Synthesis, characterization and coordination chemistry of aminophenylbenzothiazole substituted 1,4,7-triazacyclononane macrocycles

Article abstract of DOI:10.1016/j.poly.2012.10.029

The synthesis and spectroscopic characterization of four new 2-(4-aminophenyl)benzothiazole substituted 1,4,7-triazacyclononane derivatives with and without appended pyridyl groups on the macrocycle is reported: 1-(2-(4-aminophenyl)benzothiazolyl)-2-oxoethyl)-1,4,7-triazacyclononane (L1), 1-(2-(4-aminophenyl)benzothiazolyl)-2-oxoethyl)-4-(2-pyridylmethyl)-1,4, 7-triazacyclononane (L2), 1-(2-(4-N-methylaminophenyl)benzothiazolyl)-2- oxoethyl)-4-(2-pyridylmethyl)-1,4,7-triazacyclononane (L3), 1,4-bis(2- pyridylmethyl)-7-(2-(4-aminophenyl)benzothiazolyl)-2-oxoethyl)-1,4, 7-triazacyclononane (L4). The ligands have been applied in the synthesis of a series of copper (II) complexes, [Cu(L1)(OH₂)](ClO₄) ₂·0.5ACN (C1), [Cu(L3)](ClO₄)₂· ACN (C2) and [Cu(L4)(OH₂)](ClO₄)₂·0.5THF (C4) whose structures have been determined by X-ray crystallography. As commonly observed for Cu(II) complexes of 1,4,7-triazacyclononane derivatives, the geometry of the metal centre ranges from distorted square pyramidal to pseudo-octahedral. Notably, the amide carbonyl coordinates to the copper(II) centre in C1 and C2 but not in C4 where the presence of an additional pyridyl group results in an N5 coordination sphere.

Full text of DOI:10.1016/j.poly.2012.10.029

Polyhedron 52 (2013) 128–138
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis, characterization and coordination chemistry of
aminophenylbenzothiazole substituted 1,4,7-triazacyclononane macrocycles
José Barreto a, Taracad K. Venkatachalam a,b, Tanmaya Joshi a, Ute Kreher a, Craig M. Forsyth a,
David Reutens b, Leone Spiccia a,
⇑
a School of Chemistry, Monash University, Clayton, Victoria 3800, Australia
b Centre for Advanced Imaging, The University of Queensland, St. Lucia QLD 4072, Australia
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 2 November 2012
The synthesis and spectroscopic characterization of four new 2-(4-aminophenyl)benzothiazole substituted
1,4,7-triazacyclononane derivatives with and without appended pyridyl groups on the macrocycle is
reported: 1-(2-(4-aminophenyl)benzothiazolyl)-2-oxoethyl)-1,4,7-triazacyclononane (L1), 1-(2-(4-amino-
phenyl)benzothiazolyl)-2-oxoethyl)-4-(2-pyridylmethyl)-1,4,7-triazacyclononane (L2), 1-(2-(4-N-meth-
ylaminophenyl)benzothiazolyl)-2-oxoethyl)-4-(2-pyridylmethyl)-1,4,7-triazacyclononane (L3), 1,4-bis
(2-pyridylmethyl)-7-(2-(4-aminophenyl)benzothiazolyl)-2-oxoethyl)-1,4,7-triazacyclononane (L4). The
ligands have been applied in the synthesis of a series of copper (II) complexes, [Cu(L1)(OH2)](ClO4)2ꢀ0.5ACN
(C1), [Cu(L3)](ClO4)2ꢀACN (C2) and [Cu(L4)(OH2)](ClO4)2ꢀ0.5THF (C4) whose structures have been deter-
mined by X-ray crystallography. As commonly observed for Cu(II) complexes of 1,4,7-triazacyclononane
derivatives, the geometry of the metal centre ranges from distorted square pyramidal to pseudo-octahedral.
Notably, the amide carbonyl coordinates to the copper(II) centre in C1 and C2 but not in C4 where the pres-
ence of an additional pyridyl group results in an N5 coordination sphere.
Dedicated to Alfred Werner on the 100th
anniversary of his Nobel Prize in chemistry
in 1913.
Keywords:
Macrocycles
1,4,7-Triazacyclononane
Coordination chemistry
Copper(II) complexes
Benzothiazoles
X-ray structures
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
where they induce the production of cytochrome P-450 isoform
(CYP1A1). Conversion of these drugs into electrophilic species re-
The coordination chemistry of macrocycle-based ligands con-
tinues to be an exciting field of chemistry a century after the Nobel
Prize was awarded to Alfred Werner, due to the plethora of poten-
tial applications that can be envisaged. One particular area of focus
has been concerned with the development of these types of ligands
for application as ion selective chemosensors. In this regard, 1,4,7-
triazacyclonane, tacn, derivatives have been found to be particu-
larly useful principally due their extraordinary ability to bind
strongly to various metal ions. Incorporation of 2-pyridylmethyl
pendants has been shown to increase the stability of tacn metal
complexes due to coordination of the pendant arm [1–3]. A fluores-
cent molecule can be incorporated to the tacn ring, acting as fluo-
rophore for the detection of the compound and allowing the study
of the interaction between the ligand and different metal ions in
solution by fluorescence spectroscopy as complexation can give
rise to changes in the excitation state of the ligand [4–6].
sults in the formation of benzothiazole–DNA complexes which
causes DNA damage and activates the apoptotic machinery leading
to cell death [7–9].
The benzothiazolyl unit is an excellent acceptor which can par-
ticipate in the formation of donor–p–acceptor (D–p–A) type com-
pounds [10,11]. As a consequence, benzothiazole compounds have
amyloid binding capacity and can be applied in the diagnosis of
Alzheimers related diseases. Towards this end, potential amyloid
binding agents have been labeled with radioactive isotopes and
examined as imaging agents. These were found to be stable
in vivo and to possess acceptable pharmacological properties
[12]. For example, the utility of 11C-labeled (N-methyl-[11C]
2-(40-methylaminophenyl)-6-hydroxybenzothiazole [13] as an
amyloid imaging agent have been demonstrated through in vivo
humans trials.
A few studies have explored the optical properties of 2-phen-
ylbenzothiazoles attached to a macrocycle unit. The influence of
different alkali and earth alkali metals on the absorption and
fluorescence spectra of an aza-15-crown-5 macrocyclic compound
containing a phenylbenzothiazole unit was studied by Mateeva
et al. [14,15]. They found that at high concentration, Ba2+ and Ca2+
affect both the absorption and emission spectra of the compound,
whereas other smaller alkali and alkaline earth metal ions showed
The benzothiazole derivative, 2-(4-aminophenyl)benzothiazole
and its analogs constitute a class of agents with potent antitumor
activity. For example, they act as aryl hydrocarbon receptor
(AhR) agonists translocating into the sensitive tumor cell nucleus
⇑
Corresponding author. Tel.: +61 3 9905 4526; fax: +61 3 9905 4597.
E-mail address: leone.spiccia@monash.edu (L. Spiccia).
