Metallomacrocycle or coordination polymer: Spacer-directed self-assembly of transition-metal complexes based on flexible bis(benzotriazole) ligands

Article abstract of DOI:10.1039/c0ce00847h

Three structurally related flexible bis(benzotriazole) ligands, 1,2-bis(benzotriazol-1-yl)ethane (L¹), 1,5-bis(benzotriazol-1-yl)-3- oxapentane (L²) and 1,8-bis(benzotriazol-1-yl)-3,6-dioxaoctane (L³), have been synthesized. They were reacted with AgNO₃ and CuCl₂·2H₂O at room temperature, resulting in the formation of six novel complexes: {[AgL¹(NO₃)(CH ₃CN)]}_n (1), [Ag₂(L²) ₃](NO₃)₂ (2), {[Ag₂(L ³)₂(NO₃)₂]}_n (3), {[CuL¹Cl₂]}_n (4), [Cu₂(L ²)₂Cl₄] (5), and [Cu₂(L ³)₂Cl₄(DMF)₂] (6). All complexes have been characterized by X-ray diffraction analysis. In 1 and 4, they exhibit similar coordination modes in which each ligand links two metal ions to form a 1D non-linear coordination polymeric chain. In 2, two Ag^I centers are close coupled by Ag...Ag interaction and three bridging ligands to form a dinuclear cation. The structure of 3 reveals the dinuclear cluster units, formed by two ligands and two Ag^I ions, are linked by anions to self-assemble a 1D chain. Complex 5 is an isolated dinuclear structure, in which ligands and bridging chloro ligands act as the organic clips to bridge two Cu^II centres. But in 6, a pair of ligands takes on the conformation to connect two metal ions to form bimetallic a macrocyclic architecture. These results unequivocally indicate that the influence of flexible ligand spacers, which bring structural varieties for the same metal ion, is the key factor governing the molecular architectures. Moreover, the thermal stability of 1-3 and 4-6 in the solid state has also been compared.

Full text of DOI:10.1039/c0ce00847h

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PAPER
Metallomacrocycle or coordination polymer: Spacer-directed self-assembly of
transition-metal complexes based on flexible bis(benzotriazole) ligands†
*
Xiao-Liang Tang, Wei Dou, Ji-an Zhou, Guo-Lin Zhang, Wei-Sheng Liu, Li-Zi Yang and Yong-Liang Shao
Received 12th November 2010, Accepted 26th January 2011
DOI: 10.1039/c0ce00847h
Three structurally related flexible bis(benzotriazole) ligands, 1,2-bis(benzotriazol-1-yl)ethane (L1), 1,5-
bis(benzotriazol-1-yl)-3-oxapentane (L2) and 1,8-bis(benzotriazol-1-yl)-3,6-dioxaoctane (L3), have been
synthesized. They were reacted with AgNO3 and CuCl2$2H2O at room temperature, resulting in the
formation of six novel complexes: {[AgL1(NO3)(CH3CN)]}n (1), [Ag2(L2)3](NO3)2 (2),
{[Ag2(L3)2(NO3)2]}n (3), {[CuL1Cl2]}n (4), [Cu2(L2)2Cl4] (5), and [Cu2(L3)2Cl4(DMF)2] (6). All
complexes have been characterized by X-ray diffraction analysis. In 1 and 4, they exhibit similar
coordination modes in which each ligand links two metal ions to form a 1D non-linear coordination
polymeric chain. In 2, two AgI centers are close coupled by Ag/Ag interaction and three bridging
ligands to form a dinuclear cation. The structure of 3 reveals the dinuclear cluster units, formed by two
ligands and two AgI ions, are linked by anions to self-assemble a 1D chain. Complex 5 is an isolated
dinuclear structure, in which ligands and bridging chloro ligands act as the organic clips to bridge two
CuII centres. But in 6, a pair of ligands takes on the conformation to connect two metal ions to form
bimetallic a macrocyclic architecture. These results unequivocally indicate that the influence of flexible
ligand spacers, which bring structural varieties for the same metal ion, is the key factor governing the
molecular architectures. Moreover, the thermal stability of 1–3 and 4–6 in the solid state has also been
compared.
a well-designed ligand to control the assembly of molecular
Introduction
architectures have become a popular and rapidly growing disci-
One of the major goals of crystal engineering is targeted at the
pline.4
predictable assembly of molecular species.1 Considerable effort
Up to now, most coordination architectures have been widely
ꢀ
constructed by Yaghi, Williams, Ferey, Chen, Hong and their co-
has been devoted to understanding the self-assembly of organic
and inorganic molecules in the past decade because it extends the
range of new solids that can be designed to have particular
physical and chemical properties.2 Generally speaking, the
generation of self-assembling coordination architectures depends
on the combination of several factors, such as the coordination
geometry of the metal ions, the performance of the ligands, the
coordinated and/or non-coordinated counter ions, the solvent
systems and the reaction conditions.3 The ligand is no doubt the
key factor for manipulating the structures of the complexes.
