Coordination studies of copper(II), cobalt(II) and iron(II) with isomeric pyridyl-tetrazole ligands

Article abstract of DOI:10.1016/j.poly.2011.11.038

The reaction of 2-(2H-tetrazol-5-yl)pyridine (L1) with 1,6-dibromohexane results in formation of the isomers 2-(6″-bromohexyl)-(1-tetrazol-5-yl) pyridine (L2) and 2-(6″-bromohexyl)-(2-tetrazol-5-yl)pyridine (L3). Coordination reactions of L2 and L3 with CuCl₂·2H ₂O, Co(SCN)₂ and Fe(ClO₄)₂· H₂O yielded the strongly coloured solids [Cu(II)(L2)Cl ₂]₂ (1), [Cu(II)(L3)Cl₂]₂ (2), [Co(II)(L2)₂(NCS)₂] (3), [Co(II)(L3)₂(NCS) ₂] (4), [Fe(II)(L2)₂(H₂O)₂](ClO ₄)₂ (5) and [Fe(II)(L3)₂(H₂O) ₂](ClO₄)₂ (6), containing high-spin metal centres for the Co(II) and Fe(II) compounds. X-ray crystal structures were obtained for complexes 1-5. In each complex, ligands L2 and L3 coordinate to the metal centre through the pyridyl N atom and the 1-N site of the tetrazole ring, and the pyridyl-tetrazole ligand remains planar in all cases except 3. Complexes 1 and 2 comprise a central Cu₂Cl₂ dimeric core with Cu(II) in an essentially square-pyramidal coordination environment. Complexes 3 and 4 contain Co(II) in a distorted octahedral coordination environment. In 3, the pyridyl and tetrazole rings of L2 are twisted with respect to each other and the complex adopts a puckered conformation in its equatorial plane. Complex 5 contains water molecules coordinated to Fe(II) in the axial sites, which form hydrogen bonds to the perchlorate counter anions.

Full text of DOI:10.1016/j.poly.2011.11.038

Polyhedron 33 (2012) 289–296
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Coordination studies of copper(II), cobalt(II) and iron(II) with isomeric
pyridyl–tetrazole ligands
a
b
b
b
c,
⇑
Andrew D. Bond , Adrienne Fleming , Jackie Gaire , Fintan Kelleher , John McGinley
,
d
c
Vickie McKee , Ursula Sheridan
a
Department of Physics and Chemistry, University of Southern Denmark, DK-5230 Odense M, Denmark
Molecular Design and Synthesis Group, Department of Science, Institute of Technology Tallaght, Dublin 24, Ireland
Department of Chemistry, National University of Ireland Maynooth, Maynooth, Co. Kildare, Ireland
Department of Chemistry, Loughborough University, Loughborough, Leicestershire LE11 3TU, UK
b
c
d
a r t i c l e i n f o
a b s t r a c t
Article history:
The reaction of 2-(2H-tetrazol-5-yl)pyridine (L1) with 1,6-dibromohexane results in formation of the iso-
Received 11 October 2011
Accepted 21 November 2011
Available online 28 November 2011
00
00
mers 2-(6 -bromohexyl)-(1-tetrazol-5-yl)pyridine (L2) and 2-(6 -bromohexyl)-(2-tetrazol-5-yl)pyridine
L3). Coordination reactions of L2 and L3 with CuCl O, Co(SCN) and Fe(ClO ꢀH O yielded the
ꢀ2H
strongly coloured solids [Cu(II)(L2)Cl (1), [Cu(II)(L3)Cl (2), [Co(II)(L2) (NCS) ] (3), [Co(II)(L3) (NCS)
4), [Fe(II)(L2) (H O) ](ClO (5) and [Fe(II)(L3) (H O) ](ClO (6), containing high-spin metal centres
(
2
2
2
4
)
2
2
2
]
2
2
]
2
2
2
2
2
]
(
2
2
2
)
4 2
2
2
2
4 2
)
Keywords:
Coordination chemistry
Transition metal
Pyridyl–tetrazole ligand
X-ray crystal structures
for the Co(II) and Fe(II) compounds. X-ray crystal structures were obtained for complexes 1–5. In each
complex, ligands L2 and L3 coordinate to the metal centre through the pyridyl N atom and the 1-N site
of the tetrazole ring, and the pyridyl–tetrazole ligand remains planar in all cases except 3. Complexes 1
2 2
and 2 comprise a central Cu Cl dimeric core with Cu(II) in an essentially square-pyramidal coordination
environment. Complexes 3 and 4 contain Co(II) in a distorted octahedral coordination environment. In 3,
the pyridyl and tetrazole rings of L2 are twisted with respect to each other and the complex adopts a
puckered conformation in its equatorial plane. Complex 5 contains water molecules coordinated to Fe(II)
in the axial sites, which form hydrogen bonds to the perchlorate counter anions.
Ó 2011 Elsevier Ltd. All rights reserved.
1
. Introduction
A great deal of attention has been devoted toward the synthesis
razole macrocycles, including the first example of a host–guest
interaction between a tetra-tetrazole macrocycle and a solvent
molecule [11–16]. To expand this area, we are investigating the
use of tetrazole containing compounds as potential metal-based
therapeutic agents, especially as anti-cancer or anti-fungicidal
agents. In this paper, we describe the synthesis of some pyridyl–
tetrazole compounds containing bromohexyl pendant arms (see
Scheme 1) and examine their coordination chemistry with Fe(II),
Co(II) and Cu(II) salts, which are a range of metal cations which
the human body can tolerate. The biological studies of these com-
plexes will be discussed in a future paper [17].
of functional compounds containing polyazole rings, particularly
tetrazoles and their derivatives, due to their practical applications
[
1–4]. The development of ‘‘click’’ chemistry, as described by
Sharpless and co-workers [5], has resulted in a recent increase in
tetrazole structures. Tetrazole derivatives have found applications
in therapeutics as antihypertensive agents [6], antibiotics [7], and
drugs for AIDS treatment [8]. They are also studied in the field of
coordination chemistry [9]. Both tetrazole and its derivatives, nor-
mally the 5-substituted derivatives, can act as both di- and poly-
dentate ligands exhibiting several coordination modes [10].