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.10.029

J. Barreto et al. / Polyhedron 52 (2013) 128–138
129
no effect. In this case, the selective decrease of the fluorescence on
addition Ca2+ and Ba2+ is due to the ability of the metal to fit inside
the macrocycle cavity and also because of their higher charge
[14,15].
o-aminothiophenol (8.75 g, 70.0 mmol) whereupon a vigorous
reaction took place and the mixture turned into a black viscous
mass. The contents were heated to 220 °C for 9 h, cooled to
100 °C and then carefully poured into a beaker containing ice/
water mixture. The oily product thus obtained slowly solidified
upon standing (2 h) and the mixture was allowed to stir to obtain
a light yellow product. This was filtered and washed with water
(2 ꢂ 100 mL). The precipitate was then suspended in a solution
of sodium bicarbonate (50 g/500 ml of water) and stirred vigor-
ously for 2 h. A light greenish product remained in suspension
which was filtered, washed with water (2 ꢂ 100 mL) and dried
under vacuum for 48 h. The product was further purified by
re-crystallization using methanol to yield dark yellow needles of
2-aminophenylbenzothiazole 1. Yield: 8.00 g, 35.2 mmol, 50%.
Encouraged by their remarkable biological profile shown in var-
ious fields including cancer and neurology, we chose to attach ben-
zothiazole pendants to various tacn compounds and to investigate
the coordination chemistry of these tacn-benzothiazole deriva-
tives. Herein, we report the synthesis of a series of 1-(2-(4-amino-
phenyl)benzothiazolyl)-1,4,7-triazacyclononane derivatives, which
have up to two pyridyl groups attached to the macrocycle, and
their utilization in the synthesis of the corresponding copper(II)
complexes. X-ray crystallography has been used to explore the
influence of the number of pyridyl donors on the metal coordina-
tion environment.
Selected IR bands
m
(cmꢁ1) (KBr pellet): 3429s, 3178s, 1636s,
1604m, 1475s, 1433m, 1312m, 1250m, 1228m, 1182m, 1159m,
963m, 827s, 760s. 1H NMR (400 MHz) (d6-DMSO), d ppm: 8.02–
7.98 (m, 2H), 7.77–7.73 (d, 2H, J = 8.0 Hz), 7.45–7.44 (t, 1H),
7.36–7.31 (t, 1H), 6.69–6.65 (d, 2H, J = 8.0 Hz), 5.89 (s, 2H); ESI
MS (+ mode): calculated: 226, found: 227 [M+H]+.
2. Experimental
2.1. Materials and methods
All chemicals were purchased from Sigma–Aldrich and were
used without further purification. Unless otherwise noted each
reaction was conducted under a nitrogen atmosphere. The synthe-
ses of 1,4,7-triazacyclononane (tacn), 1,4,7-triazacyclo[5.2.1.04,10]-
decane, 6, and 1,4-bis(2-pyridylmethyl)-1,4,7-triazacyclononane
(dmptacn), 16, were carried out following literature procedures
[1,16,17].
2.2.1.2. N-(40-benzothiazol-2-yl-phenyl)-2-chloroacetamide, [18] 2. In
a 250 mL round bottom flask was placed 2-(4-aminophenyl)benzo-
thiazole (2.36 g, 10.3 mmol) and 60 mL of anhydrous methylene
chloride. The contents were stirred; however, the solid did not
completely dissolve at this stage. Using a dry syringe, 2 mL of tri-
ethylamine was introduced into the flask and the solution
became homogenous dissolving the benzothiazole compound. To
the clear solution, chloroacetylchloride (1 mL) was slowly added,
causing a vigorous exothermic reaction and the evolution of fumes
during the course of addition. A white insoluble precipitate formed
in the flask on stirring for 48 h, which was collected by filtration,
washed with ether and dried in vacuum (1.20 g). The filtrate was
treated with 20 mL of 5 M HCl, the organic layer separated, dried
over anhydrous sodium sulfate and subsequently filtered. Removal
of solvent left a residue which was triturated with 50 mL of diethyl
ether. The insoluble material was filtered and dried in vacuum to
yield 0.80 g of a brown colored powder. Both solids were re-crys-
tallized in 96% ethanol, resulting in a combined yield of 2.00 g,
64%. The NMR spectrum confirmed both products to be compound
NMR spectra were obtained either on a 200, 300 or 400 MHz
(Bruker or Varian) instrument with an auto probe assembly using
either CDCl3 or d6-DMSO as solvent. Chemical shifts are reported
as d values in parts per million. In the case of CDCl3, the TMS signal
was used as a reference at 0 ppm and for the d6-DMSO solvent, the
signal at 2.49 ppm was used as a reference. Splitting patterns were
designated as follows: s, singlet, d, doublets, t, triplets, m, multiplet
and br broad peak. Fourier transform infrared (FT-IR) spectra were
recorded on a on a Perkin Elmer 1600 Series FTIR Spectrometer in
the range 4000–400 cmꢁ1, with a resolution of 4.0 cmꢁ1. Samples
were prepared as KBr disks or run neat, as indicated. Abbreviations
used to describe the peak intensities are: vs (very strong), s
(strong), m (medium), w (weak), sh (shoulder) and br (broad). All
mass spectrometry was performed using a Micromass Platform II,
with an ESI source. The capillary voltage was 3.5 eV and the cone
voltage 35 V unless otherwise noted. Compounds were dissolved
in an organic solvent and ionized using an electrospray ionization
source (ESI). Ion peaks were compared with expected monoiso-
topic masses. Column chromatography was performed using silica
gel (60 mesh) from Merck. The solvent used for elution varied
depending on the compound of interest. Microanalyses were per-
formed by the Campbell Microanalytical Service, University of
Otago, New Zealand. Electronic spectra were recorded on a Cary
5G UV–Vis–NIR spectrophotometer in 1 cm quartz cells.
2. Selected IR bands
m
(cmꢁ1) (KBr pellet): 3317s, 1675vs, 1599s,
1528s, 1482m, 1435m, 1409m, 1314m, 1285m, 1252m, 1228m,
1192m, 1116m, 963m, 846m, 828m, 754s. 1H NMR (400 MHz)
(d6-DMSO), d ppm: 10.76 (br, 1H), 8.10–7.98 (m, 4H), 7.80–7.78
(d, 2H, J = 8.0 Hz), 7.52–7.50 (t, 1H), 7.43–7.40 (t, 1H), 4.25 (s,
2H). 13C NMR (100 MHz) (d6-DMSO), d ppm: 167.4, 165.7, 154.7,
141.9, 134.9, 128.7, 127.2, 125.9, 123.2, 122.9, 120.2, 44.2. ESI
MS (+mode): calculated: 302.5 [M+], found: 303 [M+H+].
2.2.1.3. 1-(2-(4-aminophenyl)benzothiazolyl)-2-oxoethyl)-4,7-diaza-
1-azoniatricyclo[5.2.1.04,10]decane chloride, 3. In a 100 mL round
bottom flask was placed 2 (0.60 g, 2.0 mmol), anhydrous acetoni-
trile (30 mL) followed by a solution of 1,4,7-triazacyclo[5.2.1.04,10]-
decane, 6, (0.67 g, 4.6 mmol) dissolved in 20 mL of acetonitrile. The
contents were heated to reflux. After 3 h of heating an insoluble
precipitate appeared in the mixture. Heating at reflux was contin-
ued for 48 h whereupon the mixture was cooled to room temper-
ature. The precipitated orthoamidinium salt was filtered, washed
with diethyl ether and dried to give a white powder. Yield:
0.80 g, 1.8 mmol, 40%.