Therefore, the application of a special metal ion and the use of
workers with rigid linear bridging ligands, such as 1,4-benzene-
dicarboxylic acid, 1,3,5-benzenetricarboxylic acid, pyrazine and
4,40-bipyridine.5 More recently, increasing attention has been
paid to employ flexible ligands for several reasons: (a) such
ligands possess stronger capability in coordination by prolonging
their arms and weakening stereo-hindrance effects; (b) they can
adopt various conformations and gain access to novel supra-
molecular structures not available from the logical combination
of rigid building blocks;6 (c) the incorporation of flexible
components may endow the molecular architectures with
potential advantages, for example, a ‘‘breathing’’ ability in the
solid state and adaptive recognition properties.7 Nevertheless,
due to the structural flexibility and conformational freedoms of
such ligands, rational design and precise control of the final
product supramolecular architectures from 0D to 3D are still
great challenges to chemists.3,8
Key Laboratory of Nonferrous Metals Chemistry and Resources
Utilization of Gansu Province and State Key Laboratory of Applied
Organic Chemistry, College of Chemistry and Chemical Engineering,
Lanzhou University, Lanzhou, 730000, China. E-mail: liuws@lzu.edu.cn;
Fax: +86-931-8912582; Tel: +86-931-8915151
† Electronic supplementary information (ESI) available: The
characterization IR of the ligands; IR, the tables of hydrogen bonds,
p–p interactions, selected bond lengths and selected bond angles of the
complexes 1–6. CCDC reference numbers 676484–676489. For ESI and
crystallographic data in CIF or other electronic format see DOI:
10.1039/c0ce00847h
Benzotriazole has been extensively used as a synthetic
auxiliary in organic chemistry and a corrosion inhibitor in
materials science.9 An important part within its application is to
obtain the deprotonated benzotriazolate anion, which can
2890 | CrystEngComm, 2011, 13, 2890–2898
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coordinate up to three metal centres via its three nitrogen
donors.10 Until recently, some substituted benzotriazoles with
rigid moieties have been investigated in supramolecular coordi-
nation chemistry because more intermolecular interactions such
as hydrogen bonds and p–p stacking interactions are often
observed in solid structures.11 However, there are relatively few
systematic studies on flexible benzotriazole ligands with different
spacers and their complexes with various structural features.
We are engaging in a detailed study on the influence of metal
ions, various terminal groups, and open-chain crown ether
spaces on the coordination supramolecular structures.12 In this
work, our idea is to introduce benzotriazoles into a flexible
oligoethyleneglycol skeleton with different length spacers to
further explore the relationship between flexible chain and low-
dimensional (0D or 1D) structural features. Therefore, we
designed three structurally related flexible ligands: 1,2-bis(ben-
zotriazol-1-yl)ethane (L1), 1,5-bis(benzotriazol-1-yl)-3-oxa-
pentane (L2) and 1,8-bis(benzotriazol-1-yl)-3,6-dioxaoctane (L3)
(Scheme 1), and obtained correlative crystal structures of six
novel complexes, {[AgL1(NO3)(CH3CN)]}n (1), [Ag2(L2)3](NO3)2
(2), {[Ag2(L3)2(NO3)2]}n (3), {[CuL1Cl2]}n (4), [Cu2(L2)2Cl4] (5),
and [Cu2(L3)2Cl4(DMF)2] (6). The structure formations of the six
compounds are presented and their thermogravimetric analyses
are discussed.
Synthesis of ligands
The three ligands were prepared by the adoption of a similar
reported procedure.11e The reactions of benzotriazole with 1,2-
bis(p-tolylsulfonyloxy)ethane, 1,5-bis(p-tolylsulfonyloxy)-3-oxa-
pentane or 1,8-bis(p-tolylsulfonyloxy)-3,6-dioxaoctane in the
presence of sodium hydroxide in absolute methanol, under reflux
conditions over 6 h, gave a mixture of isomers. The solvent was
evaporated and the mixture was taken up in CHCl3 and washed
at least three times with H2O before being dried over anhydrous
MgSO4. L1, L2 and L3 were further separated by column chro-
matography on silica gel, and the white product was character-
1
ized by H NMR and IR spectra.
For L1, yield: 28.4%; m.p. 157.6–158.9 C. H NMR (CDCl3,
ppm): d 5.25 (s, 4H), 6.83ꢂ6.88 (d, 2H), 7.14ꢂ7.21 (m, 4H),
7.86ꢂ7.91 (d, 2H). IR (cmꢀ1, KBr): 3066w, 1608w, 1493m,
1449m, 1306m, 1277m, 1218s, 1157m, 1125w, 1055vs, 996w,
789m, 752vs.
ꢁ
1
For L2, yield: 32.8%; m.p. 76.4–77.3 ꢁC. H NMR (CDCl3,
1
ppm): d 3.90ꢂ3.95 (t, 4H), 4.67ꢂ4.71 (t, 4H), 7.32ꢂ7.39 (m, 6H),
8.00ꢂ8.05 (d, 2H). IR (cmꢀ1, KBr): 3058m, 2959w, 1615w,
1495w, 1455m, 1308w, 1269m, 1227s, 1159s, 1114s, 1033m,
975m, 860w, 775m, 739vs.