Mono 1- and 2-substituted tetrazoles are often used for the con-
struction of coordination networks [9,10]. Our interest in tetrazoles
concerns their use as precursors for the formation of new function-
alised polytetrazole macromolecules, which have potential appli-
cations as sensors or in molecular recognition. We have
previously reported the addition of pendant short-chain arms to
various bis-tetrazoles, as well as the synthesis of several tetra-tet-
2
. Results and discussion
2.1. Ligand syntheses and characterisation
Synthesis of 2-(2H-tetrazol-5-yl)pyridine (L1) and its subsequent
00
reaction with 1,6-dibromoexane to give the isomers 2-(6 -bro-
00
mohexyl)-(1-tetrazol-5-yl)pyridine (L2) and 2-(6 -bromohexyl)-
(
2-tetrazol-5-yl)pyridine (L3) was carried out as in a manner sim-
⇑
Corresponding author. Tel.: +353 1 708 4615; fax: +353 1 708 3815.
E-mail address: john.mcginley@nuim.ie (J. McGinley).
ilar to that described in the literature [18], as shown in Scheme 1.
The reaction of sodium azide with 2-cyanopyridine in the presence
0
277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.11.038

2
90
A.D. Bond et al. / Polyhedron 33 (2012) 289–296
of high-spin Co(II). The magnetic moments for the Fe complexes 5
and 6 are 4.7 and 5.0 BM, respectively, which indicate the presence
of high-spin Fe(II). The observation of high-spin ions in the latter
two cases is consistent with the findings of Henderson and co-
workers who have reported several complexes of L1 all contained
high-spin Mn(II) [9a].
2.3. Crystal structures of the Cu(II) complexes 1 and 2
Dark green crystals of 1 and 2 suitable for X-ray diffraction were
obtained from methanol and ethanol solutions of CuCl
L2 and L3, respectively. Crystallographic data for all structures are
presented in Table 1. Both 3 and 7 consist of dichloro-bridged di-
2
ꢀ2H
2
O with
2
meric {Cu(II)(l-Cl)Cl} units, with the coordination sphere about
each Cu(II) atom comprising one pyridine N atom, one tetrazole
N atom and three Cl atoms (Figs. 1 and 2). Selected bond distances
and angles are listed in Tables 2 and 3, respectively. In 1, the com-
plex lies on a crystallographic inversion centre, while in 2, the bro-
mohexyl chains adopt different conformations with respect to the
central core of the complex. One of the hexyl chains in 2 is disor-
dered (Fig. 2).
Scheme 1. Reaction conditions: (i) NaN
3
, LiCl, NH
4
Cl, DMF, D, 10 h; (ii) 1,6-
dibromohexane, K CO , butanone, , 24 h; R = C H
2
3
D
6
12Br.
The geometry of the central core is closely comparable in 1 and 2:
the 28 non-H atoms in each complex (excluding the bromohexyl
chains) can be overlaid with an rms deviation of 0.13 Å. The coordi-
nation geometry of each Cu(II) centre is distorted square pyramidal.
of ammonium chloride and lithium chloride in dry dimethylform-
amide (DMF) yielded L1 as brown needles on recrystallisation from
1
3
ethanol. The C NMR and IR spectra of the needles confirmed the
1
3
presence of the tetrazole ring with a signal at 154.9 ppm in the
C
The Addison parameter,
and 0.12 for Cu(2), respectively, in 2 (where
pyramidal and = 1 for ideal trigonal–bipyramidal) [21]. Each pyr-
s, is 0.19 for 1, compared to 0.05 for Cu(1)
NMR spectrum indicating the formation of a 1,5-disubstituted tet-
s
= 0 for ideal square-
ꢁ
1
razole and the absence of a signal at 2220 cm in the IR spectrum
s
1
due to an azide band [15,19,20]. The H NMR spectrum of L1, ob-
idyl–tetrazole ligand binds to the Cu(II) atom through one tetrazole
N atom at the 1-N site of the tetrazole ring and through the pyridyl N
atom, to generate a five-membered chelate ring. The tetrazole ring is
coplanar with the pyridyl ring. This coplanarity has been seen in
other metal complexes containing pyridyl–tetrazole ligands
3
tained in CD OD, showed the expected signals for the pyridine ring,
while the NH proton on the tetrazole appeared as a broad signal at
3
.9 ppm.
The reaction of L1 with 1,6-dibromohexane in either 2-buta-
none or acetonitrile with potassium carbonate as base gave a mix-
ture of products L2 and L3, arising from alkylation at either the 1-N
or 2-N positions. Column chromatography separated the products
from the reactants. Both L2 and L3 are low melting, waxy solids.
[
2 2
9,10]. In the central core, the four-membered Cu Cl rings are pla-
nar in both cases, and the Cu(II)–Cl bond distances are comparable
to those of other dichloro-bridged dimers in the literature [22].
The Cu–Cl(apical) bond distances are longer than the Cu–Cl(equato-
rial) bond distances by ca. 0.35 Å (Table 2).
In 1, the two bromohexyl arms orient themselves above and be-
2 2
low the central Cu Cl core, pointing away from each other in a
13
The isomers are readily distinguishable by their C NMR spectra
1
3
with the C NMR chemical shift of the tetrazole C atom appearing
at ca. 154.0 or 164.0 ppm in the 1,5- and 2,5-disubstituted tetra-
zoles, respectively [15,19,20]. In this case, the 1-N isomer (L2) gave
centrosymmetric arrangement (Fig. 1), whereas in 2, both arms
point in the same direction (Fig. 2). This difference in orientation
is probably attributable to packing effects. In 1, the complexes
are arranged into well-defined layers, with the pyridyl ring of
one L2 ligand approaching the tetrazole ring of an adjacent L2 li-
gand in a side-on co-planar fashion, making C–HꢀꢀꢀN contacts (see
Figures in ESI). The bromohexyl arms form an interdigitated
arrangement between those layers, with adjacent arms lying paral-
lel to each other in a manner typical of close-packed alkyl chains.
