ270 nm and
4. X-ray crystal structures
Crystallisation of the resulting dinuclear macrocyclic complexes
from CH2Cl2/EtOH or CH2Cl2/Et2O enabled single crystals suitable
for X-ray analysis to be obtained for (2) and (4). Selected crystallo-
graphic data and refinement parameters for these are displayed in
Table 2.
The structure of (4) displays the expected dinuclear structure
with disordered dichloromethane solvent molecules occupying
half the cavities of the macrocyclic complexes (Figs. 1 and 2). Se-
lected crystallographic parameters for the structure are high-
lighted in Table 3.
The macrocycle has near planar Cu(II) dtc groups coplanar to
each other and separated in space through the spacing 2,7-disub-
stituted naphthylene group. The bridging aromatic groups are
coplanar to each other and perpendicular to the plane of the dtc
moieties. This has the result that they appear trans to each other
across the Cu(II) dtc group. The alkyl chains point away from the
central cavity and appear on the opposite side of the dtc linkage
with respect to the naphthyl spacer.
The resultant cavity of the molecule possesses is approximately
8.1 Å in length and 7.6 Å wide. This comfortably allows the inclu-
sion of suitably sized guest species, such as dichloromethane, into
the structure.
Fig. 1. X-ray crystal structure of (4ꢃ½CH2Cl2) (key – red = copper, yellow = sulphur,
grey = carbon, blue = nitrogen, green = chlorine, white = hydrogen). (For interpreta-
tion of the references to colour in this figure legend, the reader is referred to the
web version of this article.)
The carbon-nitrogen bond length of the dtc linkage is consider-
ably less than would be expected for a typical single carbon–nitro-
Table 1
UV–Vis spectroscopic data for macrocyclic receptors in CH2Cl2 at 1 ꢂ 10ꢀ5M and
293 K (errors for extinction coefficients estimated at 10%).
k (e )
, 10ꢀ3 Mꢀ1 cmꢀ1
1
2
3
4
5
229 (59.5), 275 (47.7), 434 (13.9)
225 (103.8), 271 (64.5), 430 (17.9)
226 (56.0), 270 (95.4), 439 (19.1)
228 (94.7), 271 (66.5), 433 (20.4)
269 (33.8), 289 (17.0), 435 (14.2)
Table 2
Selected crystallographic data and refinement parameters for (2*) and (4).
2*
4
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
C24H30Cu2N2S4
601.82
293(2)
0.71073
orthorhombic
Pbcn
C45H58Cl2Cu2N4S8
1109.51
150(2)
0.71073
triclinic
ꢀ
P1
14.966(17)
19.82(2)
17.48(2)
90
90
90
5185(10)
8
1.978
1.542
0.0660
0.1792
11.5001(2)
11.6296(3)
12.2003(3)
101.2510(10)
109.2882(11)
114.6315(9)
1290.37(6)
1
1.287
1.428
0.0546
0.1269
Fig. 2. Side view of X-ray crystal structure of (4ꢃ½CH2Cl2) (key – red = copper,
yellow = sulphur, grey = carbon, blue = nitrogen, green = chlorine, white = hydro-
gen). (For interpretation of the references to colour in this figure legend, the reader
is referred to the web version of this article.)
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
Volume (Å3)
gen bond (1.47 Å) and closer to that of a carbon-nitrogen double
bond (1.28 Å) [26]. This demonstrates the significant double bond
character between the two atoms due to the effective delocalisa-
tion of charge about the dtc group and subsequent high degree
of covalency within the metal–sulphur bonds. In addition, the
Z
l
(mmꢀ1
)
Dcalc (mg mꢀ3
R1 [I > 2 (I)]
wR2 [I > 2 (I)]
)
r
r

1198
J. Cookson et al. / Inorganica Chimica Acta 363 (2010) 1195–1203
Table 3
Selected crystallographic parameters for (2*) and (4).
