New flexible bis-pyridyltetrazole ligands for use in coordination polymer formation: Synthesis and structural studies

Article abstract of DOI:10.1016/j.ica.2016.06.011

In this work, we have further developed the pyridyl-tetrazole ligand systems into bis-tetrazole systems, where the linker introduced to join these moieties was a flexible (CH₂)₃ backbone, with the intention of forming frameworks with potential voids. We synthesised three different pyridyl-tetrazoles linked via this flexible backbone through the pyridine ring and not the tetrazole rings. Two crystals of ligand 1 were solved by X-ray crystallography and showed interesting polymorphism. No crystals of the copper(II) complexes of the ligands could be obtained, suggesting that they were polymeric in nature.

Full text of DOI:10.1016/j.ica.2016.06.011

Accepted Manuscript
New flexible bis-pyridyltetrazole ligands for use in coordination polymer for-
mation: synthesis and structural studies
Ursula Sheridan, John F. Gallagher, John McGinley
PII:
S0020-1693(16)30321-8
http://dx.doi.org/10.1016/j.ica.2016.06.011
ICA 17102
DOI:
Reference:
Inorganica Chimica Acta
To appear in:
Received Date:
Revised Date:
Accepted Date:
22 February 2016
11 May 2016
4 June 2016
Please cite this article as: U. Sheridan, J.F. Gallagher, J. McGinley, New flexible bis-pyridyltetrazole ligands for
use in coordination polymer formation: synthesis and structural studies, Inorganica Chimica Acta (2016), doi: http://
dx.doi.org/10.1016/j.ica.2016.06.011
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers
we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and
review of the resulting proof before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

New flexible bis-pyridyltetrazole ligands for use in coordination polymer
formation: synthesis and structural studies
Ursula Sheridan,a John F. Gallagherb,*,† and John McGinley.a,*,#
a Department of Chemistry, Maynooth University, Maynooth, Co. Kildare, Ireland,
b School of Chemical Sciences, Dublin City University, Dublin 9, Ireland.
* JMcG and JFG joint corresponding authors, email address john.mcginley@nuim.ie;
john.gallagher@dcu.ie
† On sabbatical leave at CRM2, Faculté des Sciences et Technologies, Université de Lorraine, BP 70239,
Boulevard des Aiguelettes, 54506 Vandoeuvre-dès-Nancy, France.
# Current address: Department of Chemistry, University of Copenhagen, DK-2100
Copenhagen Ø, Denmark.
Abstract
In this work, we have further developed the pyridyl-tetrazole ligand systems into bis-tetrazole
systems, where the linker introduced to join these moieties was a flexible (CH2)3 backbone,
with the intention of forming frameworks with potential voids. We synthesised three different
pyridyl-tetrazoles linked via this flexible backbone through the pyridine ring and not the
tetrazole rings. Two crystals of ligand 1 were solved by X-ray crystallography and showed
interesting polymorphism. No crystals of the copper(II) complexes of the ligands could be
obtained, suggesting that they were polymeric in nature.
Keywords
Tetrazole, synthesis, NMR, X-ray structures, polymorphism.
1

Introduction
Since the report by Robson in 2008 on the design and construction of coordination polymers
(CPs) [1], the occurrence of CPs in the literature has increased enormously and covers a
multitude of applications, including luminescence, thin films, adsorption, biomedicine,
chemical sensors and catalysts [2-9]. The design, synthesis and applications of CPs based on
flexible ligands have so far not attracted as much attention as increased flexibility makes it
more difficult to forecast and control the final structures due to different ligand
conformations. Deng and co-workers synthesised bis-tetrazole methane in situ from
malononitrile with the aim of expanding the repertoire of tetrazole based CPs [10].
Solvothermal reactions with CdSO4 and ZnSO4 and a secondary ligand, 2,2’-bipyridine,
produced 2-D networks whereas when the secondary ligand was changed to 4,4’-bipyridine, a
3-D architecture was generated. Bis-tetrazoles with more flexible (CH2)n backbone linkers
have also been employed in the synthesis of coordination polymers. Wang and co-workers
improved their rigid tetrazole-based ligands [11-13] by introducing flexible (CH2)4
backbones, aiming to construct helix/loop subunits in polyoxometalates (POMs) [14]. Their
occurrence is rare however, possibly due to the many conformations possible resulting from
their conformational freedom [15-18]. Nevertheless, it presents an alluring challenge for
supramolecular and materials chemists to harness the benefits of flexible ligands in a way that
also produces crystalline predictable structures.
In our previous work, we successfully designed a series of pyridyl-tetrazole ligands with a
tethered carboxylate group and introduced them into CP systems, and obtained novel
networks and multinuclear clusters [19-20]. Our recent work on bis-tetrazole systems with a
rigid pyrazine linker resulted in the formation of a cluster of six water molecules within a
copper(II) coordination polymer [21]. We have further developed these systems into bis-
tetrazole systems, where the linker introduced to join these moieties is a trimethylene moiety,
a flexible linker; hence we aimed to make the ligands (1-3) presented in Scheme 1. These
ligands would have some conformational freedom, and would allow an investigation into the
effect of spacer flexibility on coordination polymer structures.
2

