Four novel coordination frameworks with high degree of diamondoid interpenetration containing scarce quadruple-stranded homo-axis helices and quintuple-stranded molecular braids

Article abstract of DOI:10.1016/j.ica.2016.04.018

Four novel interpenetrated diamondoid (dia) networks, namely [Zn(1,4-bdc)(bibp)] (1), [Mn(bqdc)(bibp)] (2), [Cd(bqdc)(bibp)] (3), [Co₄(bqdc)₄(bibp)₄] (4). (bibp = 1,4-bis(4-(imidazole-1-yl)benzyl)piperazine, 1,4-bdc = 1,4-

Full text of DOI:10.1016/j.ica.2016.04.018

Accepted Manuscript
Four novel coordination frameworks with high degree of diamondoid inter-
penetration containing scarce quadruple-stranded homo-axis helices and quin-
tuple-stranded molecular braids
Yu Chen, Xi-Chi Wang, Qi Yang, Yu-Ci Xu, Jin-Tao Tong, Hao Yuan, Dong-
Rong Xiao
PII:
S0020-1693(16)30179-7
http://dx.doi.org/10.1016/j.ica.2016.04.018
ICA 17002
DOI:
Reference:
Inorganica Chimica Acta
To appear in:
Received Date:
Revised Date:
Accepted Date:
2 March 2016
7 April 2016
10 April 2016
Please cite this article as: Y. Chen, X-C. Wang, Q. Yang, Y-C. Xu, J-T. Tong, H. Yuan, D-R. Xiao, Four novel
coordination frameworks with high degree of diamondoid interpenetration containing scarce quadruple-stranded
homo-axis helices and quintuple-stranded molecular braids, Inorganica Chimica Acta (2016), doi: http://dx.doi.org/
10.1016/j.ica.2016.04.018
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Four novel coordination frameworks with high degree of
diamondoid interpenetration containing scarce
quadruple-stranded homo-axis helices and quintuple-stranded
molecular braids
Yu Chen,a Xi-Chi Wang,a Qi-Yang,a Yu-Ci Xu,a Jin-Tao Tong,a Hao Yuana and
Dong-Rong Xiao*a,b
a
College of Chemistry and Chemical Engineering, Southwest University, Chongqing,
400715, PR China. E-mail: xiaodr98@swu.edu.cn
b
State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the
Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, PR China
*Corresponding author. Tel: +86-23-68252360; fax: +86-23-68254000.
E-mail address: xiaodr98@swu.edu.cn (D. R. Xiao)
1

Abstract: Four novel interpenetrated diamondoid (dia) networks, namely
[Zn(1,4-bdc)(bibp)] (1), [Mn(bqdc)(bibp)] (2), [Cd(bqdc)(bibp)] (3),
[Co4(bqdc)4(bibp)4] (4). (bibp = 1,4-bis(4-(imidazole-1-yl)benzyl)piperazine, 1,4-bdc
= 1,4-benzenedicarboxylate, bqdc = 2,2'-biquinoline-4,4'-dicarboxylate), have been
synthesized by using mixed spacer ligands with significantly different lengths. Their
structures were determined by single-crystal X-ray diffraction analyses and further
characterized by elemental analyses, IR spectra and TG analyses. Compound 1 is an
unusual 8-fold [4+4] interpenetrated dia network containing the unique quadruple-
stranded braid (i.e. quadruple-stranded homo-axis helices), which is further entangled
by another quadruple-stranded braid to produce an unprecedented octuple-stranded
braid derived from eight individual dia nets. Compounds 2 and 3 are isostructural,
while compound 4 is isoreticular to them. They all exhibit 5-fold interpenetrating dia
networks containing an exceptional quintuple-stranded molecular braid. In addition,
the photoluminescence properties of compounds 1 and 3, and the magnetic property
of compound 4 were studied.
Keywords: Coordination polymers; Interpenetration; Molecular braid; N ligand;
Topology
2

