Dinuclear zinc(II) dithiocarbamate macrocycles: Ditopic receptors for a variety of guest molecules

Article abstract of DOI:10.1039/b415935g

The synthesis of a series of dinuclear zinc(II) dithiocarbamate (dtc) macrocyclic receptors containing aryl spacer groups of different sizes is reported. As evidenced from ¹H NMR titration investigations, these receptors have the ability to bin

Full text of DOI:10.1039/b415935g

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F U L L P A P E R
Dinuclear zinc(II) dithiocarbamate macrocycles: ditopic receptors for
a variety of guest molecules
Wallace W. H. Wong, David Curiel, Andrew R. Cowley and Paul D. Beer*
Department of Chemistry, Inorganic Chemistry Laboratory, University of Oxford, South Parks
Road, Oxford, UK OX1 3QR. E-mail: paul.beer@chem.ox.ac.uk
Received 14th October 2004, Accepted 12th November 2004
First published as an Advance Article on the web 8th December 2004
The synthesis of a series of dinuclear zinc(II) dithiocarbamate (dtc) macrocyclic receptors containing aryl spacer
groups of different sizes is reported. As evidenced from 1H NMR titration investigations, these receptors have the
ability to bind various neutral and anionic bidentate guests species, including 1,4-diazabicyclo[2.2.2]octane
(DABCO), isonicotinate and terephthalate in a cooperative 1 : 1 intramolecular inclusion complex. Stability constant
determinations reveal a correlation between the strength of complexation and complementary receptor cavity : guest
molecule size. In particular, the X-ray structure of a 1 : 1 host–guest complex between a dinuclear zinc(II) dtc receptor
and DABCO illustrates the cooperative nature in which the dinuclear receptor associates with the bidentate guest.
1
Introduction
The method of metal-directed self-assembly has lead to the syn-
thesis of numerous two- and three-dimensional macrocyclic and
cage-like systems for host–guest complexation.1 By choosing
appropriate polydentate ligands and metal centers, complicated
and unusual molecular architectures, such as helical structures,
tubes, ladders and grids, are attainable.1 In particular, some
of these examples highlight the extensive uses of polydentate
pyridyl and oligocatecholate ligands with a variety of metals.2
We have been exploiting the application of dithiocar-
bamate based ligands in the metal directed self-assembly
of a large variety of supramolecular architectures such as
calixarene3 and resorcarene4 based assemblies, catenanes5, as-
sorted macrocycles6, trinuclear cages7 and cryptands.8 In this
paper we present a new series of dinuclear zinc(II) dtc receptors
covering a range of sizes to enable the study of host : guest size
correspondence. The affinity of these receptors to bind a series of
neutral and anionic bidentate guests with varying functionalities
1
and sizes was investigated by H NMR titration experiments.
In addition, a single crystal structure determination of a 1 :
1 dinuclear zinc(II) dtc receptor: 1,4-diazabicyclo[2.2.2]octane
(DABCO) complex highlights the importance of cooperativity
in the binding of bidentate guests by these ditopic receptors.
Scheme 1
The new dinuclear zinc(II) dithiocarbamate macrocycles were
prepared in one-pot syntheses from the appropriate diamine,
triethylamine, carbon disulfide and zinc acetate hydrate to give
white solids in yields ranging from 70–85% (Scheme 3 and
4). Mononuclear zinc(II) bis-diethyldithiocarbamate (16) was
prepared following a literature procedure.11 All products were
characterised by 1H NMR spectroscopy, mass spectrometry and
elemental analysis.
2
Results and discussion
2.1 Syntheses
The general strategy used for the synthesis of the dinuclear
zinc(II) dtc macrocyclic compounds involved the metal-directed
assembly of the appropriate dtc ligand with zinc(II) acetate. The
dtc ligands were generated in situ from the appropriate sec-
ondary amines, carbon disulfide and base. The secondary amine
precursors were prepared by simple alkylation reactions of the
appropriate dichloro, dibromo or ditosyl spacer compound and
primary amine.