Scheme 1. Reagents and Conditions: i) H2O2, CH3COOH, 79 °C, 20 h, 75%; ii) DMCC,
Zn(CN)2, DMF, 0 °C, 1 h, 25 °C, 18 h, 34%; iii) NaN3, NH4Cl, DMF, 110 °C, 10 h, 93%; iv)
K2CO3, BrCH2COOEt, CH3CN, 82 °C, 24 h, 10% (1), 16% (2), 28% (3).
Results and Discussion
Synthesis of Ligands
The synthesis of 1, 2 and 3 was achieved using the approach depicted in Scheme 1. Access to
these ligands was achieved by firstly oxidising commercially available 4,4’-
trimethylenebipyridine (4) to the corresponding 1,3-bis(4-pyridyl)propane-N,N’-dioxide (5),
following a previously reported procedure [22].
The α-cyanation of 5 has been reported previously by Deng and colleagues, who employed
trimethylsilyl cyanide and benzoyl chloride to gain access to the bis-cyano derivative 6 [18].
We undertook α-cyanation of 5 using the conditions of Zn(CN)2 and dimethylcarbamoyl
chloride (DMCC) in N,N’-dimethylformamide (DMF), since 5 was insoluble in many
solvents but it did dissolve in DMF over time. The very reactive acyl chloride can react with
DMF to form N,N,N’,N’-tetramethylformamidinium chloride, which are notoriously
intractable, dark sticky oils [23-25]. To prevent this undesired reaction from occurring, the
acylating agent, DMCC, was added slowly over one hour to a reaction mixture of Zn(CN)2
and 5 in DMF at 0 °C. The reaction was then allowed to slowly warm up to room temperature
overnight. After work up and extraction with DCM, the crude mixture was analysed by 1H
NMR spectroscopy. The presence of three aromatic signals was observed, indicating
successful substitution of the pyridine ring. However, methyl peaks and a singlet at 8.17 ppm
were visible in the spectrum, indicating the formation of some N,N,N’,N’-
tetramethylformamidinium chloride. The mixture was passed through a silica plug using ethyl
3

acetate and petroleum ether (40-60) as the eluent in a 3:1 ratio. This yielded a white
1
crystalline solid with isolated yields of around 30%. As well as the H NMR spectrum
displaying three aromatic signals, there was further evidence that a nitrile group was present
at the 2-position of the pyridine ring indicated by a sharp peak positioned at 2237 cm-1 in the
IR spectrum. In the 13C NMR spectrum, a peak concomitant with a nitrile carbon was
observed at 117.2 ppm. The collated data acquired for 6 was consistent with that reported by
Deng and co-workers [18].
Synthesis of the ligands continued with a 1,3-dipolar cycloaddition using conditions
described previously [21]. The product, 7, was analysed by NMR and IR spectroscopies and
HRMS. The IR spectrum of 7 displayed a broad stretch at ~3386 cm-1 which was indicative
of the ν(N-H) vibrational mode of the protonated tetrazole. Furthermore, the ν(C≡N)
frequency was absent which was anticipated if it had been consumed during the reaction. The
presence of two tetrazole rings was also indicated by the 1H NMR spectrum which exhibited
five resonances, three aromatic signals and two alkyl chain resonances attributed to the
propyl chain protons, which implied a symmetrical system and therefore indicated bis-
substitution. The tetrazole quaternary C-5 peak was positioned at 154.9 ppm in the 13C NMR
spectrum, which is typical of C-5 resonances of protonated tetrazole rings [26-30]. Finally,
HRMS analysis revealed the presence of a molecular ion peak at m/z 335.1476 which
corresponded to a (7+H)⁺ ion. Thus, the data acquired for 7 supported the presence of two
tetrazole rings being present.
Alkylation of 7 was then carried out in the presence of base, using ethyl bromoacetate. On
1
analysis of the crude residue by H NMR spectroscopy, the spectrum initially appeared
complicated. However, it could be deduced that there were three products present in the
mixture, most plausibly the N-1, N-1’ (1), N-1, N-2’ (2) and N-2, N-2’ (3) substituted
regioisomers. The crude mixture was separated by flash column chromatography using a
gradient system. The separated fractions were analysed by NMR spectroscopy and the 13C
NMR spectra of the compounds revealed the substitution on the tetrazole rings. The first
product to elute was the N-1, N-1’ regioisomer (1), as indicated by the single C-5 resonance
peak at 152.2 ppm. The second product to elute was the N-1, N-2’ regioisomer (2) as
indicated by the additional 13C resonances present which supported the presence of
asymmetry in the molecule. The 13C NMR spectrum exhibited a C-5 resonance at 164.1 ppm
1
for the N-2 substituted ring and at 151.4 ppm for the N-1 substituted ring. The H NMR
4