Introduction
The design and synthesis of entangled metal-organic frameworks (MOFs) have
attracted much attention during the past two decades, not only stem from their
complicated architectures and various topologies, but also for their intriguing
potential applications in many fields as functional materials [1]. As an important
subclass of entanglement, interpenetrated frameworks are of great current interest
because of their intrinsic aesthetic appeal, and more importantly, due to their potential
applications originating from the intertwining nature of the lattices [2]. Diamondoid
lattices, which are formed by propagating a tetrahedral nodal point in four directions
by coordinating to linear bidentate ligands, are one of the most common types in the
interpenetrated coordination networks [3]. So far, a variety of fascinating
interpenetrated diamondoid (dia) nets with a total degree of interpenetration (hereafter
termed Z) from 2 to 12 and 25 have been reported [4].
Nevertheless, the interpenetrated dia networks with Z≥5 are still rare [5]. Moreover,
among the currently known examples of interpenetrated dia frameworks with
Z≥5—almost all constructed from single ligands [4a, 4d, 6]—only a few elegant
examples with mixed spacer ligands have been reported recently [4b, 4c, 7, 8].
However, close inspection of these structures reveals that the mixed spacer ligands
used in building the dia frameworks with high degree of interpenetration usually have
similar length. To our knowledge, only five 5-fold, two 8-fold and one 9-fold
interpenetrating dia networks are constructed from mixed spacer ligands with
significantly different lengths [8]. This may be attributed, at least in part, to the fact
3

that two linear ligands with significantly different lengths may lead to highly distorted
adamantanoid cages containing four cyclohexane-like windows with different sizes. It
is known that dia net is self-dual, that is to say, dia net can interpenetrate in such a
way that it is fully catenated. Therefore, when the cyclohexane-like windows of
different sizes coexist in the distorted adamantanoid cages, the degree of
interpenetration depends on the smallest cyclohexane-like window. The smaller the
cyclohexane-like window is in a dia net, the lower degree of interpenetration occurs.
Consequently, the use of mixed spacer ligands with significantly different lengths to
construct interpenetrated dia frameworks with Z≥5 is still a formidable challenge for
synthetic chemists, and further research is necessary to enrich and develop this
branch.
In order to address this challenge, we purposely focused our attention on a new
long linear N-donor ligand 1,4-bis(4-(imidazole-1-yl)benzyl)piperazine (bibp, Scheme
1 and 2a), to produce novel coordination polymers with high degree of dia
interpenetration in the presence of short ditopic carboxylate linkers, based on the
following considerations: (i) Usually, long organic ligands will lead to larger voids
which may thus favor the formation of interpenetrated networks [4b]. As evidenced by
the report of Champness, Schröder, and co-workers [9], lengthening of linear ligands
may increase the fold-interpenetrating number of dia networks. The bibp ligand (19.5
Å) is much longer than those N-donor ligands (4,4’-bipyridyl, 7.1 Å;
1,2-trans-(4-pyridyl)ethene, 9.4 Å, etc) used in previously reported interpenetrating
dia networks [9-10], we thus envision that it should be possible to realize the
4

relatively high degree of dia interpenetration by appropriately combining long bibp
ligand and short ditopic carboxylate ligands. (ii) The bibp ligand, a novel long linear
semi-flexible ligand with imidazole donors at either end, has never been used to
construct coordination compounds; therefore, much work is still necessary to
understand the coordination chemistry of bibp. Bearing these considerations in mind,
we have performed many experiments, and these efforts have led to the isolation of
four new interpenetrated dia networks with Z≥5, namely [Zn(1,4-bdc)(bibp)] (1),
[Mn(bqdc)(bibp)] (2), [Cd(bqdc)(bibp)] (3), [Co4(bqdc)4(bibp)4] (4) (1,4-bdc =
1,4-benzenedicarboxylate, bqdc = 2,2'-biquinoline-4,4'-dicarboxylate, Scheme 1 and
2). Compounds 1-4 have several unusual features: (1) The unusual 8-fold (4+4)
interpenetrated dia net of 1 contains unique quadruple-stranded intertwined
homo-axis helices, which can also be considered as an inextricable
quadruple-stranded braid. (2) The octuple-stranded braid constructed from two
interwoven quadruple-stranded braids in compound 1 is unprecedented. (3) The 5-fold
interpenetrating dia networks of 2-4 incorporate exceptional quintuple-stranded
molecular braid.
5