In 2, the comparable side-on approach of L3 ligands is blocked
by the presence of the bromohexyl arm, and the complexes instead
adopt a bilayer type arrangement, where the pyridyl ring of one L3
ligand approaches the Cl atoms of an adjacent complex, making
C–HꢀꢀꢀCl contacts. In this arrangement, the bromohexyl pendant
arms are forced to lie on the same side of the complex, where they
form a less well-defined packing pattern between the bilayers.
a signal at 151.4 ppm, while the 2-N isomer (L3) gave a signal at
1
1
64.7 ppm. The H NMR spectra of both L2 and L3 show four sig-
nals for the pyridyl protons, a triplet for the methylene group be-
side the Br atom, a triplet for the methylene group beside the
tetrazole and three other signals for the remaining methylene
groups of the bromoalkyl chain. The signals for the methylene pro-
tons beside the tetrazole appear at 5.00 ppm for L2 and 4.73 ppm
for L3.
2.2. Coordination reactions
The transition-metal salts CuCl
H O were reacted with L2 and L3, respectively, in methanol at reflux
2
2
ꢀ2H
2
O, Co(SCN)
2
and Fe(ClO
4
)
2
ꢂ
temperature under an inert atmosphere for 2 h. All reactions were
carried out using a 1:1 metal:ligand stoichiometry (see Schemes 2
and 3). The resulting strongly coloured solutions were allowed to
stand for several days, after which time the solid products were
filtered off. Elemental analyses on all of the products obtained
showed that the Cu complexes (1 and 2) have a 1:1 metal:ligand
composition while both the Co complexes (3 and 4) and the Fe
complexes (5 and 6) had a 1:2 metal:ligand composition.
2.4. Crystal structures of the Co(II) complexes 3 and 4
Rust-coloured crystals of 3 were obtained from a methanol
solution while green crystals of 4 were recrystallised from ethanol.
Complex 3 contains one independent molecule lying on a crystal-
lographic inversion centre, while 4 contains two independent com-
plexes, lying on distinct crystallographic inversion centres.
Selected bond distances and angles for 3 and 4 are listed in Tables
4 and 5, respectively.
The Cu complexes 1 and 2 have magnetic moments of 2.6 and
3
.2 BM, respectively, which indicate the expected presence of
Cu(II). Both Co complexes 3 and 4 have magnetic moments in the
ranges of 4.5 and 3.65 BM, which are consistent with the presence

A.D. Bond et al. / Polyhedron 33 (2012) 289–296
291
R
R
N
N
N
N
N
N
N
Cl
N
NCS
N
N
Cu
Cl
N
Cl
Cu
Co
SCN
N
N
Cl
N
N
N
R
ii)
N
3
N
i)
N
N
N
R
N
1
N
R
N
N
L2
iii)
R
N
N
2
+
N
N
OH2
N
N
Fe
H2O
N
N
N
N
5
R
Scheme 2. Reaction conditions: (i) CuCl
2
ꢀ2H
2
O, MeOH,
D
, 2 h; (ii) Co(SCN)
2
, MeOH,
D
, 2 h; (iii) Fe(ClO
4 2 2
) ꢀxH O, MeOH, D, 2 h.
In both 3 and 4, Co(II) exhibits an octahedral coordination
geometry with the equatorial plane consisting of two pyridyl–
tetrazole ligands and the thiocyanate ligands in the axial posi-
tions. Again, each pyridyl–tetrazole ligand chelates to Co(II)
through one tetrazole N atom at the 1-N site and through the
pyridyl N atom. As for 1 and 2, the tetrazole rings are coplanar
with the pyridine rings in 4, and the two pyridyl–tetrazole li-
gands within the complex are also approximately co-planar with
each other. In 3, however, there is a significant twist within the
ligand so that the planes of the tetrazole and pyridine rings form
dihedral angles of 8.9(1)° and 16.2(1)° in the two independent
ligands, and the complex as a whole displays a much more puck-
ered geometry (Fig. 3), reminiscent of the saddle conformation
frequently observed in porphyrin complexes. Again, this appears
to driven by packing effects. The complexes lie in layers where
the equatorial planes of the complexes are all essentially parallel
2.5. X-ray analysis of the Fe(II) complex of L2
Brown crystals of 5 were obtained from the reaction between
Fe(ClO O and L2. Selected bond lengths and angles for 5 are
ꢀH
4
)
2
2
given in Table 6. The complex lies on a crystallographic inversion
centre and the bromoalkyl chain is modelled as disordered over
two sets of positions (Fig. 6). The Fe(II) centre adopts a slightly dis-
torted octahedral coordination geometry with the pyridyl–tetra-
zole ligands occupying the equatorial plane and water molecules
occupying the axial positions. As for 1, 2 and 4, the tetrazole ring
is coplanar with the pyridine ring. The complexes lie in layers with
the perchlorate counter anions (modelled as disordered) between
layers accepting hydrogen bonds from the coordinated water
molecules.
(
as opposed to edge-to-face type contacts observed in 4) (Fig. 5).