2.2 X-Ray crystal structures
Crystals of 1,4-diazabicyclo[2.2.2]octane (DABCO) bound five-
coordinate zinc(II) dtc complexes suitable for single crystal X-
ray structure determination were grown by the slow diffusion of
diethyl ether into dichloromethane solutions of receptor–guest
mixtures. The structure of the 2 : 1 complex of zinc(II) bis-
diethyldithiocarbamate (16) and DABCO is shown in Fig. 1. The
bridging DABCO ligand is disordered over two positions which
are approximately related by a non-crystallographic centre of
inversion, as are the two Zn(S2CNEt2)2 groups. The large
and highly-anisotropic thermal parameters of the disordered
C atoms suggest that there is very little hindrance to rotation
ꢀ
Diamine (1) was obtained by treating a,a -dibromo-m-xylene
with excess of butylamine (Scheme 1). Compounds (4) and
(7) were similarly synthesised with excess butylamine and 2,7-
bis(bromomethyl)naphthalene9 (3) and 3,3ꢀ-bis(bromomethyl)-
1,1ꢀ-biphenyl10 (6), respectively (Scheme 1). The reaction
between benzylamine and 4,4ꢀ-bis(chloromethyl)-1,1ꢀ-biphenyl
gave compound (8) while tosylation of hydroquinone 2,2ꢀ-
bis(hydroxyethyl) ether followed by displacement of the tosyl
groups with excess benzylamine gave compound (10) (Scheme 2).
T h i s j o u r n a l i s
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 5
D a l t o n T r a n s . , 2 0 0 5 , 3 5 9 – 3 6 4
3 5 9
©

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Fig. 1 Thermal ellipsoid plot at 40% probability of two Zn(S2CNEt2)2
groups with a bridging DABCO. This view shows one orientation of the
disordered DABCO bridge and hydrogen atoms have been omitted.
Scheme 2
Tiekink for coordination complexes with the same mononuclear
zinc(II) dtc compound and trans-1,2-bis(4-pyridyl)ethylene12 and
with 4,4ꢀ-bipyridine.13
A 1 : 1 receptor–guest mixture was used to obtain crystals of
the inclusion complex of dinuclear zinc(II) dtc macrocycle (12)
and DABCO. The structure of the complex is located on a crys-
tallographic centre of inversion, which results in disorder of the
DABCO bridge over two positions (Fig. 2). Each zinc atom is five
coordinate, being bonded to two dithiocarbamate ligands with
˚
Zn–S distances 2.408(1)–2.495(1) A and to a DABCO nitrogen
˚
with a Zn–N distance of 2.157(2) A. Allowing for distortions
caused by the chelating four-membered ring of the zinc dithio-
carbamate, the metal environment can be considered as square
pyramidal with the nitrogen atom occupying the axial position.
Scheme 3
Fig. 2 Thermal ellipsoid plot of the structure of receptor (12) and
DABCO showing only one orientation of the DABCO bridge with ther-
mal ellipsoids at 40% probability. Hydrogen atoms have been omitted.
By comparing the crystal structure of receptor (12) and
DABCO to that of the mononuclear zinc(II) dtc compound (16)
and DABCO, it is apparent that the naphthyl spacer group
provides an ideal distance for the coordination of DABCO
between the two zinc centres in the dinuclear macrocycle. The
Zn(1)–Zn(2) distance in the structure of (16) and DABCO
Scheme 4
of the bridge about the N · · · N axis. Each zinc atom is five
coordinate, being bonded to two dithiocarbamate ligands with
˚
˚
Zn–S distances 2.357(1)–2.560(1) A and to a DABCO nitrogen
is 6.83 A and can be interpreted as the thermodynamically
˚
with a Zn–N distance of 2.123(3) A. The coordination geometry
favoured distance in a DABCO-bridged structure as there are
no steric constraints (Fig. 1). In the crystal structure of receptor
about each of the Zn(1) and Zn(2) atoms can be considered
as square pyramidal with the nitrogen atom occupying the
axial position. Similar structures have been reported by Lai and
˚
(12) and DABCO, the Zn(1)–Zn(2) distance is 6.92 A. This
small difference in the Zn(1)–Zn(2) distance between the two
3 6 0
D a l t o n T r a n s . , 2 0 0 5 , 3 5 9 – 3 6 4

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structures is attributed to the rigid naphthyl spacer groups that
hold the zinc(II) dtc centres apart.