Scheme 1. Synthetic conditions for compounds 1–4.
Scheme 2. Schematic drawing of (a) bibp, (b) 1,4-H2bdc and (c) Na2bqdc ligands.
Experimental
Materials and general methods
All of the available chemicals and solvents were commercially purchased and used
as received without further purification.
6

Elemental analyses (C, H and N) were performed on a Perkin-Elmer 2400 CHN
Elemental Analyzer. Zn, Mn, Cd and Co were determined by a tps-7000
Plasma-Spec(I) inductively coupled plasma-atomic emission spectrometer (ICP-AES).
IR spectra were recorded in the range 400-4000 cm-1 on a Bio-Rad FTS-185 FT/IR
Spectrophotometer using KBr pellets. TG analyses were performed on a NETZSCH
STA 449C instrument in flowing N2 with a heating rate of 10 ºC·min-1. XRPD data
were recorded on a XD-3 diffractometer using Cu Kα radiation. Excitation and
emission spectra were performed on an F-7000 FL fluorescence spectrophotometer
equipped with a 150 W xenon lamp as the excitation source. Variable-temperature
magnetic susceptibility data were obtained on a SQUID magnetometer (Quantum
Design, MPMS-7) in the temperature range of 2–300 K with an applied field of 1.0
kOe.
Preparation
Synthesis of bibp. A mixture of anhydrous piperazine (0.1 mol, 8.6 g),
1-bromo-4-(bromomethyl)benzene (0.2 mol, 50.0 g), and K2CO3 (0.2 mol, 27.6 g) in
1000 mL DMF was refluxed for three days and then poured into 5000 mL H2O
(Scheme S1). The obtained precipitate was crystallized in methanol to give
1,4-bis(4-bromobenzyl)piperazine (79% yield). Elemental analysis (%) calcd for
C18H20Br2N2: C, 50.97; H, 4.75; N, 6.60 %. Found: C, 50.75; H, 4.58; N, 6.41 %.
A mixture of 1,4-bis(4-bromobenzyl)piperazine (0.1 mol, 42.4 g), imidazole (0.4
mol, 27.2 g), copper(II) sulfate pentahydrate (4 mmol, 1.0 g), and K2CO3 (0.2 mol,
27.6 g) in 1000 mL DMF was refluxed for 12 hours and then poured into 2000 mL
7

H2O (Scheme S1). The obtained precipitate was crystallized in methanol to give bibp
ligand (65% yield). EI-MS: m/z [M-H]+, 399.22 (calcd for C24H26N6, 398.22).
Elemental analysis (%) calcd for C24H26N6: C, 72.33; H, 6.58; N, 21.09 %. Found:
72.08; H, 6.39; N, 20.92 %. FT/IR data (cm-1): 3424(br), 3101(w), 2968(w), 2949(w),
2811(m), 2764(w), 2660(w), 1630(s), 1605(s), 1523(s), 1488(w), 1458(w), 1397(m),
1349(m), 1301(m), 1284(w), 1265(w), 1247(w), 1110(m), 1059(m), 1012(w), 995(w),
857(w), 835(w), 740(m), 665(m), 539(m).
Synthesis of [Zn(1,4-bdc)(bibp)] (1). A mixture of Zn(Ac)2·2H2O (0.088 g, 0.4
mmol), 1,4-H2bdc (0.034 g, 0.2 mmol), bibp (0.080 g, 0.2 mmol), Et3N (0.25 mL) and
distilled water (10 mL) was stirred about 15 min in air, then transferred and sealed in
a 17 mL Teflon-lined autoclave, which was heated at 160 ˚C for 72 h. After slow
cooling to room temperature, light yellow block crystals of 1 were filtered off, washed
with distilled water, and dried at ambient temperature (yield: 45% based on Zn).
Elemental analysis (%) calcd for C32H30ZnN6O4: C, 61.21; H, 4.81; N, 13.38; Zn,
10.41 %. Found: C, 61.47; H, 4.62; N, 13.21; Zn, 10.63 %. FT/IR data (cm-1):
3443(br), 3129(w), 3040(w), 2953(w), 2906(m), 2804(m), 2767(m), 2726(m),
2699(m), 1889(w), 1608(s), 1523(s), 1499(m), 1460(m), 1434(m), 1342(s), 1305(s),
1268(m), 1245(m), 1152(m), 1125(s), 1107(m), 1064(s), 1007(m), 964(m), 947(m),
885(w), 849(m), 823(m), 801(m), 764(m), 746(s), 654(m), 621(w), 574(m), 527(m),
500(w), 427(w).
Synthesis of [Mn(bqdc)(bibp)] (2). A mixture of Mn(Ac)2·4H2O (0.049 g, 0.2 mmol),
Na2bqdc (0.039 g, 0.1 mmol), bibp (0.040 g, 0.1 mmol), Et3N (0.20 mL) and distilled
8

