The structural and electrochemical consequences of hydrogenating copper N2S2 Schiff base macrocycles

Article abstract of DOI:10.1016/j.ica.2010.01.012

A series of cis and trans tetradentate copper macrocyclic complexes, of ring size 14-16, that employ amine and thioether donor groups are reported. Apart from 5,6,15,16-bisbenzo-8,13-diaza-1,4-dithia-cyclohexadecane copper(I) (cis-[Cu(H₄N_b

Full text of DOI:10.1016/j.ica.2010.01.012

Inorganica Chimica Acta 363 (2010) 1529–1538
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Inorganica Chimica Acta
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The structural and electrochemical consequences of hydrogenating copper N2S2
Schiff base macrocycles
a
Katherine D. Trotter a, Michelle K. Taylor a, John C. Forgie a, John Reglinski a, , Leonard E.A. Berlouis ,
*
Alan R. Kennedy a, Corinne M. Spickett b, Rebecca J. Sowden b
a Department of Pure and Applied Chemistry, 295 Cathedral St., Strathclyde University, Glasgow G1, 1XL, United Kingdom
b Strathclyde Institute of Pharmacy and Biomedical Sciences, 27 Taylor Street, Strathclyde University, Glasgow G4 0NR, United Kingdom
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 6 October 2009
Received in revised form 31 December 2009
Accepted 9 January 2010
Available online 22 January 2010
A series of cis and trans tetradentate copper macrocyclic complexes, of ring size 14–16, that employ
amine and thioether donor groups are reported. Apart from 5,6,15,16-bisbenzo-8,13-diaza-1,4-dithia-
cyclohexadecane copper(I) (cis-[Cu(H4NbuSen)]+) all of the complexes are obtained in the copper(II) form.
Crystallographic analysis shows that the copper(II) complexes all adopt a distorted planar geometry
around the copper. In contrast, cis-[Cu(H4NbuSen)]+ is found to adopt a distorted tetrahedral geometry.
The complexes were subjected to electrochemical analysis in water and acetonitrile. The effect of the sol-
vent, positions of the donor atoms (cis/trans) on E1/2 is discussed as is the comparison of the electrochem-
ical behaviour of these complexes with their parent Schiff base macrocycles.
Keywords:
Macrocycle
Copper
Redox potential
Geometry
Ó 2010 Elsevier B.V. All rights reserved.
Donor groups
1. Introduction
these open tetradentate N2S2 Schiff base ligands (Fig. 1, 1) were
found to undergo partial hydrolysis and dissociation of the metal
Copper macrocycles are of considerable interest as low molecu-
lar weight models of biological copper-containing redox proteins.
There have been numerous reports of the synthesis of copper mac-
rocycles, including ones with tetradentate N4 or S4 ligands, and
their geometrical and electrochemical properties [1]. Comparative
studies of ligands with mixed thioether and amine donors have
also been carried out [2,3]. Ligands with an N2S2 donor set are bet-
ter models for biological copper centres as they increase the stabil-
ity of copper in the divalent form, facilitating redox reactions at the
metal centre [2–5]. However, there have been few systematic stud-
ies of the relationships between ring size, complex stability, and
electrochemical potential in such systems.
We are interested in developing copper-based redox sensors for
the detection of reactive oxygen species in biological systems,
which requires metal complexes that are stable in both the mono-
valent and divalent forms, and have a redox potential in the range
0.2–0.8 V. Preliminary work with symmetric, salicylidene based
N2S2 Schiff base copper complexes with ethylene, propylene or
butylene donor spacers suggested that it would be feasible to ob-
tain complexes with the requisite redox properties [4,5]. However,
on oxidation by biologically-relevant oxidants [5,6]. Consequently,
the corresponding Schiff base macrocycles were synthesized; these
compounds were more resistant to hydrolysis, but their general
water solubility was still poor [6,7]. Furthermore, although these
divalent copper complexes can be stoichiometrically reduced by
biologically relevant species, their re-oxidation led to significant
degradation in the organic portion of the compound [6]. On the po-
sitive side, there was no evidence of redox cycling by reaction with
molecular oxygen (Eq. (1)), as it was possible to reduce them quan-
titatively with a range of reducing agents in the presence of oxygen
[6]. This is important, as quantitative measurement of oxidant pro-
duction and biological redox balance requires that the redox sensor
should not undergo cycling of the kind observed with many simple
copper (and other transition metal) complexes [8,9] (Eq. (1)). Thus
copper macrocycles of the generic structure shown in Fig. 1 (2)
have potential as redox sensors, if they can be stabilized against
hydrolysis on chemical oxidation.
OH
OH
O
HO
HO
OH
OH
Cu+
+
O2
+
H2O2
O
O
O
O
O
* Corresponding author. Tel.: +44 0141 548 2349; fax: +44 0141 548 4822.
E-mail address: j.reglinski@strath.ac.uk (J. Reglinski).
ð1Þ
0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.01.012

1530
K.D. Trotter et al. / Inorganica Chimica Acta 363 (2010) 1529–1538
N
N
N
N
HN
S
NH
S
Cu
Cu
Cu
S
S
S
S
3
1
2
Fig. 1. The design of copper redox-sensing agents: copper Schiff base (a), copper Schiff base macrocycles (b) and copper amine macrocycles (c) [6,7]. Families of complexes
can be generated by altering the number of methylene units ((–CH2–)n, n = 2, 3) between the donor atoms. Charges and oxidation states are omitted as individual species can
exist in either of both forms.
Mass spectrometry data suggested that the copper Schiff base
macrocycles were prone to oxidation at the imine groups [6] and
it was decided to hydrogenate them, thus converting the Schiff
base macrocycles (Fig. 1, 2) into amine macrocycles (Fig. 1, 3).