spectrum also clearly showed that this was the case (Figure 1). The spectrum showed the
same trends as seen in previous alkylated tetrazoles, with the N-1 methylene group being
more deshielded in the N-1 substituted tetrazoles than the N-2 substituted tetrazole rings
[21,26-30]. The final product that eluted was the N-2, N-2’ regioisomer (3) which was
confirmed by 13C NMR spectroscopy where the single C-5 resonance for the tetrazole ring
resonated at 164.8 ppm.
h
g
f
b
e
d
f
h
a
c
g
c
d
b
e
a
1
Figure 1. The H NMR spectra, obtained in CDCl3, of 1 (blue), 2 (green) and 3 (red).
Relevant signals are labelled for 1.
These ligands would possess distinctive advantages in that they could provide multiple
coordination sites by virtue of possessing pyridine and tetrazole N donor atoms and
carboxylate O donor atoms. Furthermore, the carboxylate groups could allow for an
expansion in dimensionality and the relatively long spacer and the two pyridyl groups can
rotate along its C−C bonds to form nine main configurations, thereby enabling the ligand to
adopt versatile coordination modes and conformations [18].
X-ray structures of ligand 1 (orthorhombic and triclinic polymorphs)
Single crystals of 1 were grown and analysed by X-ray crystallography (Figures 2 and 3) and
yielded two polymorphs, one in space group Pna21 (two molecules in the asymmetric unit)
5

and the second in triclinic P-1 (No. 2). The plate-like crystal of the Pna21 polymorph was
obtained from the mother liquor whilst the block-like crystal of the P-1 polymorph was
obtained from a methanol solution of 1 with zinc chloride. No zinc complex was obtained
from the latter reaction. Molecules A and B of 1 in the Pna21 structure are similar in
conformation, but there are small but significant differences between the two e.g. the
C6…C8(A/B) distances are 9.054(16) and 8.915(15) Å, respectively, and the RMS fit
between the non-hydrogen atoms in both molecules os 0.096 Å. The ester groups are almost
orthogonal to the plane of the tetrazole rings. However, the notable feature in the molecules is
that the propyl chain is essentially co-planar with one of the pyridyl tetrazole units in both
molecules A and B. The other pyridyl tetrazole is almost perpendicular to this 11-atom plane
[89.88(15)° and 89.36(15)°]. This is a structural feature that may provide a building
block/template for distinct structural motifs and architectures and especially as their diacids
or as salts where the acid and/or salt moieties can be utilised in hydrogen bonding and
aggregation [31].12 There are no classical intermolecular hydrogen bonds present in the
packing diagrams of either crystal structure although there are weak interactions (C-H…O/N
type with C4A...O3A = 3.215(13) Å as the most noteable along the b-axis direction) and
several contacts.
Figure 2. Views of the molecular structures of molecules A and B in 1 (in Pna21); views of
conformational bending in the molecule A as ORTEP and CPK diagrams and V-shaped
stacking of molecule A along (010).
6

Figure 3. Views of the molecular structure of 1 (triclinic polymorph) as ORTEP and CPK
diagrams, and a view of the conformational bending in the molecule.
The triclinic polymorph adopts a distinctly different conformation to that noted for both of
the molecules in the orthorhombic case and also exhibits disorder in one of the ester groups.
In the triclinic polymorph, the pyridyl tetrazole units are oriented at an angle of 54.84(6)°
which is ca. 35° different to the orthogonal planes of molecules A and B in the orthorhombic
case. The isolation of two polymorphic forms is not surprising given that the ligands are
conformationally flexible and the propylene bridge acts as a flexible hinge. The occurence of
polymorphism in organic structures has been extensively commented on [32-34]. There are
some weak interactions in the crystal structure but no strong classical hydrogen bonds in a
structure lacking strong donors but with strong and weak acceptor groups.. There is a close
offset π…π contact in the structure with C13…C13i = 3.265(4) Å (i = 2-x,-y,2-z), some 0.13
Å shorter than the interplanar spacing in graphite as well as an intramolecular C5…N32
interaction.
Metal Complexation Reactions
Reactions of 1 with either CuCl2.2H2O, Cu(NO3)2 or Cu(OAc)2 in MeOH resulted in no
reaction and the attainment of unreacted ligand. Reaction of 1 with CuCl2.2H2O in EtOH,
however, did yield a green precipitate, but only when the reaction was heated. There is not
any obvious reason why there was no reaction between the ligand and the copper salts at
7