For L3, yield: 34.1%; m.p. 91.5–92.6 ꢁC. H NMR (CDCl3,
1
ppm): d 3.39 (s, 4H), 3.79ꢂ3.83 (t, 4H), 4.67ꢂ4.71 (t, 4H),
7.32ꢂ7.38 (t, 2H), 7.41ꢂ7.47 (t, 2H), 7.51ꢂ7.54 (d, 2H),
8.01ꢂ8.05 (d, 2H). IR (cmꢀ1, KBr): 3067w, 2899s, 2876m, 1615w,
1495m, 1458m, 1402w, 1358w, 1328m, 1266w, 1230s, 1124vs,
1020s, 779m, 750s
Experimental section
Materials and methods
All the reagents used for the syntheses of 1–6 were commercially
available and employed without further purification or purified
by standard methods prior to use. Elemental analyses were per-
formed on a Vario EL elemental analyzer. IR spectra were
recorded on a Nicolet Avatar 360 FT-IR instrument using KBr
discs in the 400–4000 cmꢀ1 region. 1H NMR spectra were
recorded on a Varian Mercury plus 300BB spectrometer at 25 ꢁC
in CDCl3 with tetramethylsilane as the internal reference. Ther-
mogravimetric and differential thermal analysis (TG-DTA)
experiments were performed on a Perkin-Eꢁlmer TG/DTA-6300
instrument from room temperature to 750 C under a nitrogen
Preparation of complexes 1–6
{[AgL1(NO3)(CH3CN)]}n (1). The reaction of L1 (26.4 mg, 0.1
mmol) with AgNO3 (17.0 mg, 0.1 mmol) in methanol (10 mL) for
a few minutes afforded a white solid, which was filtered, washed
with methanol, and dried in vacuum. Colorless block single
crystals suitable for X-ray analysis were obtained by slow
evaporation of methanol and acetonitrile mixed solution
(V : V ¼ 5 : 1) of the complex at room temperature in the dark.
Yield: 64%. Anal. Calcd for C16H15AgN8O3: C, 40.44; H, 3.18;
N, 23.58. Found: C, 40.61; H, 2.77; N, 23.65. IR (KBr, cmꢀ1):
3463w, 3064w, 1610w, 1495w, 1453m, 1385vs, 1307m, 1217s,
1157m, 1108w, 1055s, 997w, 751vs.
atmosphere at a heating rate of 10 ꢁC minꢀ1
.
[Ag2(L2)3](NO3)2 (2). Colorless block single crystals for X-ray
analysis were obtained by similar method as described for 1.
Yield: 70%. Anal. Calcd for C48H48Ag2N20O9: C, 45.58; H, 3.83;
N,22.15. Found: C, 45.66; H, 3.52; N, 22.31. IR (KBr, cmꢀ1):
3427w, 3062w, 2873w, 1614w, 1495w, 1454m, 1368vs, 1271m,
1230s, 1161m, 1121s, 1036m, 749vs.
{[Ag2(L3)2(NO3)2]}n (3). Colorless block single crystals for
X-ray analysis were obtained by similar method as described for
1. Yield: 51%. Anal. Calcd for C18H20AgN7O5: C, 41.40; H, 3.86;
N, 18.77. Found: C, 41.61; H, 3.39; N, 18.42. IR (KBr, cmꢀ1):
3444w, 2950w, 2920w, 2859w, 1495w, 1458m, 1415vs, 1282vs,
1229s, 1171m, 1132s, 1108s, 1041m, 1025m, 894m, 747s, 713m,
668w.
Scheme 1 Structures of the ligands, L1–L3, and schematic view of the
syntheses of the six complexes 1–6.
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{[CuL1Cl2]}n (4). The reaction of L1 (26.4 mg, 0.1 mmol) with
CuCl2$2H2O (17.1 mg, 0.1 mmol) in methanol (10 mL) for a few
minutes afforded a navy blue solid, which was filtered, washed
with methanol, and dried in vacuum. Navy blue block single
crystals suitable for X-ray analysis were obtained by slow
evaporation of methanol and DMF mixed solution (V : V ¼
10 : 1) of the complex at room temperature. Yield: 45%. Anal.
Calcd for C14H12Cl2CuN6: C, 42.17; H, 3.03; N, 21.08. Found: C,
42.20; H, 2.63; N, 21.34. IR (KBr, cmꢀ1): 3433w, 3061w, 2952w,
1592w, 1493w, 1440m, 1359w, 1292m, 1234s, 1187s, 1165m,
1124m, 964w, 772s, 747vs.
structures. The metal ions of subgroup elements Cu and Ag were
chosen as central ions of metal complexes, and both of them
belong to the family IB of the periodic table but only have
a different number of electrons in their outermost d orbital. For
Ag complexes 1, 2 and 3, they were assembled under the same
conditions except for the ligand structure, which made the study
on the effect of the ligand relatively accurate. When CuII was
used instead of AgI, complexes 4, 5 and 6, with different supra-
molecular structures, were achieved under the same crystal
growth environment (Scheme 1).
Structural investigations in the crystalline phase
[Cu2(L2)2Cl4] (5). Green block single crystals were obtained by
similar method as described for 4. Yield: 55%. Anal. Calcd for
C32H32Cl4Cu2N12O2: C, 43.40; H, 3.64; N, 18.98. Found: C,
43.35; H, 3.80; N, 19.12. IR (KBr, cmꢀ1): 3445w, 3038w, 2958w,
2912w, 2875w, 1591w, 1482w, 1451m, 1354w, 1324w, 1285m,
1234m, 1190m, 1129s, 1045w, 916w, 750vs.
