From arm-shaped layers to a new type of polythreaded array: A two fold interpenetrated three-dimensional network with a rutile topology

Article abstract of DOI:10.1039/b405016a

The self-assembly based on 2D motifs with side arms leads to the formation of a new type of polythreaded network which exhibits a 2-fold interpenetrated 3D array if H-bonds are taken into account.

Full text of DOI:10.1039/b405016a

From arm-shaped layers to a new type of polythreaded array: a two fold
interpenetrated three-dimensional network with a rutile topology†
Chao Qin,a Xinlong Wang,a Lucia Carlucci,b Mingliang Tong,c Enbo Wang,*a Changwen Hua and Lin
Xua
a Institute of Polyoxometalate Chemistry, Department of Chemistry, Northeast Normal University,
Changchun 130024, P. R. China. E-mail: wangenbo@public.cc.jl.cn
b Dipartimento di Chimica Strutturale e Stereochimica Inorganica, Via G. Venezian 21, 20133 Milano, Italy
c
School of Chemistry & Chemical Engineering, Sun Yat-Sen University, Guangzhou 510275, P. R. China
Received (in Cambridge, UK) 6th April 2004, Accepted 14th June 2004
First published as an Advance Article on the web 7th July 2004
The self-assembly based on 2D motifs with side arms leads to
the formation of a new type of polythreaded network which
exhibits a 2-fold interpenetrated 3D array if H-bonds are taken
into account.
resulting network is a 2-fold interpenetrated architecture with a
rutile topology.
Compound 1 was prepared by hydrothermal reaction of
Zn(NO3)2·6H2O, BTC, 4,4A-bpy, triethylamine and H2O in a molar
ratio of 1 : 1.2 : 1 : 1 : 1110 at 160 °C for 5 days.† Single-crystal X-
ray diffraction‡ reveals that, unlike the reported non-entangled
species of the BTC ligand,8 1 is an extended 3D threaded network
involving 2D coordination frameworks of (4,4) topology. In these
layers each Zn(II) atom is coordinated by four oxygen atoms of four
BTC ligands and one nitrogen atom of a bpy ligand to give a square-
pyramidal geometry (Fig. 1). Two Zn(II) atoms, related by a
twofold axis, are bridged by two pairs of BTC carboxylate ends into
a dinuclear unit with a Zn(1)…Zn(1A) distance of 2.9779(13) Å.
Three factors can be envisaged to play a role in the generation of
mutual polythreading in 1: (i) the presence within the 2D motif of
very large rhombic windows (with dimensions of 10.86 3 10.86 Å)
built up by eight Zn atoms and four BTC ligands, (ii) the dangling
bpy groups, occupying the axial position of each Zn atom, are just
like open arms nearly perpendicularly protruding from both sides of
the sheets and (iii) all the layers are stacked parallel and arranged in
a staggered fashion, with a distance of 8.1 Å, while the effective
length of each lateral arm is ca. 10.5 Å (from the baricentre of the
node to the uncoordinated N atom), thus providing, obviously, the
possibility for the ultimate realization of threading. Under this
premise, the bpy lateral arms of each layer are threaded into the
rhombic voids of the adjacent layers, in a mutual relationship. Each
rhombic window is therefore penetrated by two bpy molecules that
belong to two different sheets, one entering from one side and the
other from the opposite one, as shown in Fig. 2. This results in a
novel 3D polythreaded array (2D ? 3D), originating from the
entanglement of three adjacent polymeric units at a time. To our
knowledge, described here is the first polythreaded species
involving finite components built up exclusively from 2D motifs.
Interestingly, if we regard each rhombic window as a wheel and the
paired bpy groups within the windows as a single rod, the nature of
the entanglement in 1 can be described as poly-pseudo-rotaxane.
Whilst exploring the acting forces that stabilize the whole
entanglement, we found that there exists strong hydrogen bonding
interactions between the N atoms of bpy from one layer and the
uncoordinated carboxyl oxygen atoms from the second nearest
neighbouring layer, whose length is 2.644(10) Å, which make a
Entangled systems, which are common in biology as seen in
catenanes, rotaxanes, and molecular knots, have been attracting
considerable interest, not only because of their intriguing topologi-
cal structures but also due to their interesting properties and
potential applications. Interpenetrating nets, being an important
subject in the area of entanglement, have provided a long-standing
fascination for chemists, and many beautiful structures have been
constructed1,2 and well discussed in comprehensive reviews by
Batten and Robson.3 Besides the common types of interpenetrating
networks, particular attention has recently been turning to a
burgeoning family described as polythreaded coordination net-
works, which can be considered as periodic analogues of the
molecular rotaxanes or pseudo-rotaxanes. Furthermore, interest in
these compounds is increasingly heightened by their potential
applications ranging from drug delivery vehicles to sensor devices.4
Some elegant examples belonging to this family have been recently
designed.5 However, polythreading with finite components is still
rare, as evidenced in a recent review by Ciani and coworkers.6 Only
a few fascinating examples up to now, to the best of our knowledge,
have been characterized, all constructed from 0D or 1D motifs with
side arms (Scheme 1),7 exhibiting 0D ? 1D,7a 0D ? 2D,7b 1D ?
2D,7c and 1D ? 3D7d polythreaded array. Higher dimensional
motifs in this facet remain unexplored and, therefore, much work is
still necessary to enrich and develop this branch.
Taking inspiration from previous work, our synthetic strategy is
to build up a higher dimensional motif with rigid linear ligands as
threading components in an attempt to gain a new polythreaded
array. At first, construction of 2D motifs appeared to be a simple
extension of the work on 1D motifs, but it turned out to be a
challenging goal. Fortunately, by trial and error we have now
isolated a new compound, [Zn(HBTC)(4,4A-bpy)]n (1) (BTC =
1,2,4-benzenetricarboxylate; 4,4A-bpy = 4,4A-bipyridyl), consisting
of 2D motifs with dangling lateral arms suitable to give threading,
according to the aforementioned idea. This species has several
unusual features: (i) considering only the coordinative bonds, it
represents a new (2D ? 3D) polythreaded array, (ii) it is the first
time that dinuclear metal species have been introduced into a
polythreaded system with finite components and (iii) when
considering the strong hydrogen bonds between layers, the overall
Scheme 1
† Electronic Supplementary Information (ESI) available: details of the
synthesis and solid state emission spectra of 1. See http://www.rsc.org/
suppdata/cc/b4/b405016a/
Fig. 1 The structure of a single 2D motif showing the dangling arms.
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C h e m . C o m m u n . , 2 0 0 4 , 1 8 7 6 – 1 8 7 7
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4