3. Experimental
At one side of the complex, the pyridyl–tetrazole ligands with
the smaller degree of twist meet in centrosymmetric face-to-face
type contacts. At the other side of the complex, a bromohexyl
chain lies across the face of an adjacent complex, and the tetra-
zole ring of the ligand is twisted away from that chain, giving
rise to the larger twist within the ligand. The twist also intro-
1H and 13C NMR (d ppm; J Hz) spectra were recorded on a JEOL
JNM-LA300 FT-NMR spectrometer using saturated CDCl solutions
3
with Me Si reference, unless indicated otherwise, with resolutions
4
ꢁ1
of 0.18 Hz and 0.01 ppm, respectively. Infrared spectra (cm
)
were recorded as KBr discs or liquid films between KBr plates using
a Nicolet Impact 410 FT-IR spectrometer. Melting point analyses
were carried out using a Stewart Scientific SMP 1 melting point
duces relatively short NꢀꢀꢀS contacts to
a
neighbouring
thiocyanate ligand (3.325(4) Å) (Fig. 4).

2
92
A.D. Bond et al. / Polyhedron 33 (2012) 289–296
N
N
N
N
N
R
N
R
N
Cl
N
N
NCS
N
Cu
Cl
Cl
N
Co
SCN
Cu
N
N
N
Cl
N
R
N
R
N
4
ii)
N
N
i)
N
N
N
2
N
R
N
N
L3
iii)
N
2+
N
N
R
N
OH
2
N
Fe
N
2
H O
N
R
N
6
N
N
Scheme 3. Reaction conditions: (i) CuCl
2
ꢀ2H
2
O, MeOH,
D
, 2 h; (ii) Co(SCN)
2
, MeOH,
D
, 2 h; (iii) Fe(ClO
4
2 2
) ꢀxH O, MeOH, D, 2 h.
Table 1
Crystallographic data for 1–5.
1
2
3
4
5
Formula
M (g molꢁ1)
Crystal system
Space group
T (K)
C
24
H
32Br
2
Cl
4
Cu
N
2 10
C
24
H
32Br
2
Cl
4
Cu
N
2 10
C
26
H
32Br
2
CoN12
S
2
C
26
H
32Br
2
CoN12
S
2
C
24 2 2 10
H36Br Cl FeN10O
889.30
triclinic
P1ꢀ
180(2)
889.30
triclinic
P1ꢀ
150(2)
795.51
triclinic
P1ꢀ
120(2)
795.51
triclinic
P1ꢀ
150(2)
911.20
monoclinic
P2 /c
1
150(2)
a (Å)
b (Å)
c (Å)
9.2946(5)
9.4441(7)
9.5645(17)
12.213(2)
14.688(3)
92.214(3)
107.256(2)
93.937(2)
1631.5(5)
2
8.7827(4)
8.2324(15)
12.863(2)
15.951(3)
99.917(3)
93.901(3)
90.270(3)
1659.8(5)
2
9.8682(11)
12.1112(6)
16.0963(6)
83.204(2)
83.219(2)
74.195(2)
1629.23(13)
2
11.7061(12)
15.2784(16)
90
92.999(2)
90
1762.5(3)
2
1.717
10.6132(7)
76.945(2)
80.052(2)
66.114(2)
826.35(9)
1
a
(°)
b (°)
(°)
c
3
V (Å )
Z
D
calc (g cm 3
ꢁ
)
1.787
1.810
1.622
1.592
Reflections collected
Unique reflections
14734
2897
13771
6383
32290
6043
12805
5600
14802
3463
R
int
0.026
0.050
0.033
0.067
0.041
Observed reflections
I > 2(I)]
2632
3783
4855
2764
2565
[
Number of parameters
Number of restraints
190
0
415
147
398
0
426
468
319
218
R
1
[I > 2
wR (all data)
Goodness-of-fit (GOF) on F
r
(I)]
0.0264
0.074
1.09
0.066
0.217
1.03
0.041
0.108
1.04
0.081
0.252
1.05
0.047
0.115
1.05
2
2

A.D. Bond et al. / Polyhedron 33 (2012) 289–296
293
Table 4
Selected bond lengths (Å) and angles (°) for 3.
Co(1)–N(4)
Co(1)–N(5)
Co(1)–N(6)
2.142(3)
2.139(3)
2.039(3)
Co(1)–N(4A)
Co(1)–N(5A)
Co(1)–N(6A)
2.122(3)
2.144(3)
2.082(3)
N(6)–Co(1)–N(6A)
N(6A)–Co(1)–N(4A)
N(6A)–Co(1)–N(5)
N(6)–Co(1)–N(4)
N(4A)–Co(1)–N(4)
N(6)–Co(1)–N(5A)
N(4A)–Co(1)–N(5A)
N(4)–Co(1)–N(5A)
178.22(13)
87.44(12)
89.80(12)
93.09(12)
172.57(12)
91.55(12)
76.73(11)
103.37(11)
N(6)–Co(1)–N(4A)
N(6)–Co(1)–N(5)
N(4A)–Co(1)–N(5)
N(6A)–Co(1)–N(4)
N(5)–Co(1)–N(4)
N(6A)–Co(1)–N(5A)
N(5)–Co(1)–N(5A)
94.33(12)
90.03(12)
103.13(12)
85.14(12)
76.56(12)
88.62(12)
178.41(12)
Fig. 1. Molecular structure of 1 with displacement ellipsoids at the 50% probability
level (H atoms omitted). The complex lies on a crystallographic inversion centre.
Table 5
Selected bond lengths (Å) and angles (°) for 4.