2.2. Synthesis
2.2.1. 1-(2-(4-aminophenyl)benzothiazolyl)-2-oxoethyl)-1,4,7-
triazacyclononane, 5, (L1)
2.2.1.1. 2-(4-aminophenyl)benzothiazole, 1. 2-(4-Aminophenyl)ben-
zothiazole
1
and N-(40-benzothiazol-2-yl-phenyl)-2-chloroacet-
amide 2, were synthesized as reported previously with some
modifications [18]. For 1, 40 ml of polyphosphoric acid were placed
in a 250 mL round bottom flask and heated to 150 °C. In the mean-
time, p-aminobenzoic acid (9.59 g, 70.0 mmol) was transferred
into the flask in aliquots and the contents were stirred to dissolve
the aminobenzoic acid. A thick pasty brown mass was obtained
after the complete addition of the acid. To this mixture was added
2.2.1.4. 1-(2-(4-aminophenyl)benzothiazolyl)-2-oxoethyl)-2-formyl-
1,4,7-triazacyclononane, 4. In a 50 mL round bottom flask was
placed 3 (0.70 g, 1.6 mmol) and 15 mL of water. The mixture was
refluxed for 4 h, cooled to room temperature and then evaporated
to remove water. The residue was dissolved in 100 mL of

130
J. Barreto et al. / Polyhedron 52 (2013) 128–138
chloroform and the solution was washed with 20 mL of 3 M NaOH.
The organic layer was separated, dried over anhydrous sodium sul-
fate and filtered. Rotary evaporation of the solvent gave a viscous
oily residue which slowly solidified on standing. Yield: 0.52 g,
1.20 mmol, 75%.
3173br, 2929s, 2825m, 1677vs, 1592s, 1533s, 1482s, 1313m,
1177m, 908m, 731s. 1H NMR (300 MHz, CDCl3), d ppm: 10.99 (s,
1H), 8.52–8.51 (br, 1H, J = 3.0 Hz), 8.03–7.99 (m, 3H), 7.87–7.85
(d, 1H, J = 6.0 Hz), 7.81–7.78 (d, 2H, J = 9.0 Hz), 7.57–7.51 (m, 1H),
7.49–7.43 (m, 1H), 7.37–7.31 (m, 1H), 7.22–7.19 (d, 1H,
J = 9.0 Hz), 7.15–7.10 (m, 1H), 3.88 (s, 2H), 3.42–3.38 (m, 2H),
3.10–2.60 (m, 10H), 13C NMR (50 MHz, CDCl3), d ppm: 47.05,
47.92, 54.05, 54.80, 54.97, 55.54, 61.73, 62.60, 120.08, 121.73,
122.31, 123.05, 123.44, 125.12, 126.40, 128.40, 128.94, 135.05,
136.52, 141.63, 149.28, 159.07, 167.77, 171.50. ESI MS (+ mode):
calculated 486 [M+]; found 487 [M+H+], 509 [M+Na+]. Elemental
analysis: found C 59.01, H 5.54, N 15.09, S 5.81%; calculated for C27-
H30N6OS.NaCl: C 59.49, H 5.55, N 15.42, S 5.88%.
2.2.1.5. 1-(2-(4-aminophenyl)benzothiazolyl)-2-oxoethyl)-1,4,7-tri-
azacyclononane, 5, (L1). In a 100 mL round bottom flask was placed
4 (0.40 g, 0.90 mmol) and 15 mL of methanol was added followed
by 10 mL of 5 M HCl. The contents were stirred at room tempera-
ture for 48 h and the solvents removed on a rotary evaporator.
The residue was dissolved in 1 mL of water and solid sodium
hydroxide pellets (60 mg) were carefully added until the pH was
>13. A precipitate was visible in the flask which dissolved on addi-
tion of 20 mL of chloroform. The chloroform layer was separated
from the aqueous layer and dried over anhydrous sodium sulfate.
Filtration and removal of the solvent on a rotary evaporator gave
a light yellowish solid. Yield of L1: 0.30 g, 0.74 mmol, 82%. Selected
2.2.3. 1-(2-(4-N-methylaminophenyl)benzothiazolyl)-2-oxoethyl)-4-
(2-pyridylmethyl)-1,4,7-triazacyclononane, 14, (L3)
2.2.3.1. 2-(4-N-methylaminophenyl) benzothiazole, 11. 2-(4-N-
methylaminophenyl)benzothiazole, 11, and N-(40-benzothiazol-2-
yl-phenyl)-methyl-2-chloroacetamide 12, were synthesized
following a similar procedure as for compounds 1 and 2. For 11,
polyphosphoric acid (60 mL) was placed in a 250 mL round bottom
flask and heated to 150 °C. In the meantime, N-methyl-p-amino-
benzoic acid (12.00 g, 79.47 mmol) was transferred into the flask
in aliquots and the contents were stirred to dissolve the
N-methyl-p-aminobenzoic acid. To the thick pasty brown mass
obtained after addition of the acid, o-aminothiophenol 10.00 g
(80.00 mmol) was added whereupon a vigorous reaction took place
and the mixture turned into a black viscous mass. The contents
were heated to 220 °C for 9 h and cooled to 100 °C and carefully
poured into a beaker containing an ice/water mixture. The oily
product thus obtained slowly solidified upon standing (2 h). The
mixture was stirred to obtain a light yellow product. This was fil-
tered and washed with water (2 ꢂ 100 mL). The precipitate was
then suspended in a solution of sodium bicarbonate (50 g/500 ml
of water) and stirred vigorously for 2 h to obtain a light greenish
product. This was filtered and, washed with water (2 ꢂ 100 mL)
and dried under vacuum for 48 h. The product was further purified
by column chromatography on silica gel using 1% methanol in
dichloromethane as eluent to yield 2-(4-N-methylaminophe-
nyl)benzothiazole, 11, as a green powder. Yield: 3.02 g, 12.6 mmol
IR bands
m
(cmꢁ1) (KBr pellet): 3316br, 2918s, 2804m, 1663vs,
1588s, 1538s, 1477s, 1436m, 1407m, 1368m, 1351m, 1305m,
1260m, 1228m, 1172m, 1138m, 1036m, 972m, 844m, 756s. 1H
NMR (300 MHz, CDCl3) d ppm: 11.39 (s, 1H), 8.05–8.03 (d, 3H,
J = 6.0 Hz), 7.90–7.79 (m, 3H), 7.50–7.45 (t, 1H), 7.39–7.34 (t, 1H),
3.44 (s, 2H), 2.96–2.73 (m, 12H), 1.94-(bs, 2H) 13C NMR (75 MHz,
CDCl3) d ppm: 47.21, 48.41, 54.94, 61.66, 120.14, 121.87, 123.24,
125.27, 126.56, 128.53, 128.58, 128.61, 129.25, 129.34, 135.25,
141.63, 154.50, 167.99, 171.37; ESI MS (+ mode): calculated 395
[M+]; found 396 [M+H+]. Elemental analysis: found C 56.27, H
5.42, N 14.83, S 7.01%; calculated for C21H25N5OS.NaCl C 55.56, H
5.55, N 15.43, S 7.06%.
