Coordination polymers derived from a flexible bis(pyridylurea) ligand: Conformational change of the ligand and structural diversity of the complexes

Article abstract of DOI:10.1039/c0ce00200c

The assembly of a bis(pyridylurea) ligand, N,N′-ethane-1,2-diylbis(3- pyridin-4-ylurea) (L), with Zn(AcO)₂, CdCl₂, CdSO ₄ or CuSO₄ led to four coordination polymers, {[Zn(AcO)₂L]·H₂O·CH₃OH} _n (1), {[CdCl₂L₂]·2DMF}_n (2), {[CdSO₄L(H₂O)₃]·3H₂O} _n (3), and {[CuSO₄L(H₂O)₂] ·2H₂O}_n (4). Compound 1 is an infinite 1D zigzag chain with alternate Zn(AcO)₂ units and L molecules. The cadmium(ii) dichloro complex 2 features a corrugated sheet structure with a (4,4) net topology, while the sulfato complex 3 shows a unique 1O/2U interwoven 3D structure assembled from zigzag chains. The copper(ii) complex 4 is an exceptional diamondoid network with an unusual 12-fold [6 + 6] interpenetration mode. Interestingly, the ligand shows the expected flexibility in the formation of the coordination polymers. In 1, 3 and 4, the central ethylene spacer adopts the anti conformations and is roughly linear, whereas in 2 it assumes a gauche form and exists as a V-shaped linker. The structural variation of these coordination polymers as well as the conformational change of the ligand in the presence of different counter anions and metal ions is discussed.

Full text of DOI:10.1039/c0ce00200c

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PAPER
Coordination polymers derived from a flexible bis(pyridylurea) ligand:
conformational change of the ligand and structural diversity of the complexes†
ab
Yongjing Hao,ac Biao Wu,
Shaoguang Li,ac Chuandong Jia,ac Xiaojuan Huanga and Xiao-Juan Yangab
*
Received 12th May 2010, Accepted 8th July 2010
DOI: 10.1039/c0ce00200c
The assembly of a bis(pyridylurea) ligand, N,N0-ethane-1,2-diylbis(3-pyridin-4-ylurea) (L), with
Zn(AcO)2, CdCl2, CdSO4 or CuSO4 led to four coordination polymers, {[Zn(AcO)2L]$H2O$CH3OH}n
(1), {[CdCl2L2]$2DMF}n (2), {[CdSO4L(H2O)3]$3H2O}n (3), and {[CuSO4L(H2O)2]$2H2O}n (4).
Compound 1 is an infinite 1D zigzag chain with alternate Zn(AcO)2 units and L molecules. The
cadmium(II) dichloro complex 2 features a corrugated sheet structure with a (4,4) net topology, while
the sulfato complex 3 shows a unique 1O/2U interwoven 3D structure assembled from zigzag chains.
The copper(II) complex 4 is an exceptional diamondoid network with an unusual 12-fold [6 + 6]
interpenetration mode. Interestingly, the ligand shows the expected flexibility in the formation of the
coordination polymers. In 1, 3 and 4, the central ethylene spacer adopts the anti conformations and is
roughly linear, whereas in 2 it assumes a gauche form and exists as a V-shaped linker. The structural
variation of these coordination polymers as well as the conformational change of the ligand in the
presence of different counter anions and metal ions is discussed.
leading to diverse structures of the metal–organic networks.4
Introduction
The pyridyl moiety is probably the most popular building
block for the construction of metal–organic networks due to
its strong coordination ability to metal ions. Many oligo-
pyridyl ligands with both rigid and flexible bridges have been
used in the assembly of coordination architectures, and the
structural topologies and chemical and physical properties of
them were extensively studied.3
Great interest has focused on coordination polymers not only
because of their unique advantages in functional solid mate-
rials, ion exchange, catalysis and optics, etc., but also for their
fascinating structures.1 The variety of self-assembled structures
relies largely on the presence of suitable metal–ligand inter-
actions and supramolecular contacts (hydrogen bonding and
other weak interactions). By careful selection of metal ion
‘nodes’ and rigid organic ‘linkers’ with definite coordination
preferences, numerous coordination networks with specific
topologies have been successfully constructed.1b,2 On the other
hand, the structures of metal complexes which contain rela-
tively flexible bridging ligands are less predictable due to the
possible supramolecular isomerism, such as the different
conformations the ligand may adopt.2,3 Nevertheless, the
flexible ligands could accommodate different coordination
environments by adjusting their conformation, length or
inherent angle of the terminal coordinative groups, thus
The oligo(pyridylurea) ligands, which contain two or more
pyridyl ends separated by various linkers, have proven to be both
promising anion receptors and excellent building blocks for
novel supramolecular architectures.5 Recently, some bis(pyr-
idylurea) ligands with different spacers between the two pyr-
idylurea fragments have been used for the construction of
metal–ligand supramolecular complexes.6 By varying the length
of the alkyl spacer and the coordination site of the terminal
pyridines (3- or 4-position), we have obtained various coordi-
nation networks, such as metallomacrocycles and helical
chains,5d 3-fold interpenetrated MOFs5e and 1D / 1D inter-
penetrated coordination polymers.5f Herein, we report
a
bis(4-pyridylurea) receptor bearing a flexible ethylene spacer,
N,N0-ethane-1,2-diylbis(3-pyridin-4-ylurea) (L) and four metal–
organic coordination complexes constructed with L, including
a 1D chain {[Zn(AcO)2L]$H2O$CH3OH}n (1), a 2D layered
structure {[CdCl2L2]$2DMF}n (2), a 3D interwoven structure
assembled from 1D zigzag chains, {[CdSO4L(H2O)3]$3H2O}n
(3), and a diamondoid network with an unusual 12-fold
[6 + 6] interpenetration mode, {[CuSO4L(H2O)2]$2H2O}n (4)
(Scheme 1).