The synthesis and structure of one of these copper complexes, with
ethylene bridges between both pairs of donor atoms (Fig. 1), has
previously been reported by Bentfield et al. [10]. Importantly, they
were able to isolate both forms of the complex, i.e. Cu(I) and Cu(II),
and their electrochemical analysis suggests that, similar to the
Schiff base complexes [3], it would be possible to oxidise this spe-
cies reversibly with chemical oxidants. Complexes of the same li-
gands, but with nickel as the metal, have also been synthesized
and their stability investigated previously [11]. However, as yet a
systematic study of the effect of ring size and geometry on the
electrochemical properties of the copper macrocycle family shown
in Fig. 1 (3) has not been reported. These macrocycles should have
important advantages for biological applications over some of
those described previously [2,3], in terms of their electrochemical
properties and resistance to loss of the metal ion. Hence the aim
of this work was to synthesize a small family of cis and trans
amine-thioether copper macrocycles with differing ring sizes and
geometries, and investigate their aqueous stability and electro-
chemical properties.
were glassy carbon, platinum wire and silver wire as the working,
counter and reference electrodes, respectively. All solutions were
degassed with argon and contained sample concentrations
2 ꢀ 10ꢁ3 M for water and 4 ꢀ 10ꢁ3 M for acetonitrile, together with
the supporting electrolyte; NaCl (0.1 M) and tBu4NBF4 (0.1 M),
respectively. Measurements in aqueous and non-aqueous solution
were referenced against the redox couples (E1/2) of potassium fer-
ricyanide/ferrocyanide and ferrocene/ferrocenium, respectively.
This allowed for the data to be referred back to silver wire, which
is the common reference electrode for both series of experiments.
2.1. Preparation of cis-amine macrocycles
Briefly 4.5 g (excess) NaBH4 was added to a stirred solution of
0.66 mmol of the relevant Schiff base macrocycle in 500 ml ethanol
in small portions over approximately 1 h, upon which the solution
became pale yellow. The reaction mixture was cooled in an ice bath
and kept under a N2 blanket during addition of NaBH4 for safety.
The solvent was removed and 100 ml distilled water added.
The product was then extracted into 3 ꢀ 200 ml chloroform.
The extracts were combined, washed with 100 ml distilled water
and dried over anhydrous sodium sulphate. The solution was
filtered and the solvent removed to give yellow oils apart from
cis-H4NbuSbu which was obtained as a white mass. Typical yields
of 80% were obtained.
2. Experimental
2.1.1. cis-H4NenSen
Unless otherwise stated all chemicals were commercially ob-
tained and used without further purification. The Schiff base mac-
rocycles and cis-[Ni(H4NprSen)Cl(OH2)]+ are prepared as previously
reported [6,7,11,12]. Solvents were used as supplied, apart from
the acetonitrile, which was re-distilled over calcium hydride prior
to its use in the electrochemical studies. All NMR spectra were re-
corded on either a Bruker DPX400 or a Bruker AV500. The spectra
were referenced to internal solvent peaks and thus to TMS. Solid
reflectance spectra (400–900 nm) were recorded on a Photonics
CCD array UV–Vis spectrophotometer. Mass spectra were recorded
using a Thermo Finnigan LCQDuo by electrospray ion trap.
1H NMR (400 MHz, CDCl3; dH) 7.39 (m, 2H, arom), 7.29 (m, 2H,
arom), 7.18 (m, 4H, arom), 3.81 (s, 4H, –CH2–), 3.27 (s, 4H, –SCH2–),
2.92 (s, 4H, –NCH2). 13C NMR (100 MHz, CDCl3; dC) 141, 134, 131,
130, 128, 127 (arom), 52 (–CH2–), 48 (–SCH2–), 34 (–NCH2–). Mass
spec. (ESI) m/z 331 [MH]+.
2.1.2. cis-H4NprSen
1H NMR (400 MHz, CDCl3; dH) 7.55 (d, 2H, arom), 7.26 (m, 2H,
arom), 7.18 (d, 4H, arom), 4.16 (s, 4H, –CH2–), 3.36 (s, 4H,
–SCH2–), 2.94 (t, 4H, –NCH2), 2.07 (p, 2H, –NCH2CH2–). 13C NMR
(100 MHz, CDCl3; dC) 136, 134, 133, 131, 128, 127 (arom), 54
(–CH2–), 49 (–SCH2–), 33 (–NCH2–), 19 (–NCH2CH2–). Mass spec.
(ESI) m/z 345 [MH]+.
Crystals were coated in mineral oil and mounted on glass fibres.
Data were collected at 123 K on a Nonius Kappa CCD diffractome-
ter using graphite monochromated Mo Ka radiation. The heavy
atom positions were determined by Patterson methods and the
remaining atoms located in the difference electron density maps.
Full matrix least squares refinement was based on F2 with all
non-hydrogen atoms anisotropic. While the hydrogen atoms were
mostly observed in the difference maps, they were placed in calcu-
lated positions riding on the parent atoms. The positions of the
protons on the coordinated water in cis-[CuII(H4NprSpr)(OH2)]2+
were calculated using CALC-OH [13]. The structure solution and
refinement used the programs SHELX-97 [14] or SIR 92 [15] and the
graphical interface WINGX [16]. A summary of the crystallographic
parameters are given in Table 1.
2.1.3. cis-H4NbuSen
1H NMR (400 MHz, CDCl3; dH) 7.40 (m, 4H, arom), 7.23 (m, 4H,
arom), 3.95 (s, 4H, –CH2–), 3.27 (s, 4H, –SCH2–), 2.73 (t, 4H,
–NCH2), 1.73 (m, 4H, –NCH2CH2–). 13C NMR (100 MHz, CDCl3; dC)
134, 132, 131, 129, 128, 127.5 (arom), 48 (–SCH2–), 34 (–NCH2–),
27 (–NCH2CH2–). Mass spec. (ESI) m/z 359 [MH]+.
2.1.4. cis-H4NenSpr
1H NMR (400 MHz, CDCl3; dH) 7.53 (d, 2H, arom), 7.36 (d, 2H,
arom), 7.18 (m, 4H, arom), 3.83 (s, 4H, –CH2–), 3.18 (t, 4H,
–SCH2–), 2.79 (s, 4H, –NCH2), 1.85 (p, 2H, –SCH2CH2–). dC
(100 MHz; solvent CDCl3) 141, 135, 132, 131, 128, 127 (arom), 53
(–CH2–), 49 (–SCH2–), 35 (–NCH2–), 28 (–SCH2CH2–). Mass spec.
(ESI) m/z 345 [MH]+.