Job plot experiments revealed 1 : 1 and 2 : 1 host–guest binding
stoichiometries depending on the relative sizes of the hosts and
guests (Fig. 4). Due to the small macrocyclic cavity size, receptor
(11) with the m-xylyl spacer group only forms 2 : 1 host–guest
complexes. On the other hand, 4,4ꢀ-bipyridine is too large for any
of the macrocycles in this study and the binding stoichiometry
for receptors (12)–(15) with 4,4ꢀ-bipyridine was also found to
be 2 : 1 host–guest in Job plot experiments (Fig. 4b).14 The
host–guest binding stoichiometry for receptors (12)–(15) with
bidentate guests DABCO, isonicotinate and terephthalate was
found to be 1 : 1 indicating the formation of intramolecular
inclusion complexes (Fig. 4a).
2.3 Host–guest binding properties
The incorporation of the zinc(II) dithiocarbamate Lewis acid
centre into a cyclic framework structure allows the potential
coordination of axial ligands converting the tetrahedral Zn(dtc)2
moiety into a five-coordinate square pyramidal Zn(dtc)2L
12–14
complex.
The new series of ditopic dinuclear zinc(II)
dtc macrocyclic receptors are designed to cooperatively bind
appropriate bidentate guest species. The mononuclear zinc(II)
bis-diethyldithiocarbamate compound (16) was used for com-
parison in the binding studies. Moreover, with the aim of
studying the effect of size complementarity on the magnitude
of receptor-guest binding, the interaction between the dinuclear
zinc(II) dtc macrocycles and a range of bidentate guests 4,4ꢀ-
bipyridine, DABCO, pyrazine and tetrabutylammonium (TBA)
salts of terephthalate and isonicotinate, were investigated.
The binding of the guests of different sizes by dinuclear zinc(II)
EQNMR15 analysis of the resulting titration curves gave
stability constant values shown in Table 1. Interestingly, all
stability constant values obtained by applying 2 : 1 host–guest
binding stoichiometry are similar in magnitude (Table 1). The
binding of bidentate guest species outside the receptor cavity is
expected to be unaffected by receptor macrocyclic ring size.
In general for the 1 : 1 complexes, Table 1 reveals a
correlation between host–guest size complementarity and the
magnitude of stability constant values. All the receptors (12)–
(15) bind strongly the bidentate anionic guest, terephthalate
(Table 1). Simple molecular models16 reveal the terephthalate
1
dtc macrocycles was examined by H NMR titration studies.
Preliminary titration experiments were performed by titrating
the potential coordinating guests into solutions of receptors in
9 : 1 mixtures of CDCl3 : DMSO-d6. No significant change in
the proton chemical shift values of the receptors was observed,
however, substantial perturbations in the proton chemical shifts
of the guest species were apparent.
In order to determine stability constant values, further titra-
tion experiments were carried out by adding small aliquots of the
receptor dissolved in a 9 : 1 or 3 : 1 mixture of CDCl3 : DMSO-d6,
depending on solubility requirements, to a solution of the coor-
dinating guest in the same mixture of solvents and the change
in chemical shift of the guest molecule protons was monitored.
Typically, significant downfield shifts were detected in the proton
resonances of the bidentate guests as a result of the deshielding
effect caused by the interaction with the zinc centres (Fig. 3).