Co(1A)–N(6A)
Co(1A)–N(4A)
Co(1A)–N(5A)
2.080(7)
2.142(6)
2.158(6)
Co(1B)–N(6B)
Co(1B)–N(4B)
Co(1B)–N(5B)
2.061(9)
2.137(7)
2.156(6)
N(6A)–Co(1A)–N(4A)
N(6A)#1–Co(1A)–N(4A)
N(6A)–Co(1A)–N(5A)
N(6A)–Co(1A)–N(5A)#1
N(4A)–Co(1A)–N(5A)
N(4A)–Co(1A)–N(5A)#1
92.4(3)
87.6(3)
92.1(2)
87.9(2)
76.7(2)
103.3(2)
N(6B)–Co(1B)–N(4B)
N(6B)–Co(1B)–N(4B)
88.6(3)
91.4(3)
87.4(3)
92.6(3)
102.8(2)
77.2(2)
#2
N(6B)#2–Co(1B)–N(5B)
N(6B)–Co(1B)–N(5B)
N(4B)#2–Co(1B)–N(5B)
#2
N(4B)–Co(1B)–N(5B)
Symmetry code #1: ꢁx, ꢁy, ꢁz, #2: 1 ꢁ x, ꢁy, 1 ꢁ z.
apparatus and are uncorrected. Mass spectra were collected in the
Mass Spectrometry unit in the Centre for Synthesis and Chemical Biol-
ogy, University College, Dublin. Magnetic susceptibility measurements
were carried out at room temperature using a Johnson Matthey Mag-
Fig. 2. Molecular structure of 2 with displacement ellipsoids at the 50% probability
level (H atoms omitted). One bromohexyl pendant arm is modelled as disordered
over three orientations.
4
netic Susceptibility Balance with [HgCo(SCN) ] as reference. Microa-
nalyses were carried out at the Microanalytical Laboratory of
University College, Dublin. Standard Schlenk techniques were used
throughout. Starting materials were commercially obtained and used
without further purification. Caution! Nitrogen-rich compounds such
as tetrazole derivatives are used as components for explosive mixtures
Table 2
Selected bond lengths (Å) and angles (°) for 1.
Cu(1)–Cl(1)
Cu(1)–Cl(1)#1
Cu(1)–Cl(2)
2.2553(7)
2.6392(8)
2.2257(8)
Cu(1)–N(4)
Cu(1)–N(5)
1.987(2)
2.088(2)
[1]. In our laboratory, the reactions described were run on a few gram
scale, and no problems were encountered. However, great caution
should be exercised when heating or handling compounds of this type.
Caution! Although not encountered in our experiments, perchlorate
saltsofmetalionsarepotentiallyexplosiveandshouldbemanipulated
with care and used only in small quantities.
Cl(1)–Cu(1)–Cl(2)
Cu(1)–Cl(1)–Cu(1)
94.32(3)
89.97(2)
106.12(3)
94.28(6)
160.64(7)
91.20(6)
N(4)–Cu(1)–Cl(1)
N(4)–Cu(1)–Cl(2)
N(4)–Cu(1)–Cl(1)
N(4)–Cu(1)–N(5)
172.29(7)
92.38(7)
91.82(7)
78.19(9)
90.03(2)
#1
Cl(2)–Cu(1)–Cl(1)#1
#1
N(5)–Cu(1)–Cl(1)
N(5)–Cu(1)–Cl(2)
N(5)–Cu(1)–Cl(1)#1
Cl(1)–Cu(1)–Cl(1)#
1
Symmetry code #1: 2 ꢁ x, ꢁy, ꢁz.
3.1. Synthesis of 2-(2H-tetrazol-5-yl)pyridine (L1)
A suspension of 2-cyanopyridine (4.14 g, 40 mmol), sodium
azide (5.72 g, 88 mmol), ammonium chloride (4.70 g, 88 mmol)
and lithium chloride (1.20 g, 28 mmol) in anhydrous dimethylform-
amide (40 mL) was stirred for 10 h at 110 °C. After this time, the
solution was cooled and the insoluble salts were removed by filtra-
tion. The solvent was then evaporated under reduced pressure and
the residue was dissolved in deionised water (200 mL) and acidified
with concentrated HCl (3 mL), to initiate precipitation. The product
was removed by filtration, washed with water (3 ꢂ 40 mL) and dried
to give a brown solid. This was recrystallised from hot ethanol to af-
ford L1 as brown needles (3 g, yield 51.3%). M.p. 221–223 °C. Anal.
Table 3
Selected bond lengths (Å) and angles (°) for 2.
Cu(1)–Cl(3)
Cu(1)–Cl(1)
Cu(1)–Cl(2)
Cu(1)–N(4A)
Cu(1)–N(5A)
2.235(2)
2.716(2)
2.2637(19)
2.012(6)
2.085(6)
Cu(2)–Cl(4)
Cu(2)–Cl(2)
Cu(2)–Cl(1)
Cu(2)–N(4B)
Cu(2)–N(5B)
2.229(2)
2.671(2)
2.3178(18)
2.013(6)
2.090(6)
Cl(3)–Cu(1)–Cl(2)
Cl(2)–Cu(1)–Cl(1)
Cl(3)–Cu(1)–Cl(1)
N(4A)–Cu(1)–Cl(3)
N(4A)–Cu(1)–Cl(2)
N(4A)–Cu(1)–Cl(1)
N(4A)–Cu(1)–N(5A)
N(5A)–Cu(1)–Cl(1)
N(5A)–Cu(1)–Cl(2)
N(5A)–Cu(1)–Cl(3)
Cu(2)–Cl(1)–Cu(1)
93.87(8)
92.36(7)
101.41(8)
91.79(19)
167.9(2)
97.0(2)
Cl(4)–Cu(2)–Cl(1)
Cl(1)–Cu(2)–Cl(2)
Cl(4)–Cu(2)–Cl(2)
N(4B)–Cu(2)–Cl(4)
N(4B)–Cu(2)–Cl(1)
N(4B)–Cu(2)–Cl(2)
N(4B)–Cu(2)–N(5B)
N(5B)–Cu(2)–Cl(1)
N(5B)–Cu(2)–Cl(2)
N(5B)–Cu(2)–Cl(4)
Cu(1)–Cl(2)–Cu(2)
94.10(7)
92.30(7)
104.93(8)
90.89(18)
169.71(19)
95.09(19)
78.5(2)
94.41(17)
90.10(19)
162.39(19)
88.75(7)
Calc. for C
6 5 5
H N (147.14): C, 48.98; H, 3.42; N, 47.60. Found: C,
1
4
8.97; H, 3.44; N, 47.61%. H NMR (CD OD): d = 8.76 (d, 1H,
3
J = 7.9 Hz, pyr-H), 8.25 (d, 1H, J = 7.9 Hz, pyr-H), 8.03 (t, 1H,
78.5(2)
91.24(19)
93.66(18)
165.0(2)
86.57(6)
J = 7.9 Hz, pyr-H), 7.56 (t, 1H, J = 7.9 Hz, pyr-H), 3.9 (s, 1H, tet-H)
13
3 4
ppm. C NMR (CD OD): d = 154.9 (CN ), 150.1, 143.7, 138.3, 126.2,
+
1
1
22.7 ppm. ESI-HRMS: calc. for C
47.054.