2.2.2. 1-(2-(4-aminophenyl)benzothiazolyl)-2-oxoethyl)-4-(2-pyridyl-
methyl)-1,4,7-triazacyclononane, 10, (L2)
2.2.2.1. 1-(2-(4-aminophenyl)benzothiazolyl)-2-oxoethyl)-4-(2-pyri-
dylmethyl)-7-formyl-1,4,7-triazacyclononane, 9. This synthesis was
accomplished using 1-(2-pyridylmethyl)-4-formyl-1,4,7-triazacy-
clononane 8, which was prepared following the procedure
described by Gasser et al. [1] as shown in Scheme 2. Compound
8 (1.24 g, 5.00 mmol) was loaded into a 100 mL round bottom flask
and 50 mL of anhydrous acetonitrile were added. The mixture was
stirred and compound 2 (3.00 g, 9.90 mmol) was added followed
by anhydrous potassium carbonate (3.00 g) and potassium iodide
(0.60 g). The contents were stirred and the solution was refluxed
for 5 days. After this period, the mixture was cooled to room tem-
perature and filtered. The insoluble precipitate was further washed
with 2 ꢂ 10 mL of acetonitrile. The acetonitrile solutions were
combined and reduced in volume on a rotary evaporator to yield
a viscous residue which was dissolved in 100 mL of chloroform
and washed with 2 ꢂ 10 mL of 3 M NaOH. The organic layer was
separated from the aqueous layer and dried over anhydrous so-
dium sulfate. Filtration and rotary evaporation of the solvent gave
an oily residue of 9. Yield: 1.01 g, 1.90 mmol, 38%.
16%. Selected IR bands
m
(cmꢁ1) (KBr pellet): 3487br, 3307vs,
2925m, 1607vs, 1512m, 1464s, 1439s, 1415m, 1341s, 1225m,
1180s, 961m, 822m, 757s. 1H NMR (200 MHz) (CDCl3), d ppm:
7.80–8.00 (m, 4H), 7.25–7.60 (m, 2H), 6.60–6.67 (m, 2H), 4.14 (s,
br, 1H), 2.89 (s, 3H); ESI MS (+ mode): calculated 240; found 241
[M+H]+.
2.2.3.2. N-(40-benzothiazol-2-yl-phenyl)-methyl-2-chloroacetamide,
12. 2-(4-N-methylaminophenyl)benzothiazole (1.00 g, 4.16 mmol)
was placed in a 250 mL round bottom flask, and anhydrous meth-
ylene chloride (60 mL) was added. The contents were stirred, how-
ever, the solid did not fully dissolve at this stage. Using a dry
syringe, triethylamine (1 mL) was introduced into the flask fully
dissolving the benzothiazole derivative. To the clear solution, chlo-
roacetylchloride (1 mL) was slowly added, resulting in a vigorous
exothermic reaction and the development of fumes. On stirring
for 48 h, a white precipitate appeared in the flask, which was col-
lected by filtration, washed with diethyl ether and dried in vacuum
(0.38 g). The filtrate was treated with 20 mL of 5 M HCl, the organic
layer separated and dried over anhydrous sodium sulfate and sub-
sequently filtered. Removal of solvent left a residue, which was
triturated with 50 mL of diethyl ether and the insoluble material
collected by filtration and dried in vacuum to yield 0.30 g of brown
colored powder. Combined yield: 0.68 g, 2.15 mmol, 52%. An NMR
spectrum confirmed both samples to be compound 12. Selected IR
2.2.2.2. 1-(2-(4-aminophenyl)benzothiazolyl)-2-oxoethyl)-4-(2-pyri-
dylmethyl)-1,4,7-triazacyclononane, 10 (L2). Compound 9 (0.70 g,
1.35 mmol) and 10 mL of methanol were added to a round bottom
flask and the mixture stirred at room temperature whilst hydro-
chloric acid (5 M, 15 mL) was added. Stirring was continued for
48 h whereupon the solvent was removed under vacuum. The
residue was dissolved in minimum amount of water (1.5 mL) and
sodium hydroxide pellets (0.08 g) were added. The precipitated
product was extracted with 40 mL of chloroform and the organic
layer was separated from the aqueous layer and dried over anhy-
drous sodium sulfate. Filtration and evaporation of the solvent
yielded the desired product as a foamy light yellow solid. Yield:
0.54 g, 1.10 mmol, 81%. Selected IR bands
m
(cmꢁ1) (KBr disc):
bands m
(cmꢁ1) (KBr pellet): 3317br, 1675s, 1599s, 1528m, 1482s,

J. Barreto et al. / Polyhedron 52 (2013) 128–138
131
1435m, 1409m, 1314m, 1285m, 1252m, 1228m, 1192m, 1116m,
963m, 846m, 828m, 754s. 1H NMR (200 MHz) (CDCl3), d ppm:
7.90–8.30 (m, 4H), 7.80–7.78 (m, 4H), 3.93 (s, 2H), 3.38 (s, 3H).
13C NMR (50 MHz) (CDCl3), d ppm: 168.4, 165.8, 154.6, 143.9,
133.9, 128.8, 126.4, 125.5, 124.2, 122.3, 120.9, 43.2, 35.4. ESI MS
(+mode): calculated 316 [M+]; found: 317 [M+H+].
contents of the flask for 72 h, the mixture was cooled and filtered.
The insoluble precipitate was further washed with 2 ꢂ 10 mL of
acetonitrile and the combined acetonitrile fractions were evapo-
rated to dryness. The residue thus obtained was dissolved in
100 mL of chloroform and washed with NaOH (5 M, 2 ꢂ 10 mL).
The organic layer was separated from the aqueous layer and dried
over anhydrous sodium sulfate. Filtration followed by rotary evap-
oration of the solvent gave 17 as a light brownish solid. Yield:
2.2.3.3. 1-(2-(4-N-methylaminophenyl)benzothiazolyl)-2-oxoethyl)-4-
(2-pyridylmethyl)-7-formyl-1,4,7-triazacyclononane, 13. 1-(2-Pyridyl-
methyl)-4-formyl-1,4,7-triazacyclononane, 8, (0.87 g, 3.50 mmol)
was added to a 100 mL round bottom flask followed by 30 mL of
anhydrous acetonitrile. Whist stirring compound 12 was added
(1.10 g, 3.50 mmol) followed by anhydrous potassium carbonate
(2.00 g) and potassium iodide (0.02 g). The mixture was refluxed
for 3 days, cooled to room temperature and filtered. The insoluble
precipitate was washed with 2 ꢂ 10 mL of acetonitrile and the sol-
vent removed from the combined acetonitrile solutions on a rotary
evaporator to yield an oily product. This was purified by column
chromatography on silica gel with dichloromethane:methanol
10:1 as eluent, yielding a reddish oil, on evaporation of the solvent.
0.58 g, 1.00 mmol, 38%. Selected IR bands
2924s, 1678s, 1588s, 1532m, 1482m, 1434m, 1409m, 1311m,
1251m, 1226m, 1175m, 1048m, 966m, 841m, 757s cmꢁ1 1H
m
(cmꢁ1) (KBr pellet):
;
NMR (300 MHz, CDCl3) d ppm: 10.91 (s, 1H), 8.50–8.48 (d, 2H,
J = 6.0 Hz), 8.0–7.98 (m, 3H), 7.88–7.78 (m, 3H), 7.56–7.42 (m,
3H), 7.37–7.31 (m, 2H), 7.21–7.09 (m, 3H), 3.87 (s, 4H), 3.31 (s,
2H), 2.99–2.68 (m, 12H); 13C NMR (50 MHz, CDCl3), d ppm: 54.5,
55.3, 55.8, 62.8, 63.9, 119.2, 120.3, 121.0, 121.8, 124.0, 124.6,
125.3, 126.8, 129.1, 133.8, 138.7, 139.8, 148.5, 154.8, 157.8,
168.3, 169.7. ESI MS (+ mode): calculated 579 [M+]; found 580
[M+H+]. Elemental analysis: found C 56.46, H 5.23, N 13.60, S
5.19%; calculated for C33H35N7OS.2NaCl C 57.06, H 5.08, N 14.12,
S 4.62%.