˚
guest (∼7.2 A in length) fits best between the two zinc(II) dtc
centers of receptors (12) and (13), which have Zn–Zn distances
˚
of 8.1 and 8.7 A, respectively. It is difficult to rationalise why
receptors (14) and (15) form such strong complexes as the Zn–
˚
Zn distances in these hosts are much larger ca. 12 A. The
flexible ethylene linkers to the hydroquinone spacer groups of
receptor (15) may allow for variation in the intramolecular Zn–
Zn distance of the receptor.
The strongest host–guest complex for isonicotinate was ob-
tained with receptor (14) bearing a p-biphenyl spacer (Table 1).
Related to the recognition of terephthalate and isonicotinate
it is worth mentioning that none of the zinc(II) dtc receptor
systems interacted with benzoate in control experiments carried
out during this study. This again highlights the importance
of the cooperativity between the two Lewis acidic zinc(II) dtc
centers in the dinuclear systems for the binding of bidentate
guests. Additional evidence for the formation of 1 : 1 inclusion
complexes was observed using electrospray mass spectrometry
(ESMS). The molecular ion for the host–guest complex of
isonicotinate and receptor (15) were observed in the negative
ion mode of ESMS (Fig. 5).
In the binding studies of DABCO, a large stability constant
value (6000 M−1) was obtained for zinc(II) dtc receptor (12).
Evidence for the formation of an inclusion complex of receptor
(12) and DABCO in solution was observed by NOE experi-
ments. An intermolecular NOE signal was detected between the
DABCO protons and the receptor naphthalene protons at the
1-position. The crystal structure of receptor (12) and DABCO
highlights the host–guest complementarity of the complex in the
solid state (Fig. 2).
Fig. 3 1H NMR spectra of isonicotinate and after the addition of one
equivalent of receptor (14) in CDCl3/d6-DMSO.
Fig. 4 Illustrations of the two binding modes observed in 1H NMR titration experiments.
D a l t o n T r a n s . , 2 0 0 5 , 3 5 9 – 3 6 4
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Table 1 Stability constant values (M−1) for zinc(II) dtc receptors and a variety of guestsa
(11)
(12)
(13)
5500/250
>10000
3500
(14)
(15)
4000/300
>10000
2000
b
4,4ꢀ-Bipyridine
Terephthalatec
Isonicotinate
DABCO
5400/250
5000
700
5200/300
8000
6500
5000/200
b
3000/300
6000
400
3800
1500
>10000
b
b
b
b
Pyrazine
a Titrations were performed at 295 K in CDCl3/d6-DMSO 9 : 1 unless stated otherwise. Stability constant values (error = 10%) were calculated
from 1 : 1 (K) and 2 : 1 (K1/K2) host–guest stoichiometric models. b Negligible change in the chemical shifts of the guest protons was observed.
c Titration experiments with terephthalate were performed in CDCl3/d6-DMSO 3 : 1.
in a cooperative intramolecular manner between the receptors’
two Lewis acidic zinc(II) dtc centers. A correlation between the
strength of complexation and complementary receptor cavity :
guest molecule size was observed generally. For example, the
biphenyl spaced receptor (14) preferably binds terephthalate
over DABCO whereas with the smaller rigid naphthalene spaced
receptor (12), the reverse trend is observed. This highlights
the importance of cooperative binding of bidentate guests of
complementary size between the respective receptor’s zinc(II)
dtc centers.
3
Experimental
3.1 General details
Fig. 5 Negative ion ESMS spectrum of the inclusion complex of
receptor (15) and isonicotinate.
NMR spectra were recorded on a Varian 300 MHz and
500 MHz spectrometers. Mass spectrometry was carried out on
a Micromass LCT electrospray mass spectrometer (ESMS, cone
voltage = 20–50 V, desolvation temperature = 80 ◦C, source
temperature = 60 ◦C). Elemental analysis was performed at the
Inorganic Chemistry Laboratory, Oxford.
It is noteworthy that the magnitude of DABCO stability
constant values decreases in the order (12) > (13) > (14) as
the macrocycle cavity size increases. Interestingly, although of
similar size to (14), receptor (15) forms a very stable 1 : 1 complex
with DABCO which, as observed with the terephthalate guest,
may reflect this macrocycle’s ability to alter its cavity size.
