Synthesis, crystal structure and Hirshfeld surfaces of a CuII complex with an ICL670-related ligand

Article abstract of DOI:10.3184/174751912X13503977364032

The complex [Cu₂(μ-L)₂].DMF (L = 2, 2'-[1-(2, 4, 6-trichlorophenyl)-1H-1, 2, 4-triazole-3, 5-diyl] diphenolate) has been prepared and its structure determined. The two CuII ions are four-coordinated in a planar structure, with the DMF molecule wrapped in the wings of ligand L. Hirshfeld surface and fingerprint plots reveal that the complex structure is stabilised mainly by H···H, C-H Cl, C-H···π, π···π and lone-pair···π (C-Cl) intermolecular interactions.

Full text of DOI:10.3184/174751912X13503977364032

JOURNAL OF CHEMICAL RESEARCH 2012
RESEARCH PAPER 697
DECEMBER, 697–700
Synthesis, crystal structure and Hirshfeld surfaces of a CuII complex with
an ICL670-related ligand
Yang-Hui Luo, Jian Xu and Bai-Wang Sun*
College of Chemistry and Chemical Engineering, Southeast University, Nanjing 210096, P. R. China
The complex [Cu2(µ−L)2].DMF (L = 2, 2’-[1-(2, 4, 6-trichlorophenyl)-1H-1, 2, 4-triazole-3, 5-diyl] diphenolate) has
been prepared and its structure determined. The two CuII ions are four-coordinated in a planar structure, with the
DMF molecule wrapped in the “wings” of ligand L. Hirshfeld surface and fingerprint plots reveal that the complex
structure is stabilised mainly by H···H, C–H…Cl, C–H···π, π···π and lone-pair···π (C–Cl) intermolecular interactions.
Keywords: copper complex, crystal structure, ICL670 analogue, Hirshfeld surface, antimalarials, chelators
There has been increasing interest in ICL670 (deferasirox, 4-
[3, 5-bis (2-hydroxyphenyl))-1, 2, 4-teiazol-1-yl] benzoic acid)
and its derivatives due to their potential as antimalarials and
new orally-active iron chelators.1–4 These chelators are used
not only in the treatment of patients suffering from chronic
iron overload due to blood transfusion, but also play a key role
in the development of new iron sensors that enable selective
detection (such as electrochemical detection or potentiometric
detection) of specific ions.5–11
The structure of ICL670 is shown in Scheme 1a. The 1, 2,
4-triazole nucleus unites the coordination geometry of both
pyrazoles and imidazoles, and exhibits a strong and typical
property of acting as a bridging ligand between two metal
centres. With this bridging capacity, the triazole nucleus shows
even greater coordination diversity when substituted with
additional donor groups.8–12 A ICL670 derivative, 4-salicylim-
ine-3, 5-bis (2-hydroxyphenyl)-1, 2, 4-triazole, has been syn-
thesised and its binding mode and stacking interaction strength
elucidated.13 The selective ability and complex formation of
ICL670 with Fe3+ and Fe2+ has been investigated.14
It has been shown recently that the Hirshfeld surface is a
powerful tool for elucidating molecular crystal structures. It
is a space partitioning construct that summarises the crystal
packing into a single three-dimensional surface, and the sur-
face can be further reduced to a two-dimensional fingerprint
plot, which summarises the intermolecular interactions present
in molecular crystals.15,16 The principles of Hirshfeld surfaces
and fingerprint plots are reported elsewhere.16,17
Results and discussion
The crystal structure of complex 1 is shown in Fig. 1a, the H
atoms are omitted for clarity. Complex 1 crystallises in the
triclinic space group P-1 and the asymmetric unit consists of
two CuII cations, two L ligands and one lattice DMF molecule.
In the structure, both CuII cations show four-coordination
geometry with the basal plane defined by the O–N–O donor set
of ligand L and shift ca 0.0183 (Cu1) and 0.0162 Ǻ (Cu2) out
of the basal plane, the basal planes themselves being distorted
with a dihedral angle of 37.53° (Fig. 1b). The Cu–O lengths in
the basal plane differ from 1.872 to 1.987 Ǻ, and the Cu–N
bonds with distances of 1.904 and 1.927 Ǻ. These bond lengths
fall in expected ranges.14 The two phenol moieties and trichlo-
rophenyl moiety in the ligand L are twisted with the central
triazole ring having dihedral angles of 12.74°, 6.3° (12.21°,
16.82°) and 79.86° (88.037°), respectively.
The molecules in the crystal structure of 1 first buckle
together to form a double-hook dimer structure in symmetry,
with the DMF molecules located in the inner of the double-
hooks (Fig. 2). The double-hook unit then stabilised by non
classical C–H...Cl, C–H...N and C–H...O hydrogen bonds
and π–π stacking interactions [centroid–centroid distance =
3.878 (2) Ǻ] between the phenol and the triazole moieties into
a 3D architecture.
In our previous work, we have successfully synthesised a
new ICL670 derivative (C20H12Cl3N3O2): 2, 2′-[1-(2, 4, 6-
trichlorophenyl)-1H-1, 2, 4-triazole-3, 5-diyl] diphenol (L,
Scheme 1b).18 In the present work, we investigated the com-
plex formation of this ligand with copper (II) nitrate trihydrate
in dimethylformamide DMF at 50°C, and obtained a complex:
(1). [(C20H12Cl3N3O2)2Cu2.C3H7NO]. We have prepared and
analysed its Hirshfeld surface and fingerprint plots.
Fig. 1 (a) Molecular structure of complex 1 with the atom-
labelling scheme. Displacement ellipsoids are drawn at the
30% probability level. H atoms are omitted for sake of clarity.
(b) The coordinate environment of the Cu ions of the complexes
1, basal planes are illustrated in red/black, the DMF solvent
molecule is omitted for sake of clarity.
Scheme 1 Structure of ICL670 (left) and ligand L (right).
* Correspondent. E-mail: chmsunbw@seu.edu.cn