aState Key Laboratory for Oxo Synthesis & Selective Oxidation, Lanzhou
Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou,
730000, China. E-mail: wubiao@lzb.ac.cn; Fax: +86 931 4968286
bState Key Laboratory of Applied Organic Chemistry, Lanzhou University,
Lanzhou, 730000, China
cGraduate University of Chinese Academy of Sciences, Beijing, 100049,
China
† CCDC reference numbers 761485, 761486, 777155–777157. For
crystallographic data in CIF or other electronic format see DOI:
10.1039/c0ce00200c
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Scheme 1 Illustration of the conformation of L in compounds 1–4.
Results and discussion
The ligand N,N0-ethane-1,2-diylbis(3-pyridin-4-ylurea) (L) was
synthesized from 4-isocyanatopyridine and 1,2-diaminoethane
by a similar procedure to that reported previously for related
ligands.5 Reaction of L with Zn(AcO)2$2H2O, CdCl2$2.5H2O,
3CdSO4$8H2O or CuSO4$5H2O afforded the complexes (1–4)
with variable structures, which are dependent on the counter
anion and metal ion employed. Very recently, the same ligand
was reported, but it was synthesized by a different reaction
of 4-aminopyridine and triphosgene in the presence of
triethylamine.6f
Fig. 1 (a) Molecular structure of L. Symmetry code: (i) 1 ꢁ x, 2 ꢁ y, 2 ꢁ
z. (b) The four water chains around each L molecule. Hydrogen bond
parameters (A, ꢀ): O2/O1, 2.732(2); O2–H2A/O1, 172(3); O3/N1,
ꢁ
2.766(2); O3–H3A/N1, 166(3); N2/O2i, 2.935(2); N2–H2/O2i, 176.2;
N3/O3ii, 2.950(2); N3–H3/ O3ii, 156.4. Symmetry codes: (i) 1 + x, y, z;
(ii) 1 + x, 1 + y, 1 + z. (c) Part of the infinite chain of the ligand bridged by
solvent water molecules. Hydrogen bond parameters (A, ꢀ): N2/O2,
2.935(2); N2–H2/O2, 176.2; O2/O1, 2.732(2); O2–H2C/O1, 172(3).
ꢁ
Crystal structures
ꢀ
L$4H2O. Colourless crystals (space group P1) of ligand L were
obtained through slow evaporation of its water–methanol
(1 : 1 v/v) solution. The asymmetric unit contains half ligand
molecule and two crystal water molecules. The ligand adopts
a roughly linear (GAG) conformation with torsion angles of
87.01ꢀ, ꢁ180.00ꢀ and ꢁ87.01ꢀ for the ethylene diamine spacer.
Here the A (anti) or G (gauche) conformation is given when the
N–C–C–N or C–C–N–C torsion angle (q) is in the range 180 $
q > 90ꢀ and 0 # q # 90ꢀ, respectively (Fig. 1a).7 Interestingly, in
the packed structure, each L molecule is surrounded by four
infinite water chains through Nurea–H/Ow (N/O: 2.935(2)–
H2O (v/v 1 : 1) afforded colourless block crystals of {[Zn(A-
cO)2L]$H2O$CH3OH}n (1). Complex 1 crystallizes in the triclinic
ꢀ
space group P1. The asymmetric unit consists of one Zn atom,
two AcOꢁ ions, two halves of the ligand, one solvent CH3OH
molecule and one water molecule. As shown in Fig. 2a, the Zn(II)
ion is coordinated by two pyridyl nitrogen atoms from two
ligands and four oxygen atoms of two chelating AcOꢁ anions in
a distorted octahedral geometry. The ligands act as bridges,
linking the zinc atoms to form a one-dimensional zigzag chain
ꢁ
(Fig. 2a) with a Zn/Zn separation of 19.62 A and Zn/Zn/Zn
angle of 114.68ꢀ. Like the free ligand, the L molecule adopts
a roughly linear GAG conformation in 1. Selected bond lengths
and bond angles for the complexes 1–4 are given in Table 1.