Despite the similarity in size between pyrazine and DABCO,
pyrazine does not interact significantly with any of the zinc(II)
dtc receptors except for receptor (12) (Table 1). A stability
constant value of 6000 M−1 was found for DABCO with
receptor (12) compared to 400 M−1 for pyrazine. This difference
between the stability of the complexes is probably due to the
different electron density distributions of DABCO and pyrazine
whereby DABCO is a better r donor than pyrazine. This is in
agreement with earlier work reported by Maverick et al.17 They
found DABCO and their dinuclear copper(II) acetoacetonate-
type (acac) macrocycle with naphthyl spacer groups formed a
relatively strong 1 : 1 inclusion complex (K = 220 M−1 in CDCl3)
but the binding of pyrazine (K = 5 M−1 in CDCl3) by their
receptor was significantly weaker.
3.2 Syntheses
Mononuclear zinc(II) bis-diethyldithiocarbamate11 (16) was pre-
pared by following procedures in the literature as were 2,7-
bis(bromomethyl)naphthalene9 (3) and 3,3ꢀ-bis(bromomethyl)-
1,1ꢀ-biphenyl10 (6). Tetrabutylammonium terephthalate and
isonicotinate were prepared from their respective acids by
reacting with tetrabutylammonium hydroxide (40% wt/v aq.).
All other reagents were obtained from commercial sources and
used without further purification.
Hydroquinone 2,2ꢀ-bis(tosylethyl) (9). An aqueous sodium
hydroxide solution (14 g in 20 ml) was added to a solution of
hydroquinone bis(hydroxyethyl) ether (11.5 g) in THF (100 ml)
and the mixture was cooled to 0 ◦C with stirring. Tosyl chloride
(25 g) in THF (50 ml) was added dropwise and the mixture was
stirred for 2 h at 0 ◦C. The reaction mixture was poured into ice
water (100 ml) and the product was extracted with CH2Cl2. The
organic layer was washed with water and dried over anhydrous
MgSO4. A white powder (30 g, 82% yield) was collected on
solvent removal.
The mononuclear zinc(II) bis-diethyldithiocarbamate receptor
(16) was titrated with the whole series of bidentate guests. In
general, binding was found to be extremely weak. Only small
changes in the chemical shifts of the guest species were observed
and the stoichiometry of binding did not fit well with either 1 :
1 or 1 : 2 guest–host models. As a consequence, reliable stability
constant values could not be determined.
1H NMR (300 MHz, CDCl3, 288 K) d = 7.80 (d, 6.3 Hz, 2H,
tosyl), 7.33 (d, 6.3 Hz, 2H, tosyl), 6.66 (s, 4H, hydroquinone),
4.30 (t, 6.6 Hz, 4H, -CH2-), 4.06 (t, 6.6 Hz, 4H, -CH2-), and 2.42
(s, 6H, CH3). MS (ESI positive ion, MeOH/CH2Cl2): m/z 507
[M + H+].
Conclusion
A series of new dinuclear zinc(II) dithiocarbamate macrocyclic
receptors containing various aryl spacer groups of different
sizes have been prepared. H NMR titration studies revealed
these ditopic receptor systems form strong 1 : 1 inclusion
complexes with a variety of bidentate guests such as tereph-
thalate, isonicotinate and DABCO where the guest is bound
Secondary diamine compounds (1), (4), (7), (8) and (10).
Ditosyl, bis(chloromethyl) and bis(bromomethyl) compounds
were treated with excess amine (butylamine or benzylamine).
The reaction mixtures were stirred overnight and the excess
amine was removed under vacuum. The residue was redissolved
in CH2Cl2 (50 ml) and washed with water (3 × 50 ml). The
1
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D a l t o n T r a n s . , 2 0 0 5 , 3 5 9 – 3 6 4

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organic layer was collected and dried over anhydrous MgSO4.