Crystal structure of complex 1. Crystals of 1 belong to
ꢂ
a centrosymmetric space group P1. The asymmetric unit contains
one ligand L1, one nitrate anion and one CH3CN molecule—all
coordinated to the metal center AgI. As shown in Fig. 1a, the AgI
center adopts a distorted tetrahedron coordination consisting of
two benzotriazole N-donors, an O-donor from the nitrate anion
and a N-donor from the CH3CN molecule with a long Ag–N
[Cu2(L3)2Cl4(DMF)2] (6). Green block single crystals were
obtained by similar method as described for 4. Yield: 46%. Anal.
Calcd for C42H54Cl4Cu2N14O6: C, 45.05; H, 4.86; N, 17.51.
Found: C, 45.21; H, 4.39; N, 17.74. IR (KBr, cmꢀ1): 3427w,
2925w, 2865w, 1652vs, 1446w, 1383m, 1330m, 1234m, 1183w,
1134m, 1106m, 1061m, 1033w, 914w, 741s, 668w.
1
ꢁ
bond length [Ag(1)–N(8) ¼ 2.553(4) A]. In this structure, L
displays a folded V-shape and two N coordination sites in ben-
zotriazole groups point outwards in the opposite direction to
make L1 form a trans-conformation bridging ligand. The dihe-
dral angle of two benzotriazole planes is 37.77ꢁ. Coordination of
the V-shaped ligand with the adjacent metal centers leads to the
formation of a 1D non-linear coordination polymeric chains
along the crystallographic b axis, which are further self-assem-
bled in an anti-parallel fashion and arranged alternately in the
solid state via two sets of interchain p–p interactions between the
benzotriazole–benzotriazole groups (Fig. 1b). The corresponding
X-ray data collection and structure determination
Single-crystal X-ray diffraction measurements were carried out
on a Bruker Smart APEX II or 1000 CCD diffractometer
equipped with a graphite crystal monochromator situated in the
incident beam for data collection at room temperature. The
determination of unit cell parameters and data collections was
ꢁ
face-to-face minimum distances are 3.54 and 3.68 A, respectively.
Moreover, these 1D non-linear coordination polymeric chains
ꢁ
performed with Mo-Ka radiation (l ¼ 0.71073 A). Multi-scan
are further held together by weak C–H/O and C–H/N
absorption correction was applied with the SADABS program.13
Unit cell dimensions were obtained with least-squares refine-
ments, and all structures were solved by direct methods using
SHELXS-97.14 Metal atoms in each complex were located from
E-maps. The non-hydrogen atoms were located in successive
difference Fourier syntheses (in complex 2, the oxygen atoms of
the nitrate anions are disordered and treated isotropically). The
final refinement was performed by full matrix least-squares
methods with anisotropic thermal parameters for non-hydrogen
atoms on F2. The hydrogen atoms were introduced at calculated
positions and not refined (riding model). The details of the
crystal parameters, data collections and refinement for 1–6 are
summarized in Table 1. Selected bond lengths, with the estimated
standard deviations, hydrogen bonds and p–p interactions in the
crystals are listed in Tables S1–S6 (ESI†).
ꢁ
hydrogen bonds [C(8)/O(1) ¼ 3.307(5) A, C(8)/O(3) ¼
ꢁ
ꢁ
3.292(5) A and C(15)/N(5) ¼ 3.353(6) A], and the supramo-
lecular architecture is stabilized.
Crystal structure of complex 2. The structure of complex 2 is
ꢂ
crystallized in the trigonal space group R3c, with each unit cell
containing six independent [Ag2(L2)3]2+ cations. The complex has
D3 symmetry, and Fig. 2a clearly shows a three-dimensional view
of the dinuclear [Ag2(L2)3]2+ cation, viewed approximately along
the threefold axis, whose direction is the same as the crystallo-
graphic c axis. In the dinuclear unit of complex 2, two AgI centers
are close coupled via an Ag/Ag interaction along the threefold
ꢁ
axis, and the distance between them is 3.186(1) A. The two metal
centres are further bridged by three ligands each of which
coordinates to the silver atom in a monodentate mode via the
N(1) of the benzotriazole ring. The triangle coordination
geometry of the silver atom is equilateral, with the N–Ag–N
angle being 120ꢁ. As shown in Fig. 2b, three benzotriazole rings
attaching to the AgI center are all lying approximately co-planar,
although there are slight deviations from the idealistic coordi-
nation plane consisting of three N(1) atoms. The dihedral angle
