New binuclear copper(ii) coordination polymer based on mixed pyrazolic and oxalate ligands: Structural characterization and mechanical properties

Article abstract of DOI:10.1039/c5ra04028k

A new inorganic-organic coordination polymer based on a copper(ii) binuclear complex coordinated with pyrazole (L1), 1-(hydroxymethyl)pyrazole) (L2) and oxalate (Ox) ligands has been unexpectedly obtained. The crystal structure of this coordination polymer has been unequivocally determined from single crystal X-ray diffraction. One copper(ii) center (Cu1) is four-coordinated with two nitrogens (N2, L1 and N3, L2), one oxygen (O1, L1) and one chlorine atom, while the other copper(ii) nucleus (Cu2) is five-coordinated with one nitrogen (N1, L1), three oxygens (O1, L2; O2 and O3, Ox) and one chlorine atom, giving slightly distorted square-planar and square-pyramidal geometries, respectively. To the best of our knowledge, such coordination environments have never been previously observed to coexist in the same structure. The terminal chlorine (Cl1) forms the connecting bridge between the planar binuclear [Cu₂Cl(Ox)_0.5(L1)(L2)]_n units ending in an attractive structural framework. An extended layered structure staggered along the b-axis is observed in the supramolecular view. Nanoindentation experiments were carried out and relevant mechanical parameters such as hardness, Young's modulus, indentation energies and elastic recovery were determined. Additionally, a comparative analysis between the supramolecular structure and the mechanical properties is reported. This journal is

Full text of DOI:10.1039/c5ra04028k

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New binuclear copper(II) coordination polymer
based on mixed pyrazolic and oxalate ligands:
structural characterization and mechanical
properties†
Cite this: RSC Adv., 2015, 5, 32369
Received 6th March 2015
Accepted 23rd March 2015
a
b
c
d
Adaris M. Lopez Marzo,‡ Miguel Guerrero,‡* Teresa Calvet, Merce Font-Bardia,
´
`
DOI: 10.1039/c5ra04028k
b
b
a
e
Eva Pellicer, Maria Dolors Baro, Josefina Pons* and Jordi Sort
´
www.rsc.org/advances
A new inorganic–organic coordination polymer based on a cop-
per(II) binuclear complex coordinated with pyrazole (L1), 1-
1
. Introduction
(
hydroxymethyl)pyrazole) (L2) and oxalate (Ox) ligands has The design of hybrid metal–organic materials (MOMs), which is
been unexpectedly obtained. The crystal structure of this coor- a burgeoning topic in the crystal engineering domain, is
dination polymer has been unequivocally determined from single nowadays one of the fastest growing areas in the elds of
1,2
crystal X-ray diffraction. One copper(II) center (Cu1) is four- Materials Science and Supramolecular Chemistry. This new
coordinated with two nitrogens (N2, L1 and N3, L2), one oxygen class of materials attracts signicant attention due to their
(
O1, L1) and one chlorine atom, while the other copper(II) nucleus enormous chemical, structural and topological diversity and
Cu2) is five-coordinated with one nitrogen (N1, L1), three oxygens due to their promising applications, including catalysis, gas
O1, L2; O2 and O3, Ox) and one chlorine atom, giving slightly storage, magnetism, luminescence, drug delivery, sensing or
(
(
3–6
distorted square-planar and square-pyramidal geometries, host/guest inclusion.
Interestingly, such hybrid systems
respectively. To the best of our knowledge, such coordination present strong covalent and/or intermolecular bonds to yield 1D
environments have never been previously observed to coexist in chains, 2D layers or 3D frameworks, which incorporate 3d-
the same structure. The terminal chlorine (Cl1) forms the con- metal ions and bridging ligands at the same time. The
necting bridge between the planar binuclear [Cu
2
Cl(Ox)0.5
-
synergy between the organic and inorganic components brings
(
L1)(L2)] units ending in an attractive structural framework. An about an outstanding combination of properties that are not
n
extended layered structure staggered along the b-axis is observed common in purely inorganic and organic systems alone.
in the supramolecular view. Nanoindentation experiments were Furthermore, the use of different ligands with similar coordi-
carried out and relevant mechanical parameters such as hardness, nation abilities but different exibilities as building blocks
Young’s modulus, indentation energies and elastic recovery were could be considered as a smart procedure for obtaining periodic
7–9
determined. Additionally, a comparative analysis between the frameworks.
supramolecular structure and the mechanical properties is
In contrast to the large number of recent publications
describing the synthesis and characterization of MOM struc-
tures, studies focusing on understanding the mechanical
properties of these hybrid materials are still scarce due to the
reported.