Oily solids were obtained on solvent removal.
8.1 Hz, 4H, ArH), 7.41 (t, J = 7.5 Hz, 4H, ArH), 7.21 (d, J =
7.2 Hz, 4H, ArH), 5.21 (s, 8H, ArCH2), 3.79 (br, 8H, NCH2CH2),
1.70 (m, 8H, NCH2CH2), 1.26 (m, 8H, CH2CH3), 0.88 (m, 12H,
CH3). 13C NMR (75.43 MHz, CDCl3) d = 205.1 (CS2), 141.0,
135.7, 129.1, 126.9, 126.2 (ArC), 57.4, 54.0, 28.8, 20.0, (CH2)
13.7 (CH3). MS (ESI positive ion, MeCN): m/z 1080 [M]+. Anal.
Calcd. for C48H60N4S8Zn2: C, 53.36; H, 5.60; N, 5.19. Found: C,
50.21; H, 5.65; N, 5.06.
(1): A pale yellow oil was collected after drying in vacuo (0.5 g,
1
95% yield). H NMR (300 MHz, CDCl3) d = 7.2–7.3 (m, 4H,
ArH), 3.81 (s, 4H, ArCH2-), 2.67 (t, J = 7.2 Hz, 4H, N–CH2-),
1.54 (m, 4H, -CH2-), 1.36 (m, 4H, -CH2-), 0.94 (t, J = 7.2 Hz, 6H,
CH3). MS (ESI positive ion, MeOH/CH2Cl2) m/z: 249 [M +
H]+.
1
(4): A yellow oil was collected after drying in vacuo. (0.45 g,
(14): A white solid (2 g, 70% yield) was collected. H NMR
1
96% yield). H NMR (300 MHz, CDCl3) d = 7.76 (d, J =
(300 MHz, CDCl3) d = 7.61 (d, J = 7.2 Hz, 8H, ArH2/6), 7.44
(d, J = 7.2 Hz, 8H, ArH3/5), 7.37 (m, 20H, benzyl), 5.09 (s,
16H, ArCH2). 13C NMR (75.43 MHz, CDCl3) d = 206.1 (CS2),
140.4, 134.4, 133.7, 128.9, 128.5, 128.3, 128.0, 127.6 (ArC), 52.9,
55.4 (CH2). MS (ESI positive ion, CH2Cl2/MeOH): m/z 1214
[M]+. Anal. Calcd. for C60H52N4S8Zn2: C, 59.24; H, 4.31; N, 4.61.
Found: C, 58.46; H, 4.49; N, 4.81.
8.4 Hz, 2H, ArH4/5), 7.70 (s, 2H, ArH1/8), 7.41 (d, J =
8.7 Hz, 2H, ArH3/6), 3.94 (s, 4H, ArCH2), 2.66 (t, J = 7.2 Hz,
4H, NHCH2CH2), 1.53 (m, 4H, NHCH2CH2), 1.36 (m, 4H,
CH2CH3), 0.91 (t, J = 7.2 Hz, 6H, CH3). 13C NMR (75.47 MHz,
CDCl3) d = 137.75, 133.29, 131.68, 128.37, 127.04, 125.61 (ArC),
54.10, 49.11, 32.20, 20.57 (CH2), 14.11 (CH3). MS (ESI positive
ion, MeOH/CH2Cl2) m/z: 298.6 [M]+, 227.2 [M − NHBu]+
(7): A yellow oil was collected after drying in vacuo (0.89 g,
94% yield). 1H NMR (300 MHz, CDCl3) d = 7.55 (t, J = 1.5 Hz,
(15): A white solid (5 g, 85% yield) was collected. 1H
NMR (300 MHz, CDCl3) d = 7.37 (m, 20H, benzyl) 6.82
(s, 8H, hydroquinone), 5.30 (s, 8H, -OCHCH2N-), 4.29 (t,
J = 5.4 Hz, 8H, -OCH2CH2N-), 4.11 (t, J = 5.4 Hz, 8H,
NCH22CH2). 13C NMR (75.43 MHz, CDCl3) d = 205.7, 152.6,
134.9, 134.7, 128.9, 128.0, 65.6, 59.7 and 52.3 ppm. MS (ESI
positive ion, CH2Cl2/MeOH): m/z 1205 [M]+. Anal. Calcd. for
C52H52N4O4S8Zn2: C, 52.74; H, 4.43; N, 4.73. Found: C, 52.02;
H, 4.56; N, 5.02.