In the extended structure, the zigzag chains are arranged
parallel to each other and are further interlinked into a ladder-
like two-dimensional network through N–H/O interactions
between urea NH groups and oxygen atoms of the coordinated
AcOꢁ anions (Fig. 2b). Such hydrogen bonds play an important
role in creating the higher-dimensional structure, as observed
in many systems.8 A similar Zn(II) chloro complex with L,
[(Zn(m-L)Cl2)$X]n (X ¼ disordered lattice solvents), was reported
ꢁ
ꢁ
2.950(2) A), Ow–H/Npy (O/N: 2.766(2) A) and Ow–H/OC]O
ꢁ
(O/O: 2.762(3) A) hydrogen bonds between the urea NH
groups, the terminal pyridyl N atoms, and the urea carbonyl
groups, respectively, and the water molecules (Fig. 1b). The
ligands are further extended to an infinite chain bridged by two
water molecules between two adjacent molecules (Fig. 1c), while
the typical urea tape formed by self-association of the urea
groups does not occur in this structure.
{[Zn(AcO)2L]$H2O$CH3OH}n (1). Slow evaporation of
a solution of Zn(AcO)2$2H2O and L (Zn : L ¼ 1 : 1) in CH3OH–
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in 1. As a result, the zigzag shape of [(Zn(m-L)Cl2)$X]n is deter-
mined by the ligands but not metal nodes, since the Zn atoms
within each chain is co-linear rather than bent as in the present
work.
{[CdCl2L2]$2DMF}n (2). The reaction of L and CdCl2 in
CH3OH–H2O–DMF (v/v/v 1 : 1 : 1) gave the complex
{[CdCl2L2]$2DMF}n (2) as colourless block crystals crystallizing
in the monoclinic space group C2/c. The asymmetric unit
contains half a Cd atom, one Cl atom, one ligand and one solvent
DMF molecule. In the crystal structure, the Cd(II) center resides
on a center of inversion, being coordinated by four pyridyl
nitrogen atoms of four ligands and two chloride ions in an
octahedral geometry (Fig. 3a). Unlike that in complex 1, the
ligand adopts a V-shaped AGA conformation in 2.
The structure of this complex can be best described as
a corrugated 2D sheet in which four ligands bridge four Cd(II)
centers to form a (4,4) network topology (Fig. 3b). It is note-
worthy that the (4,4) nets are one of the most frequently occur-
ring motifs in metal coordination polymers; however most of
them are constructed with rigid organic linkers, which result in
largely planar two-dimensional grids. In contrast, the structures
of corrugated grid-like sheet are not very common.1d,9 In the
current case, the flexible ligand with the bent conformation it
adopts is responsible for the corrugated (4,4) grids which show
an approximate chair conformation (one unit is shown in yellow
in Fig. 3b). Moreover, these corrugated sheets are further linked
ꢁ
by N–H/O (N4/O1 ¼ 2.862 A) hydrogen bonds of the urea
Fig. 2 (a) Part of the zigzag chain in 1; (b) 2D network formed by N–H/
O hydrogen bonding. Hydrogen bond parameters (A, ꢀ): N2i/O6ii,
ꢁ
groups from adjacent layers, and the solvent DMF molecules are
trapped between the layers by N–H/O hydrogen bonds with the
urea groups (Fig. 3d).
2.8987(52); N2i–H2A/O6ii, 141.47; N3i/O3ii, 2.9521(61); N3i–H3/O3ii,
164.82. Symmetry codes: (i) ꢁ1 ꢁ x, 4 ꢁ y, 1 ꢁ z; (ii) ꢁ1 ꢁ x, 3 ꢁ y, 1 ꢁ z.
a
ꢀ
{[CdSO4L(H2O)3]$3H2O}n (3). When the counter anion was
changed from Clꢁ to SO4
ꢁ
Table 1 Selected bond lengths (A) and angles ( ) for 1–4.