6 5 5
H N [M] 147.054, found

2
94
A.D. Bond et al. / Polyhedron 33 (2012) 289–296
Fig. 3. Molecular structure of 3 with displacement ellipsoids at the 50% probability level (H atoms omitted). One bromohexyl pendant arm displays disorder.
Fig. 4. Molecular structure of 4 with displacement ellipsoids at the 50% probability level (H atoms omitted). Two independent complexes lie on crystallographic inversion
centres. Both display disorder of the bromohexyl pendant arms.
Fig. 5. Neighbouring complexes in the crystal structure of 3. In the centre, the face-to-face interaction between pyridyl–tetrazole ligands with the smaller degree of twist is
visible. On the left and right sides, the tetrazole rings are twisted away from the planes of the pyridyl rings in order to accommodate the neighbouring bromohexyl chains.
Table 6
on silica gel (initially at a ratio of petroleum ether:ethyl acetate
Selected bond lengths (Å) and angles (°) for 5.
8
0:20, followed by the ratio of 60:40). This gave the products L2
and L3.
L2: Waxy white solid (0.55 g, yield 26%). M.p. 39–41 °C. Anal.
Calc. for C12 Br (310.19): C, 46.46; H, 5.20; N, 22.58. Found:
C, 46.50; H, 5.17; N, 22.62%. H NMR (CDCl
Fe(1)–O(1W)
Fe(1)–N(4)
2.122(3)
2.141(3)
Fe(1)–N(5)
C(12)–Br(1)
2.198(3)
1.947(4)
O(1W)–Fe(1)–N(4)
O(1W)#1–Fe(1)–N(5)
N(4)–Fe–N(5)
88.10(11)
89.46(10)
75.03(11)
O(1W)–Fe(1)–N(4)#1
O(1W)–Fe(1)–N(5)
N(4)# –Fe(1)–N(5)
91.90(11)
90.54(10)
104.97(11)
16 5
H N
1
): d = 8.77 (d, 1H,
1
3
J = 7.5 Hz, pyr-H), 8.37 (d, 1H, J = 7.5 Hz, pyr-H), 7.96 (t, 1H,
J = 7.5 Hz, pyr-H), 7.52 (t, 1H, J = 7.5 Hz, pyr-H), 5.00 (t, 2H,
Symmetry code #1: ꢁx, ꢁy, ꢁz.
J = 6.9 Hz, CH
J = 7.1 Hz, CH
NMR (CDCl ): d = 151.4 (CN
2
N), 3.42 (t, 2H, J = 6.9 Hz, CH
), 1.87 (m, 2H, CH ), 1.48 (m, 4H, CH
), 149.3, 144.6, 137.1, 125.1, 124.2,
2
Br), 2.02 (q, 2H,
) ppm. 13
C
2
2
2
0
0
3
2
.2. Synthesis of 2-(6 -bromohexyl)-(1-tetrazol-5-yl)pyridine (L2) and
3
4
0
0
-(6 -bromohexyl)-(2-tetrazol-5-yl)pyridine (L3)
49.2 (CH N), 33.5 (CH Br), 32.3, 32.1, 29.4, 27.2 ppm. ESI-HRMS:
2
2
+
5
calc. for C12H17BrN [M+1] 310.067, found 310.068.
To L1 (1 g, 6.8 mmol) dissolved in either acetonitrile or 2-buta-
L3: Waxy white solid (0.35 g, yield 17%). M.p. 36–38 °C. Anal.
Calc. for C12 Br (310.19): C, 46.46; H, 5.20; N, 22.58. Found:
none (30 mL) was added potassium carbonate (9.38 g, 68 mmol).
The resulting solution was refluxed for 30 min and to the hot solu-
tion was added 1,6-dibromohexane (4.97 g, 24 mmol). The reaction
mixture was then stirred at reflux temperature for a further 24 h.
After cooling, the solvent was removed under reduced pressure
to afford an oil, which was purified by column chromatography
16 5
H N
1
C, 46.44; H, 5.17; N, 22.63%. H NMR (CDCl ): d = 8.80 (d, 1H,
J = 7.7 Hz, pyr-H), 8.27 (d, 1H, J = 7.7 Hz, pyr-H), 7.90 (t, 1H,
J = 7.7 Hz, pyr-H), 7.43 (t, 1H, J = 7.7 Hz, pyr-H), 4.73 (t, 2H,
3
2 2
J = 6.8 Hz, CH N), 3.39 (t, 2H, J = 6.8 Hz, CH Br), 2.13 (q, 2H,
13
J = 6.8 Hz, CH ), 1.83 (m, 2H, CH ), 1.51 (m, 4H, CH ) ppm.
2
2
2
C

A.D. Bond et al. / Polyhedron 33 (2012) 289–296
295
Fig. 6. Molecular structure of 5 with displacement ellipsoids at the 50% probability level (H atoms omitted). The complex lies on a crystallographic inversion centre. The
bromohexyl chains and the perchlorate anions are modelled as disordered.
NMR (CDCl
3.2 (CH N), 33.4 (CH
calc. for C12 17BrN [M+1] 310.067, found 310.066.