2*
4
d(Cu–S) (Å)
d(N–C(S2)) (Å)
2.241(3), 2.272(3) (monodentate) 2.266(3), 2.267(3), 2.261(3), 2.303(3) (bidentate)
1.334(9), 1.313(9)
2.54, 2.71, 2.80, 2.89
2.301(1), 2.288(1), 2.298(1), 2.295(1)
1.317(5), 1.325(4)
7.623(1)
d(Cu–Cu) (Å)
0
d(ArH1–ArH1 ) (Å)
8.224(5)
h(S–Cu–Sadj) (°)
h(S–Cu–Sopp) (°)
h(N–N–Cu) (°)
77.59(4), 77.65(4)
175.82(4), 178.54(11)
0.8
metal dtc group is near planar, with the Cu centre only 0.8° out of
the plane. This is possibly a result of a lack of steric strain in the
macrocycle and also a consequence of an absence of metal–metal
interactions.
In contrast, recrystallisation of (2) repeatably gave an unex-
pected Cu(I) dtc structure (Fig. 3, Table 3). A central Cu4 tetrahedral
cage (2*) containing a crystallographic two fold axis is found. Each
metal is coordinated to three different sulphur donors, in addition
to three other Cu centres, resulting in a distorted octahedral geom-
etry about each Cu (Fig. 4). The dtc ligands coordinate unsymmet-
rically to different three metal atoms; one sulphur binds to one
metal and the other to two Cu centres. There are four unique
Cu–Cu bond lengths; 2.54, 2.71, 2.80 and 2.89 Å, of which the first
is significantly shorter than the other three. Indeed, the short bond
length is comparable to those in the metal phase of the element
(2.56 Å). The dtc carbon–nitrogen bonds are 1.31 and 1.32 Å, also
suggesting a high covalent character for this complex. It is further
noteworthy that the biphenyl rings are not coplanar, with the two
rings twisted at a 29.2° angle.
Fig. 4. View of central (CS2Cu)4 tetrahedral core of (2*) (key
yellow = sulphur, grey = carbon). (For interpretation of the references to colour in
this figure legend, the reader is referred to the web version of this article.)
– red = copper,
This tetrameric cage-like structure has been previously ob-
served for Cu(I) dtc complexes [27,28] (Fig. 5). However, it is very
surprising that the Cu(I) dtc species has crystallised since such
complexes are relatively difficult to synthesise. The electrochemis-
try of Cu(II) bis-(N,N0-diethyldithiocarbamate) (5) shows a revers-
Fig. 5. X-ray crystal structure of Cu(I) tetra-(N,N0-diethyldithiocarbamate) taken
from Ref. [26] (key – red = copper, yellow = sulphur, grey = carbon, blue = nitrogen).
(For interpretation of the references to colour in this figure legend, the reader is
referred to the web version of this article.)
ible reduction at ꢀ0.96 V in forming a Cu(I) dtc species. They
have previously been formed by treatment of sodium dtc salts with
Cu(I) oxide in an inert atmosphere [29], oxidation of copper bronze
or metallic copper with tetraalkylthiuram disulphides in non polar
solvents [30] and aqueous reactions of alkali metal N,N0-dial-
kyldithiocarbamates with a cuprous halide [31], however, frequent
Fig. 3. X-ray crystal structure of (2*) (key
grey = carbon, blue = nitrogen, white = hydrogen). (For interpretation of the refer-
ences to colour in this figure legend, the reader is referred to the web version of this
article.)
– red = copper, yellow = sulphur,

J. Cookson et al. / Inorganica Chimica Acta 363 (2010) 1195–1203
1199
contamination with the corresponding cuprous salts is observed
[32].
macrocyclic complexes 1, 3, and 4, where the analogous process is
observed to be 20 mV more cathodic than that of (5).
Examination of the 1H NMR of the crude product revealed the
presence of a paramagnetic product. Furthermore, electrospray
mass spectrometry and elemental analysis also demonstrated the
presence of the Cu(II) dtc complex. This suggests that the reduction
must have occurred during the recrystallisation stage of the pro-
cess. This is surprising as the recrystallisations were undertaken
open to the atmosphere.