room temperature, as there are many CPs in the literature with trimethylene linkers within
ligands which have been obtained through room temperature stirring. This green solid (8) was
filtered, dried and analysed by IR spectroscopy, elemental analysis and magnetic moment
measurements. Room temperature magnetic moment measurements yielded a typical µeff
value of 1.9 B.M. The IR spectrum of 8 displayed frequency shifts when compared to the
starting ligand 1. Complexation to the ester moiety was not alluded to as there were no
significant shifts observed for the ν(C=O) vibration. Complexation to the pyridine and
tetrazole moieties was suggested as shifts in the heterocyclic frequencies were observed.
Elemental analysis alluded to a 1:1 metal to ligand composition. The material was very
insoluble which led us to believe that the material was polymeric. A structure was proposed
which can be seen in Figure 4. It was proposed that the Cu(II) ion was in an octahedral
environment, coordinated by two pyridine and tetrazole N-1 nitrogens and two chloride
anions. The Cu(II) ion was proposed to connect two different ligands, propagating a 1-D
coordination polymer.
O
O
O
O
N
N
N
N
N
N
N
N
Cl
N
N
Cu
Cl
n
Figure 4. Proposed structure of a subunit of coordination polymer 8.
Reacting 2 with CuCl2.2H2O in EtOH resulted in a dark green precipitate (9) forming in
solution. The solid was analysed by IR spectroscopy and compared to that of the starting
material. The ν(C=O) vibrational mode had shifted to a lower wavenumber and was now
positioned at 1743 cm-1 compared to 1750 cm-1 which indicated that no complexation was
occurring to the ester moiety but that complexation to the ligand had occurred. Shifts in the
heterocyclic stretches were observed which indicated that there were interactions with the
heterocyclic nitrogens and the metal atom. Elemental analysis suggested that the solid had a
2:1 metal to ligand ratio. The solid was insoluble in most solvents, so it was proposed that the
material was polymeric. With this in mind, a structure was tentatively assigned to the solid
and this structure can be seen in Figure 5. The structure consists of dichloro-bridged subunits
with each Cu(II) centre possessing a square pyramidal geometry. The polymeric chain
8

propagates through coordination of another subunit to the coordinatively unsaturated Cu(II)
centre, shown in Figure 5. Elemental analysis correlated well with the calculated values for
this structure, and chloride bridging has been observed before in pyridyl-tetrazole complexes
[19,35,36].
Figure 5. Proposed structure of 9, which could be a subunit of a polymeric chain.
Conclusions
In previous papers, carboxylate functionalised pyridyl tetrazoles were employed in the
synthesis of CPs with the result of forming 1-D CPs or isolated bimetallic units [19-21]. The
work outlined in this paper aimed to increase the dimensionality of these polymers by
utilising carboxylate functionalised bis-tetrazole systems, which were linked via a flexible
propyl chain backbone, allowing an examination of how flexibility of the backbone affects
the final structures. Elucidation of the CPs formed in experiments utilising trimethylene
linked pyridyl tetrazoles proved difficult. Crystalline samples were difficult to obtain which
hampered elucidation of the structures by X-ray crystallography. Although dramatic
advancement has been made, research into CPs based on flexible ligands is still at an early
stage of development. Further research efforts are indispensable to fully understand the
structural features and the structure-property relationship in framework materials, in order to
establish reliable strategies for the design and synthesis of targeted flexible based CPs.
Experimental
Instrumentation
1H and 13C NMR (δ ppm; J Hz) spectra were recorded on a Bruker Avance 300 MHz NMR
spectrometer using saturated CDCl3 or d6-DMSO solutions with a SiMe4 reference, with
9