Cyclic voltammetry in aqueous solution was carried out on a CH
Instruments 660A Electrochemical Workstation with iR compensa-
tion, using ultra high purity water (Elga: 0.22
l filtered, 17 MX/cm)
and acetonitrile (redistilled from calcium hydride). The electrodes

K.D. Trotter et al. / Inorganica Chimica Acta 363 (2010) 1529–1538
1531
Table 1
Crystallographic details. Problems were encountered with the [BF4]ꢁ anions associated with cis-[Cu(H4NbuSen)]+ which influenced the refinement process. This is discussed further
in the supplementary material where a view of the extend structure is given.
cis-[Cu(H4NprSen)] (BF4)2
cis-[Cu(H4NprSpr)OH2] (BF4)2
cis-[Cu(H4NbuSen)] BF4
cis-[Cu(H4NenSpr)] (BF4)2
Empirical formula
FW
C19H24B2CuF8N2S2
581.68
C20H28B2CuF8N2OS2
613.7
C20H26BCuF4N2S2
500.76
C19H24B2CuF8N2S2
584.1
Crystal system
Space group
a (Å)
b (Å)
c (Å)
monoclinic
P21/c
8.3990(8)
17.1050(17)
15.5630(15)
92.425(3)
monoclinic
P21/n
14.1716(7)
11.5191(5)
15.6357(10)
105.621(6)
monoclinic
C2/c
25.6592(10)
16.7535(7)
16.3163(4)
91.221(3)
monoclinic
P21/c
12.7779(4)
20.5576(7)
19.0148(6)
108.178(2)
a
(°)
b (°)
c
(°)
Z
4
4
12
8
V (Å3)
2233.94(5)
1.243
9804
5036
3832
2458.2(2)
1.137
23,331
6092
7012.5(4)
1.151
21,486
6149
4745.6(3)
1.172
21,367
10,882
4780
lcalc (mmꢁ1
Number of refections measured
Number of unique refections
No. observed
)
3666
4621
No. parameters
307
339
438
621
R (I > 2
wR2 (all reflns)
Goodness-of-fit
r
(I))
0.0574
0.1571
1.164
0.0457
0.1095
0.926
0.0609
0.0913
1.109
0.0699
0.1740
1.023
cis-[Ni(H4NprSen)Cl(OH2)] BF4
cis-[Cu(H4NprSen)Cl] BF4
[CuCl2(cis-H6NbuSpr)2] (PF6)2
H6NprSbu (BF4)2
Empirical formula
FW
C19H26BClF4N2NiOS2
543.51
C19H24BClCuF4N2S2
530.32
C44H66Cl2CuF12N4O2 P2S4
1235.63
C21H30B2F8N2S2
548.21
Crystal system
Space group
a (Å)
b (Å)
c (Å)
triclinic
P1
monoclinic
P21/a
8.392(12)
19.206(12)
13.12(2)
triclinic
P1
monoclinic
C2/c
17.1185(10)
10.0403(6)
16.0010(10)
118.358(3)
ꢀ
ꢀ
8.3859(10)
10.9303(13)
13.3650(15)
111.698(2)
99.918(2)
92.152(2)
2
1114.4(2)
1.226
13,065
8.2322(9)
10.2439(11)
16.1675(17)
86.941(2)
76.566(2)
85.969(2)
1
1321.9(2)
0.816
12,432
6420
a
(°)
92.07(13)
b (°)
c
(°)
Z
2
4
V (Å3)
2113(5)
1.402
19,363
4868
3169
339
2420.13(3)
0.296
4882
2623
1609
lcalc (mmꢁ1
)
Number of refections measured
Number of unique refections
No observed
6616
4991
384
4400
335
No. parameters
159
R (I > 2
wR2 (all reflns)
Goodness-of-fit
r
(I))
0.042
0.1273
1.061
0.0945
0.2541
1.024
0.0555
0.1523
1.048
0.0488
0.1125
1.009
2.1.5. cis-H4NprSpr
2.1.8. cis-H4NprSbu
1H NMR (400 MHz, CDCl3; dH) 7.42 (d, 2H, arom), 7.31 (d, 2H,
arom), 7.19 (m, 4H, arom), 3.94 (s, 4H, –CH2–), 3.05 (t, 4H,
–SCH2–), 2.77 (t, 4H, –NCH2), 1.97 (p, 2H, –SCH2CH2–), 1.82 (s, br,
2H, NH), 1.72 (p, 2H, –NCH2CH2–). 13C NMR (100 MHz, CDCl3; dC)
141, 135, 131, 130, 128, 127 (arom), 52 (–CH2–), 48 (–SCH2–), 34
(–NCH2–), 30 (–SCH2CH2–), 29 (–NCH2CH2–). Mass spec. (ESI) m/z
359 [MH]+.
1H NMR (500 MHz, CDCl3; dH) 7.33 (d, 2H, arom), 7.31 (d, 2H,
arom), 7.20 (t, 2H, arom), 7.15 (t, 2H, arom) 3.91 (s, 4H, –CH2–),
2.96 (t, 4H, –SCH2), 2.70 (t, 4H, –NCH2–), 1.78 (m, 6H, –SCH2CH2–,
–NCH2CH2-,). 13C NMR (125 MHz, CDCl3; dC) 140, 135, 130, 129,
128, 126 (arom), 52 (–CH2–), 47 (–SCH2–), 34 (–NCH2–), 30
(–SCH2CH2–), 28 (–NCH2CH2–). Mass spec. (ESI) m/z 373.
2.1.9. cis-H4NbuSbu
1H NMR (500 MHz, CDCl3; dH) 7.34 (m, 4H, arom), 7.21 (m, 4H,
arom), 4.78 (s, 1H, –NH–), 4.56 (s, 1H, –NH–), 4.00 (m, 2H,
–PhCH2N–), 3.82 (m, 2H, –PhCH2N–), 3.07, (m, 4H, NCH2–), 2.72
(m, 4H, SCH2–), 1.85 (m, 4H, SCH2CH2), 1.71 (m, 4H, SCH2CH2).
13C NMR (125 MHz, CDCl3; dC) 135 (ꢀ2), 133 (ꢀ2) 132 (ꢀ2), 130
(ꢀ2) 129 (ꢀ2), 126 (ꢀ2) (all arom), 60 (N–CH2), 55 (N–CH2–CH2),
33 (S–CH2), 28 (N–CH2–CH2), 24 (S–CH2–CH2) Proton assignments
are made using 2D [1H, 1H] COSY and 2D [1H, 13C] HSQC NMR spec-
tra.n Mass spec. (ESI) m/z 387 [MH]+.