water (10 mL) was stirred about 15 min in air, then transferred and sealed in a 17 mL
Teflon-lined autoclave, which was heated at 160 ˚C for 72 h. After slow cooling to
room temperature, light yellow block crystals of 2 were filtered off, washed with
distilled water, and dried at ambient temperature (yield: 46% based on Mn).
Elemental analysis (%) calcd for C44H36MnN8O4: C, 66.41; H, 4.56; N, 14.08; Mn,
6.90 %. Found: C, 66.18; H, 4.39; N, 14.33; Mn, 7.11 %. FT/IR data (cm-1): 3411(br),
3159(m), 3139(m), 3120(s), 2940(w), 2816(m), 2800(m), 2769(w), 2690(w), 1599(w),
1556(s), 1536(s), 1517(s), 1500(m), 1456(m), 1418(s), 1372(s), 1307(s), 1288(m),
1258(w), 1153(m), 1129(m), 1116(s), 1066(s), 1013(w), 965(w), 933(m), 834(m),
815(m), 787(s), 762(m), 667(w), 635(s), 621(w), 597(w), 540(m), 525(m), 487(w),
453(w), 415(w).
Synthesis of [Cd(bqdc)(bibp)] (3). The preparation of 3 was similar to that of 2
except that Cd(Ac)2·2H2O (0.054 g, 0.2 mmol) was used instead of Mn(Ac)2·4H2O.
Colorless block crystals of 3 were collected (yield: 41% based on Cd). Elemental
analysis (%) calcd for C44H36CdN8O4: C, 61.94; H, 4.25; N, 13.13; Cd, 13.17 %.
Found: C, 62.19; H, 4.11; N, 12.94; Cd, 13.35 %. FT/IR data (cm-1): 3439(br),
3117(w), 3044(w), 2910(m), 2800(m), 2771(m), 1598(m), 1557(s), 1537(s), 1519(s),
1456(m), 1416(m), 1367(s), 1307(s), 1288(m), 1238(m), 1200(m), 1153(m), 1119(s),
1012(m), 964(m), 932(m), 886(w), 836(m), 814(m), 787(s), 763(m), 666(m), 539(w),
525(w), 487(w), 416(w).
Synthesis of [Co4(bqdc)4(bibp)4] (4). A mixture of Co(Ac)2·4H2O (0.100 g, 0.4
mmol), Na2bqdc (0.078 g, 0.2 mmol), bibp (0.080 g, 0.2 mmol), Et3N (0.25 mL) and
9