Yield: 1.42 g, 2.59 mmol, 74%. Selected IR bands
m
(cmꢁ1) (KBr disc):
3449m br, 3052m, 2923m, 2854m, 1664vs, 1604s, 1484s, 1435s,
1370s, 1314s, 1266m, 1121m, 968m, 731s. 1H NMR (200 MHz,
CDCl3), d ppm: 8.45 (m, 1H), 7.90–8.20 (m, 4H), 7.85 (m, 1H),
7.55–7.65 (m, 1H), 7.10–7.49 (m, 4H), 6.95–7.15 (m, 1H), 3.75–
4.25 (m, 4H), 3.05–3.68 (m, 12H), 2.45–3.05 (m, 4H), 13C NMR
(50 MHz, CDCl3), d ppm: 37.32, 46.55, 47.30, 50.27, 52.96, 52.97,
53.78, 57.86, 63.29, 121.84, 122.39, 123.21, 123.61, 125.65, 126.64,
127.41, 128.42, 135.02, 136.86, 137.02, 145.30, 148.75, 149.05,
153.91, 164.10, 166.61, 170.86. ESI MS (+ mode): calculated 528;
found 529 [M+H+].
2.2.5. [Cu(L1)(OH2)(ACN)](ClO4)2ꢀ0.5ACN (C1)
L1 (50 mg, 0.13 mmol) was dissolved in 1 mL of acetonitrile. A
solution of Cu(ClO4)2ꢀ6H2O (37 mg, 0.13 mmol) in 1 mL of acetoni-
trile was added whereupon a dark green solution was formed. Suit-
able crystals for X-ray analysis were obtained on diffusion of
diethyl ether into the acetonitrile solution of the complex. Yield:
51 mg, 0.067 mmol, 53%. IR (ATR in KBr,
3284m, 2927m, 2887m, 1627s, 1599vs, 1560s, 1483m, 1438m,
m
in cmꢁ1): 3504s,
1323m, 1110vs, 766m, 625s. Solution UV–Vis (k (nm),
e
(Mꢁ1
-
cmꢁ1)): 650 (29), 312 (18200), 208 (22500). Diffuse reflectance (k
(nm)): 646 nm. Elemental analysis: found C 40.01, H 4.15, N
12.25%; calculated for C23H28Cl2CuN6O9S C 39.52, H 4.04, N 12.02%.
2.2.3.4. 1-(2-(4-N-methylaminophenyl)benzothiazolyl)-2-oxoethyl)-
4-(2-pyridylmethyl)-1,4,7-triazacyclononane, 14 (L3). In a round
bottom flask was placed 13 (1.42 g, 2.59 mmol) and 25 mL of
methanol. The mixture was stirred at room temperature until dis-
solution. Hydrochloric acid (5 M, 25 mL) was added and the solu-
tion was stirred at room temperature for 3 days. The solvent was
removed under vacuum and the residue was dissolved in mini-
mum amount of water (3 mL) and NaOH pellets (0.08 g) were
added. A precipitate formed on addition of the base which was ex-
tracted with 40 mL of chloroform. The organic layer was then sep-
arated from the aqueous layer and dried over anhydrous sodium
sulfate. Filtration and evaporation of the solvent isolated the de-
sired product, 14, as a red solid. Yield: 1.28 g, 2.56 mmol, 99%. Se-
2.2.6. [Cu(L3)](ClO4)2ꢀACN (C2)
L3 (50 mg, 0.10 mmol) was dissolved in 1 mL of acetonitrile. A
solution of Cu(ClO4)2ꢀ6H2O (27 mg, 0.10 mmol) in 1 mL of acetoni-
trile was added resulting in a dark green solution. Suitable crystals
for X-ray analysis were obtained as in the case of C1. Yield: 48 mg
0.060 mmol, 60%. IR (ATR in KBr,
2936m, 1616s, 1593vs, 1482m, 1447m, 1315w, 1292w, 1088vs,
762m, 624s. Solution UV–Vis (k (nm),
(Mꢁ1 cmꢁ1)): 615 (32),
m
in cmꢁ1): 3449s, 3333s, 3068m,
e
305 (17400), 257 (11600), 205, (35000). Diffuse reflectance (k
(nm)): 595 nm. Elemental analysis: found C 40.26, H 4.33, N
9.96%; calculated for C28H40Cl2CuN6O13S C 40.27, H 4.83, N 10.06%.
lected IR bands
m
(cmꢁ1) (KBr disc): 3386m br, 3061w, 2911s,
2861s, 1663vs, 1605s, 1592m, 1484s, 1435s, 1381w, 1314m,
1120m, 968m, 909m, 729vs. 1H NMR (300 MHz, CDCl3), d ppm:
8.42 (d, 1H), 8.18–8.00 (m, 3H), 7.98–7.70 (m, 1H), 7.58–7.20 (m,
7H), 7.08–6.95 (m, 1H), 3.83 (s, 2H), 3.42–3.10 (m, 5H), 2.92–2.45
(m, 11H), 13C NMR (50 MHz, CDCl3), d ppm: 37.65, 46.83, 47.25,
50.45, 53.05, 52.90, 53.85, 57.93, 63.18, 121.75, 122.56, 123.31,
123.65, 125.70, 126.61, 127.45, 128.48, 135.10, 136.95, 137.45,
145.33, 148.78, 149.06, 153.95, 166.66, 170.90. ESI MS (+ mode):
Calculated: 500 [M+], found: 501 [M+H+]. Elemental analysis:
found C 54.66, H 5.91, N 13.57, S 5.68%; calculated for C28H32N6-
OS.2NaCl C 54.46, H 5.22, N 13.61, S 5.19%.
2.2.7. [Cu(L4)](ClO4)2ꢀ0.5THF (C4)
L4 (0.17 g, 0.24 mmol) was dissolved in a mixture of THF and
acetonitrile (5 ml of each) and solid Cu(ClO4)2ꢀ6H2O (0.087 g,
0.24 mmol) was added. The dark green solution was reduced in
volume to 5 mL by rotary evaporation. Slow evaporation of this
solution gave pale blue crystals suitable for X-ray analysis. Yield:
43 mg, 0.05 mmol, 22%. IR (ATR in KBr,
1671s, 1600s, 1542s, 1481m, 1438m, 1315m, 1147s, 1114vs,
1088vs, 766m, 625s. Solution UV–Vis (k (nm),
(Mꢁ1 cmꢁ1)): 690
(25), 320 (16500), 259 (12100), 200 (35500). Elemental analysis:
m
in cmꢁ1): 3423s br,
e
found C 35.45, H 3.63, N 8.71%; calculated for C33H44Cl9CuN7O10
C 35.60, H 3.98, N 8.81%.