ꢀ
ꢀ
2H, ArH2/2 ), 7.46 (dt, J = 7.5 Hz, Jꢀ = 1.5 Hz, 2H, ArH6/6 ),
ꢀ
7.37 (t, J = 7.5 Hz, 2H, ArH5/5 ), 7.29 (dt, J = 7.8 Hz, Jꢀ =
ꢀ
1.5 Hz, 2H, ArH4/4 ), 3.88 (s, 4H, ArCH2), 2.66 (t, J = 7.2 Hz,
4H, NHCH2CH2), 1.52 (m, 4H, NHCH2CH2), 1.36 (m, 4H,
CH2CH3), 0.92 (t, J = 7.2 Hz, 6H, CH3). 13C NMR (75.47 MHz,
CDCl3) d = 141.08, 140.59, 128.63, 126.98, 126.88, 125.66 (ArC),
54.08, 49.02, 32.17, 20.56 (CH2), 14.11 (CH3). MS (ESI positive
ion, MeOH/CH2Cl2) m/z: 325.3 [M + H]+, 252.2 [M − NHBu]+
(8): A yellow oil was collected after drying in vacuo (1.0 g, 92%
yield). 1H NMR (300 MHz, CDCl3) d = 7.57 (d, J = 8.1 Hz, 4H,
ArH), 7.41 (d, J = 8.1 Hz, 4H, ArH), 7.31 (s, 10H, benzyl), 3.84
(s, 4H, ArCH2-). MS (ESI positive ion, MeOH/CH2Cl2) m/z:
393 [M + H]+.
3.3 X-Ray crystallography
Sinlge crystals of the zinc(II) bis-diethyldithiocarbamate and
DABCO complex were grown by slow diffusion of methanol
into a dichloromethane solution of a 1 : 1 mixture of zinc(II)
bis-diethyldithiocarbamate (16) and DABCO while crystals of
the complex of receptor (12) and DABCO were grown by
slow diffusion of methanol into a dichloromethane solution
of a 1 : 1 mixture of receptor (12) and DABCO. Crystals
were mounted on a glass fibre and cooled rapidly to 150 K
in a stream of cold nitrogen using an Oxford Cryosystems
CRYOSTREAM unit. Intensity data were processed using
the DENZO-SMN package.18 Structures were solved by direct
methods using the SIR92 program.19 Full-matrix least-squares
refinement was carried out using the CRYSTALS program
suite.20 Hydrogen atoms were positioned geometrically after
each cycle of refinement. A Chebychev polynomial weighting
scheme was applied.
(10): A yellow oil was collected after drying in vacuo (0.9 g,
1
90% yield). 1H NMR (300 MHz, CDCl3, 288 K) d = H NMR
(300 MHz, CDCl3, 288 K) d = 7.31 (m, 10H, benzyl), 6.80 (s, 4H,
hydroquinone), 4.02 (t, J = 5.1 Hz, 4H, -NHCH2CH2O-), 3.85
(s, 4H, Ar–CH2-), 2.98 (t, J = 5.1 Hz, 4H, -NHCH2CH2O-). MS
(EI+): m/z 377 (MH+).