6. Electron paramagnetic resonance
The EPR spectra of simple Cu(II) dtc complexes have previously
been examined, revealing structural and coordination information
of the structures [37,38]. Examination of the dinuclear macrocyclic
Cu(II) dtc complexes 1–4 were undertaken (Table 5), in particular
examining the variations in g-values and hyperfine coupling con-
stants, which can reveal much information about the bonding of
the metal ion [39].
5. Electrochemistry
The EPR spectrum of the mononuclear complex 5, displays a
characteristic sharp four line spectrum in CH2Cl2 (Fig. 7). The four
lines are a result of hyperfine splitting (A) between the unpaired
electron and the Cu nucleus (I = 3/2). The g-value of (5) is close to
that of a free electron (2.002), which confirms that the metal–sul-
phur bond in Cu(II) dtc complexes has a high degree of covalency
(Table 5), a feature also illustrated through X-ray crystallographic
studies. The sharp-line nature of the solution spectrum observed
is evidence that there is little chemical exchange on and off the
fifth and sixth coordination sites of the Cu, hence very little chem-
ical exchange broadening is seen [40,41]. There is also a shoulder
on the high field peak, which is just resolvable, due to isotopic
splitting with the Cu nucleus 63Cu (69.2%) and 65Cu (30.8%).
In contrast to the four lines observed in the EPR spectrum of (5),
the dinuclear m-xylyl spaced Cu(II) dtc complex 1 displays seven
lines in its spectrum (Fig. 8).
The observed 1:2:3:4:3:2:1 multiplet would be expected from
electron hyperfine interactions between two I = 3/2 nuclei, indicat-
ing that the unpaired electrons on each Cu nucleus interact with
both Cu nuclei. The observed isotropic hyperfine coupling for the
dinuclear complex is apparently half that for the monomeric (5),
due to strong electron–electron through-bond coupling (J-cou-
pling) between the two Cu centres, causing the observed A-value
to be halved. This also shows that J ꢄ A, [42] a feature which has
been previously observed in many paramagnetic dinuclear
tris(pyrazolyl)boratomolybdenum centres [43]. Thus the A-value
for (1) 1 is 7.6 mT, very similar to the A/2 for the monomeric com-
plex 5.
The electrochemical properties of Cu(II) dtc complexes have
been well established [33,34]. They have been shown to undergo
two metal-based, one-electron redox processes, corresponding to
a Cu(II/III) oxidation and a Cu(II/I) reduction. The Cu(II/III) oxida-
tion process is reversible, predominantly a consequence of the
preservation of the square planar geometry of the Cu centre upon
its oxidation [35,36]. The Cu(II/I) reduction is only reversible on the
electrochemical timeframe [28], with clusters being formed over
longer time periods.
The electrochemical properties of the Cu(II/III) redox couple of
the Cu(II) dtc macrocyclic complexes have been investigated by
both cyclic and square wave voltammetry. The electrochemical
properties of the acyclic analogue (5) were also recorded as a com-
parison to the dinuclear complexes.
The voltammograms for the Cu(II) dtc macrocycles all display
quasi-reversible oxidation Cu(II/III) redox couples at similar poten-
tials (Table 4). As expected, one oxidation wave is observed for the
mononuclear complex 5. However, two redox couples are observed
for the m-xylyl spaced macrocycle (1) (Fig. 6). In this case, the two
Cu centres are electronically coupled as they are in close proximity
to each other through space. On electrostatic grounds, the oxida-
tion of one Cu(II) centre perturbs the subsequent oxidation of the
other, resulting in an anodic shift in the second oxidation potential.
Similarly, the cyclic and square wave voltammogram of the 3,30-
biphenyl spaced complex 2, also displays two redox waves,
although it appears broader than those of the m-xylyl spaced mac-
rocycles (Fig. 6). This is also due to the metal centres electrochem-
ically coupling through space, which is somewhat unexpected
considering the longer distance between the metal centres.
In contrast, the 4,40-biphenyl and naphthyl spaced macrocyclic
complexes 3 and 4, only show one, albeit broad, redox process in
their cyclic and square wave voltammograms (Fig. 6). This suggests
that both Cu(II) centres are oxidised at very similar potentials and
are sufficiently far apart from one another to behave indepen-
dently. This is a result of the greater metal–metal distances in
the structures (7.62 Å in the crystal structure of (4)), and a lack
of flexibility in the ligands to allow communication.