2.1.6. cis-H4NbuSpr
1H NMR (400 MHz, CDCl3; dH) 7.38 (d, 2H, arom), 7.29 (d, 2H,
arom), 7.19 (m, 4H, arom), 3.90 (s, 4H, –CH2–), 3.09 (t, 4H,
–SCH2–), 2.62 (t, 4H, –NCH2), 2.06 (p, 2H, –SCH2CH2–), 1.57 (p,
4H, –NCH2CH2–). 13C NMR (100 MHz, CDCl3; dC) 141, 135, 131,
130, 129, 127 (arom), 52 (–CH2–), 48 (–SCH2–), 34 (–NCH2–), 29
(–SCH2CH2–), 27 (–NCH2CH2–). Mass spec. (ESI) m/z 373 [MH]+.
2.1.7. cis-H4NenSbu
1H NMR (500 MHz, CDCl3; dH) 7.37 (d, 2H, arom), 7.30 (d, 2H,
arom), 7.20 (t, 2H, arom), 7.15 (t, 2H, arom) 3.89 (s, 4H, –CH2–),
2.93 (t, 4H, –SCH2), 2.89 (s, 4H, –NCH2–), 1.74 (p, 4H, –SCH2CH2–).
13C NMR (125 MHz, CDCl3; dC) 141, 135, 131, 130, 128, 127 (arom),
53 (–CH2–), 49 (–SCH2–), 34 (–NCH2–), 28 (–SCH2CH2–). Mass spec.
(ESI) m/z 359.
2.2. Preparation of trans-amine macrocycles
Briefly, 0.2 g (5.3 mmol) LiAlH4 was added under a blanket of N2
to a cooled (4 °C), stirred solution of 2.66 mmol of the relevant
Schiff base macrocycle in 75 ml THF in small portions over approx-
imately 1 h. The reaction mixture was stirred overnight under a N2

1532
K.D. Trotter et al. / Inorganica Chimica Acta 363 (2010) 1529–1538
blanket after which time the reaction was quenched by the drop-
wise addition of water (0.2 ml), 20% potassium hydroxide solution
(0.2 ml) and water (0.6 ml). The solution was filtered and the sol-
vent removed leaving an oil which was used without further puri-
fication. Typical yield 70%.
2.7. Preparation of cis-[Cu(II)H4NprSpr] (BF4)2
Cu(BF4)2ꢂH2O (0.067 g, 0.28 mmol) in methanol (5 ml) was
added dropwise to a solution of H4NprSpr (0.1 g, 0.28 mmol) in
methanol (10 ml). The dark green solution was refluxed for 1 h,
hot filtered and cooled. The dark green brown solution was then
filtered through Celite and recrystallised by vapour diffusion with
diethyl-ether to give dark green crystals suitable for X-ray analysis.
The structure shows that the resulting complex contains a coordi-
nated water molecule. Anal. Calc. for C20H28N2B2CuF8OS2: C, 39.14;
H, 4.60; N, 4.56%, Calc. for C20H26N2S2Cu.B2F8: C, 40.32; H, 4.40; N,
4.70%. Found: C, 40.14; H, 4.29; N, 4.52%. Mass spec (ESI) m/z 421
[MH+]. kmax = 440 nm, 570 nm.
2.2.1. trans-H4(N-en-S)2
1H NMR (400 MHz, CDCl3; dH) 7.45 (m, 8H, arom), 3.72 (s, 4H,
–PhCH2N–), 3.22, (t, 4H, NCH2–), 2.89 (t, 4H, SCH2–). Mass spec.
(ESI) m/z 331 [MH]+.
2.2.2. trans-H4(N-pr-S)2
1H NMR (400 MHz, CDCl3; dH) 7.20 (m, 8H, arom), 3.94 (s, 4H,
–PhCH2N–), 3.04, (t, 4H, NCH2–), 2.82 (t, 4H, SCH2–), 1.93 (q, 4H,
–CH2–). Mass spec. (ESI) m/z 359 [MH]+.
2.8. Preparation of cis-[Cu(I)H4NbuSen] BF4
2.3. Preparation of cis-[Cu(II)H4NenSen] (BF4)2 [10]
Cu(BF4)2ꢂH2O (0.24 g, 1 mmol) was added to a solution of
H4NbuSen (0.35 g, 1 mmol) in chloroform (20 ml). The mixture
was placed in an ultrasonic bath (5 min) to disperse the copper
salt. The resulting yellow mixture was refluxed for 2 h and then
hot filtered. The solvent was removed to give a pale yellow solid,
which was dissolved in the minimum amount of acetonitrile and
recrystallised by vapour diffusion with diethyl-ether. Anal. Calc.
for C20H26N2BCuF4S2ꢂ2H2O: C, 44.08 ; H, 5.55; N, 5.14. Found: C,
44.12; H, 5.16; N, 5.14%. 1H NMR (400 MHz, DCM; dH) 7.47–7.39
(m, 4H, arom), 7.34–7.29 (m, 4H, arom), 4.10, (t, 2H, SCHa), 3.95,
(d, 2H, –CHaN–), 3.69, (d, 2H, –SCHb–), 3.42 (MeOH), 3.39, (t, 2H,
NCHa), 2.99, (br d, 4H, NCHb and NH) 2.73 (t, 2H, –CHbN–), 2.17,
(p, 2H, –NCH2CHa), 1.86, (q, 2H, –NCH2CHb–). 13C NMR (100 MHz,
DCM; dC) 137, 133, 131, 129, 128, 127 (arom), 56 (–SCH2–) 48
(–NCH2–), 33 (–CH2N–), 25 (–NCH2CH2–). Mass spec. (ESI) m/z
421 [MH+].
Cu(BF4)2ꢂH2O (0.24 g, 1 mmol) in methanol (5 ml) was added
dropwise to a solution of H4NenSen (0.35 g, 1 mmol) in methanol
(20 ml). The solution, which turned dark green, was refluxed for
1 h and hot filtered. The solvent was removed to give a dark green
solid. The solid was redissolved in the minimum amount of meth-
anol, filtered through Celite and recrystallised by vapour diffusion
with diethyl-ether to give a dark green crystalline material. Anal.
Calc. for C18H22N2B2CuF8S2: C, 38.09; H, 3.91; N, 4.94. Found: C,
38.00; H, 4.04; N, 4.45%. Mass spec. (ESI) m/z 196.5, 393 [MH2+],
[MH+]. kmax = 425 nm, 560 nm.
2.4. Preparation of cis-[Cu(II)H4NenSpr] (BF4)2
Cu(BF4)2ꢂH2O (0.07 g, 0.29 mmol) in methanol (5 ml) was added
dropwise to a solution of H4NenSpr (0.1 g, 0.29 mmol) in methanol
(10 ml). The dark green/brown solution was refluxed for 1 h, hot
filtered and cooled. The dark green brown solution was filtered
through Celite and recrystallised by vapour diffusion with
diethyl-ether to give dark green crystals suitable for X-ray analysis.