10
a
lack of proper measurement tools. Nonetheless, recent
Departament de Qu ´ı mica, Universitat Aut `o noma de Barcelona, E-08193 Bellaterra,
advances in this eld are shedding some light on the funda-
Departament de F ´ı sica, Universitat Aut `o noma de Barcelona, E-08193 Bellaterra, mental structure–mechanical property relationships, which are
Spain
b
Spain. E-mail: Miguel.Guerrero@uab.cat; Tel: +34 93 581 1401
needed for optimized design and successful performance in
diverse technological applications. Nanoindentation has
c
11
Cristal lograa, Mineralogia i Dip `o sits Minerals, Universitat de Barcelona, 08028-
Barcelona, Spain
emerged as a widely adopted technique for measuring the
mechanical properties of different kinds of materials, such as
ceramics, organics, inorganics and MOMs at the nanoscale
d
Unitat de Difracci ´o de RX, Centres Cient ´ı cs i Tecnol `o gics de la Universitat de
Barcelona (CCiTUB), Universitat de Barcelona, 08028-Barcelona, Spain
e
Instituci ´o Catalana de Recerca i Estudis Avançats (ICREA), Departament de F ´ı sica,
12
`
onoma de Barcelona, E-08193 Bellaterra, Spain
level. This technique, where load (P) and penetration depth (h)
Universitat Aut
†
Electronic supplementary information (ESI) available: X-ray crystallographic le are measured at high resolution, enables not only the evalua-
in CIF format for the structure determination of the polymeric Cu(II) complex is tion of the mechanical properties but also the correlation
enclosed. CCDC 1036962. For ESI and crystallographic data in CIF or other
between the measured responses and the underlying structural
electronic format see DOI: 10.1039/c5ra04028k
13
features and intermolecular interactions.
This makes
‡
These authors have contributed equally to this work.
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nanoindentation a complementary technique to structural KBr pellets. Conductivity measurements were performed at
ꢀ3
analysis for the development of novel smart materials. In room temperature in 10 M methanol solutions, employing a
general, MOMs have been reported to be mechanically harder CyberScan CON 500 (Eutech instrument) conductimeter. Elec-
than inorganic polymers, while oen exhibiting lower density tronic spectra were collected on a Kontron-Uvikon 860 in
14
values, similar to those of metallic foams.
methanol, between 750 and 350 nm.
In this paper we present for the rst time an inorganic–
organic polymeric complex containing two different copper(II)
cores with mixed oxalate ion and pyrazolic ligands. This new
2.3 Mechanical properties
coordination polymer presents a 2D network along the b-axis The mechanical properties (hardness, reduced elastic modulus
formed by layers of stepped chains interconnected by bridging and elastic recovery) were evaluated by means of nano-
chlorine atoms (Cl1) through the Cu(1)–Cl(1)–Cu(2) bond. The indentation, using a UMIS device from Fischer-Cripps Labora-
hardness, Young’s modulus, indentation energies and elastic tories, equipped with a Berkovich pyramidal-shaped diamond
recovery of this Cu(II) supramolecular inorganic/organic tip, operating in the load control mode. The nanoindentation
framework have been investigated by means of the nano- tests were performed perpendicular to the planar base (100) of
indentation technique and are compared with similar examples the crystal sheet. Other orientations were not possible due to
from the literature.
the crystal exfoliation of the material. Indentations using
maximum applied load values ranging from 1 to 5 mN were
applied to ensure that the maximum penetration depth was
much smaller than the crystal thickness. The indentations were
separated from each other by 20 mm, to ensure that the stress
2. Experimental part
2.1 Reagents and synthesis

elds underneath the indents did not overlap with each other.
All reagents were purchased from Sigma-Aldrich and used as
received without further purication. 1-(Hydroxymetyl)pyrazole
The thermal dri during nanoindentation was lower than 0.05
ꢀ1
15
nm s . Proper corrections for the contact area (calibrated with
a fused quartz specimen), instrument compliance, and initial
penetration depth (a pre-contact load of 0.02 mN was used) were
applied. The hardness (H) and reduced elastic modulus (E
values were derived from the load–displacement curves using
(
L2) was synthesized as described previously.