S
2.2.4. 1,4-bis(2-pyridylmethyl)-7-(2-(4-aminophenyl)benzothiazolyl)-
2-oxoethyl)-1,4,7-triazacyclononane, 17 (L4)
Compound 2 (0.80 g, 3.29 mmol) was placed in a 100 mL round
bottom flask together with 30 mL of anhydrous acetonitrile. The
mixture was stirred and a solution of 16 (0.81 g, 2.62 mmol) dis-
solved in 20 mL of acetonitrile was added. The mixture was stirrred
for 10 min before the addition of 2.00 g of anhydrous potassium
carbonate and 0.50 g of potassium iodide. After refluxing the
2.3. X-ray structure Determinations
Single crystals were mounted on thin glass fibers. X-ray crystal-
lography data were obtained on a Nonius Kappa CCD or Bruker
Apex II CCD (C2) with monochromated Mo°
Ka radiation
(k = 0.71073 Å) at 123(2) or 173 (2) (C1) K using phi and/or omega

132
J. Barreto et al. / Polyhedron 52 (2013) 128–138
Table 1
Crystallographic data for C1, C2 and C4.
C1
C2
C4
Crystal data
Chemical formula
M (g/mol)
Crystal system
Space group
a (Å)
C
24H33.5N6.5O11SCl2Cu
C30H35N7O9SCl2Cu
804.15
orthorhombic
P212121
8.7319(7)
9.1285(9)
42.461(4)
90
90
90
3384.6(5)
4
1.578
C70H78N14O19S2Cl4Cu2
1752.46
monoclinic
P21/c
8.0231(16)
25.399(5)
19.103(4)
90
99.23(3)
90
3842.4(13)
2
1.515
755.57
triclinic
P1
ꢀ
7.67000(10)
9.0231(2)
25.2426(7)
98.62(10)
91.73(10)
112.44(10)
1589.12(6)
2
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
Volume (Å3)
Z
Dc (Mg mꢁ3
h range (°)
)
1.579
1.64–30.00°
Phi and omega scans
Multi-scan (SORTAV)
22349
2.38–27.50°
Phi and omega scans
Multi-scan (SADABS)
25553
1.34–25.00°
Phi and omega scans
Multi-scan (SORTAV)
35348
Data collection method
Absorption corrections
Reflections collected
Unique reflections (Rint
Goodness-of-fit on F2
F(000)
)
8947 (0.0519)
1.039
780
7779 (0.0666)
1.049
1660
6726 (0.1512)
1.038
1812
Rint
0.0519
0.0554, 0.1280
0.464, ꢁ0.587
0.0843
0.0598, 0.1171
0.545, ꢁ0.548
0.1512
0.0838, 0.1968
0.680, 1.411
b
R1a, wR2 [I > 2
r(I)]
Largest diff. peak and hole (e Åꢁ3
)
a
R1
wR2 = [
=
R
||F0| ꢁ |Fc||/
R|F0|.
b
2
R
w(F0 ꢁ Fc2)2/
R
w(F02)2]1/2
.
scans. The absorptions have been corrected by semi-empirical ap-
proach using the SORTAV or SADABS software [19,20]. The structures
were solved by direct method and refined by full matrix least
squares using SHELX-97 software [21,22]. The program X-Seed
[23] was used as an interface to the SHELX programs and to pre-
pare the figures. All hydrogen atoms were placed in idealized posi-
tions, except for the hydrogens on the nitrogen atoms and the
oxygen atoms of the water molecules, which were located on the
Fourier difference map and refined with restrained N–H and O–H
distances. The isotropic thermal parameters for N–H and O–H
hydrogen atoms were fixed at 1.2 times that of the respective
nitrogen or oxygen atom. The perchlorate counteranions in C1
were found disordered and refined anisotropically using part com-
mand. Where applicable, # indicates symmetry-generated atoms.
For C4, the tetrahydrofuran molecule was disordered over an
inversion centre. The high residual peaks between 1.41 and 2.09
represent part of the disorder. Crystallographic data for C1, C2
and C4 are presented in Table 1.
shows a peak corresponding to the parent ion (m/z = 395, M+H+),
and by elemental analysis.
The synthesis of 10 (L2) and 14 (L3) was achieved following the
procedures outlined in Schemes 2 and 3. For L2, reaction of 2-pic-
olylchloride with 6 followed by hydrolysis generates the formyl
derivative, 8, [1] which was further condensed with 2 to produce
compound 9, which was deprotected in acid to give L2. For L3, a
similar procedure was implemented in which the meth-
ylatedbenzothiazole derivative, 2-(4-N-methylaminophenyl)ben-
zothiazole, 11, produced following a similar procedure as for 1,
was converted into the chloroacetamide derivative of 12 by con-
densation with chloroacetylchloride. Reaction of 12 with 8 yielded
13, which was further hydrolyzed in acid to obtain L3. Formation of
the compounds was confirmed by mass spectrometry which shows
a unique parent peak at 487 and 501 (M+H+), respectively.
Compound 17, L4 (Scheme 4) was obtained by alkylation of
dmptacn, 16, itself prepared following the procedure of Gasser
et al. [1] Formation of the benzothiazole derivative was confirmed
by 1H NMR spectroscopy, which shows a shift in the position of the
methylene protons signal in the chloroacetamide derivative from
4.26 ppm to 3.31 ppm due to attachment to a nitrogen of the tacn
ring, and by observation of the parent peak at 580 (M+H+) in the
mass spectrum.
3. Results and discussion
3.1. Synthesis and characterization of ligands
Crystals of the copper (II) complexes of L1, L3 and L4 were ob-
tained either by ether diffusion into an acetonitrile solution (C1
and C2) or by slow evaporation of a solution of the complex (C3).
The complexes were characterized by IR spectroscopy, UV–Vis.
spectrophotometry and elemental analysis. The complexes exhibit
bands around 610–690 nm in the visible spectrum recorded in ace-
tonitrile, which are characteristic of copper(II) complexes in either
a square pyramidal or a tetragonally distorted octahedral geome-
try, for which dz2 ! dx2 ꢁ dy2 and dyz dxz ! dx2 ꢁ dy2 transitions
are expected, rather than trigonal bipyramidal [24,25]. As for C1–
C3, UV–Vis analysis of a solution of the copper(II) complex of L2,
formed in situ by reacting equimolar amounts of L2 and Cu(ClO4)2-
ꢀ6H2O, revealed a band at 618 nm (28 Mꢁ1 cmꢁ1) similar to those
observed for C2 {efforts to prepare the Cu(II)–L2 complex were
unsuccessful}. Square pyramidal complexes typically exhibit a
The synthesis of 5 was achieved following the protocol de-
scribed in Scheme 1 from 1,4,7-triazacyclo[5.2.1.04,10]decane, 6.
First, 2-(4-aminophenyl)benzothiazole, 1,[18] was prepared and
reacted with chloroacetylchloride to yield N-(40-benzothiazol-2-
yl-phenyl)-2-chloroacetamide, 2,[18] which crystallized from eth-
anol as white-yellowish crystals. Formation of the product was
confirmed by 1H NMR which shows the appearance of a peak at
4.26 ppm corresponding to the methylene protons of the chloro-
acetamide. Condensation of 6 with 2 gave 4 which was converted
to the formyl derivative by refluxing in water. Deprotection using
hydrochloric acid at room temperature furnished the required
mono aminophenylbenzothiazole substituted tacn derivative 5
(L1) in 60% yield as a light yellow foam. Formation of the monosub-
stituted product was confirmed by mass spectrometry which only

J. Barreto et al. / Polyhedron 52 (2013) 128–138
133
Scheme 1.