Anal. Calc. for C19H24N2S2CuB2F8: C, 39.23; H, 4.16; N, 4.82. Found:
C, 39.68; H, 4.33; N, 4.75%. Mass spec. (ESI) m/z 407 [MH+].
kmax = 415 nm.
2.9. Preparation of [CuCl2(cis-H6NbuSpr)2] (PF6)2
Cu(MeCN)4 PF6 (0.100 g, 0.27 mmol) was treated with H4NbuSpr
(0.100 g, 0.27 mmol) in methanol (50 ml). The solution was re-
fluxed for 2 h. The solution was allowed and the solvent removed.
The yellow oil was crystallised from methanol/diethyl-ether by va-
pour diffusion. After a prolonged period a few crystals formed
which were identified crystallographically as [CuCl2(cis-
H4NbuSpr)2]2+ 2PF6.
2.5. Preparation of cis-[Cu(II)H4NenSbu] (BF4)2
Cu(BF4)2ꢂH2O (0.07 g, 0.29 mmol) in methanol (5 ml) was added
dropwise to a solution of H4NenSbu (0.1 g, 0.29 mmol) in methanol
(50 ml). The solution was refluxed for 1 h allowed to cool and then
filtered. The solvent was removed under pressure and the brown
residue extracted with methanol. The product was crystallised di-
rectly from this solution by vapour diffusion with diethyl-ether to
give dark green crystals which were unsuitable for X-ray analysis.
Anal. Calc. for C20H26N2S2CuB2F8ꢂ1H2O: C, 39.14; H, 4.49; N, 4.56.
Found: C, 39.24; H, 4.74; N, 4.84%. Mass spec. (ESI) m/z 421
[MH+]. kmax = 455 nm.
2.10. Preparation of trans-[Cu(II)H4(N2S2)] (BF4)2
Cu(BF4)2ꢂH2O (0.25 g, 0.8 mmol) in methanol (10 ml) was added
to a solution of the relevant trans-H4(N2S2) macrocycle (0.26 g,
ꢃ0.8 mmol) in methanol (40 ml). The solution was refluxed for
3 h and then allowed to cool. The solvent was removed and result-
ing sticky material redissolved in a methanol from which the prod-
uct was crystallised using vapour diffusion with diethyl-ether.
2.6. Preparation of cis-[Cu(II)H4NprSen] (BF4)2
2.11. trans-[Cu(II)H4(N-en-S)2] (BF4)2.OEt2
Cu(BF4)2ꢂH2O (0.24 g, 1 mmol) in methanol (5 ml) was added
dropwise to a solution of H4NprSen (0.35 g, 1 mmol) in methanol
(20 ml). The solution, which turned dark green, was refluxed for
1 h and hot filtered. The solvent was removed to give a dark green
solid. The solid was redissolved in the minimum amount of meth-
anol, filtered through Celite and recrystallised by vapour diffusion
with diethyl-ether to give dark green crystals suitable for X-ray
analysis. Anal. Calc. for C19H24N2B2CuF8S2: C, 39.23; H, 4.16; N,
4.82. Found: C, 39.82; H, 3.78; N, 4.50%. Mass spec. (ESI) m/z 407
[MH+]. kmax = 430 nm, 580 nm.
Anal. Calc. for C22H32N2B2CuF8OS2: C, 41.17; H, 5.03; N, 4.36.
Found: C, 41.45; H, 4.72; N, 4.97%. Mass spec. (ESI) m/z 393
[MH+]. kmax = 455 nm, 601 nm.
2.12. trans-[Cu(II)H4(N-pr-S)2] (BF4)2
Anal. Calc. for C20H26N2B2CuF8S2: C, 40.52; H, 4.40; N, 4.76.
Found: C, 40.10; H, 4.76; N, 4.42%. Mass spec. (ESI) m/z 421
[MH+]. kmax = 436 nm, 595 nm.

K.D. Trotter et al. / Inorganica Chimica Acta 363 (2010) 1529–1538
1533
proportion of the desired complex, which could then be separated
from the mixture. However, mass spectroscopy suggested that the
symmetric en/en and pr/pr complexes were dominant, and it was
not possible to retrieve the mixed species in sufficient amounts
and at an acceptable level of purity. Suitable crystals of
trans-[Cu(II)H4(N-pr-S)2] (BF4)2 for X-ray analysis could also not
be generated. However, comparison of the spectroscopic data (vis-
ible reflectance, mass spectrometry) with that of trans-[Cu(II)H4(N-
en-S)2] (BF4)2, the reports of Bentfield et al. [10] and Martin et al.
[12] and to a lesser extent the cis macrocycles (Fig. 3), indicate that
it has an iso-structural motif.
3. Results and discussion
The cis-[Cu(H4N2S2)]n+ Schiff base macrocycles were prepared
using previously published methods [6,7,12]. They were hydroge-
nated using sodium borohydride to form the required amine mac-
rocycles (Fig. 2). The macrocycles were obtained as sticky oily
materials apart from cis-H4NbuSbu which was obtained as an off-
white mass. All of the macrocycles gave suitable analysis by NMR
and mass spectrometry and were subsequently used without fur-
ther purification. They were converted into their respective copper
complexes by treating them with copper(II) tetrafluoroborate. The
majority of the complexes were obtained in their divalent form,
apart from cis-[Cu(H4NbuSen)]+, which was obtained in its monova-
lent form (Fig. 3). Consistent with our previous studies on Schiff
base macrocycles [6], the stability of the complexes is reduced as
the ring sizes increase and consequently we were unable to syn-
3.1. Structure of the macrocyclic complexes
The smallest member of the series of complexes under investi-
gation here, cis-[Cu(H4NenSen)]2+, has been reported previously
thesise cis-[Cu(H4NprSbu)]2+ and cis-[Cu(H4NbuSbu)]2+
.