In order to obtain the copper(II) based coordination complex,
pyrazole (L1) and L2 ligands were mixed with CuCl $2H O
2
2
r
)
(
1 : 1 : 2 molar ratio) for 18 h using ethanol as the solvent under
aerobic conditions. The pH was adjusted to 9 with ammonium
hydroxide solution (30% NH ). The green powder obtained as
16
the method of Oliver and Pharr. From the initial unloading
slope, the contact stiffness, S, was determined as:
3
the product was washed via vacuum ltration with a few milli-
liters of cold diethyl ether and dried at room temperature.
Minority fraction and translucent blue prism-like monocrystals
suitable for X-ray analysis were obtained through the crystalli-
zation of the synthesis product using an ethanol–dichloro-
methane (1 : 1) diffusion technique.
dP
S ¼ dh
(1)
The reduced Young’s modulus was evaluated based on its
relationship with the contact area, A, and S:
pffiffiffiffi
2
S ¼ b pffiffiffi E
A
(2)
2
.2 Characterization techniques
For X-ray crystallographic analysis, a translucent blue prism-like
r
p
where b is the King’s factor, which depends on the geometry of
ꢀ
1
specimen of C H ClCu N O (M ¼ 370.71 g mol ), 0.145 mm
8
8
2
4
3
w
17
the indenter (b ¼ 1.034 for a Berkovich indenter). The reduced
ꢁ
0.252 mm ꢁ 0.290 mm, was used. X-ray intensity data were
Young’s modulus takes into account the elastic displacements
that occur in both the specimen, with Young’s modulus E and
Poisson’s ratio n, and the diamond indenter, with elastic
constants E and n (for diamond, E ¼ 1140 GPa and n ¼ 0.07):
measured on a D8 Venture system equipped with a multilayer
˚
monochromator and a Mo microfocus (l ¼ 0.71073 A). A total of
6
82 frames were collected. The total exposure time was 1.89
i
i
i
i
hours. The frames were integrated with the Bruker SAINT
Soware Package using a narrow-frame algorithm. The inte-
gration of the data using a monoclinic unit cell yielded a total of
2
2
1
1 ꢀ v
1 ꢀ v
i
¼
þ
(3)
E
r
E
E
i
3 166 reections, to a maximum q angle of 26.37 (0.80 A˚
ꢂ
1
resolution), out of which 2283 were independent (average
The hardness was calculated from the following expression:
redundancy 5767, completeness ¼ 99.8%, Rint ¼ 3.44%, Rsig
¼
2
P
max
2
.24%) and 2121 (92.90%) were greater than 2s(F ). Elemental
H ¼
(4)
A
analysis (C, H, N) of the monocrystal-like specimen was carried
out on a Carlo Erba CHNS EA-1108 instrument, separated by a where Pmax is the maximum load applied during nano-
chromatographic column and thermoconductivity detector. indentation. Finally, the elastic recovery was evaluated as the
Copper elemental analysis was carried out using inductively ratio between the elastic and the total (plastic + elastic) energies
coupled plasma mass spectrometry (ICPMS) with an Agilent during nanoindentation, W /Wtot. The values of Wel were
el
7
500ce model system. Infrared (IR) spectra were recorded on a calculated as the area between the unloading curve and the
ꢀ1
Perkin-Elmer FT spectrophotometer series 2000, in cm and as displacement axis. In turn, Wtot is the area between the loading
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1
8
ꢂ
curve and the displacement axis. The results presented in this Table 1 Selected bond lengths ( A˚ ) and bond angles ( ) for the (a)
square-planar and (b) square-pyramidal copper(II) geometries of the
work are the statistical average of a set of 10 indentations at the
complex. Symmetry code: #1 ꢀx + 1,ꢀy + 1,ꢀz
applied maximum load.