between the benzotriazole ring plane and the coordination plane
is ca. 6.53ꢁ. On the other hand, the two coordination planes in the
dinuclear cation are further linked through a set of p–p inter-
actions between phenyl–phenyl groups, with the distances
Results and discussion
The construction of supramolecular structures is highly influ-
enced by several factors, such as the geometric preference of
metal ions, the size and shapes of the organic building blocks, the
metal–ligand ratio, templates, the solvent systems and the
counter-ions. Therefore, it is necessary to decrease various
different disturbance factors as much as possible to explore the
contributions of ligands, especially flexible spacers, on complex
2892 | CrystEngComm, 2011, 13, 2890–2898
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Table 1 Crystallographic data and structure refinement summary for 1–6
Complex
1
2
3
4
5
6
Chemical formula
Formula weight
Crystal system
Space group
C16H15AgN8O3
475.23
Triclinic
C48H48Ag2N20O9
1264.80
Rhombohedral
C18H20AgN7O5
522.28
Monoclinic
P21/c
11.302(4)
9.866(3)
19.300(5)
90.00
107.972(15)
90.00
2047.1(11)
294(2)
4
1.695
1.032
1056
11 391
4367 (0.0236)
1.034
0.0290
C14H12Cl2CuN6
398.74
Triclinic
C32H32Cl4Cu2N12O2
885.58
Triclinic
C42H54Cl4Cu2N14O6
1119.87
Orthorhombic
Pbca
35.704(6)
33.360(5)
8.2196(13)
90.00
90.00
90.00
9790(3)
294(2)
8
1.520
1.149
4624
55 832
11 128 (0.1315)
1.012
0.0916
ꢂ
ꢂ
ꢂ
ꢂ
P1
R3c
P1
P1
ꢁ
a/A
9.7616(13)
9.9673(13)
11.530(3)
104.062(3)
99.128(3)
115.917(2)
932.6(3)
294(2)
2
1.692
1.117
476
4777
15.282(2)
15.282(2)
40.377(4)
90.00
7.7004(14)
9.5195(18)
11.112(2)
79.404(3)
86.652(3)
80.058(3)
788.3(3)
294(2)
2
1.680
1.731
402
3987
8.7198(7)
10.1265(9)
10.9772(9)
88.4220(10)
73.7320(10)
72.3070(10)
884.72(13)
294(2)
1
1.662
1.555
450
4525
ꢁ
b/A
ꢁ
c/A
a/ꢁ
b/ꢁ
g/ꢁ
V/A
T/K
90.00
120.00
8166.3(17)
293(2)
6
1.543
0.792
3852
11 063
1545 (0.0327)
1.013
0.0704
0.1886
3
ꢁ
Z
Dc/g cmꢀ3
m/mmꢀ1
F(000)
Refl. measured
Unique refl. (Rint
GOF on F2
)
3329 (0.0182)
1.004
0.0318
2765 (0.0236)
1.031
0.0453
3149 (0.0140)
1.016
0.0310
R1 [I > 2s(I)]a
wR2 [I > 2s(I)]b
0.0755
0.0716
0.1075
0.0703
0.1546
a
b
2
2
½
R1 ¼ SkFo| ꢀ |Fck/|Fo|. wR2 ¼ {S[w(Fo ꢀ Fc )]2/S[w(Fo2)]2} .
ꢁ
between phenyl ring centroids all being 3.66 A. As counterions,
effectively connected by these nitrate counterions via the weak
ꢁ
two non-coordinated nitrate groups are disordered over two
orientations and are located near the dinuclear cation. In addi-
tion, as displayed in Fig. 2c, the spacious dinuclear cations are
hydrogen bonds C–H/O [C(6)/O(2) ¼ 3.219(10) A, C(7)/
ꢁ
ꢁ
O(2) ¼ 3.214(9) A and C(8)/O(2) ¼ 2.947(13) A], accompanied
with parallel p–p interactions between the dinuclear cations, to
form the three-dimensional stacking.
Crystal structure of complex 3. Complex 3 is a one-dimensional
polymeric chain comprised of the neutral [Ag2(L3)2(NO3)2] as the
repeating unit (Fig. 3a). Each AgI center is bonded to two N
donors of two benzotriazole rings from two distinct L3 ligands
and two O donors from two nitrate anions. The coordination
geometry can be described as a distorted tetrahedron. In the
polymeric structure, two species of rings with different sizes are
assembled and linked alternately by AgI ions. One of them is
a centrosymmetric 30-membered macrometallacycle formed by
two L3 ligands bridging two AgI ions. The Ag/Ag non-bonding
ꢁ
distance in the dinuclear unit is 8.241 A, and the two terminal
benzotriazole rings in the same ligand have a dihedral angle of ca.
63.68ꢁ. In addition, it is shown that the cavity encircled by the
macrometallacycle is S-shaped and there are no molecules filling
it in. The other ring species are also centrosymmetric, with two
oxygen atoms from two nitrate groups bridging the two silver
atoms to obtain an obligate-planar 4-membered Ag(m–O)2Ag
ꢁ
ring. The distance of Ag/Ag is 3.953 A. As indicated in Fig. 3b,
there are a series of weak C–H/O hydrogen bonds [C(14)/O(5)
ꢁ
ꢁ
¼ 3.499(4) A, C(12)/O(3) ¼ 3.447(3) A and intra C(8)/O(2) ¼
ꢁ
3.016(3) A] in the crystal. Moreover, the centroid–centroid
Fig. 1 (a) ORTEP drawing showing the molecular structure of 1 (30%
probability ellipsoids). Hydrogen atoms are omitted for clarity.