[10]. X-ray quality crystals of the BF4 salts of cis-[Cu(H4NprSen)]2+
,
ꢁ
The 1H NMR of cis-H4NbuSbu is extremely complex, indicative of
a compact folded structure.n As the ring size increases, folding of
the organic chains for the neutral species becomes more favourable
and the energy of metal internalisation falls. During protracted ef-
forts to generate cis-[Cu(H4NbuSpr)]2+, we were able to retrieve
small amounts of the protonated ligand (H6NbuSpr (BF4)2) and an
unexpected exo-complex of copper(II) chloride (Fig. 4). Conse-
quently it appears that metal-centred complex formation is no
longer favourable with these macrocycles. A similar observation
regarding the limiting effects of large rings was reported for the
parent Schiff base macrocycles [6].
cis-[Cu(H4NprSpr)(OH2)]2+, cis-[Cu(H4NenSpr)]2+ and cis-[Cu(H4Nbu
-
Sen)]+ were successfully isolated, thus expanding the catalogue of
this family of compounds sufficiently for us to investigate the nat-
ure of the copper binding site (Fig. 3). For the divalent species, the
copper typically sits in an almost planar environment, apart from
[Cu(H4NenSen)]2+, where the placement and nature of the donor
atoms within the small 14-membered ring enforces a slight distor-
tion at copper centre and small compression in the Cu–S and Cu–N
distances (Table 2). The larger rings afford greater flexibility and
this distortion is absent. During the early stages of this work we
also synthesised [Ni(H4NprSen)Cl(OH2)]+ using an approach re-
ported by Lindoy and Smith [11]. In this instance H4NprSen ligand
occupies the meridial plane of the nickel and it is notable that
the metrical parameters in this region are indistinguishable from
those observed for the three new copper macrocycles.
In order to gauge the effect of the position of the donor atoms,
two trans-[Cu(H4N2S2)]n+ amine complexes were also prepared (13,
14). These were constructed using the template approach (Fig. 5)
[7,12]. Equimolar amounts of 11 were mixed with 12 (Fig. 5), in
an attempt to prepare the mixed en/pr complex, based on the pre-
mise that the statistical distribution would lead to a significant
Of the three additional structurally characterised species, cis-
[Cu(H4NprSen)]2+ and cis-[Cu(H4NenSpr)]2+ contain orientated BF4
ꢁ
Fig. 2. A schematic representation of the synthesis of the cis-[Cu(H4N2S2)]n+ (n = 1, 2) Schiff base and amine macrocycles. Charges and oxidation states are omitted as
individual species can exist in either of both forms.

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K.D. Trotter et al. / Inorganica Chimica Acta 363 (2010) 1529–1538
Fig. 3. The X-ray crystal structures of cis-[CuII(H4NprSen)]2+
, , ,
cis-[CuII(H4NprSpr)(OH2)]2+ cis-[CuII(H4NenSpr)]2+ cis-[CuI(H4NbuSen)]+, cis-[CuII(H4NprSen)Cl]+ and cis-
[NiII(H4NprSen)Cl(OH2)]+. The metric parameters are given in Table 2. Only the ‘coordinated’ BF4 anions are shown. Problems were encountered with the [BF4]ꢁ anions
associated with cis-[CuI(H4NbuSen)]+; these and the solution used are discussed further in Supplementary material, where a view of the extend structure is given.
anions. These sit above and below the plane of the CuN2S2 motif at
fixed positions with a fluoride in an axial position. The positions of
the fluorines (ꢃ2.5 Å) are typical of this type of interaction.1 In par-
ticular they are not dissimilar to the Cu–Cl distance (Table 2) found
in cis-[Cu(H4NprSen)Cl]+, which is formed when HCl is used to isolate
the ligand. The third species, cis-[Cu(NprSpr)(OH2)]2+ (Fig. 3), is differ-
ent in that it is five coordinate with a water molecule occupying the
axial position. Occupation of this site means that, in this instance,
there is only space for one weakly bound BF4 counter ion.
ꢁ
The copper species became more difficult to generate as the ring
size increased. Significantly, cis-[Cu(H4NbuSen)]+ was isolated in its
univalent form (Fig. 3) and as expected the macrocyclic ligand
reorganises to accommodate the tetrahedral preference of the d10
ion. The movement of the ligand to accommodate the univalent
cation forces the ligand to move from the plane occupying donor
sites that sit on the circumference of a circle (ꢃ4.8 Å diameter; data
for cis-[Cu(H4NprSpr)]+) to the points of a tetrahedron which can be
considered to occupy points on the surface of a sphere (ꢃ4.6 Å
1
45 of the 66 structures deposited in the crystallographic database (Feb. 2009)
which contain copper and tetrafluoroborate have Cu–F distances within the limits of
the range (2.4–2.8 Å) defined by the complexes reported here.

K.D. Trotter et al. / Inorganica Chimica Acta 363 (2010) 1529–1538
1535
Fig. 4. The X-ray crystal structures of [CuCl2(cis-H4NbuSpr)2]2+ and [H6NprSbu 2+. [CuCl2(cis-H4NbuSpr)2]2+ is an exo-complex where incorporation of the metal within the ring or
]
between pairs of donors is no longer favoured. The source of the halides is unknown.
Fig. 5. A schematic representation of the synthesis of the trans-N2S2 Schiff base macrocycle. These were hydrogenated as described above to form the relevant amine
macrocycle.
diameter). The necessary twist in the ligand required to reach these
positions requires that the diameter of the pocket in which the me-
tal sits changes. Thus, rather than the expected expansion in the
Cu–S and Cu–N distances with the larger, reduced metal centre,
we find that there is a small contraction in the Cu–S and Cu–N
bond distances as compared to the divalent complex cis-
[Cu(H4NprSpr)]+, which has the same number of atoms in the ring.
A similar effect has been commented on by Nanda et al. [17] and
was reported in our studies on Schiff base macrocycles [6]. Another
notable similarity to the behaviour of this family of complexes
with their parent Schiff base complexes is the influence of the poly-
methylene spacers between the nitrogen donors. Expansion here
forces the macrocycle out of the plane, favouring a tetrahedral
form and thus copper(I). This effect is not seen with the corre-
sponding complex [Cu(H4NenSbu)]2+, which has the butylene group
between the sulphur donors. Unfortunately, increasing the ring’s
size to 17, i.e. [Cu(H4NbuSpr)]2+ compromises the stability of the
macrocyclic complex and it was not possible to produce a viable
complex from the standard reaction scheme (Fig. 2). By resorting
to alternative counter ions, a small amount of complex was ob-
tained and characterised (Fig. 4). Here, the bonds to sulphur do
not form and the metal centre remains in an exo-position. Two
chlorides are found in the coordination sphere despite the absence
of chloride salts in the reaction mixture. The halide probably arises
from the chlorinated solvents. Since the desired complex did not
form, the problems encountered in the synthesis of [CuCl2(cis-
H4NbuSpr)2]2+ are of little relevance at this stage, and we have not
investigated this finding further.