˚
ꢂ
Geometries
Bond lengths (A) and bond angles ( )
3
. Results and discussion
Cu(1)–N(2)
Cu(1)–N(3)
Cu(1)–O(1)
Cu(1)–Cl(1)
N(2)–Cu(1)–O(1)
N(3)–Cu(1)–O(1)
N(2)–Cu(1)–Cl(1)
N(3)–Cu(1)–Cl(1)
Cu(2)–N(1)
Cu(2)–O(1)
Cu(2)–O(2)
Cu(2)–O(3)#1
Cu(2)–Cl(1)
N(1)–Cu(2)–O(1)
O(2)–Cu(2)–O(1)
N(1)–Cu(2)–O(3)#1
O(2)–Cu(2)–O(3)#1
O(3)#1–Cu(2)–Cl(1)
1.9371(17)
1.9441(18)
1.9448(14)
2.2569(5)
89.18(7)
81.17(7)
95.45(5)
94.26(5)
1.9257(17)
1.9318(14)
1.9679(14)
1.9991(14)
2.795(4)
89.00(7)
95.59(6)
89.92(7)
84.78(6)
3.1 Crystal structure of the binuclear copper(II) based
coordination polymer
2 2
The reaction of L1 and L2 ligands with CuCl $2H O (1 : 1 : 2
molar ratio) was carried out in ethanol. The recrystallization of
the reaction product afforded minority fraction blue prism-like
monocrystals. The X-ray diffraction measurements performed
on the obtained monocrystals revealed that the complex crys-
tallizes in the P2(1)/c space group with two independent Cu(II)
metal centers having square-planar and square-pyramidal
geometries, respectively (Fig. 1). The complex presents a poly-
meric structure showing a one-dimensional (1D) innite neutral
chain of planar binuclear [Cu Cl(Ox)0.5(L1)(L2)] units, wherein
2 n
both L1–L2 ligand bridges are adjacent the different copper(II)
centers. Additional characterization of these monocrystals was
carried out.
92.57(5)
19
The local coordination environment around the four-
coordinated Cu(II) atom (Cu1) is formed by two pyrazolyl (pz)
nitrogen atoms (N2 and N3 in L1 and L2 ligands, respectively),
one alcohol oxygen atom (O1, L2) and one bridged chlorine
atom (Cl1). The coordination sphere of Cu1 can be described as
a slightly distorted square-planar geometry with N2–Cu1–O1
and N3–Cu1–Cl1 angles between 81.17(7) and 94.26(5) ,
respectively, which is within the expected range for copper(II)
compounds with a square-planar geometry. The Cu1–O1, Cu1–
oxalate anion (O2 and O3, Ox). These four coordinated atoms
together with the Cu2 ion dene an almost perfect planar
arrangement. The Cu2 atom is slightly displaced 0.124(2) A˚
from the basal NO3 plane. The chlorine atom (Cl1) is
ꢂ
ꢂ
Table 2 Crystallographic data for the copper(II) complex
N2 and Cu1–N3 bond distances have similar values in the
Molecular formula
C
8
H
8
ClCu
2
N
4
O
3
˚
1
.937–1.945 A range, indicating a stronger coordination than
˚
Formula weight
Temperature (K)
Wavelength ( A˚ )
370.71
100 (2)
0.71073
the Cu1–Cl1 bond (2.25 A). The [CuClO(Npz
)
2
] core has been
20–23
previously reported in the literature
block of a polymeric structure. Selected values of bond lengths
and bond angles for the complex as well as the corresponding
but never as a building
System, space group
Monoclinic, P2
1
/c
crystallographic data are shown in Table 1 and Table 2, Unit cell dimensions
˚
a (A)
10.5078(7)
9.1266(6)
11.7875(8)
90
99.869(3)
90
1113.70(13)
4
2.211
respectively.