698 JOURNAL OF CHEMICAL RESEARCH 2012
the crystal of complex 1, as is reflected in the middle of
scattered points in the two-dimensional fingerprint plot with
di=de=1.0 Ǻ, and it comprises 22.4% of the total Hirshfeld
surfaces. The C–H ··· π interactions, which is indicated by the
“wings” in the upper left and lower right of the two-dimensional
fingerprint plot, comprises 20.3% of the total Hirshfeld sur-
faces. The C–H…Cl interactions have the most significant
contribution to the total Hirshfeld surfaces (26.5%). The π…π
(C…C) and lone-pair…π (C–Cl) interactions are indicated in
the corner of the two-dimensional fingerprint plot, and
comprise 3.5% and 7.7% to the total Hirshfeld surfaces. Also
shown in Fig. 3 is the two-dimensional fingerprint plot of
C–H...O interactions, which contributes 4.4% to the total
Hirshfeld surfaces. Apart from those detailed above, the pres-
ence of N–C, C–O, Cu–O, Cu–C, interactions are observed.
These are summarised in Table 4.
Conclusions
Fig. 2 Packing diagram of complex 1.
In conclusion, a new copper (II) complex has been synthesised
from a ICL670 related ligand L (2, 2′-[1-(2, 4, 6-trichlorophe-
nyl)-1H-1, 2, 4-triazole-3, 5-diyl] diphenolate) and character-
ised by X-ray single-crystal analysis. The complex exhibits
stable δδ (or λλ) conformation and the crystal structure of it
is stabilised mainly by H···H, C–H···Cl, C–H···π, π···π and
lone-pair···π (C–Cl) intermolecular interactions.
For bis-complexes of this kind, interligand interaction
can affect their stability.10 The phenol moieties twist with
the triazole moieties in two manners: the λ and δ form (see
Scheme 2b), and their combination in a bis-complex would
give either a λδ or a δδ (or λλ) forms. In the λδ isomer, the two
ligands are oriented perpendicularly, whereas the δδ (or λλ)
isomer has an almost parallel orientation of the four phenyl
rings that allow for some intramolecular π–π stacking to occur,
thus leading to stabilisation of the complex.14
The structure of complex 1 is observed to have the δδ (or λλ)
conformation, the plane of these two ligands form a dihedral
angle of 35.06°. Moreover, the solvent molecule plays a key
role, the oxygen atom in the DMF has accessibility to the two
CuII cations and hinders the formation of the perpendicular
structure.
Experimental
All chemicals used (reagent grade) were commercially available.
Elemental analyses (C, H, N) were carried out by using a Germen
Elementar Analysensysteme GmbH Vario EL instrument.
Complex formation of L with CuII: Solid copper(II) nitrate trihy-
drate (48.4 mg, 0.2 mmol) was added to a DMF solution (20 mL) of 2,
2′-[1-(2, 4, 6-trichlorophenyl)-1H-1, 2, 4-triazole-3, 5-diyl] diphenol
(L) (86.4 mg, 0.2 mmol) under continuous stirring at about 50 °C. The
blue solution which resulted from the mixture was filtered off and
allowed to evaporate at room temperature. Single crystals of 1 as blue
prisms were grown from the solution by slow evaporation at room
Hirshfeld surfaces analysis
The three-dimensional Hirshfeld surfaces and two-dimensional
fingerprint plots of complex 1 are illustrated in Fig. 3, showing
surfaces that have been mapped over a fixed dnorm colour scale
of −0.32(blue) to 1.6(red). The red regions on the dnorm surfaces
correspond to significant C–H ··· π, C–H…Cl and Cu–O inter-
actions. There are also cavities opposite the DMF molecules,
which attribute to the space between the double-hook units.
The two-dimensional fingerprint plots, which analyse all of
the intermolecular contacts at the same time, reveal that the
H–H intermolecular interactions are the shortest contacts in
Table 1 Crystallographic data for complex 1
Complex
1
Empirical formula
C43H27Cl6 Cu2 N7 O5
1061.5
0.25 x 0.2 x 0.2
Triclinic
P-1
0.71073
Formula weight
Crystal size(mm)
Crystal system
Space group
λ(Mo Ka) (Å)
a/Å
12.281(13)
13.023(14)
14.351(15)
107.341(16)
93.730(6)
95.336(14)
2171
b/Å
c/Å
α/°
β/°
γ/°
V, Å3
Z
2
Dcalcd (Mg m−3)
1.624
µ (mm−1)
1.404
F(000)
T/K
1063
293(2)
Theta range for data collection(°)
Reflections collected
Unique reflections
Goodness-of-fit on F2
2.47≤θ≤25
18468
7627
1.029
–14<=h<=14
–15<=k<=15
–17<=l<=17
0.0718, 0.1314
0.1398, 0.1573
0.459, −0.448
hkl range
R1a, wR2b ((I>2σ(I))
R1, wR2 (all data)
∆ρmin and max (e Å−3)
a R1=Σ|Fo–Fc|/ΣFo, b wR2=[Σw(Fo-Fc)2/Σw Fo2]1/2, where w=1/[σ2
(Fo2)+(0.0808*P)2+0.17*P], P=(Max(Fo2,0)+2*Fc2)/3; b w=1/[σ2
(Fo2)+(0.0163*P)2+0.63*P], P=(Max(Fo2,0)+ 2*Fc2)/3.
Scheme 2 λ and δ forms conformation.