Scheme 2.
weaker transition in the 900–1100 nm region. This was not ob-
served for the complexes reported herein indicating that the geom-
etry adopted by C2 and C4 in solution may be different to that
obtained by X-ray crystallography. The diffuse reflectance spectra
of the complexes in solid state confirmed the absence of a band
in the 900–1100 nm region for C1 supporting the octahedral nature
of the complex. In the case of C2, a weak band around 1050 nm
supports the adoption of a square pyramidal geometry by the com-
plex in the solid state.
binds weakly to the Cu(II) centre. As a consequence, the geometry
around the Cu(II) centre in C1 may be described as pseudo-
octahedral with a strong Jahn–Teller distortion along the z axis.
The coordination sphere for copper(II) consists of three facially
coordinating nitrogen atoms of the tacn ring (N1–N3), carbonyl
oxygen O1 from the pendant benzothiazole arm (Cu1–
O1 = 1.9759(19) Å), oxygen atom O2 from
a water molecule
(Cu1–O2 = 1.972(2) Å), and a weakly coordinating nitrogen (N5)
from an acetonitrile molecule with the corresponding Cu–N bond
length of 2.681 Å (Fig. 1). The Cu–N bond distances (av. 2.089 Å)
and the N–Cu–N bond angles for copper(II) coordination to the
macrocyclic nitrogens are in agreement to those generally ob-
served in Cu(II)–tacn derivatives (Table 2) [26,27].
3.2. X-ray crystal structure determinations
3.2.1. [Cu(L1)(OH2)](ClO4)2ꢀ0.5ACN (C1)
The asymmetric unit of C1 comprises of one [Cu(L1)(H2O)(CH3-
CN)]2+ complex cation, two perchlorate anions, one water and an
acetonitrile molecule of crystallization. One acetonitrile ligand
As illustrated in Fig. 2, the crystal structure shows an anti-par-
allel
p
ꢀ ꢀ ꢀ
p stacking of the cations, which is stabilized by extensive
intermolecular H-bonding interactions within the lattice space

134
J. Barreto et al. / Polyhedron 52 (2013) 128–138
Scheme 3.
Scheme 4.

J. Barreto et al. / Polyhedron 52 (2013) 128–138
135
Table 3
Hydrogen bonds for C1 [Å and °].
D–H. . .A
d(D–H)
d(H. . .A)
d(D. . .A)
\(DHA)
N(9)–H(9N). . .O(3)#1
N(1)–H(1N). . .O(5)
N(1)–H(1N). . .O(10)
N(2)–H(2N). . .O(10)#2
N(2)–H(2N). . .O(5)#2
O(2)–H(4O). . .O(11)
O(2)–H(4O). . .N(6)
O(2)–H(3O). . .O(13)
O(2)–H(3O). . .O(18)
O(2)–H(3O). . .O(19)
O(3)–H(2O). . .N(4)#3
O(3)–H(1O). . .O(17)
O(3)–H(1O). . .O(16)
0.868(19)
0.878(19)
0.878(19)
0.886(19)
0.886(19)
0.875(19)
0.875(19)
0.833(18)
0.833(18)
0.833(18)
0.871(19)
0.854(19)
0.854(19)
1.93(2)
2.03(2)
2.31(2)
2.15(2)
2.52(3)
2.20(3)
1.88(2)
2.49(3)
2.24(3)
1.84(4)
2.033(19)
2.19(2)
2.08(3)
2.795(3)
2.873(8)
3.186(9)
3.019(7)
3.295(10)
2.881(8)
2.717(7)
3.161(12)
3.033(9)
2.59(3)
176(4)
161(4)
172(4)
166(4)
146(3)
134(4)
159(4)
138(4)
159(4)
149(4)
177(4)
156(4)
153(4)
2.904(3)
2.989(5)
2.865(13)
Fig. 1. Thermal ellipsoid representation of the cationic unit in C1 showing the
pseudo-octahedral geometry around the Cu(II) centre (ellipsoids drawn at 30%
probability; selected hydrogen atoms, non-coordinating solvent molecule and the
counter anions have been omitted for clarity; dashed bonds indicate weak bonding
interactions).
Symmetry transformations used to generate equivalent atoms: #1 x + 1, y + 1, z ; #2
x + 1, y, z; #3 x ꢁ 1, y, z.
molecular structure together with the atom numbering scheme is
depicted in Fig. 3. Fig. 4 shows the H-bonding interactions between
the components of the unit cell and p. . .p interactions between the
Table 2
Selected bond distances (Å) and angles (°) for C1.
aromatic rings of the benzothiazole pendant group. Selected bond
parameters and the hydrogen bonding characteristic for the mole-
cule are listed in Table 4. The Cu(II) centre is in a distorted square
pyramidal geometry where the metal atom is centered in the base
of the pyramid defined by atoms N1, N2, N4 and O1. The axial
nitrogen (N3) is inclined towards one face of the pyramid forming
N–Cu–N angles of 83.47(15) and 84.08(15)° with the nearest donor
atoms (N1 and N2) while moving away from the opposite face of
the pyramid, exhibiting more obtuse N(3)–Cu(1)–O(1) and N(3)–
Cu(1)–N(1) angles (106.19(15) and 117.80(15)°, respectively).
Cu(1)–O(2)
Cu(1)–O(1)
Cu(1)–N(1)
Cu(1)–N(3)
Cu(1)–N(2)
1.972(2)
1.9759(19)
2.001(3)
2.029(2)
2.237(3)
O(1)–Cu(1)–N(1)
O(2)–Cu(1)–N(3)
O(1)–Cu(1)–N(3)
N(1)–Cu(1)–N(3)
O(2)–Cu(1)–N(2)
O(1)–Cu(1)–N(2)
N(1)–Cu(1)–N(2)
N(3)–Cu(1)–N(2)
168.71(10)
173.50(10)
83.78(8)
86.17(11)
100.92(12)
101.11(10)
82.97(12)
84.35(11)
O(2)–Cu(1)–O(1)
O(2)–Cu(1)–N(1)
91.42(10)
98.18(12)
(Table 3). These interactions arise due to the water molecules and
the perchlorate anions co-existing within the crystal lattice. Stabil-
ization of such interactions occurs due to the fact that the water
molecules coordinate to the metal center while simultaneously
hydrogen bonding with the perchlorate oxygen atoms. These per-
chlorate molecules serve as bridge by H-bonding to second water
molecule which in turn is linked to the aromatic nitrogen of the
benzothiazole moiety via a H-bond (O(3)–H(2O). . .N(4), 2.904 Å,
#3 denoting the symmetry operator: x ꢁ 1, y, z).
The Addison equation [28],
the two largest angles can be employed to further analyze the cop-
s
= (b ꢁ
a)/60, where b is the larger of
per(II) geometry. An ideal square pyramid will have a distortion
parameter
trigonal bipyramidal structure will have
= 120°). The value in this case is 0.17 indicating that the com-
s
of 0 since both angles,
a
and b should be 180°, but a
s
of 1 (b = 180° and
a
s
plex is close to a square pyramidal geometry with only slight devi-
ation towards a trigonal bipyramidal geometry.
3.2.2. [Cu(L3)](ClO4)2ACN (C2)
3.2.3. [Cu(L4)](ClO4)2ꢀ0.5THF (C4)
C2 consists of [Cu(L3)]2+ complex cation, two perchlorate
counteranions and a non-coordinating acetonitrile molecule. The
The asymmetric unit of C4 contains the complex cation, two
perchlorate anions and a disordered tetrahydrofuran molecule.