3
): d = 164.7 (CN
4
), 150.2, 146.7, 137.1, 124.8, 122.3,
3.3.6. [Fe(L3)
Yellow solid (0.11 g, yield 20%). Anal. Calc. for C24
FeN10 10 (911.16): C, 31.64; H, 3.98; N, 15.37. Found: C, 31.59;
H, 3.98; N, 15.48%. IR (KBr): = 3410, 2942, 2862, 1638, 1451,
2 2 2 4 2
(H O) ](ClO ) (6)
5
2
2
Br), 32.4, 32.2, 29.0, 27.3 ppm. ESI-HRMS:
2 2
H36Br Cl
+
H
5
O
t
ꢁ1
1
384, 1145, 1117, 1089, 731 cm
.
k
max (CH
3
CN) 348 nm,
3.3. General coordination reactions (1–6)
ꢁ
1
ꢁ1
e
= 219 M cm . Magnetic moment: 5.0 BM. To date, we have
not been able to obtain crystals of 6 suitable for X-ray diffraction
analysis.
The appropriate tetrazole ligand, L2 or L3 (0.20 g, 1.36 mmol),
was dissolved in methanol (30 mL) and was added to a solution
of the appropriate metal salt (1.36 mmol) in methanol (25 mL).
The resulting strongly-coloured solution was then heated to reflux
for 2 h before being allowed to stand at room temperature for sev-
eral days.
3.4. Crystallography
X-ray diffraction data were collected on a Bruker APEX-II CCD
diffractometer using graphite-monochromated Mo K
a radiation
(
k = 0.7107 Å). In each case, a multi-scan correction was applied
3
.3.1. [Cu(L2)Cl
Dark green crystals (0.137 g, yield 49%). Anal. Calc. for
Cl Cu 10 (889.29): C, 32.41; H, 3.63; N, 15.75. Found:
= 2923, 2852, 1648, 1610,
2
]
2
(1)
2
and the structures were refined against F using all reflections
23]. All non-H atoms were refined with anisotropic atomic dis-
[
C
24
H32Br
2
4
2
N
placement parameters and H atoms were placed at calculated posi-
tions and refined using a riding model. One of the hexyl chains in 2
is disordered, and the terminal CH Br unit was refined over three
2
orientations with site occupancies of 0.40, 0.40 and 0.20. Similarity
restraints were applied to the bond distances and to the displace-
ment parameters. For 3, one of the Br atoms appears to be disor-
dered and was included in two positions with refined site
occupancies 0.81(1):0.19(1). Corresponding disorder of the neigh-
C, 32.52; H, 3.71; N, 15.73%. IR (KBr):
1
8
t
ꢁ1
3
482, 1256, 1167, 1139, 1019, 803, 723 cm . kmax (CH CN)
ꢁ1
ꢁ1
32 nm,
e = 93 M cm . Magnetic moment: 2.6 BM.
3
.3.2. [Cu(L3)Cl
Dark green crystals (0.14 g, yield 50%). Anal. Calc. for
Cl Cu 10 (889.29): C, 32.41; H, 3.63; N, 15.75. Found:
= 2923, 2856, 1648, 1610,
2 2
] (2)
C
24
H32Br
2
4
2
N
C, 32.42; H, 3.51; N, 15.78%. IR (KBr):
t
bouring CH
lies ca. 2.3 Å from the CH
2
group could not be resolved, so one of the Br positions
group. Comparable results were ob-
ꢁ
1
1
e
483, 1278, 1165, 1019, 803, 721 cm . kmax (CH
= 55 M cm . Magnetic moment: 3.2 BM.
3
CN) 812 nm,
2
ꢁ1
ꢁ1
tained from full data collections for two crystals within the batch.
In 4, both independent bromohexyl chains are modelled as disor-
dered over two orientations, one with site occupancies 0.50:0.50
and one with 0.70:0.30. Similarity restraints were applied to the
bond distances and to the displacement parameters. In 5, the bro-
mohexyl chain is modelled over two orientations with site occu-
pancies 0.50:0.50, and the perchlorate anion is also modelled as
disordered. The H atoms of the coordinated water molecules were
visible in difference Fourier maps and their positions were refined
with restrained O–H distances.
3
.3.3. Co(L2)
Rust coloured crystals (0.130 g, yield 26%). Anal. Calc. for
CoN12 (795.48): C, 39.26; H, 4.05; N, 21.13. Found: C,
9.31; H, 4.09; N, 21.18%. IR (KBr): = 2933, 2861, 2075, 1648,
473, 1368, 1247, 1159, 1105, 1047, 795, 728 cm . kmax (CH
2 2
(NCS) (3)
C
3
1
5
26
H32Br
2
S
2
t
ꢁ1
3
CN)
ꢁ1
ꢁ1
12 nm,
e = 37 M cm . Magnetic moment: 4.5 BM.
3
.3.4. Co(L3)
Green crystals (0.146 g, yield 29%). Anal. Calc. for
CoN12 (795.48): C, 39.26; H, 4.05; N, 21.13. Found: C,
9.65; H, 4.19; N, 20.86%. IR (KBr): = 2928, 2858, 2075, 1654,
474, 1368, 1247, 1159, 1105, 1047, 796, 728 cm . kmax (CH
2 2
(NCS) (4)
4
. Conclusions
C
3
1
5
26
H32Br
2
S
2
t
The X-ray structures of several M(II) complexes of 2-(2H-tetra-
ꢁ1
3
CN)
zol-5-yl)pyridine derivatives, containing a 6-bromohexyl pendant
arm at either the 1-N (L2) or 2-N (L3) position of the tetrazole ring,
have been studied. In all cases, the 5-(2-pyridyl)tetrazole ligand
coordinates in a bidentate fashion through the pyridine N atom
and the 1-N atom of the tetrazole ring to form a five-membered
chelate ring with the metal ion. The coordination geometries in
the two Cu(II) complexes (1 and 2) are slightly distorted square-
ꢁ1
ꢁ1
12 nm,
e = 45 M cm . Magnetic moment: 3.65 BM.