The observed isotropic g-values and A-values for the dinuclear
complex are in agreement with published values for other square
planar Cu(II) bis-(dialkyldithiocarbamates) and other square pla-
nar CuS4 ligand sets. Analysis of the g- and A-parameters in such
complexes is consistent with a very strong covalent interaction be-
tween the Cu and the sulphurs, and an essentially square planar
ground state. The strong covalency of the Cu–S bonds allows the
hyperfine interaction between the Cu nuclei, which occurs via
two 12-bond paths through the connecting ligands.
The EPR spectrum of the 3,30-biphenyl spaced Cu(II) dtc macro-
cycle (2) was also recorded in CH2Cl2 (Fig. 9). The spectrum of the
(2), appears significantly more complicated than the m-xylyl
spaced macrocycle [44] (1), possessing different sets of signals, cor-
responding to varying degrees of electronic coupling between the
two Cu centres in solution.
Unlike the Cu(II/III) oxidation potential, the Cu(II/I) reduction
wave always occurs as a single peak (Fig. 6). The reduction of the
3,30-biphenyl spaced macrocycle (2) is 50 mV more anodic than
the acyclic, mononuclear complex 5. This is in contrast to the other
Table 4
Electrochemical data of Cu(II) dtc-based macrocycles in CH2Cl2/MeCN (4:1) with
0.1 M TBABF4 as the supporting electrolyte using glassy carbon as the working
7. Discussion of the 3,30-biphenyl-spaced macrocyclic complex 2
electrode and Ag/AgNO3 reference electrode, sample 1 ꢂ 10ꢀ3M. Scan rate 100 mVsꢀ1
frequency 5 Hz, T = 293 K, errors 5 mV.
,
It was originally assumed that the Cu(II) dtc 3,30-biphenyl-
spaced macrocyclic complex 2 assumed a dinuclear structure
whereby the transition metal dtc moieties are separated via a pla-
nar aromatic group. This conformation would be in agreement
with the X-ray crystal structures of the various m-xylyl and naph-
thyl spaced complexes that have been solved for these two spacers.
Whilst it is not possible to record NMR spectra of the paramagnetic
Cu (II/I) reduction E (V)
Cu(II/III) oxidation E (V)
½
½
1
2
3
4
5
ꢀ0.98
ꢀ0.91
ꢀ0.98
ꢀ0.98
ꢀ0.96
0.01, 0.16
0.01, 0.14
0.08
0.13
0.08

1200
J. Cookson et al. / Inorganica Chimica Acta 363 (2010) 1195–1203
Fig. 6. Square wave voltammograms of the Cu(I/II) and Cu(II/III) oxidation waves of (5), (1), (2) and (4) (frequency = 5 Hz) performed using a glassy carbon working electrode
in CH2Cl2/MeCN (4:1) containing 0.1 M TBABF4 with reference to Ag/AgNO3 at 293 K, samples ꢁ2 ꢂ 10ꢀ3 M.
being too distant. In addition, the Cu(II/I) redox couple of the
Table 5
3,30-biphenyl spaced macrocycle (2) is 50 mV easier than the acy-
EPR data for mono- and dinuclear Cu(II) dtc complexes in CH2Cl2 at 296 K.
clic, mononuclear complex 5 and 70 mV more facile than the anal-
ogous dinuclear macrocyclic complexes..
We propose that these differences are due to structural confor-
mation effects in solution, which allow the flexible ligand to wrap
up on itself; a feature which the more rigid aromatic spacer groups
do not permit (Fig. 10).
giso
Aiso (mT)
5
1
2
2.047
2.046
2.048
7.90
3.84
7.90 and 3.90
We propose that the flexibility within the ligand allows a num-
ber of conformations to exist in solution (Fig. 10) and that the
twisted, ‘‘figure of eight” structure is a major contribution in solu-
tion. This structure has the effect that the metal centres are in close
proximity through space, and this may in turn be stabilised by
favourable axial Cu–S interactions. It is the presence of these short
intermetallic distances that enables electrochemical communica-
tion in the Cu(II/III) redox couple of the 3,30-biphenyl spaced mac-
rocycle (2).