Symmetry code: (A) x, ꢀ1 + y, z. (b) Aggregations of alternate 1D chains
link each other through a series of hydrogen bonds and p–p stacking
interactions. Hydrogen bonds are denoted by the turquoise broken line;
p–p stacking interactions are indicated by the orange broken line. The
lavender symbol represents 1D non-linear chains, constructed by a V-
shaped ligand in an anti-parallel fashion, to arrange alternately in the
solid state.
ꢁ
distance of 3.549 A between the parallel benzotriazole rings of
adjacent chains, indicates significant intermolecular face-to-face
p-stacking interactions, which further link polymeric chains
together with H-bonds to form layer-like supermolecules and
stabilize the structure.
Crystal structure of complex 4. In a similar fashion, complex 4,
formed through the combination of L1 with CuCl2, is also
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Fig. 3 (a) An ORTEP diagram showing the polymeric chain of 3 (20%
probability ellipsoids). Hydrogen atoms are omitted for clarity.
Symmetry code: (A) ꢀ1 ꢀ x, 2 ꢀ y, 2 ꢀ z. (b) 2D layer-like super-
molecules formed by aggregations of polymeric chains via weak inter-
molecular hydrogen bonds and p–p stacking interactions. Hydrogen
bonds are denoted by the turquoise broken line; p–p stacking interac-
tions are indicated by the orange broken line.
ribbon architecture, which is not found in complex 1. Then, these
Fig. 2 (a) An ORTEP diagram showing the dinuclear cations of 2 (30%
probability ellipsoids). Hydrogen atoms are omitted for clarity. (b) View
of Ag/Ag interaction and p–p stacking interactions in the dinuclear
unit. (c) The aggregation of the dinuclear cations and the filling of nitrate
groups in the packing. Hydrogen bonds are denoted by the turquoise
broken line; Ag/Ag interaction and p–p stacking interactions are
indicated by the lavender and orange broken lines, respectively.
1D polymeric ribbons are further connected by weak hydrogen
ꢁ
bonding C–H/Cl [C(7)/Cl(1) ¼ 3.716(4) A] and two sets of
interchain p–p interactions between the benzotriazole-groups
ꢁ
(face-to-face distances are 3.68 and 3.80 A) forming a three-
dimensional architecture.
Crystal structure of complex 5. The crystal structure of 5
consists of isolated dinuclear molecules with two bridging chloro
ligands. The geometry at each five-coordination CuII centre is
triangle bipyramidal with the basal plane comprising of
a terminal chlorine and two bridging chlorine atoms; the apical
positions are occupied by the two nitrogen atoms from two
bridging ligands, Fig. 5a. The bridging Cu(m–Cl(1))2Cu unit is
strictly planar with a 4-membered ring, with a crystallographi-
cally imposed inversion centre in the middle of the dinuclear unit.
a neutral 1D non-linear coordination polymeric chain running
along the crystallographic b axis like complex 1. The crystals
suitable for X-ray crystallography conform to the space group
II
ꢂ
P1; an ORTEP diagram of 4 is shown in Fig. 4a. The Cu center
resides in a distorted trans-square planar coordination sphere,
which consists of two benzotriazole N-donors and two chlorine
atoms.11n The cis-angles of all ligands around the metal ion are in
the range of 90.85ꢁ–93.18ꢁ and the trans-angles are 156.24(6)ꢁ
and 158.19(13)ꢁ respectively. The deviation of CuII atom from
ꢁ
The distance of the out-of-ring Cu–Cl(2) is 2.2744(8) A, but the
in-ring Cu–(m–Cl(1)) distances are within the normal range of
ꢁ
2.3784(7) and 2.5332(7) A respectively, which are slightly longer
ꢁ
the N2–Cl2 mean plane is equal to 0.04 A. However, it is
for the bridging chlorine as expected. In addition, the separated
ꢁ
worthwhile to note here that in comparison with the structure of
complex 1, the difference of the coordinated anion results in
a slight change in the crystal packing. For the V-shaped L1 with
trans-conformation, the dihedral angle of two benzotriazole
planes is 28.61ꢁ, which is 9.15ꢁ smaller than that in complex 1. As
indicated in Fig. 4b, two side-by-side chains related by inversion
centers close to each other are linked firstly by hydrogen bonding
Cu/Cu distance is 3.469 A and the angles for the 4-membered
ring are almost orthogonal [90.20(2)ꢁ and 89.80(2)ꢁ]. As shown in
Fig. 5b, two benzotriazole groups of L2 in fold mode are
approximately parallel to each other with the angle between them
being 13.1ꢁ. There appear to be intra-dimer stacking interactions
on the two sides of the molecule; the shortest distance between
ꢁ
benzotriazole planes is 3.83 A. Moreover, there is a set of
ꢁ
C–H/N [C(8)/N(5) ¼ 3.347(5) A] forming a 1D polymeric
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Fig. 4 (a) ORTEP drawing showing the molecular structure of 4 (30%
probability ellipsoids). Hydrogen atoms are omitted for clarity.