2ꢁ
, the complex {[CdSO4L-
Compound 1
Zn–N(1)
Zn–N(4)
Zn–O(5)
O(5)–Zn–N(1)
O(5)–Zn–O(3)
N(1)–Zn–O(3)
N(4)–Zn–O(4)
O(3)–Zn–O(4)
Compound 2
Cd–N(1)
(H2O)3]$3H2O}n (3) was obtained as colourless block crystals
2.049(3)
2.023(2)
2.016(2)
97.32(10)
96.94(11)
100.52(11)
94.36(10)
57.54(11)
Zn–O(3)
Zn–O(4)
2.066(3)
2.342(3)
O(5)–Zn–N(4)
N(4)–Zn–N(1)
N(4)–Zn–O(3)
O(5)–Zn–O(4)
N(1)–Zn–O(4)
O(5)–Zn–O(6)
103.50(10)
108.48(11)
141.67(11)
153.13(11)
95.81(10)
51.079(78)
2.3610(15)
2.6294(6)
87.65(5)
Cd–N(6)A
N(1)–Cd–Cl
N(6)A–Cd–Cl
2.3898(15)
89.91(4)
89.67(4)
Cd–Cl
N(1)–Cd–N(6)A
Compound 3
Cd–O(6)
2.285(3)
2.312(3)
89.54(11)
Cd–N(4)
O(6)–Cd–N(4)
N(4)–Cd–N(1)
2.312(3)
93.81(12)
91.56(12)
Cd–N(1)
O(6)–Cd–N(1)
Compound 4
Cu–O(1)
Cu–O(3)
Cu–N(1)
O(5)–Cu–O(3)
O(3)–Cu–N(1)
O(3)–Cu–N(4)
2.443(5)
1.991(3)
1.999(3)
91.09(11)
89.76(12)
176.49(13)
Cu–O(2)
Cu–O(5)
Cu–N(4)
O(5)–Cu–N(1)
O(5)–Cu–N(4)
N(1)–Cu–N(4)
2.627(5)
1.975(3)
2.010(3)
175.77(13)
88.36(12)
90.54(13)
a
Symmetry code: (A) x, ꢁy, 0.5 + z.
Fig. 3 Crystal structure of 2. (a) The coordination environment of the
cadmium atom; (b, c) top view and side view of the corrugated sheet with
the (4,4) net topology; (d) Hydrogen bonds between the 2D sheets; (e)
Topological representation of the (4,4) connected network. Symmetry
codes:(i)0.5ꢁx, 0.5ꢁ y,1ꢁz;(ii)x, ꢁy, 0.5+z;(iii)0.5ꢁx, 0.5+y, 0.5ꢁz.
recently which is also a 1D zigzag polymeric chain.6f However,
the ligand molecule adopts a G conformation with a disordered
ethylene spacer in this complex, which is different from that (A)
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through diffusion of a solution of L in CH3OH and a solution of
CdSO4 in H2O. Complex 3 crystallizes in the monoclinic space
group C2/c, with one Cd atom, one SO42ꢁ ion, two halves of the
ligand and six water molecules (three coordinated and three
crystallized) in an asymmetric unit. Compared to the cadmium
chloro complex 2, in which the Cd2+ ion is coordinated by four
ligands and two anions, the octahedral Cd2+ center in 3 is coor-
dinated by only two L ligands together with a monodentate
every interwoven sheet containing chains propagating along two
directions (A and B in Fig. 4e) further interweaves with the
chains (B0 and A0) in the neighbouring sheets, also in the 1O/2U
mode, and an overall 3D interlocking network is formed
(Fig. 4e).
{[CuSO4L(H2O)2]$2H2O}n (4). Needle-like blue crystals of the
copper(II) complex 4 were obtained through slow diffusion of
CuSO4$5H2O and L in CH3OH–H2O. Compound 4 crystallizes
in the orthorhombic space group Pnna. The asymmetric unit
consists of one Cu atom, two halves of SO42ꢁ ion, two halves of
the ligand, and four water molecules (two coordinated and two
crystallized) with the composition {[CuSO4L(H2O)2]$2H2O}n.
Notably, complex 4 features a 12-fold [6 + 6] interpenetrated
diamondoid net. According to the classification of the inter-
penetration patterns proposed by Blatov et al., the structure
belongs to the interpenetration class IIIa. For class III (trans-
lational and non-translational), the overall entanglement is
generated both by pure translations (TIVs, translating inter-
penetration vector; or PIVs, partial interpenetration vector) and
by space group symmetry elements (NISEs, non-translating
interpenetration symmetry element; or PISEs, partial interpen-
etration symmetry element). If a TIV exists, the array belongs to
class IIIa.12
2ꢁ
SO4 anion and three H2O molecules (Fig. 4a). The ligand
molecules show a linear AAA conformation, which is different
from that in 1 and 2. The two ligands that coordinate to the metal
center in a cis fashion further bridge other Cd atoms to form
a one-dimensional zigzag chain structure (Fig. 4b) rather than
ꢁ
the 2D (4,4) net in 2. The Cd/Cd separation is 20.21 A and
Cd/Cd/Cd angle is 70.53ꢀ in each chain.