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great contribution to the structural stabilization. The most inter-
esting feature is that when these hydrogen bonds are taken into
account, the resulting structure displays a 2-fold interpenetrated 3D
structure of rutile topology.9 All the (4,4) 2D layers stack on top of
each other with an ABAB sequence in the [21 0 1] direction. The
bpy ligands of the A layers penetrate the B ones to connect the next
A layers via H-bonds, thus forming a binodal net with 6-co-
ordinated (Zn dimer) and 3-coordinated (Y-shaped ligand) (see
ESI†) centers, with a stoichiometry of 1 : 1 as in rutile. Finally, the
two nets of the 2-fold interpenetrating 3D array originate
respectively from layers of type A only or type B only (Fig. 3). To
our knowledge, few examples of coordination networks with 2-fold
rutile topology have been previously reported.10
obtained only from low-dimensional (0D or 1D) motifs, whereas 1
is constructed from a higher dimensional (2D) motif.
This work was financially supported by the National Natural
Science Foundation of China (No. 20171011).
Notes and references
‡ Crystal data for 1: C19H12N2ZnO6, M = 429.68, monoclinic, a =
9.869(2), b = 16.781(3), c = 11.299(2) Å, b = 100.02(3)°, U = 1842.8(6)
Å3, T = 293 K, space group P2(1)/n, Z = 4, m(Mo–Ka) = 1.372 mm21
,
7284 reflections measured, 4122 unique (Rint = 0.0541) which were used in
all calculations. R1 = 0.0658 and wR2 = 0.1148 for I > 2(I). CCDC
233352. See http://www.rsc.org/suppdata/cc/b4/b405016a/ for crystallo-
graphic data in .cif format.
In the solid state 1 exhibits an intense emission at 426 nm in the
blue region (lex
= 353 nm), a blue shift compared with
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Fig. 2 Schematic illustration of the mutual polythreading of the 2D sheets
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Fig. 3 A schematic view of the self-penetrating network. Highlighted are
two interpenetrating motifs with rutile topology.
C h e m . C o m m u n . , 2 0 0 4 , 1 8 7 6 – 1 8 7 7
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