˚
b (A)
Regarding the ve-coordinated Cu2 atom, the basal plane is
formed by one pyrazolyl nitrogen atom (N1, L1), one alcohol
oxygen atom (O1, L2) and two chelated oxygen atoms from the b ( )
˚
c (A)
ꢂ
a ( )
ꢂ
ꢂ
G ( )
3
˚
U (A )
Z
D
ꢀ3
calc (mg m
)
ꢀ
1
m (mm
F (000)
)
4.062
732
3
Crystal size (mm )
0.290 ꢁ 0.252 ꢁ 0.145
hkl ranges
ꢀ13 # h # 13
ꢀ
11 # k # 11
14 # l # 14
ꢀ
ꢂ
2
q range ( )
2.84 to 26.37
Reections collected/unique/[Rint
Completeness to q
Absorption correction
]
13166/2283 [R(int) ¼ 0.0344]
ꢂ
99.8% (q ¼ 25.242 )
Semi-empirical from equivalents
Data/restraints/parameters
2283/54/163
1.058
2
Fig. 1 X-Ray structure of the [Cu
Cu
chain. Colour scheme: copper, orange; oxygen, red; chlorine, green; R indices (all data)
4 2 2 2
Cl (Ox)(L1) (L2)
] complex, where Goodness-of-t on F
[
2
Cl(Ox)0.5(L1)(L2)] is the basic monomeric unit of this polymeric Final R indices [I > 2s(I)]
R
R
1
¼ 0.0208, wR
2
2
¼ 0.0545
¼ 0.0559
1
¼ 0.0232, wR
ꢀ3
Largest diff. peak and hole (e A˚
)
0.444 and ꢀ0.412
nitrogen, blue and carbon, grey.
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coordinated to the apical position of the Cu2 site with a longer effective for catalysing various organic reactions, such as azide–
˚
bond distance of 2.795(3) A. The coordination sphere of Cu2 can alkyne cycloaddition, oxidative coupling reactions, Henry or
36–38
39
be described as a slightly distorted square-pyramidal geometry Diels–Alder reactions,
or water oxidation, among others.
with O(2)–Cu(2)–O(1) and O(2)–Cu(2)–O(3) angles between
This binuclear copper(II) based coordination polymer owes
ꢂ
84.78(6) and 95.59(6) , respectively, and Cu(2)–O(1), Cu(2)–O(2), its particularity to the fact that it is composed of three different
3
Cu(2)–O(3) and Cu(2)–N(1) bond distances of 1.932, 1.968, 1.999 ligands, where neither of the [CuClO Npz] and [Npz–Cu–Ox–Cu–
4
0
˚
and 1.926 A, respectively. Such angles and bond distances are
N
pz] coordination environments have been reported before.
] core presents a similar coordination
within the expected range for copper(II) compounds with Only the [CuClO(Npz
square-pyramidal geometry. In the crystal structure of the Cu2 sphere to that already described.
)
2
20–23
,
Such special coordination
metal centers with square-pyramidal geometry are connected to spheres provide interesting structures in the network of this
each other via one oxalate anion (Ox) ligand through a bis- complex.
bidentate chelating mode, with adjacent Cu(II) atoms at 5.164
In the supramolecular crystal arrangement, each [Cu Cl (Ox)
4 2
2
1
2
1a 2a
˚
A (m-oxalato-1ƙ O ,O :2ƙO ,O ). The Cu–Ox distances fall (L1)
2
(L2)
2
] molecule is surrounded by 4 other neighbouring
24–26
within the typical range for oxalate bridged Cu(II) complexes.
molecules in the unit cell. The disposition of these molecules in
˚
The Cu1/Cu2 distance of 3.350 A is out of the limit of the the unit cell is a typical ABAB structure. Zig-zag layers of poly-
interactive range between the different copper atoms (van der meric chains interconnected by chloride bridges between the
˚
Waals radius of Cu(II) is 2.8 A). The pyrazole rings are nearly intermolecular copper centers afford a 2D structure along the b
ꢂ
parallel with a dihedral angle of 3.15(1) between their planes. axis in the supramolecular framework (Fig. 2A). The chlorine
The unexpected formation of the oxalate anion in the reac- atoms (Cl1) are the bridges between one molecule and the other
ꢂ
tion medium could be attributed to the ethanol oxidation by through the Cu2–Cl1–Cu1 bond with a 93.02 angle. In addi-
dissolved O
2
, favored by the basicity of the medium and the tion, the intramolecular contacts between the N3/Cl1/N2
˚
catalytic properties of the copper(II) ions (the reaction took place atoms (3.086 and 3.111 A, respectively) contribute to support
under aerobic and basic conditions). Copper(II) ions could the supramolecular network (Fig. 2B). The staggered layered
ꢀ
cause the catalytic activation of O
2
and OH to produce reactive structure determines the mechanical properties measured for
ꢀ
species (i.e. hydroxyl radicals, OHc ) capable of oxidizing a this polymer using the nanoindentation technique.
minor fraction of the ethanol solvent. Using the spectrophoto-
metric method, traces of oxalic acid were found aer stirring a
27
3.2 Mechanical properties of the binuclear copper(II) based
coordination polymer
basic solution of ethanol and CuCl under aerobic conditions.