The two trans-[Cu(N2S2)]2+ amines were also isolated. trans-
[Cu(H4N-en-S)2]2+ has been reported previously as the perchlorate
salt [12]. We have been trying to avoid the presence of oxidising
ligands such as perchlorate in our work as they might interfere
in the ensuing chemical reactions and we have hence prepared
the [BF4]ꢁ salts. In our previous experience, changing the counter
anions has little effect on the structures of these entities, and the
mass spectrometry and visible spectroscopy of both complexes,
trans-[Cu(H4N-en-S)2]2+ and trans-[Cu(H4N-pr-S)2]2+ indicate that
the desired complexes have been formed.
4. Electrochemical studies
The amine macrocycles reported here remain relatively flexible
(compared to simple macrocycles reported previously in 2 & 3) and
appear to be able to adjust to the geometric preferences of the
encapsulated metal (Cu(I), tetrahedral; Cu(II), planar). We were
thus interested to investigate the electrochemical behaviour of
these geometrically accommodating macrocyclic complexes in

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K.D. Trotter et al. / Inorganica Chimica Acta 363 (2010) 1529–1538
comparison to their more rigid parent Schiff base macrocycles,
which are more limiting for the metal centre geometry [6]. Conse-
quently, this aspect of the study was carried out in organic solvent
to allow comparison of the data for the two types of macrocycles.
However, the enhanced water stability and solubility of these cis-
amine thioether complexes also allowed us to study their behav-
iour in aqueous solution. This was important to the underlying
aim to obtain copper complexes with potential for use in biological
systems.
In non-aqueous solvent the oxidation potentials of the amine
macrocycles are observed to display
a comparable range
(ꢃ0.32 V) to that of their analogous Schiff base species (ꢃ0.38 V).
However, although the replacement of the imine (ꢁ0.42 to
0.04 V) with a secondary amine (ꢁ0.68 to ꢁ0.36) does produce
the expected anodic shift in E1/2 [4,18] (CuI/CuII) the corresponding
values suggest that the change is not uniform. Indeed the two com-
plexes based on the NenSen are observed to have a comparable E1/2
.
Similarly, the two series of complexes based on Sen have widely dif-
fering behaviour. While the Schiff base complexes show a marginal
rise in E1/2 as the macrocyclic ring size increases, the amine macro-
cycles do not follow a definite pattern. Repeating the experiment in
aqueous solution we observed a solvent-dependent shift in all the
E
1/2 values recorded (Table 3). This probably arises from the polar-
ity differences between the two solvents. This is particularly appar-
ent in the values for [Cu(H4NprSen)]2+, with an E1/2 value in
acetonitrile of ꢁ0.15 V (the lowest w.r.t Ag wire), whereas in aque-
ous solution this species gave the highest value (0.16 w.r.t Ag
wire). The reason for this non-uniform change is unclear but prob-
ably stems from the manner in which the copper macrocycle sol-
vates (Fig. 3). Based on this observation it is surprising that this
species was not isolated in the copper(I) form (cf. cis-
[Cu(H4NbuSen)]+).
It was not possible to investigate the geometric effects (bond
length, bond angles, torsion angles) underlying the shift in E1/2 in
the Schiff base macrocycles synthesized previously, as this family
of species were isolated in both mono and divalent forms [6]. How-
ever, a subset of the compounds reported here, cis-[Cu(H4Npr
-
Sen)]2+ cis-[Cu(H4NprSpr)(OH2)]2+ cis-[Cu(H4NenSpr)]2+
,
,
,
and the
previously reported cis-[Cu(H4NenSen)]2+ [10] were all isolated in
their divalent form (Fig. 3, Table 2). Focusing on these divalent spe-
cies we find that the bond lengths (Cu–N, Cu–S) generally increase
with ring size and that the notional torsion (measured through N–
N–S–S) and simple bond angles (D–Cu–D at ꢃ90° D = donor atom)
all move to a less strained conformation (i.e. 0° and 90°, respec-
tively) as the ring size increases (Supplementary material). These
observations are in line with previous studies on S4 and N4 macro-
cyclic complexes of copper and cobalt [19–21]. Studies on these
highly flexible (S4 and N4) ligand complexes have further investi-
gated the effects of torsion angles, bond angles and bond distance
on E1/2 of these species [19–21]. These homoatomic donor species
are chemical extremes of the heteroatomic N2S2 donor set being
reported here. Consistent with these studies, we also observe a
small increase in E1/2 as the torsional strain increases (Fig. 6).
The effect of bond angle and bond length is more interesting. In
acetonitrile, we observe an increase in E1/2 as the Cu–N and Cu–S
distances increases. However, this effect is absent in water, sug-
gesting that the solution phase species in the two solvents differ
(e.g. [Cu(H4N2S2)]2+ vs [Cu(H4N2S2)(OH2)]2+, Fig. 3). A pronounced
effect of the >S–Cu–S angle on E1/2 is also observed, suggesting that
we can raise the E1/2 by making the angle more obtuse. While this
is true in both acetonitrile and water, the corresponding influence
of <N–Cu–N on E1/2 is markedly different in the two solvents. In
acetonitrile E1/2 falls as the angle increases, whereas in water it
falls as the angle becomes more acute. This supports the argument
that the solution phase species in these solvents differ. However, it
also emphasises the care that should be taken in correlating the

K.D. Trotter et al. / Inorganica Chimica Acta 363 (2010) 1529–1538
1537
Table 3
Electrochemical data for the cis/trans Cu½ðH4NxxSyyÞꢄnþBF4 complexes.
n
MeCN (V)a
Water (V)b
Corresponding Schiff base in MeCNc (V)
Potential vs. Ag wired
Ring size
MeCN (V)
Water (V)
Cu(II) cis-H4NenSenꢂ2BF4
Cu(II) cis-H4NprSenꢂ2BF4
Cu(II) cis-H4NprSpr.(OH2)ꢂ2BF4
Cu(II) cis-H4NenSprꢂ2BF4
Cu(II) cis-H4NenSbuꢂ2BF4
Cu(II) trans-H4NenSenꢂ2BF4
Cu(II) trans-H4NprSprꢂ2BF4
ꢁ0.36
ꢁ0.68
ꢁ0.48
ꢁ0.48
ꢁ0.40
ꢁ0.52
ꢁ0.36
ꢁ0.10
0.04
ꢁ0.42
ꢁ0.04
ꢁ0.34
ꢁ0.40
14
15
15
16
16
14
16
0.17
ꢁ0.15
0.05
0.05
0.13
ꢁ0.01
0.16
0.02
ꢁ0.14
ꢁ0.19
ꢁ0.03
Insol.