An unusual feature of this compound is that the zigzag chains
interweave in a ‘one-over/two-under’ (1O/2U) fashion to create
a cloth-like sheet structure as shown in Fig. 4c and 4d. In such
a supramolecular entanglement, each chain is chemically inde-
pendent but physically interwoven with the perpendicular
chains.10 Thus, in contrast to the interpenetrated networks,
breaking of chemical bonds is not required to take apart this
network structure. It is noteworthy that only a few interwoven
‘‘warp-and-woof’’ sheet networks of zigzag chains have been
reported so far.11 For example, Ciani and co-workers11a
described a 2D sheet (1O/1U) which represents the first inter-
woven network of 1D rigid zigzag coordination strands. Li
et al.11b reported a 2D interwoven network (2O/2U), while Cheng
et al.11c illustrated how the 1D zigzag chains in four different
directions were hierarchically entangled to generate an unprec-
edented 3D interwoven framework. Very recently, Peedikakkal
et al.11d reported a 1O/1U interwoven fabric structure formed by
spiral 1D coordination polymeric chains of the PbII complex. To
the best of our knowledge, compound 3 is the first 1O/2U
interwoven fashion in coordination networks. In complex 3,
The diamond structure, as one of the most common and
important types of topology, has attracted great attention for its
potential applications in non-linear optics (NLO) since the pio-
neering work of Ermer.13 For the diamondoid coordination
polymers, the n-fold interpenetrated networks have been an
invariable highlight. As reviewed by Robson,14 the common
interpenetration mode of diamond structure is that the nodes of
independent nets are aligned and equally spaced along one of the
2-fold axes. However, exceptional interpenetration modes have
also been reported in the literature.13b,15 Recently, Hsu et al.15a
reported a 12-fold interpenetrated diamondoid net with a flexible
Fig. 4 (a) The molecular structure of 3 showing the local coordination geometry around the metal center. (b) Perspective view of the 1D coordination
polymeric strand. (c) 1O/2U interwoven 2D network. (d) Top view of the schematic representation of the 1O/2U cloth-like sheet. (e) Schematic
representation of the 3D network in 3.
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ligand N,N0-di(4-pyridyl)adipoamide, [CuSO4(L0)(H2O)2]N,
which is the maximum number of interpenetration presently
known for coordination polymers, though a hydrogen-bonded
structure has been reported very recently to show a 18-fold
interpenetration of diamond frame.16
can see that it acts as a tetrahedral node which connects four
other neighbours through four bis(pyridylurea) ligands (Fig. 5b).
The ligand molecules show two different conformations (AAA
and GAG) in 4, and the adjoining nodes are separated by two
ꢁ
different distances of 24.03 and 23.46 A, respectively, which are
ꢁ
similar to the reported compound (24.46 and 23.62 A). The
Compound 4 represents the second example of the highest
interpenetrating number (12) for diamondoid coordination
polymers. Although compound 4 shows a similar 3D diamond-
like topology as the reported first 12-fold interpenetrated dia-
mondoid compound [CuSO4(L0)(H2O)2]N, its composition and
the local coordination environment of the Cu2+ ions are signifi-
cantly different from the latter.15a Compound 4 contains two
coordinated and two crystal waters molecules, respectively, while
the reported first example has only one coordinated and one
crystal water molecule. Consequently, the Cu2+ ions in 4 have
a six-coordinate, Jahn–Teller distorted octahedral geometry,
being coordinated by two nitrogen atoms from two bridging
ligands, two oxygen atoms from two bridging sulfate ions, and
two water molecules on the axial positions (Fig. 5a). In contrast,
the Cu2+ centers in [CuSO4(L0)(H2O)2]N show a five-coordinate
distorted square pyramidal geometry with only one coordinated
water (in the apical position).15a The Cu–Ow distances (Cu–O1,
structure of 4 consists of a three-dimensional framework with the
extended diamondoid topology. The maximum dimensions of
3
ꢁ
the adamantane cage (37.72 ꢂ 80.92 ꢂ 32.28 A ) are similar to
3
15a
ꢁ
the reported compound (37.36 ꢂ 82.27 ꢂ 32.61 A ). Such
a large cavity allows the unusual 12-fold interpenetration of the
networks. This interpenetration mode differs from the normal
mode and can be described as two sets of normal 6-fold nets.
Fig. 5c shows a view from the b axis, in which the two sets of the
normal sixfold net are interpenetrated with a relative translation
vector of a/2 + b/2.2a,15a Thus, this mode is named a [6 + 6]
interpenetrated diamondoid system.