Dinuclear zinc(II) dithiocarbamate receptors. Diamine com-
pound (1), (4), (7), (8) or (10) was dissolved in THF/MeCN and
two equivalents of Et3N and CS2 were added. The mixture was
stirred at room temperature for 2 h and an equivalent of zinc
acetate hydrate was added. The mixture was stirred overnight
and solvent removed. The remaining solid was extracted with
CH2Cl2 (100 ml) and the organic solution was washed with
water (50 ml) followed by brine (50 ml). The organic layer was
dried over anhydrous MgSO4 and then filtered. The filtrate was
concentrated in vacuo to leave a solid residue as the product. The
zinc(II) dtc macrocycles were further purified by recrystallisation
from CH2Cl2/MeOH.
Crystal data for zinc(II) bis-diethyldithiocarbamate (16) and
DABCO, C26H52N6S8Zn2, M = 836.03, Orthorhombic, a =
˚
21.7324 (3), b = 7.2463 (2), c = 24.1595 (4) A, a = b = c =
◦
3
˚
90 , U = 3804.63 (13) A , T = 150 K, space group Pca 21, Z =
4, l = 1.727 mm−1, 27083 reflections measured, 8373 unique
(Rint = 0.041). The final wR(F2) was 0.0365 (all data).
Crystal data for receptor (12) and DABCO, C50H86N6S8Zn2,
M = 1140.42, Triclinic, a = 11.6711 (4), b = 11.9393 (4), c =
(11): A white solid (0.5 g, 81% yield) was collected. 1H NMR
(300 MHz, CDCl3, 288 K) d = 7.29 (m, 2H, ArH), 7.11 (m, 6H,
ArH), 5.20 (br, 8H, ArCH2), 3.80 (br, 8H, NCH2CH2), 1.68 (m,
8H, NCH2CH2), 1.28 (m, 8H, CH2CH3), 0.88 (m, 12H, CH3). 13C
NMR (75.43 MHz, CDCl3) d = 205.6 (CS2), 135.7, 128.6, 127.0
(ArC), 57.4, 54.3, 29.0, 20.0, (CH2) 13.7 (CH3). MS (ESI positive
ion, MeCN): m/z 928 [M]+. Anal. Calcd. for C36H52N4S8Zn2: C,
46.59; H, 5.65; N, 6.04. Found: C, 46.45; H, 5.62; N, 6.06.
(12): A white solid (0.5 g, 80% yield) was collected. 1H NMR
(300 MHz, DMSO) d = 7.92 (d, J = 8.4, 4H, ArH), 7.76 (4H, s,
ArH), 7.51 (d, J = 8.4, 4H, ArH), 5.29 (s, 8H, ArCH2), 3.76
(br, 8H, NCH2CH2), 1.65 (br, 8H, NCH2CH2), 1.20 (br m,
8H, CH2CH3), 0.83 (br, 12H, CH3). 13C NMR (75.43 MHz,
DMSO) d = 205.4 (CS2), 134.4, 132.8, 131.8, 128.2, 125.7 (ArC),
57.1, 53.8, 28.3, 19.5 (CH2), 13.7 (CH3). MS (ESI positive ion,
MeCN): m/z 1028 [M]+. Anal. Calcd. for C44H56N4S8Zn2: C,
51.40; H, 5.49; N, 5.45. Found: C, 52.11; H, 6.07; N, 5.96.
(13): A white solid (0.5 g, 77% yield) was collected. 1H NMR
(300 MHz, CDCl3, 288 K) d = 7.97 (s, 4H, ArH), 7.30 (d, J =
◦
12.4675 (4) A, a = 110.2029 (15), b = 100.1626◦ (15), c =
˚
◦
3
˚
115.6632 (17), U = 1360.59 (9) A , T = 150 K, space group
−1
¯
P1, Z = 1, l = 1.228 mm , 16123 reflections measured, 6073
unique (Rint = 0.043). The final wR(F2) was 0.0509 (all data).
CCDC reference numbers 252800–252801.
See http://www.rsc.org/suppdata/dt/b4/b415935g/ for cry-
stallographic data in CIF or other electronic format.
Acknowledgements
We gratefully acknowledge the Marie Curie Fellowship of the
European Union for a postdoctoral fellowship (DC) and the
EPSRC for a studentship (WWHW).
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