Cu(II) dtc 3,30-biphenyl-based structures, both electrospray mass
spectrometry and elemental analysis are consistent with the for-
mation of the desired pure dinuclear products. However, further
electrochemical, EPR, and X-ray crystallographic studies upon the-
ses samples have been difficult to rationalise using this original
model.
Firstly, the electrochemical studies of (2) reveal that the two Cu
centres are electrochemically communicating, as a broad oxidation
wave with two peaks is observed. This is somewhat surprising con-
sidering that in the similar sized macrocyclic complex 4 no such
communication is observed, presumably due to the metal centres
In addition, if the molecule were to adopt conformation II
in solution, then it could help to explain the formation of the
Cu(I) cage-like configuration in the X-ray structure of (2*). The
3200
3250
3300
3350
3400
Gauss
3450
3500
3550
3600
Fig. 7. EPR spectrum of mononuclear Cu(II) dtc complex 5 in CH2Cl2 at 296 K.

J. Cookson et al. / Inorganica Chimica Acta 363 (2010) 1195–1203
1201
3100
3200
3300
3400
3500
3600
3700
Gauss
Fig. 8. EPR spectrum of (1) in CH2Cl2 at 296 K.
3100
3200
3300
3400
3500
3600
3700
Gauss
Fig. 9. EPR spectrum of (2) in CH2Cl2 at 296 K.
conformation of the biphenyl-based ligands found in the X-ray
crystal structure is similar to that proposed for conformation II. It
is proposed that the adoption of this conformer preorganises the
structure such that, over time, the reduced form of the complex
is able to crystallise out. It is likely that the reduction of the Cu(II)
to Cu(I) may occur via the corresponding oxidation of the liberated
dtc ligands to thiuram disulphides (R2NCS2S2NCR2). The likelihood
of this reduction is increased by the fact that it is considerably eas-
ier to reduce the Cu(II) in (2) in comparison to analogous macrocy-
clic complexes with more rigid aromatic spacer groups or to its
acyclic analogue (5). The less negative redox potential is attributed
to the preorganisation of the metal centres, via the twisted confor-
mation, towards a (Cu4CS2)4 core.
R
S
R
S
N
N
N
S
N
R
R
S
S
S
S
S
S
Cu
Cu
Cu
Cu
N
S
S
R
S
S
R
S
N
S
S
R
R
N
N
8. Experimental
Data for the X-ray crystal structure of (4) was obtained using
Mo K
a radiation on an Enraf-Nonius Kappa CCD diffractometer,
I
II
in Oxford. The crystal was mounted on a glass fibre and cooled rap-
idly to 150 K in a stream of cold N2 using an Oxford Cryosys-
tems CRYOSTREAM unit. Intensity data was processed using the
Fig. 10. Possible conformations of Cu(II) 3,30-biphenyl-spaced dinuclear macrocy-
clic complex 2 I – planar; II – twisted.

1202
J. Cookson et al. / Inorganica Chimica Acta 363 (2010) 1195–1203
DENZO-SMN [45] package. Structures were solved by direct meth-
ods using the SIR92 [46] program. Full-matrix least-squares refine-
ment was carried out using the CRYSTALS [47] program suite.
Data for the X-ray crystal structure of (2*) was recorded in
3.81 (4H, t, J = 8.0 Hz, NCH2CH2), 1.50 (4H, m, NCH2CH2), 1.06
(4H, m, CH2CH3), 0.66 (6H, t, J = 7.5 Hz, CH3).
13C NMR (75.40 MHz, D2O) dC: 209.89 (CS2), 135.24, 133.29,
131.70, 128.30, 125.27 (ArC), 57.26, 54.10, 28.46, 19.71 (CH2),
13.29 (CH3).
Reading was obtained by using Mo Ka radiation and the MAR re-
3
search Image Plate System. Data analysis was performed with
the XDS program [48]. The structures were solved by direct meth-
ods using the SHELX86 program [49]. Empirical absorption correc-
tions were applied using the DIFABS program [50]. Structures were
refined on F2 to convergence using SHELXL [51].