resolutions of 0.18 Hz and 0.01 ppm, respectively. Infrared spectra (cm-1) were recorded as
KBr discs or liquid films between NaCl plates using a Perkin Elmer System 2000 FT-IR
spectrometer. Solution UV-Vis spectra were recorded using HPLC grade solvents using a
Unicam UV 540 spectrometer. Melting point analyses were carried out using a Stewart
Scientific SMP 1 melting point apparatus and are uncorrected. Electrospray (ESI) mass
spectra were collected on an Agilent Technologies 6410 Time of Flight LC/MS. Compounds
were dissolved in acetonitrile:water (1:1) solutions containing 0.1% formic acid, unless
otherwise stated. The interpretation of mass spectra was made with the help of the program
“Agilent Masshunter Workstation Software”. Microanalyses were carried out at the
Microanalytical Laboratory of the National University of Ireland Maynooth, using a Thermo
Finnigan Elementary Analyzer Flash EA 1112. The results were analysed using Eager 300
software. Starting materials were commercially obtained and used without further
purification. Solvents used were of HPLC grade. Compounds 5 [22] and 6 [18] have been
previously reported.
Caution! Nitrogen-rich compounds such as tetrazole derivatives are used as components for
explosive mixtures [37]. 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.
Synthesis of 1,3-bis(4-pyridyl-3-cyano)propane (6)
To a suspension of 5 (0.20 g, 0.87 mmol) in anhydrous DMF (20 mL) was added Zn(CN)2
(0.31 g, 2.61 mmol). The mixture was stirred at room temperature under argon for 30 min
before DMCC (0.32 mL, 3.47 mmol) was added dropwise at 0 °C over 1 h. The reaction was
then brought up to room temperature and stirred for 24 h. 10% aqueous K2CO3 (10 mL) was
added to the solution and stirred for 15 min. The solution was then extracted with DCM (3 ×
10 mL) and the combined organic extracts were washed with brine and dried over MgSO4.
After removing the insoluble solids by filtration the volatiles were removed under reduced
pressure to yield a brown oil. This crude product was passed through a silica plug using
EtOAc and Pet. ether (3:1) as the eluent and recrystallised from a mixture of DCM and Pet.
ether to yield a white crystalline solid (6, 0.07 g, 34%). m.p. 120-122 °C, IR (KBr, cm-1):
3030, 2921, 2237, 1597, 1552, 1462, 1405, 1384, 1261, 1147, 1086, 1069, 1022, 991, 902,
840, 758; δH NMR (300 MHz, CDCl3): 8.63 (d, J=5.0 Hz, 2H, pyr-H), 7.54 (s, 2H, pyr-H),
7.34 (d, J=5.0 Hz, 2H, pyr-H), 2.75 (t, J=7.8 Hz, 4H, pyr-CH2), 2.03 (quin, J=7.8 Hz, 2 H,
10

CH2); δC NMR (75 MHz, CDCl3): 151.6, 151.2, 134.2, 128.5, 126.8, 117.2, 34.2, 30.1; ESI
(HRMS) (m/z) calcd for C15H13N4 [M+H]⁺ 249.1135, found: 249.1140. The NMR and IR
data are in agreement with the reported literature values [18].
Synthesis of 1,3-bis(2-(2H-tetrazol-5-yl)pyridin-4-yl)propane (7)
The compound 6 (0.83 g, 3.34 mmol), NaN3 (0.48 g, 7.35 mmol), NH4Cl (0.39 g, 7.35 mmol)
and LiCl (0.07 g, 1.67 mmol) were heated to reflux in DMF (20 mL) for 10 h. The inorganic
solids were removed by filtration and the filtrate was concentrated under reduced pressure.
The residue was then redissolved in deionised H2O (20 mL) and acidified with 1 M HCl until
precipitation ceased. The precipitate was filtered off and washed with deionised H2O and air
dried. Yellow solid (7, 1.04 g, 93%). m.p. 220-223 °C, IR (KBr, cm-1): 3386, 3042, 2874,
2777, 1597, 1633, 1613, 1562, 1493, 1484, 1406, 1384, 1261, 1149, 1086, 1069, 1024, 1000,
846, 760; δH NMR (300 MHz, d6-DMSO): 8.66 (d, J=5.1 Hz, 2H, pyr-H), 8.09 (s, 2H, pyr-
H), 7.50 (d, J=5.1 Hz, 2H, pyr-H), 2.81 (t, J=7.8 Hz, 4H, pyr-CH2), 2.03 (quin, J=7.8 Hz, 2H,
CH2); δC NMR (75 MHz, d6-DMSO): 154.9, 152.9, 149.8, 143.7, 126.0, 122.5, 33.7, 29.9;
ESI (HRMS) (m/z) calcd for C15H15N10 [M+H]⁺ 335.1476, found: 335.1476.
Synthesis of 1, 2 and 3
The compound 7 (0.90 g, 2.69 mmol) and K2CO3 (0.78 g, 5.66 mmol) were heated to reflux
in MeCN (10mL) for 30 min after which time ethyl bromoacetate (0.62 mL, 6.66 mmol) was
added. The reaction was then further heated under reflux for 24 h. The solution was then
cooled and filtered and the filtrate was concentrated under reduced pressure. The remaining
brown oil consisted of three regioisomers which were separated by column chromatography,
starting with 2:1 EtOAc:Pet. Ether and finishing with 100% EtOAc.
Diethyl 2,2'-(5,5'-(4,4'-(propane-1,3-diyl)bis(pyridine-4,2-diyl))bis(1H-tetrazole-5,1-diyl))-
diacetate (1)
Yellow solid (0.14 g, 10%). m.p. 116-119 °C, IR (KBr, cm-1): 2989, 2960, 1748, 1603, 1537,
1479, 1462, 1431, 1403, 1379, 1298, 1230, 1118, 1030, 993, 852; δH NMR (300 MHz,
CDCl3): 8.54 (d, J=5.0 Hz, 2H, pyr-H), 8.27 (s, 2H, pyr-H), 7.26 (d, J=5.0 Hz, 2H, pyr-H),
5.74 (s, 4H, CH2-tet), 4.20 (q, J=7.1 Hz, 4H, OCH2), 2.80 (t, J=7.7 Hz, 4H, pyr-CH2), 2.11
(quin, J=7.7 Hz, 2H, CH2), 1.20 (t, J=7.1 Hz, 6H, CH3); δC NMR (75 MHz, CDCl3): 166.0,
11