JOURNAL OF CHEMICAL RESEARCH 2012 699
Fig. 3 The full fingerprint appears beneath each decomposed plot as a grey shadow.
temperature within 4 days. The yield is 82%. C43H27Cl6Cu2N7O5
(1061.50): Calcd: C, 48.65; N, 9.24; H, 2.56. Found: C, 48.62; N,
9.25; H, 2.57%.
Crystal data collection and refinement
The single-crystal X-ray diffraction data of complex 1 were collected
on a Rigaku Scxmini 1 K CCD areadetector diffractometer with
graphite monochromated Mo-Kα radiation (λ=0.71073 Å). Crystal
data are summarised in Table 1, selected bond lengths and angles of 1
are listed in Table 2. All the data were collected, processed, and cor-
rected using the Bruker SADABS program with a multi-scan method.
Table 2 Selected bond distance (Å) and angles (°) for complex
1
Complex 1
Table 3 Hydrogen-bonding arrangement /Å, ° for complex 1
Cu1–N1
Cu1–O2
Cu1–O3
Cu1–O4
N(2)–N(3)
Cu2–O1
Cu2–O2
Cu2–O4
Cu2–N4
1.927(5)
1.986(4)
1.872(5)
1.951(4)
1.373(7)
1.886(5)
1.933(4)
1.950(4)
1.905(5)
Cu(2)–O(2)–Cu(1)
Cu(2)–O(4)–Cu(1)
O(3)–Cu(1)–N(1
O(3)–Cu(1)–O(4)
N(1)–Cu(1)–O(4)
O(3)–Cu(1)–O(2)
N(1)–Cu(1)–O(2)
N(4)–Cu(2)–O(2)
N(4)–Cu(2)–O(2)
N(4)–Cu(2)–O(4)
O(2)–Cu(2)–O(4)
95.40(18)
96.02(19)
91.8(2)
D–H···A
D–H
H···A
D···A
D–H···A
173.1(2)
C17–H17A···Cl6i
C19–H19A···Cl1ii
C16–H16A···N2
C19–H19A···O1
C36–H36A···N5
C36–H36A···O3
C42–H42A···N5
0.93
0.93
0.93
0.93
0.93
0.93
0.93
2.82
2.82
2.53
2.47
2.53
2.47
2.37
3.6411
3.5838
2.8564
2.9243
2.8701
3.0447
2.7725
148
140
101
110
102
120
104
91.25(19)
99.46(19)
168.19(18)
93.45(19)
93.45(19)
172.19(19)
79.18(18)
Symmetry codes: (i) x, y–1, z; (ii) –x+1, –y, –z.

700 JOURNAL OF CHEMICAL RESEARCH 2012
7627 independent reflections with I>2.0 σ (I) were observed. The
structure was solved by direct methods and refined by a full-matrix
least-squares technique based on F2 using the SHELXS-97 and
SHELXL-97 program.19 Reliability factors were defined as R1 =Σ(|Fo|
– |Fc|)/Σ|Fo| and the function minimised was Rw = [Σw(Fo2 – Fc 2)2/
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dnorm surfaces were mapped over a fixed colour scale of –0.32 (red) to
1.6 Ǻ (blue). The 2-D fingerprint plots are displayed by using the
standard 0.6–2.6 Ǻ view with the de and di distance scales displayed
on the axes.
This work was supported by the National Natural Science
Foundation of China (Project 20671019).
Received 17 June 2012; accepted 27 September 2012
Paper 1201375 doi: 10.3184/174751912X13503977364032
Published online: 5 December 2012

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