Noticeably, the framework is supported by extensive hydrogen
bonds. Each m2-coordinated sulfate ion is surrounded by two urea
fragments and four water molecules (both coordinated and
solvent), accepting six hydrogen bonds, including two direct
ꢁ
N–H/O contacts (N/O ¼ 2.853, 2.921 A) with the urea NH
ꢁ
2.443(5) A; Cu–O2, 2.627(5) A) in 4, however, are longer than
ꢁ
ꢁ
groups, two O–H/O bonds (O/O ¼ 2.866, 2.966 A) with the
ꢁ
that in the latter (2.275(5) A). Like the case in its analogue
2ꢁ
crystal water molecules, and two O–H/O contacts (O/O ¼
[CuSO4(L0)(H2O)2]N, the SO4 anions in 4 also adopt the
ꢁ
2.794, 2.916 A) with the coordinated water molecules, respec-
m2-h1,h1-bridging coordination fashion, linking two Cu ions to
tively (Fig. 5d). Notably, the two urea groups do not display the
eight-membered R22(8) hydrogen bonding mode, but donate only
a single N–H/O hydrogen bond using one of the NH donors,
while the other NH is bridged to the sulfate ion through an
O–H/O interaction with a crystal water molecule. In addition,
form an eight-membered cycle with a comparable Cu/Cu
ꢁ
ꢁ
separation
(4.797
A
compared
to 4.681
A
in
[CuSO4(L0)(H2O)2]N) (Fig. 5a). When the midpoint of the two
SO4-bridged copper atoms is viewed as a connecting node, we
Fig. 5 Crystal structure of 4. (a) The coordination environment around the Cu(II) ions. Symmetry codes: (i) x, 1.5 ꢁ y, 1.5 ꢁ z; (ii) ꢁx, 1 ꢁ y, ꢁz;
(iii) 1 ꢁ x, 2 ꢁ y; ꢁz; (b) Schematic views of the 12-fold interpenetration; (c) The [6 + 6] interpenetration viewed from the b axis; (d) Hydrogen bonds
around the sulfate ion. Hydrogen bond parameters (A, ꢀ): N2i/O6, 2.853(4); N2i–H2Ai/O6, 165.5; O1/O6, 2.966(6); O1–H1Bi/O6, 145(5); N3i/
ꢁ
O9, 2.864(6); N3i–H3i/O9, 148.9; O9/O5i, 2.795(5); O9–H9C/O5i, 127(5). Symmetry code: (i) x, 1.5 ꢁ y, 1.5 ꢁ z.
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release of the two DMF molecules and loss and/or combustion of
the organic components. The TGA curve of 3 showed a weight
loss from room temperature to 151 ꢀC corresponding to five
water molecules (observed 1ꢀ4.0%, calculated 15.0%). The
compound decomposed at 230 C. Complex 4 has a reasonable
stability in the solid state.ꢀThere is a 13.0% weight loss in the
temperature range 49–195 C, which is attributed to the loss of
the two coordinated and two crystal water molecules (calculated
13.5%). The compound began to decompose at above 241 ꢀC
with a sharp weight loss. It should be noted that the decompo-
sition temperature of the first 12-fold diamondoid network is
relatively low (around 80 ꢀC).15a Thus, complex 4 exhibits an
improved stability, which is probably due to the enhanced
hydrogen bonding interactions in 4 as mentioned above.
Conclusions
We report four coordination polymers constructed from a flex-
ible bis(pyridylurea) ligand (L). The supramolecular structures of
the complexes vary from 1D zigzag chain (1) to 2D corrugated
sheet (2) and interwoven 3D network (3), and then to a rare 3D
diamondoid network with a 12-fold [6 + 6] interpenetration
mode (4). Interestingly, the flexible ligand adopts different
conformations in the complexes (roughly linear in 1, 3, and 4,
and V-shaped in 2), and geometric needs of the metal atoms and
coordination of the anions also play important roles in the
construction of the complexes. Moreover, the urea groups
participate in various hydrogen bonding interactions in all the
complexes, which are essential in the formation of the secondary
(or higher-dimensional) supramolecular structures.
Fig. 6 Powder X-ray diffraction patterns: as-synthesized (red) and
simulated from the single-crystal diffraction data (black): (a) 1; (b) 2;
(c) 3; (d) 4.
different O–H/O interactions from the urea carbonyls of the
ꢁ
ꢁ
ligand L (O/O ¼ 2.866 A) or the crystal water (O/O ¼ 2.806 A)
to the coordinated water molecules are also observed. It is noticed
that there are only four hydrogen bonds around the sulfate ion in
the first 12-fold diamondoid network.15a The enhanced anion
binding in our compound 4 should be the result of the existence of
two more water molecules (one coordinated and one crystal),
which can serve as good hydrogen bond donors and acceptors.