3
.3.5. [Fe(L2)
Yellow crystals (0.09 g, yield 16%). Anal. Calc. for
Cl FeN10 10 (911.16): C, 31.64; H, 3.98; N, 15.37. Found:
= 3407, 2924, 2852, 1637,
2 2 2 4 2
(H O) ](ClO ) (5)
C
24
H36Br
2
2
O
C, 31.62; H, 3.91; N, 15.41%. IR (KBr):
t
ꢁ1
1
3
478, 1379, 1250, 1143, 1112, 798, 727 cm . kmax (CH
3
CN)
pyramidal, due mainly to the formation of a dimeric Cu
The coordination geometry at the metal centres in the other three
2 2
Cl core.
ꢁ
1
ꢁ1
64 nm,
e = 1718 M cm . Magnetic moment: 4.7 BM.

2
96
A.D. Bond et al. / Polyhedron 33 (2012) 289–296
(b) W. Zhang, F. Zhao, T. Liu, M. Yuan, Z.-M. Wang, S. Gao, Inorg. Chem. 46
structures (3, 4 and 5) can be described as slightly distorted octa-
hedral, with two 5-(2-pyridyl)tetrazole ligands occupying the
equatorial plane in all cases. The axial positions are occupied by
the two thiocyanate anions in the Co(II) complexes, while they
are occupied by two water molecules in the case of the Fe(II) com-
plex. The biological studies of these complexes and complexes
involving other first row transition metal ions will be published
in a separate paper [17].
(
(
2007) 2541;
c) S. Stagni, E. Orselli, A. Palazzi, L. De Cola, S. Zacchini, C. Femoni, M.
Marcaccio, F. Paolucci, S. Zanarini, Inorg. Chem. 46 (2007) 9126;
(d) G.-W. Yang, Q.-Y. Li, Y. Zhou, P. Sha, Y.-S. Ma, R.-X. Yuan, Inorg. Chem.
Commun. 11 (2008) 723;
(
e) S. Stagni, S. Colella, A. Palazzi, G. Valenti, S. Zacchini, F. Paolucci, M.
Marcaccio, R.Q. Albuquerque, L. De Cola, Inorg. Chem. 47 (2008) 10509;
(f) A. Biało n´ ska, R. Bronisz, Tetrahedron 64 (2008) 9771;
(
g) B. Liu, Y.-C. Qiu, G. Peng, L. Ma, L.-M. Jin, J.-B. Cai, H. Deng, Inorg. Chem.
Commun. 12 (2009) 1200;
h) Q.-Y. Li, G.-W. Yang, X.-Y. Tang, Y.-S. Ma, F. Zhou, W. Liu, J. Chen, H. Zhou,
Inorg. Chem. Commun. 13 (2010) 254;
(
Acknowledgments
(
(
(
i) T. Hu, L. Liu, X. Lv, X. Chen, H. He, F. Dai, G. Zhang, D. Sun, Polyhedron 29
2010) 296;
j) Y. Qiu, B. Liu, G. Peng, J. Cai, H. Deng, M. Zeller, Inorg. Chem. Commun. 13
J.G. thanks the Postgraduate R&D Skills programme (Technolo-
gical Sector Research, Strand I) and IT Tallaght Dublin for financial
assistance. U.S. thanks NUIM for a John & Pat Hume Fellowship.
A.D.B. is grateful to the Danish Natural Sciences Research Council
and the Carlsberg Foundation for provision of the X-ray equipment.
(2010) 749;
k) Y. Huang, L.-Z. Chen, R.-G. Xiong, X.-Z. You, Inorg. Chim. Acta 363 (2010)
512;
l) J.M. Seco, M. de Araújo Farias, N.M. Bachs, A.B. Caballero, A. Salinas-Castillo,
A. Rodríguez-Diéguez, Inorg. Chim. Acta 363 (2010) 3194;
m) B.K. Tripuramallu, R. Kishore, S.K. Das, Inorg. Chim. Acta 368 (2011) 132.
10] (a) X. He, C.-Z. Lu, D.-Q. Yuan, Inorg. Chem. 45 (2006) 5760;
b) H. Zhao, Z.-R. Qu, H.-Y. Ye, R.-G. Xiong, Chem. Soc. Rev. 37 (2008) 84.
11] A. Fleming, J. Gaire, F. Kelleher, J. McGinley, V. McKee, Tetrahedron 67 (2011)
260.
12] A.D. Bond, A. Fleming, J. Gaire, F. Kelleher, J. McGinley, V. McKee, Tetrahedron
5 (2009) 7942.
(
2
(
(
[
[
[
Appendix A. Supplementary data
(
3
CCDC 827225, 759312, 827226, 759313 and 759314 contain the
supplementary crystallographic data for 1–5. These data can be ob-
tained free of charge via http://www.ccdc.cam.ac.uk/conts/retriev-
ing.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. Supplementary data associated
with this article can be found, in the online version, at doi:10.1016/
j.poly.2011.11.038.
6
[13] A.D. Bond, A. Fleming, F. Kelleher, J. McGinley, V. Prajapati, S. Skovsgaard,
Tetrahedron 63 (2007) 6835.
[
14] A.D. Bond, A. Fleming, F. Kelleher, J. McGinley, V. Prajapati, Tetrahedron 62
2006) 9577.
(
[15] A. Fleming, F. Kelleher, M.F. Mahon, J. McGinley, V. Prajapati, Tetrahedron 61
(2005) 7002.
[
16] A.F.M. Fleming, F. Kelleher, M.F. Mahon, J. McGinley, K.C. Molloy, V. Prajapati,
Acta Crystallogr., Sect. E 60 (2004) 2388.
[
17] A. Fleming, J. Gaire, F. Kelleher, J. McGinley, U. Sheridan, unpublished results.
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2