Symmetry code: (A) x, 1 + y, z. (b) Aggregations of alternate 1D chains
link each other through a series of hydrogen bonds and p–p stacking
interactions. Hydrogen bonds are denoted by the turquoise broken line;
p–p stacking interactions are indicated by the orange broken line.
hydrogen bonds C(15)–H(15)/Cl(1) [C(15)/Cl(1) ¼ 3.405(3)
ꢁ
A] in the molecule to stabilize the structure. In the intermolecular
packing, these dimer units are closely stacked together by p–p
ꢁ
interactions (3.67 A and 3.85 A) and a series of hydrogen bonds,
ꢁ
ꢁ
C(7)–H(7B)/O(1) [C(7)/O(1) ¼ 3.524(4) A], C(10)–H(10B)/
ꢁ
N(5) [C(10)/N(5) ¼ 3.423(4) A] and C(14)–H(14)/Cl(1)
ꢁ
[C(14)/Cl(1) ¼ 3.676(4) A].
Crystal structure of complex 6. The reaction of CuCl2 with L3
Fig. 5 (a) An ORTEP diagram showing dinuclear structure of 5 (30%
probability ellipsoids). Hydrogen atoms are omitted for clarity.
Symmetry code: (A) 2 ꢀ x, ꢀy, ꢀz. (b) View of intramolecular hydrogen
bonds and p–p stacking interactions in the dimer unit. (c) Aggregations
of dimer units through weak intermolecular hydrogen bonds and p–p
stacking interactions. Hydrogen bonds are denoted by the turquoise
broken line; p–p stacking interactions are indicated by the orange broken
line.
leads to the formation of
a
neutral bimetallic ring
[Cu2(L3)2Cl4(DMF)2], in which two ligands act as the organic
clips to bridge two metal atoms forming a 30-membered mac-
ꢁ
rometallacycle with a Cu/Cu separation of ca. 8.973 A. As
shown in Fig. 6a, two ligands are nearly related by a mirror plane
located through two crystallographically independent CuII atoms
and four chlorine atoms. In the dinuclear unit, each CuII center is
bound to two chlorine atoms and an O donor from a DMF
molecule to form the basal plane; two coordinated N atoms of L3
are located at the two apical positions of the axis. Thus, both CuII
centers adopt a five-coordination and the coordination spheres
could be described as having a slightly distorted triangle bipyr-
amid geometry, in which the axial Cu–N bonds are significantly
shorter than those in the basal plane. In addition, two coordi-
nated DMF molecules are located inside and outside the mac-
rocycle with stronger Cu–O interactions [Cu(1)–O(5) ¼ 2.090(7)
ꢁ
ꢁ
A and Cu(2)–O(6) ¼ 2.340(6)A]. Similarly to the previous
complexes, there are also many extensive weak hydrogen
ꢁ
bonding systems, C–H/Cl [C(7)/Cl(2) ¼ 3.523(8) A, C(25)/
ꢁ
ꢁ
Cl(2) ¼ 3.562(7) A, C(11)/Cl(3) ¼ 3.538(10) A, C(29)/Cl(3) ¼
ꢁ
ꢁ
3.560(8) A and C(30)/Cl(4) ¼ 3.667(7) A] and C–H/O
ꢁ
[C(12)/O(2) ¼ 3.500(11) A]. Moreover, a series of the centroid–
ꢁ
centroid distances [3.668(5) A, 3.840(4) A, 3.785(5) A and
ꢁ
ꢁ
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a V-shape with trans-conformation because of the short spacer.
Ligand L2 with the longer spacer is folded completely and takes
on a U-shape with trans-conformation for 2 but cis-conforma-
tion for 5, and the dihedral angle of the two benzotriazole planes
are 0.65ꢁ and 13.85ꢁ, respectively. With the increasing length of
the ligand spacer, the shape of ligand L3 becomes curved and the
type of ligand is more uncertain. The corresponding torsion
angles can be found in Tables S1–S6 (ESI†).
For two groups of complexes containing the same metal ions
reported in this work, X-ray diffraction studies reveal that they
can be classified into three kinds of typical structure featuring
mostly 0D dinuclear units for 2 and 5,1D non-linear coordina-
tion polymeric chains for 1 and 4, and a relatively stable dinu-
clear metallomacrocycle skeleton for 3 and 6.
As shown in Scheme 3, it is clearly demonstrated that choosing
suitable flexible chain organic ligands is crucial for the formation
of complexes with special structures. For ligand L1 with a shorter
spacer, it could not change the configuration easily due to
a relatively rigid skeleton structure and can only act as a bridge
connecting the adjacent coordination groups of benzotriazoles,
resulting in the formation of the similar 1D non-linear coordi-
nation polymeric chain for different metal ions. Fortunately, the
1D non-linear chain constructed by 1,2-bis(benzotriazol-1-
yl)ethane under mild conditions has not yet been found and is
quite different from previously reported using AgNO3 or those
metal complexes of L1 despite the same ligand structure.3f,11d,j,k
The variety is mostly due to different preparation conditions or
the solvent systems for complexes crystal growth.
In 2 and 5, the spacer of ligand L2 is longer and the flexibility is
enhanced remarkably compared with ligand L1, which not only
leads to ligand molecules adopting multi-bridge modes to
connect two metal ions, but the two metal ions are closer to each
other to a greater extent to form a dinuclear unit. For ligand L3
with the longest spacer and most flexible structure, it could not
encircle a metal ion to form a 1 : 1 mode complex owing to the
disturbance of anion and the limit of chain length. Therefore, it is
relatively easy to form the 2 : 2 mode dinuclear metallomacro-
cycle for 3 and 6 through the connectivity of two ligand bridges.