PXRD and TG analyses of the complexes
Experimental
Compounds 1, 2, 3 and 4 were further confirmed by elemental
analyses, IR spectroscopy and powder X-ray diffraction. The
PXRD patterns (Fig. 6) revealed the phase purity of the
complexes. The thermal stability of the compounds was studied
by TGA (Fig. 7). Compound 1 showed a slight weight loss from
room temperature to 119 ꢀC corresponding to the release of
a CH3OH and a H2O molecule (observed weight loss 9.4%,
calculated 10.8%), as well as a major weight loss occurring at
above 208 ꢀC due to the decomposition of the organic ligand.
Compound 2 began to decompose from about 210 ꢀC due to
General procedures
All starting chemicals were commercially available and were used
as received. Elemental analyses were done on a VarioEL
instrument from Elementaranalysensysteme GmbH. IR spectra
were recorded on a Bruker IFS 120HR spectrometer as KBr
disks (500–4000 cmꢁ1). 1H NMR spectra were recorded at
ambient temperature on a Mercury Plus 400 MHz FT spec-
trometer in DMSO-d6. Melting points were detected on an X-4
Digital Vision MP Instrument. Powder X-ray diffraction
(PXRD) data were collected on a Philips X’Pert PRO SUPER
ꢁ
diffractometer with Cu-Ka radiation (l ¼ 1.54187 A). TG
analyses were carried out with a Pyris diamond instru-
ment (Perkin Elmer) under N2 atmosphere with a heating rate of
10 C minꢁ1
.
ꢀ
Synthesis of L. 4-Pyridyl acyl azide (3.00 g, 20.2 mmol) in
freshly dried toluene (100 mL) was refluxed under a nitrogen
atmosphere for 1 h to give a pale yellow solution. Then 1,2-
diaminoethane (0.61 g, 10.1 mmol) was added and the mixture
was refluxed for 30 min and then cooled to r.t. A white powder
was collected and washed with toluene, diethyl ether and dried in
vacuo. Yield: 1.5 g (50%). M.p.: 245–247 ꢀC. Anal. calcd for
C14H16N6O2$0.7H2O: C 53.73, H 5.60, N 26.80. Found: C 53.41,
H 5.25, N 26.98%. 1H NMR (DMSO-d6, 400 MHz): 9.05 (s, 2 H,
pyridyl-NH-), 8.28 (d, 4 H, J ¼ 6.4 Hz, Py-H2), 7.37 (dd, 4 H, J ¼
1.4, 6.4 Hz, Py-H3), 6.46 (s, 2 H, CH2–NH-), 3.21 (t, 4 H,
Fig. 7 TGA curves of the compounds 1–4.
220 | CrystEngComm, 2011, 13, 215–222
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Table 2 Crystallographic data for L, 1, 2, 3, and 4
Compound
L
1
2
3
4
Empirical formula
FW /g molꢁ1
C14H24N6O6
372.39
Triclinic
C19H28N6O8Zn
533.84
Triclinic
C34H46CdCl2N14O6
930.15
Monoclinic
C2/c
31.510(7)
8.534(2)
18.891(4)
90.00
122.100(2)
90.00
C14H28CdN6O12
616.88
Monoclinic
C2/c
30.671(12)
7.551(3)
24.101(10)
90.00
122.271(4)
90.00
S
C14H24CuN6O10S
531.99
Orthorhombic
Pnna
18.861(5)
16.141(4)
13.487(4)
90.00
90.00
90.00
Crystal system
Space group
ꢀ
ꢀ
P1
P1
ꢁ
a /A
7.2549(13)
7.7629(15)
9.1054(16)
98.095(3)
99.513(3)
110.281(3)
463.39(15)
1
10.447(2)
10.755(3)
12.473(3)
104.330(4)
102.140(4)
110.924(3)
1197.3(5)
2
ꢁ
b /A
ꢁ
c /A
a /ꢀ
b /ꢀ
g /ꢀ
V /A
Z
Dc /g cmꢁ3
3
ꢁ
4303.4(17)
4
1.436
4720(3)
8
1.736
4106.0(18)
8
1.721
1.334
0.30 ꢂ 0.25 ꢂ 0.22
1.481
0.30 ꢂ 0.28 ꢂ 0.25
Crystal size /mm
F(000)
m /mmꢁ1
q range
Reflections collected
Independent reflections
Observed reflections [I > 2s(I)]
Rint
0.40 ꢂ 0.35 ꢂ 0.30
0.25 ꢂ 0.20 ꢂ 0.20
0.40 ꢂ 0.25 ꢂ 0.20
198
0.11
556
1.08
1912
0.69
2512
1.09
2200
1.23
2.32–25.00
2373
1620
1410
0.018
1.79–25.97
6647
4614
3353
0.027
1.53–28.20
17 308
5184
4634
0.018
1.57–25.55
15 660
4383
3125
0.057
1.86–26.62
22 679
4299
2552
0.084
R1; wR2 [I > 2s(I)]
R1; wR2 (all data)
GOF (F2)
0.0477, 0.1654
0.0535, 0.1729
1.384
0.0462, 0.0941
0.0722, 0.1042
1.015
0.0269, 0.0693
0.0313, 0.0721
1.062
0.0396, 0.0787
0.0665, 0.0888
1.024
0.0486, 0.1190
0.0986, 0.1450
1.045
J ¼ 2.8 Hz, urea-CH2). 13C NMR (DMSO-d6, 100 MHz): 154.8
(C]O), 149.9 (Py-C4), 147.0 (Py-C2), 111.8 (Py-C3), 39.3 (urea-
CH2-). IR (KBr pellet, cmꢁ1): 3312 (N–H), 3087, 1681 (C]O),
1601, 1534, 1211, 1004, 826, 530.