Insol.
ꢁ0.03
0.04
ꢁ0.26
ꢁ0.03 (Cu(I))
a
b
c
Acetonitrile (0.1 M tBu4NBF4: potentials reported vs. ferrocene at 100 mV/s).
Water (0.1 M NaCl: potentials reported vs. [Fe(CN)6]3ꢁ at 100 mV/s). The trans-amine macrocycles were not sufficiently soluble (insol.) in water for analysis.
Data collected for the related Schiff base complexes in acetonitrile (0.1 M tBu4NBF4: potentials reported vs. ferrocene at 100 mV/s).
For comparison between solvents, potentials are also reported vs. Ag wire.
d
fifth coordination site. However, the formation of acetonitrile ad-
ducts cannot be ruled out. Indeed an acetonitrile adduct of the cop-
per(II) Schiff base macrocycle derived from NprSen has been
reported [6].
The values obtained for the two trans-amine complexes lie at
the extremes of the ranges reported (Table 3). It has been reported
previously [18] that the trans disposition of the donors in N2S2
complexes creates a more confined metal binding pocket com-
pared to the respective cis analogues. This could contribute to
the difference observed.
Cu-S MeCN
Cu-N MeCN Cu-S Water
2.2 2.3 2.4
Cu-N Water
Cu-donor atom distance Å
1.9 2.0 2.1
0.2
0
Bond distance Å
-0.2
-0.4
-0.6
-0.8
o
MeCN
20 25
Water
30
Notional torsion angle ( )
5. Concluding remarks
0
5
10
15
0.1
0
Angle (o)
The family of [Cu(H4N2S2)]n+ macrocycles have been structur-
ally characterised. Electrochemical analysis suggests that in these
amine complexes the redox potential is not heavily influenced by
ring size. This contrasts with our previous study employing Schiff
base macrocycles, where an effect of ring size on redox potential
was detected [6]. Furthermore, the anomalous behaviour of
[Cu(H4NprSen]+ indicates that more subtle effects may be involved,
which we might expect to translated into their chemical behaviour.
Our ability to obtain redox potentials from aqueous solution sug-
gests that, unlike their Schiff base analogues, these complexes
should have some utility as redox sensors for biological applica-
tions. While it is evident that ring sizes in excess of 17 can be ex-
pected to be unstable, the disparate electrochemical behaviour of
the remaining rings suggests that it is unwise to focus efforts on
a single ring size. Unlike their Schiff base and tetrathioether
[19,20] analogues, the aqueous solubility and stability of these
amine-thioether species suggest that they should be stable enough
to withstand reactions with biologically-relevant reducing (e.g.
ascorbate, glutathione) and oxidising agents (hypochlorite and
hydrogen peroxide), and the future aim of our work is to test this
hypothesis.
-0.2
-0.4
-0.6
-0.8
Bond angles vs E1/2 in MeCN
N-Cu-N
90
Angle (o)
S-Cu-S N-Cu-S
92 94 96
82
84
86
88
-0.3
-0.4
-0.5
-0.6
-0.7
Bond angles vs E1/2 in water
82 84 86 88
Angle (o)
N-Cu-N
90
S-Cu-S
92
N-Cu-S
96
94
0.1
0.0
-0.1
-0.2
Acknowledgements
M.K.T. and K.D.T. would like to thank Strathclyde University and
WestChem for financial assistance. J.R. gratefully acknowledges the
support of the Cunningham Trust. J.R., C.M.S. and R.J.S. gratefully
acknowledge the support of the BBSRC (BBS/B/01553). Thanks
are due to the EPSRC National X-ray Crystallography Service at
the University of Southampton for data collection on samples
[Cu(II)(H4NprSen)Cl] (BF4)2 and [Cu(II)H4NenSpr] (BF4)2 and the
CCLRC for award of beamtime at the Daresbury SRS which allowed
us to collect data on [Cu(II)Cl2(H6NbuSpr)] PF6 and [Ni(II)(H4NprSen)-
Cl(OH2)] BF4.
Fig. 6. The notional torsion angles (N–N–S–S), bond angles (at 90°) and the metal
donor bond distances for cis-[Cu(H4NprSen)]2+, cis-[Cu(H4NprSpr)(OH2)]2+, cis-[Cu(H4-
NenSpr)]2+ and cis-[Cu(H4NenSen)]2+ [10] plotted as
a . Simple
function of E1/2
regression lines are drawn only for data sets which show some proportional
change between E1/2 and the metric being plotted.
metrical parameters derived from the crystallographic data and the
E
1/2. Indeed, the results presented here suggest that in water these
complexes will be five coordinate with a water molecule filling the

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K.D. Trotter et al. / Inorganica Chimica Acta 363 (2010) 1529–1538
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cis-H4NenSen: 5,6,13,14-bisbenzo-8,11-diaza-1,4-dithia-cyclotetradecane
cis-H4NprSen: 5,6,14,15-bisbenzo-8,12-diaza-1,4-dithia-cyclopentadecane
cis-H4NbuSen: 5,6,15,16-bisbenzo-8,13-diaza-1,4-dithia-cyclohexadecane
cis-H4NenSpr: 6,7,14,15-bisbenzo-9,12-diaza-1,5-dithia-cyclopentadecane
cis-H4NprSpr: 6,7,15,16-bisbenzo-9,13-diaza-1,5-dithia-cyclohexadecane
cis-H4NbuSpr: 6,7,16,17-bisbenzo-9,14-diaza-1,5-dithia-cycloheptadecane
cis-H4NenSbu: 7,8,15,16-bisbenzo-10,13-diaza-1,6-dithia-cyclohexadecane
cis-H4NprSbu: 7,8,16,17-bisbenzo-10,14-diaza-1,6-dithia-cycloheptadecane
cis-H4NbuSbu: 7,8,17,18-bisbenzo-10,15-diaza-1,6-dithia-cyclooctadecane
trans-H4(N-en-S)2: 6,7,13,14-bisbenzo-4,11-diaza-1,8-dithiacyclotetradecane
trans-H4(N-pr-S)2: 7,8,15,16-bisbenzo-5,13-diaza-1,9-dithiacyclohexadecane
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