152.2, 152.2, 149.3, 144.5, 125.6, 124.0, 62.1, 51.1, 34.5, 30.3, 14.0; ESI (HRMS) (m/z)
calcd for C23H27N10O4 [M+H]⁺ 507.2211, found: 507.2232.
Ethyl 2-(5-(4-(3-(2-(1-(2-ethoxy-2-oxoethyl)-1H-tetrazol-5-yl)pyridin-4-yl)propyl)pyridin-2-
yl)-2H-tetrazol-2-yl)acetate (2)
Yellow solid (0.21 g, 16%). m.p. 58-60 °C, IR (KBr, cm-1): 2930, 1750, 1733, 1606, 1560,
1430, 1387, 1223, 1118, 1025, 854, 793; δH NMR (300 MHz, CDCl3): 8.68 (d, J=4.8 Hz, 1H,
pyr-H), 8.54 (d, J=5.1 Hz, 1H, pyr-H), 8.29 (s, 1H, pyr-H), 8.11 (s, 1H, pyr-H), 7.24-7.27 (m,
2H, pyr-H), 5.74 (s, 2H, tet-CH2), 5.50 (s, 2H, tet-CH2), 4.28 (q, J=7.2 Hz, 2H, OCH2), 4.19
(q, J=7.2 Hz, 2H, OCH2), 2.77-2.82 (m, 4H, pyr-CH2), 2.07-2.17 (m, 2H, CH2), 1.29 (t, J=7.2
Hz, 3H,CH3), 1.19 (t, J=7.2 Hz, 3H, CH3); δC NMR (75 MHz, CDCl3): 165.0, 164.1, 163.8,
151.4, 151.2, 150.6, 149.4, 148.2, 145.5, 143.4, 124.6, 124.1, 123.0, 121.5, 61.7, 61.0, 52.5,
50.1, 33.5, 29.3, 13.1; ESI (HRMS) (m/z) calcd for C23H27N10O4 [M+H]⁺ 507.2211, found:
507.2229.
Diethyl 2,2'-(5,5'-(4,4'-(propane-1,3-diyl)bis(pyridine-4,2-diyl))bis(2H-tetrazole-5,2-diyl))-
diacetate (3)
Orange solid (0.38 g, 28%). m.p. 138-141 °C, IR (KBr, cm-1): 2999, 2956, 1743, 1632, 1607,
1559, 1523, 1479, 1419, 1387, 1370, 1348, 1222, 1053, 1021, 994, 840; δH NMR (300 MHz,
CDCl3): 8.68 (d, J=5.1 Hz, 2H, pyr-H), 8.13 (s, 2H, pyr-H), 7.24 (d, J=5.1 Hz, 2H, pyr-H),
5.50 (s, 4H, CH2-tet), 4.28 (q, J=7.1 Hz, 4H, OCH2), 2.80 (t, J=7.7 Hz, 4H, pyr-CH2), 2.13
(quin, J=7.7 Hz, 2H, CH2), 1.28 (t, J=7.1 Hz, 6H, CH3); δC NMR (75 MHz, CDCl3): 165.0,
164.8, 151.8, 150.4, 146.5, 125.1, 122.6, 62.8, 53.5, 34.6, 30.5, 14.0; ESI (HRMS) (m/z)
calcd for C23H27N10O4 [M+H]⁺ 507.2211, found: 507.2198.
Metal Complexation Reactions with 1 and 2
Synthesis of [Cu(1)Cl2]n (8)
The ligand 1 (0.04 g, 0.08 mmol) was dissolved in EtOH (15 mL). CuCl2.2H2O (0.01 g, 0.08
mmol) in EtOH (5 mL) was added to the solution. The resulting mixture was heated to reflux
12