an aqueous solution (5 mL) of CuSO4$5H2O (25 mg, 0.1 mmol),
and the mixture was allowed to diffuse at room temperature.
Blue block crystals were formed at the interface in several days.
Yield: 26 mg, (50%). Mp: 230–231 ꢀC. Anal. calcd for
CuSO4L$3H2O: C 32.72, H 4.31, N 16.35. Found: C 32.56,
H 4.42, N 16.17%. FT-IR (KBr pellet, cmꢁ1): 3399 (N–H), 3253,
1688 (C]O), 1601, 1519, 1209, 1092, 1027, 842, 533.
Synthesis of {[Zn(AcO)2L]$H2O$CH3OH}n (1). The ligand L
(20 mg, 0.07 mmol) and Zn(OAc)2$2H2O (12.2 mg, 0.07 mmol)
were dissolved in a mixed solvent of CH3OH–H2O (1 : 1 v/v,
5 mL). Slow evaporation at r.t. for several days yielded colourless
crystals of 1 (27 mg, 71%). M.p.: 206–207 ꢀC. Anal. calcd for
Zn(AcO)2L$H2O$CH3OH: C 42.75, H 5.29, N 15.74%. Found: C
42.42, H 4.94, N 15.93%. IR (KBr pellet, cmꢁ1): 3357 (N–H),
3157, 3010, 2946, 1714 (C]O), 1600, 1507, 1437, 1270, 1201,
1026, 835, 682, 632, 532.
X-Ray crystallography
Data collection was performed on a Bruker-AXS SMART
CCD area detector diffractometer at 293 K using u rotation
scans with a scan width of 0.3ꢀ and Mo-Ka radiation (l ¼
ꢁ
0.71073 A). Multi-scan corrections were applied using
SADABS.17 Structure solutions and refinements were performed
with the SHELX-97 package.18 All non-hydrogen atoms were
refined anisotropically by full-matrix least-squares on F2. The
hydrogen atoms were included in idealized geometric positions
with thermal parameters equivalent to 1.2 times those of carbon
and nitrogen atoms. Hydrogen atoms of water molecules in L
and 1 were located from the difference Fourier map and then
Synthesis of {[CdCl2L2]$2DMF}n (2). The ligand L (20 mg,
0.07 mmol) and CdCl2$2.5H2O (15.2 mg, 0.07 mmol) were dis-
solved in methanol–water–DMF (1 : 1 : 1 v/v/v, 5 mL). Slow
evaporation at r.t. for a month yielded colourless crystals of 2
(14 mg, 42%). M.p.: > 300 ꢀC. Anal. calcd for CdCl2L2$2DMF:
C 43.90, H 4.98, N 21.08%. C 43.85, H 4.89, N 20.78%. IR (KBr
pellet, cmꢁ1): 3367 (N–H), 3068, 1699 (C]O), 1595, 1517, 1427,
1263, 1208, 1096, 1011, 835, 715, 537.
ꢁ
refined by restraints (O–H ¼ 0.85(1) A), with U(H) fixed at 0.08
2
ꢁ
A . Crystallographic data for the compounds are summarized in
Table 2.
Synthesis of {[CdSO4L(H2O)3]$3H2O}n (3). A methanol
solution (5 mL) of L (10 mg, 0.03 mmol) was layered on top of an
aqueous solution of 3CdSO4$8H2O (8.5 mg, 0.01 mmol), and the
mixture was allowed to diffuse at room temperature. After two
weeks, colourless needle-like crystals were obtained at the
Acknowledgements
This work was supported by the National Natural Science
Foundation of China (grant no. 20872149).
ꢀ
interface. Yield: 8.5 mg (46%). M.p.: > 300 C. Anal. calcd for
CdSO4L$5H2O: C 28.08, H 4.38, N 14.03%. Found: C 28.47, H
4.53, N 14.00%. IR (KBr pellet, cmꢁ1): 3328 (N–H), 3086, 1696
(C]O), 1599, 1527, 1435, 1338, 1264, 1213, 1092, 1016, 829, 602,
529.
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