2
28
Similar oxalate occurrence was reported by Jing Su et al. and
29
Mansour Arab et al. The possible reactions involved in the Representative nanoindentation curves, performed perpendic-
synthesis process of the complex presented here are illustrated ular to the planar base of the crystal, that corresponds to the
in Scheme 1.
(100) face, and up to maximum loads of 1.2 and 2.8 mN, are
The “in situ” formation of oxalic acid from solvent during the shown in Fig. 3a and S1.† Measurement of the mechanical
30,31
complex formation reaction has been previously reported.
In properties by nanoindentacion along the other directions was
addition, there are also previous reports of aerobic alcohol not possible because of the high tendency for the crystals
oxidation during the formation of copper coordination
32–34
complexes or in the presence of copper salts.
In all these
cases the alcohol oxidation is related to the catalytic properties
of copper(II) ions.
35
Copper, with a dynamic Jahn–Teller distortion, efficiently
catalyzes the oxidation of organic compounds under mild
conditions and can provide open Lewis acid sites which are
Scheme 1 Chemical reactions involved in obtaining the polymeric Fig. 2 (A) Polymeric layer structure with zig-zag distribution along the
complex: synthesis of the L2 ligand (a), in situ formation of oxalic acid b axis. (B) The close-up view displays the distances and the angles
(
b) and complex formation (c).
formed by the Cu1–Cl1–Cu2 intermolecular bridges.
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Fig.
perpendicular to the crystal sheet, and up to maximum loads of 1.2 mN
red line) and 2.8 mN (black line). (b) Atomic force microscopy and
optical (inset) images of an indentation performed using a maximum Fig. 4 Values of (a) hardness and reduced Young’s modulus and (b)
load of 2.8 mN.
indentation energies and elastic recovery (Wel/Wtot) of the complex.
3 (a) Representative nanoindentation curves performed
(
towards brittle fracture. Discontinuities or pop-in events in the [OZn
4
(BDC)
3
]
n
, where BDC stands for 1,4-benzenedicarboxylate
loading segments are oen observed and are ascribed to the anion. The increase of E with the applied load indicates a
breakage of molecular stacks and the concomitant sudden higher resistance against elastic deformation as the penetration
penetration of the indenter deeper into the sample.
depth is progressively increased. This could be due to the larger
44
r
The atomic force microscopy image (Fig. 3b) of an indenta- amount of molecular bonds which hinder the elastic deforma-
tion performed using a maximum load of 2.8 mN shows that tion as the applied load is progressively increased. Nevertheless,
pile-up effects are virtually absent, while crack formation from no clear changes in the elastic energy or the elastic recovery are
the edge of the triangular imprint sometimes occurs, an observed in the range of applied loads used in this study
observation which is in agreement with the occurrence of (Fig. 4b). The value of elastic recovery (Wel/Wtot z 0.6) is clearly
45
serrations in the loading segments of the indentation curves larger than those of other types of organic–inorganic materials
(
Fig. 3a). The lack of pile-up avoids artifacts related to the and is comparable to the values in some recent reports on 3D
46
determination of the contact area from the contact depth, when inorganic composite lms.
16
using the method of Oliver and Pharr.
The values of hardness, reduced Young’s modulus, inden-
4. Conclusions
tation energies and elastic recovery (W /Wtot) are shown in
el
Fig. 4a and b. Hardness remains rather constant (H z 0.4–0.5
GPa) as a function of the applied maximum load (Fig. 4a). This
value is a bit higher than the ones reported by C. M. Reddy
A new binuclear copper(II) complex with a polymeric structure
has been unexpectedly obtained from a mixture of pyrazolic
ligands and CuCl
different coordination numbers and geometries. The Cu1 atom
is four-coordinated in the [CuClO(Npz ] core with a square-
2
in ethanol. The two copper(II) centers have
41
et al. for 2-(methylthio)nicotinic acid and similar to values
reported by J. C. Tan et al. for different low-symmetry poly-
morphs of copper phosphonoacetates [Cu (H O)(O PCH -
)
2
1
.5
2
3
2
planar molecular geometry, while the Cu2 nucleus is ve-
coordinated with [CuClO N ] core and exhibits square-
4
2
CO )]. Conversely, the Young’s modulus is a bit lower than the
2
3
pz
13,42,43
values reported for some other molecular crystals
but
pyramidal geometry. Furthermore, the Cu2 centers of
different molecular units are interconnected in the polymeric
similar to the values reported by A. Samanta et al. for
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structure via one unexpected oxalate anion. The terminal 10 J. C. Tan and A. K. Cheetham, Chem. Soc. Rev., 2011, 40,
chlorine atoms act as bridges between the monomeric units in 1059–1080.