Elemental Anal. Calc. for C22H28N2S4K2ꢃ /2H2O: C, 47.70; H, 5.64;
N, 5.06. Found: C, 47.89; H, 5.60; N, 4.96%.
11. Macrocycle (1)
EPR spectra of solutions of paramagnetic Cu(II) complexes were
measured in dry CH2Cl2 at 296 K and recorded with a Bruker
ESP300E instrument (X-band). Parameters used were: modulation
frequency, 100 kHz; modulation amplitude, 2.0G; microwave
power, 20 mW; microwave frequency, 9.74 GHz.
Electrochemical studies were undertaken on a Princeton Ap-
plied Research potentiostat/galvanostat model 673 using a glassy
carbon working electrode and an Ag/AgNO3 reference electrode
(0.33 V 10 mV versus SCE). Electrochemical solutions were de-
gassed with argon and maintained under a positive pressure for
the duration of the experiment.
NMR spectra were recorded on a Varian Unity Plus 500 spec-
trometer. Electrospray mass spectrometry was recorded on a
Micromass LCT instrument and UV–Vis spectroscopy experiments
were performed on a Perkin Lambda 6 spectrophotometer.
The syntheses of the bis-amine ligands (L1), (L2), (L3), and (L4)
have been described previously [15]. The preparation of Cu(II) bis-
(diethyldithiocarbamate) complex 5 has also been widely reported
[22].
Bis-amine (L1) (1.20 g, 4.83 mmol) was reacted, yielding a black
crystalline solid (1.14 g, 51%). ESIMS(m/z): 924.05 [M]+. ESIMS(m/z)
with NOBF4: 462.04 [M]2+, 1011.02 [M+BF4]+. Elemental Anal. Calc.
for C36H52N4S8Cu2: C, 46.77; H, 5.67; N, 6.06. Found: C, 46.72; H,
5.65; N, 6.08%.
12. Macrocycle (2)
Bis-amine (L2) (0.25 g, 0.77 mmol) was reacted. A brown pow-
der was isolated (0.23 g, 55%). ESIMS(m/z) (with NOBF4): 537.2
[M]2+, 1076.4 [M]+. Elemental Anal. Calc. for C48H60N4S8Cu2ꢃ½H2O:
C, 52.27; H, 5.08; N, 5.08. Found: C, 52.26; H, 5.68; N, 5.11%.
13. Macrocycle (3)
Bis-amine (L3) (0.25 g, 0.77 mmol) was reacted to generate a
brown solid (0.27 g, 64%). ESIMS(m/z): 1075.0 [M]+, 1114.3
[M+K]+. Elemental Anal. Calc. for C48H60N4S8Cu2: C, 53.55; H,
5.63; N, 5.20. Found: C, 55.64; H, 5.63; N, 5.31%.
9. Macrocyclic syntheses
In general, dinuclear Cu(II) dtc-based macrocyclic complexes
were synthesised via a one-pot reaction (without isolating the
intermediate bis-potassium dtc salts (Lxa). Where there were pre-
pared the following method was used:
14. Macrocycle (4)
Bis-amine (L4) (0.10 g, 0.33 mmol) was reacted yielding a
brown powder (0.06 g, 35%). The reaction was also undertaken
using the potassium bis-dtc salt: one equivalent of the bis-potas-
sium dtc salt (L4a) (0.25 g, 0.47 mmol) was dissolved in THF/H2O
(2:1, 100 ml). One equivalent of Cu(OAc)2ꢃH2O was then added
and the solution stirred at room temperature for 18 h. The solution
was filtered and the residue dissolved in CH2Cl2 (100 ml), dried
over K2CO3 and layered with EtOH (150 ml) in order to induce crys-
tallisation. The resulting solid was dried in vacuo. Affording a black
crystalline solid (0.19 g, 78%). ESIMS(m/z): 1025.5 [M+H]+, 1063.4
[M+K]+. ESIMS(m/z) with NOBF4: 512.1 [M]2+. Elemental Anal. Calc.
for C44H56N4S8Cu2ꢃ½CH2Cl2: C, 50.09; H, 5.38; N, 5.25. Found: C,
49.84; H, 5.31; N, 5.54%.