for 2 h, cooled to room temperature and filtered. Green solid (8, 0.03 g, 59%).
C23H26Cl2CuN10O4: calcd. C 43.10, H 4.09, N 21.85%; found C 43.85, H 4.11, N 21.99%. IR
(KBr): ν = 3414, 2961, 1747, 1637, 1622, 1554, 1481, 1490, 1459, 1430, 1401, 1376, 1342,
1296, 1249, 1219, 1116, 1013, 867, 852, 623 cm-1. Magnetic moment: 1.92 B.M.
Synthesis of [Cu2(2)Cl4]n (9)
The ligand 2 (0.10 g, 0.20 mmol) was dissolved in EtOH (20 mL). CuCl2.2H2O (0.03 g, 0.20
mmol) in EtOH (5 mL) was added to the solution. The resulting mixture was heated to reflux
for 2 h, cooled to room temperature and filtered. Green solid (9, 0.07 g, 92%).
C23H26Cl4Cu2N10O4: calcd. C 35.63 , H 3.38, N 18.06%; found C 35.98, H 3.69, N 18.09%.
IR (KBr): ν = 3440, 2982, 2938, 1750, 1622, 1565, 1475, 1440, 1397, 1372, 1347, 1262,
1220, 1063, 1019, 874, 853, 771, 580 cm-1. Magnetic moment: 1.78 B.M.
X-ray Structure Determination
Single crystal X-ray data collection, data reduction,[38] structure solution and
refinement[39,40] are as described previously [34,41]. Selected crystallographic and
structural information are available on the Cambridge Structural Database. Molecular and
hydrogen bonding diagrams (Figure 2) were generated using ORTEP (with displacement
ellipsoids drawn at the 30% probability level) and with atoms as their van der Waals spheres
[42]. CCDC reference codes 1411580-1411581 and copies available, e-
mail:deposit@ccdc.cam.ac.uk).
Acknowledgements
We are thankful to Maynooth University and to the Irish Research Council for financial
assistance through the provision of a John & Pat Hume Fellowship and a Postgraduate
Scholarship, respectively (US). JFG thanks Dublin City University for grants in aid of
research and facilitating a sabbatical year at the University of Lorraine, Nancy, France.
References
1.
R. Robson, Dalton Trans. (2008) 5113.
13

2.
3.
4.
5.
Y. Cui, Y. Yue, G. Qian, B. Chen, Chem. Rev. 112 (2012) 1126.
A. Bétard, R. A. Fischer, Chem. Rev. 112 (2012) 1055.
H. Wu, Q. Gong, D. H. Olson, J. Li, Chem. Rev. 112 (2012) 836.
P. Horcajada, R. Gref, T. Baati, P. K. Allan, G. Maurin, P. Couvreur, G. Férey, R. E.
Morris, C. Serre, Chem. Rev. 112 (2012) 1232.
6.
L. E. Kreno, K. Leong, O. K. Farha, M. Allendorf, R. P. Van Duyne, J. T. Hupp,
Chem. Rev. 112 (2012) 1105.
7.
8.
C. Petit, T. J. Bandosz, Dalton Trans. 41 (2012) 4027.
P. K. Allan, P. S. Wheatley, D. Aldous, M. I. Mohideen, C. Tang, J. A. Hriljac, I. L.
Megson, K. W. Chapman, G. De Weireld, S. Vaesen, R. E. Morris, Dalton Trans. 41
(2012) 4060.
9.
F. G. Cirujano, F. X. Llabrés i Xamena, A. Corma, Dalton Trans. 41 (2012) 4249.
L. Sun, L. Ma, J.-B. Cai, L. Liang, H. Deng, CrystEngComm 14 (2012) 890.
X. Wang, Y. Wang, G. Liu, A. Tian, J. Zhang, H. Lin, Dalton Trans. 40 (2011) 9299.
A. Tian, X. Lin, J. Ying, J. Zhang, H. Lin, G. Liu, D. Zhao, N. Li, X. Wang, Dalton
Trans. 42 (2013) 9809.
10.
11.
12.
13.
14.
15.
16.
17.
X. Wang, N. Li, A, Tian, J. Ying, G. Liu, H. Lin, J. Zhang, Y. Yang, Dalton Trans. 42
(2013) 14856.
X.-L. Wang, N. Li, A.-X. Tian, J. Ying, T.-J. Li, X.-L. Lin, J. Luan, Y. Yang, Inorg.
Chem. 53 (2014) 7118.
M. J. Plater, M. R. S. J. Foreman, T. Gelbrich, S. J. Coles, M. B. Hursthouse, Dalton
Trans. (2000) 3065.
X.-J. Feng, W. Yao, M.-F. Luo, R.-Y. Ma, H.-W. Xie, Y. Yu, Y.-G. Li, E.-B. Wang,
Inorg. Chim. Acta 368 (2011) 29.
L.-L. Liu, C.-X. Yu, Y. Zhou, J. Sun, P.-P. Meng, D. Liu, R.-J. Sa, Inorg. Chem.
Commun. 40 (2014) 194.
18.
19.
D. Deng, L, Liu, B.-M. Ji, G. Yin, C. Du, Cryst. Growth Des. 12 (2012) 5338.
U. Sheridan, J. McGinley, J. F. Gallagher, M. J. Bjerrum, A. Fleming, F. Kelleher,
Inorg. Chim. Acta 421 (2014) 200.
20.
21.
22.
U. Sheridan, J. F. Gallagher, A. Philippidis, J. McGinley, Inorg. Chim. Acta 432
(2015) 50.
U. Sheridan, J. F. Gallagher, E. Fadda, M. J. Bjerrum, J. McGinley, Supramol. Chem.
(2016) DOI:10.1080/10610278.2015.1123261.
L.-P. Zhang, W.-J. Lu, T. C. W. Mak, Chem. Commun. (2003) 2830.
14