this coordination polymer. As far as we know, this is the rst 11 W. Li, M. S. R. N. Kiran, J. L. Manson, J. A. Schlueter,
time that the [CuClO N ] and [N –Cu–Ox–Cu–N ] coordina-
A. Thirumurugan, U. Ramamurty and A. K. Cheetham,
3
pz
pz
pz
tion environments are reported. In the supramolecular network
Chem. Commun., 2013, 49, 4471–4473.
an interesting 2D structure with layered architecture formed 12 S. Varughese, M. S. R. N. Kiran, U. Ramamurty and
from polymeric chains interconnected by Cu2–Cl1–Cu1 bridges G. R. Desiraju, Angew. Chem., Int. Ed., 2013, 52, 2701–2712.
is formed along the b-axis. Additionally, the values of hardness, 13 J. C. Tan, J. D. Furman and A. K. Cheetham, J. Am. Chem.
Young’s modulus, and elastic recovery of this structure have Soc., 2009, 131, 14252–14254.
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important asset to crystal engineering since durability and 15 W. L. Driessen, Recl. Trav. Chim. Pays-Bas, 1982, 101, 441–
reliability, which are dictated by the mechanical properties, are 443.
important factors for their potential applications in sensors, 16 W. C. Oliver and G. M. Pharr, J. Mater. Res., 1992, 7, 1564–
catalysts and gas storage, among others.
1583.
1
1
7 A. Fischer-Cripps, Nanoindentation, Springer, New York,
USA, 2004.
8 E. Pellicer, A. Varea, S. Pan ´e , B. J. Nelson, E. Men ´e ndez,
M. Estrader, S. Suri n˜ ach, M. D. Bar ´o , J. Nogu ´e s and J. Sort,
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Acknowledgements
The nancial support from the MAT2011-27380-C02-01 and the
MAT2011-27225 research projects from the Spanish MINECO,
8 8 2 4 3
and the 2014-SGR-1015 and the 2014-SGR-260 projects from the 19 Analysis for C H ClCu N O calcd/found (%): C, 25.92/25.72;
Generalitat de Catalunya are acknowledged. M. D. B. was
partially supported by an ICREA-Academia award. A. L_M.
thanks the FI-2010 scholarship given by the Government of
Catalonia. M. G. acknowledges the support of the Secretary for
Universities and Research of the Government of Catalonia and
the COFUND Programme of the Marie Curie Actions of the 7th R
H, 2.17/2.13, N, 15.11/15.04, Cu, 34.28/33.96, giving
satisfactory C, H, N and Cu elemental analyses. IR (KBr,
cm ): 3190, 3120 n(C–H)ar; 2940, 2920 n(C–H)al; 1650
[n(C]C), n(C]N)]ar; 1400 [d(C]C), d(C]N)]ar and 773 g(]
C–H)oop present shis (in relation with the free ligand)
produced by the coordination with copper(II); moreover,
ꢀ
1
&
‘
D Framework Programme of the European Union for the
Beatriu de Pinos’ contract (2013 BP-B 00077). E. P. acknowl-
edges the Spanish MINECO for the ‘Ramon y Cajal’ contract
RYC-2012-10839).
the bands at 472, 428 n(Cu–N); 550, n(Cu–O); 600 g (Cu–O)
as
and 356, 322 n(Cu–Cl) also corroborate the copper
ꢀ
3
coordination. Conductivity (1.02 ꢁ 10 M in methanol):
ꢀ
1
2
ꢀ1
(
32 U
cm mol , in agreement with a non-electrolyte
ꢀ
3
complex; UV-vis (1.1 ꢁ 10
M in methanol) exhibits a
single band at 620 nm.
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