The difference is that there are two nitrate anions to link dinu-
clear building blocks to self-assemble a 1D chain for 3 but not for
6. The progressive variation from the 1D non-linear coordina-
tion polymeric chain (1 and 4) to 0D dinuclear units (2 and 5) to
Fig. 6 (a) An ORTEP diagram showing the 30-membered bimetallic
ring of 6 (30% probability ellipsoids). Hydrogen atoms are omitted for
clarity. (b) 2D layer formed by weak hydrogen bonds and intermolecular
p–p aromatic stacking interactions in 6.
ꢁ
3.722(5) A] between the parallel benzotriazole rings of adjacent
ligands indicates significant intramolecular face-to-face p-
stacking interactions, Fig. 6b. Therefore, the thick layered
structure is linked and stabilized by these interactions.
Structural comparison of complexes 1–6 and the influencing
factors
For three structurally related ligands, each of them has a number
of changes in the conformation due to the relative orientations of
two terminal groups and the flexible spacer. In these metal
complexes, ligands are mainly divided into two types, the same
direction (cis-) and the opposite direction (trans-), according to
the difference in the relative orientations of two benzotriazole
rings in the ligand without taking into account the shape of the
bridging spacer (Scheme 2). As a bridging spacer, the length
directly influences the flexibility and the shape of the ligand. In
complexes 1 and 4, ligand L1 is folded incompletely and takes on
a
stable dinuclear metallomacrocycle skeleton is mainly
Scheme 2 Types and shapes of ligands in the metal complexes.
2896 | CrystEngComm, 2011, 13, 2890–2898
Scheme 3 Schematic view of six complexes in this work.
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attributed to the change of the flexible ligand spacers. In other
words, the structural diversity and the dimensional change of
these complexes are effectively controlled by choosing suitable
flexible chain organic ligands.
Conclusions
We have designed three structurally related flexible bis(benzo-
triazole) ligands, and illustrated some useful results of ligand
design for self-assembly of diverse coordination aggregates with
AgI and CuII ions. Without the influence of counteranions, the
work clearly indicates that the length of flexible ligand spacers
plays an important role in influencing the formation of the
coordination architectures. For flexible chain ligands L2 and L3
with longer spacers, all complexes are self-assembled to form
different dinuclear units, among which 3 is further linked by
anions to form an extended 1D chain. But for L1 with a short
spacer, 1 and 4 show similar 1D non-linear coordination poly-
meric chains despite having different metal centers and different
stacking modes. Moreover, the introduction of oxygen atoms in
flexible chains could form a series of weak hydrogen bonds,
which may provide an effective method for controlling the crystal
structures of complexes. The studies on TGA of complexes reveal
that the length of flexible chain ligands greatly affects the
stability of the complex framework, and the decomposition
temperature of complexes gradually increases with progressive
structural variation from the flexible metallomacrocycle skel-
eton, to 0D dinuclear units to 1D non-linear coordination
polymeric chains. Accordingly, we believe that further investi-
gation on flexible ligands and understanding various weak
interactions will allow a more efficient control of the three-
dimensional structure of supramolecular compounds with
suitable thermal stability and extend a wide variety of metal-
losupramolecular architectures.
Thermal analysis
To evaluate the contribution of the correlative flexible ligands
with different chain spacer to the thermal stability of complexes
with low-dimensional structural features, thermal gravimetric
analyses (TGA) of complexes 1–6 were carried out under
a nitrogen atmosphere with a heating rate of 10 ꢁC minꢀ1 (Fig. 7).
For Ag complex 1, the first weight loss of 6.0% observed from
100 to 125 ꢁC is related to the decomposition of the coordinated
acetonitrile molecules (calcd 5.7%). Then, the complex remains
largely unchanged until the decomposition of the whole coordi-
nation network occurs at the temperature of 262 ꢁC. The TGA of
2 shows that the whole complex structure is stable up to 255 ꢁC.
For Ag complex 3, the weight loss curves also indicate that the
frameworks do not collapse until 234 ꢁC. The results reveal
clearly that the length of the flexible chain ligand greatly affects
the structure and stability of the complex framework, and the
decomposition temperature of the complexes gradually increases
with progressive structural variation from the flexible metal-
lomacrocycle skeleton (3), to 0D dinuclear units (2) to 1D
coordination polymeric chain (1). In other words, the complexes
formed by ligands with shorter spacer are more stable than those
with longer spacer ligands. In addition, the TGA curves of Cu
complexes 4–6 indicate that the decomposition degree of the 1D
coordination polymeric chain (4) is higher than that of the 0D
dinuclear units (5 and 6), which are stable up to 290, 254 and 209
ꢁC, respectively. The results also suggest that the complexes with
multidimensional structure formed by shorter spacer ligands are
more thermally stable, which is similar to Ag complexes 1–3.
Acknowledgements
This work was financially supported by the National Natural
Science Foundation of China (Grants 20771048, 20931003,
21001059) and the Fundamental Research Funds for the Central
Universities (lzujbky-2009-k06, lzujbky-2009-114).
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2898 | CrystEngComm, 2011, 13, 2890–2898
This journal is ª The Royal Society of Chemistry 2011