One equivalent of bis-amine was dissolved in a THF/H2O (2:1,
100 ml) solvent system and stirred at room temperature. 2.5
equivalents of KOH were added and the solution stirred for 10
min. 2.5 equivalents of CS2 were then added and the solution stir-
red for a further 10 min, generating a yellow solution. 1.25 equiv-
alents of Cu(OAc)2ꢃH2O, was then added and the solution stirred at
room temperature for 18 h. The solution was filtered and the res-
idue dissolved in CH2Cl2 (100 ml), dried over K2CO3 and layered
with ethanol (150 ml) in order to induce crystallisation. The result-
ing solid was dried in vacuo.
In the case of (4), a higher yield was found to be obtained by
first isolating the bis dtc salt (L4a).
15. Conclusions
10. Naphthyl-spaced bis-potassium dithiocarbamate salt -
ligand (L4a)
Within this paper we have demonstrated the successful synthe-
sis of a variety of new dinuclear Cu (II) dtc-based macrocyclic com-
plexes. These structures have been characterised by numerous
techniques including electrospray mass spectrometry, UV–Vis
spectroscopy, EPR, electrochemistry and X-ray crystallography.
Varying the aromatic spacer groups within the complexes has al-
lowed the formation of Cu-dtc macrocycles of varying dimensions.
Tuning the dimensions of these cavities permit guests (such as
dichloromethane) to be encapsulated within the cavity. A variety
of techniques suggest that when the 3,30-biphenyl spacer group
is used; a conformationally flexible structure is adopted in solu-
tion, with the molecule folding up on itself. This conformational ef-
fect gives rise to the crystallisation of a Cu(I) dtc-cage-like
complex.
Bis-amine (L4) (0.25 g, 0.84 mmol) was dissolved in THF/H2O
(2:1, 100 ml) and stirred at room temperature. KOH (0.11 g,
2.10 mmol) was added and the solution stirred for 10 min. Addi-
tion of CS2 (0.16 g, 2.10 mmol) resulted in a yellow solution which
was stirred for a further 18 h. The solvent was then removed under
reduced pressure and the resulting residue dissolved in MeOH
(50 ml). The suspension was filtered and the solvent reduced in
volume to 5 ml. Et2O (200 ml) was added and the resulting solution
was stored at ꢀ18 °C for 18 h. The resulting white solid was filtered
off, washed with Et2O (100 ml) and dried in vacuo. (0.33 g, 75%).
1H NMR (500 MHz, D2O) dH: 7.77 (2H, d, J = 8.5 Hz, ArH4/5), 7.54
(2H, s, ArH1/8), 7.41 (2H, d, J = 8.5 Hz, ArH3/6), 5.39 (4H, s, ArCH2),

J. Cookson et al. / Inorganica Chimica Acta 363 (2010) 1195–1203
1203
[13] (a) M.S. Vickers, J. Cookson, P.D. Beer, P.T. Bishop, B.J.S. Thiebaut, J. Mater.
Chem. 16 (2006) 209;
Acknowledgements
(b) L. Guerrini, J.V. Garcia-Ramos, C. Domingo, S. Sanchez-Cortes, Langmuir 22
(2006) 10924;
(c) A.A. Memon, M. Afzaal, M.A. Malik, C.Q. Nguyen, P. O’Brien, J. Raftery,
Dalton Trans. (2006) 4499.
We gratefully acknowledge EPSRC and Johnson Matthey for the
provision of CASE studentships (JC and CJS). We also thank the
EPSRC and the University of Reading for funds for the crystallo-
graphic Image Plate system.
[14] (a) J.D.E.T. Wilton-Ely, Dalton Trans. (2008) 25;
(b) E.R. Knight, N.H. Leung, Y.H. Lin, A.R. Cowley, D.J. Watkin, A.L. Thompson, G.
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(d) L. Guerrini, J.V. Garcia-Ramos, C. Domingo, S. Sanchez-Cortes, Phys. Chem.
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Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
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