Fig. 2. Stick diagram showing a segment of the anti-parallel
cationic units, co-crystallized water molecules and perchlorate counter anions present in the crystal lattice (dashed bonds indicate hydrogen- and weak-bonding
interactions).
pꢀ ꢀ ꢀp interstacked linear chains, formed due to extensive intermolecular H-bonding interactions between the

136
J. Barreto et al. / Polyhedron 52 (2013) 128–138
Fig. 3. Molecular diagram as shown with 50% thermal ellipsoids and hydrogen atoms as spheres of arbitrary size. Perchlorate anions and lattice solvent have been omitted for
clarity. The ligand substituent connected via N5 is modeled as disordered over two positions (approximately related by a 180° rotation about the long axis of the group) with
each component fixed at 50% occupancy. Only one disordered component is shown.
Fig. 4. Unit cell contents of C2 as viewed down the ‘a’ axis direction.
Table 4
bond length of 2.122 Å and two nitrogen atoms (N4 and N5) of
the picolyl pendant arms (2.003(6) and 2.015(6), respectively).
Selected bond distances (Å) and angles (°) and hydrogen bonds for C2.
Cu(1)–O(1)
Cu(1)–N(4)
Cu(1)–N(2)
Cu(1)–N(1)
Cu(1)–N(3)
1.968(4)
1.971(4)
2.000(4)
2.031(4)
2.193(4)
N(4)–Cu(1)–N(2)
O(1)–Cu(1)–N(1)
N(4)–Cu(1)–N(1)
N(2)–Cu(1)–N(1)
O(1)–Cu(1)–N(3)
N(4)–Cu(1)–N(3)
N(2)–Cu(1)–N(3)
N(1)–Cu(1)–N(3)
84.49(16)
83.69(15)
155.25(14)
86.93(16)
106.19(16)
117.80(15)
83.47(15)
84.08(15)
The Cu–Npyridyl bond distances are shorter than the Cu–Ntacn
distance (Table 5) and are within the range reported for other
pyridyl-containing copper(II) complexes [1,29,30]. This indicates
a stronger coordination of the macrocyclic ligand L4 to the Cu(II)
centre. The calculated value of
s is 0.28 for C3 indicates a SP
O(1)–Cu(1)–N(4)
O(1)–Cu(1)–N(2)
99.67(16)
165.70(14)
structure with some degree of distortion towards TBP. This is
further supported by the fact that both trans-N–Cu–N angles,
N(4)–Cu(1)–N(2) = 161.2(2)° and in particular N(5)–Cu(1)–
N(3) = 144.8(2)°, are less than the expected 180° (Table 5).
Intermolecular hydrogen bond interactions were observed only
between the nitrogen atom N6 of the benzothiazole pendant arm
As depicted in Fig. 5, the Cu(II) ion is facially coordinated to the
three nitrogen atoms of the tacn ring (N1–N3) with an average

J. Barreto et al. / Polyhedron 52 (2013) 128–138
137
Fig. 5. Structure of the complex–cation C4 with atom-numbering scheme. Thermal ellipsoids are drawn at 30% probability level. Hydrogen atoms, perchlorate anions and
solvent molecules are omitted for clarity.
Table 5
Selected bond distances (Å) and angles (°) for C4.
Cu(1)–N(1)
Cu(1)–N(2)
Cu(1)–N(3)
Cu(1)–N(4)
Cu(1)–N(5)
2.154(6)
2.027(6)
2.186(6)
2.003(6)
2.015(6)
N(2)–Cu(1)–N(1)
N(4)–Cu(1)–N(1)
N(4)–Cu(1)–N(2)
N(4)–Cu(1)–N(3)
N(4)–Cu(1)–N(5)
N(5)–Cu(1)–N(1)
N(5)–Cu(1)–N(2)
N(5)–Cu(1)–N(3)
85.0(2)
80.3(2)
161.2(2)
106.6(2)
97.5(2)
129.6(2)
83.0(3)
144.8(2)
N(1)–Cu(1)–N(3)
N(2)–Cu(1)–N(3)
80.5(2)
82.2(2)
and the oxygen atom O8 of a perchlorate anion (N(6)–H(6). . .O(8),
2.903(8) Å, \(DHA) = 161.7. The lattice is stabilized by intermolec-
ular aromatic p–p stacking interaction between the pyridine rings
of the benzothiazole moiety with the inter-planar separation of
3.698 Å (centre-to centre, Fig. 6).
3.2.4. Comparison of structures
Analysis of the three structures, simplified view presented in
Fig. 7, reveals that the introduction of pyridyl groups into the tacn
ring modifies the coordination properties of the carbonyl group
connecting the benzothiazole moiety to the macrocycle. Further-
more, the copper(II) center prefers the pyridyl group over the car-
bonyl group for metal coordination. Thus, introduction of these
groups in the azamacrocyclic ring can limit the ability of the benzo-
thiazole moiety to coordinate to the metal center. The geometry of
the coordination complex formed with copper(II) varies according
to the number and type of pendant arms. As discussed above, one
pendant arm on the tacn macrocycle presents a pseudo-octahedral
geometry around copper centre whereas the introduction of an
Fig. 7. Representation of the copper(II) cationic units of complexes C1, C2 and C4.
additional pyridyl pendant alters the geometry to distorted square
pyramidal with the degree of distortion being further enhanced to-
wards trigonal bipyramidal upon introduction of a second pyridyl
group on the macrocycle. This is expected due to the steric hin-
drance generated by the benzothiazole pendant arm and the mac-
rocyclic constraints. In copper(II)-tacn complexes containing
smaller pendant arms like acetate together with two pyridyl arms
it has been concluded that steric hindrance produced by these pen-
dant arm can cause the change of geometry from distorted octahe-
dral to distorted square pyramidal [1]. Han et al. have shown that in
the copper(II)-1,4,7-tris(2-pyridylmethyl)-1,4,7-triazacyclononane
complex the copper center coordinates six nitrogen, three from
the tacn ring and three from the pyridyl groups, presenting a
distorted octahedron [31]. In the case of tris-o-aminobenzyl
substituted tacn (1,4,7-tris(o-aminobenzyl)-1,4,7-triazacyclo-
nonane) the copper(II) center adopts a square pyramidal geometry
Fig. 6. Intermolecular p–p-interaction between two C4 molecules.

138
J. Barreto et al. / Polyhedron 52 (2013) 128–138
similar to that found in this study [32]. A related trisubstituted tacn
ligand consisting of two benzimidazole pendant arms and an
additional benzimidazole-2-yl-methyl group, which is linked to
the deprotonated nitrogen atom of benzimidazole-2-yl-methyl, as
the third arm (1-R-4,7-bis(benzimidazole-2-yl-methyl)-1,4,7-tri-
can be obtained free of charge via http://www.ccdc.cam.ac.uk/con-
ts/retrieving.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223
336 033; or e-mail: deposit@ccdc.cam.ac.uk.
azacyclononane,
[R = 1-(benzimidazole-2-yl-methyl)benzimid-
References
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three benzimidazole pendant arms coordinated to the copper(II)
forming an octahedral complex rather than distorted square
pyramidal as found for C3 in this study.
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CCDC # 881571, 881569 and 881570 contain supplementary
crystallographic data for C1, C2 and C4, respectively. These data