23.
24.
25.
H. H. Wasserman, J. L. Ives, J. Org. Chem. 50 (1985) 3573.
L. De Vries, J. Am. Chem. Soc. 100 (1978) 926.
R. W. Alder, M. E. Blake, S. Bufali, C. P. Butts, A. G. Orpen, J. Schutz, S. J.
Williams, J. Chem. Soc., Perkin Trans. 1 (2001) 1586.
R. N. Butler, A. F. M. Fleming, J. Heterocycl. Chem. 34 (1997) 691.
P. A. Bethel, M. S. Hill, M. F. Mahon, K. C. Molloy, J. Chem. Soc., Perkin Trans. 1
(1999) 3507.
26.
27.
28.
29.
30.
A. Fleming, F. Kelleher, M. F. Mahon, J. McGinley, V. Prajapati, Tetrahedron 61
(2005) 7002.
A. D. Bond, A. Fleming, J. Gaire, F. Kelleher, J. McGinley, V. McKee, Tetrahedron
65 (2009) 7942.
A. Fleming, J. Gaire, F. Kelleher, J. McGinley, V. McKee, Tetrahedron 67 (2011)
3260.
31.
32.
33.
34.
35.
J. F. Gallagher, S. Alley, M. Brosnan, A. J. Lough, Acta Crystallogr. B66 (2010) 196.
J. Bernstein, Cryst. Growth Des. 11 (2011) 632.
H. G. Brittain, J. Pharm. Sci. 100 (2011) 1260.
P. Mocilac, K. Donnelly, J. F. Gallagher, Acta Crystallogr. B68 (2012) 189.
U. Sheridan, J. McGinley, J. F. Gallagher, A. Fleming, F. Kelleher, Polyhedron 59
(2013) 8.
36.
37.
38.
A. D. Bond, A. Fleming, J. Gaire, F. Kelleher, J. McGinley, V. McKee, U. Sheridan,
Polyhedron 33 (2012) 289.
R. N. Butler in Comprehensive Heterocyclic Chemistry II (Eds.: A. R. Katritzky, C.
W. Rees, E. F. V. Scriven), Permagon, Oxford, 1996, 4, pp. 621.
Oxford Diffraction Ltd. ABSFAC and CrysAlisPro CCD/RED, Version 1.171.33.55,
Oxford Diffraction, Abingdon, Oxfordshire, U.K.
39.
40.
41.
42.
G. M. Sheldrick, Acta Crystallogr. A64 (2008) 11.
P. McArdle, J. Appl. Cryst. 28 (1995) 65.
P. Mocilac, M. Tallon, A. J. Lough, J. F. Gallagher, CrystEngComm. 12 (2010) 3080.
C. F. Macrae, I. J. Bruno, J. A. Chisholm, P. R. Edgington, P. McCabe, E. Pidcock, L.
Rodriguez-Monge, R. Taylor, J. van de Streek, P. A. Wood, J. Appl. Cryst. 41 (2008)
466.
15

New flexible bis-pyridyltetrazole ligands for use in coordination polymer
formation: synthesis and structural studies.
U. Sheridan, J. F. Gallagher, J. McGinley.
Three novel bis-tetrazole ligands containing carboxylate functional groups on the tetrazole
rings and a flexible (CH2)3 linker unit, for the construction of coordination polymers when
coordinated to copper(II) ions, were synthesised and structurally characterised.
Polymorphism was exhibited by one of the ligands.
16

New flexible bis-pyridyltetrazole ligands for use in coordination polymer
formation: synthesis and structural studies.
U. Sheridan, J. F. Gallagher, J. McGinley.
17

Highlights
•
Three novel bis-tetrazole ligands containing carboxylate functional groups on the
tetrazole rings and a flexible (CH2)3 linker unit, for the construction of coordination
polymers, were synthesised and structurally characterised.
•
•
Formation of coordination polymers and metal-organic frameworks.
Polymorphism was exhibited by one of the ligands.
18