distilled water (10 mL) was stirred about 15 min in air, then transferred and sealed in
a 17 mL Teflon-lined autoclave, which was heated at 160 ˚C for 72 h. After slow
cooling to room temperature, dark purple block crystals of 4 were filtered off, washed
with distilled water, and dried at ambient temperature (yield: 43% based on Co).
Elemental analysis (%) calcd for C176H144Co4N32O16: C, 66.08; H, 4.51; N, 14.02; Co,
7.38 %. Found: C, 66.32; H, 4.33; N, 13.83; Co, 7.54 %. FT/IR data (cm-1): 3402(br),
3121(m), 2944(w), 2805(m), 2373(w), 1603(m), 1562(s), 1521(s), 1419(s), 1367(s),
1306(s), 1237(m), 1200(m), 1154(m), 1119(s), 1062(s), 1009(m), 965(w), 933(m),
885(w), 844(m), 814(s), 785(s), 761(m), 736(w), 666(m), 653(m), 601(w), 526(m),
486(w), 425(w).
X-Ray crystallography
Suitable single crystals of 1-4 were selected for single-crystal X-ray diffraction
analysis (diffractometer device type: SuperNova, Dual, Cu at zero, EosS2).
Compounds 1-4 were collected with Cu Ká radiation (λ = 1.54184 Å) at 289 K, 284.5
K, 284.5 K and 290 K, respectively. Using Olex2 [11], the structures of 1 and 3 were
solved with the ShelXS [12] structure solution program using Direct Methods, while
the structures of 2 and 4 were solved with the Superflip [13] structure solution
program using Charge Flipping. Moreover, the structures of 1-4 were refined with the
ShelXL [12] refinement package using Least Square minimization. All non-hydrogen
atoms were refined anisotropically. The organic hydrogen atoms were generated
geometrically. The disordered C atoms (C20, C21) of bibp ligand in compound 1 were
refined using C atoms split over two sites, with a total occupancy of 1. The crystal
10

data and structure refinement of compounds 1-4 are summarized in Table 1. Selected
bond lengths for 1-4 are listed in Table S1. The topological analyses were done with
the TOPOS program [14].
Table 1 Crystal data and structure refinements for compounds 1–4.
Compound
1
2
3
C44H36CdN8O4
853.21
4
Empirical formula
Mr (g mol-1)
C32H30N6O4Zn
627.99
C44H36MnN8O4
795.75
C176H144Co4N32O16
3198.94
Crystal system
Orthorhombic
Monoclinic
Monoclinic
Triclinic
Space group
Pna21
P21/n
P21/n
P
15.8128(2)
12.2565(1)
15.4615(2)
90
13.7817(2)
17.4459(2)
17.0228(3)
90
13.805(4)
17.346(3)
17.465(4)
90
16.1255(8)
22.960(2)
23.044(2)
107.831(9)
100.641(6)
100.815(6)
7705.7(12)
2
a (Å)
b (Å)
c (Å)
α (o)
β (o)
γ (o)
90
109.507(2)
90
110.57(3)
90
90
V (Å3)
2996.61(5)
4
3857.95(10)
4
3915.8(18)
4
Z
ρcalcd (g·cm-3)
µ (mm-1)
1.392
1.370
1.447
1.377
1.527
3.233
4.911
3.943
1304.0
1652.0
1744.0
3310.0
F(000)
2Θ range/ o
Reflections collected
Unique data (Rint)
GOF on F2
R1a /wR2b [I>2σ (I)]
R1a /wR2b (all data)
9.128-143.066
41888
8.794-143.284
27458
8.72-144.862
21366
7.956-134.158
69362
5815 (0.0385)
1.044
7336 (0.0420)
1.015
7115 (0.0327)
1.073
27111 (0.0392)
1.101
0.0311/0.0873
0.0492/0.1188
0.0355/0.0799
0.0476/0.0841
0.1306/0.3165
0.1467/0.3251
0.0315/0.0879
0.0637/0.1275
2
2
a R1 = ∑||F0|-|FC||/∑|F0|; b wR2 = ∑[w(F0 -FC2)2]/∑[w(F0 )2]1/2
Results and discussion
Crystal structure of 1
Single crystal X-ray diffraction analysis reveals that 1 crystallizes in the polar space
group Pna21 and exhibits an 8-fold [4+4] interpenetrating dia network containing the
exceptional quadruple-stranded homo-axis helices. The asymmetric unit of 1 consists
of one Zn(II) ion, one 1,4-bdc ligand and one bibp ligand. As shown in Fig. 1, the
11

coordination environment around Zn1 can be described as a distorted tetrahedral
geometry, being coordinated by two carboxylate oxygen atoms (Zn-O 1.946(2) and
1.972(3) Å) from two different 1,4-bdc ligands and two nitrogen atoms (Zn-N 2.029(3)
and 2.009(2) Å) from two different bibp ligands. In addition, each long ligand, bibp
acts as a linear bridging ligand connecting two Zn atoms, so does each 1,4-bdc ligand
(Scheme S2). Based on these connection modes, each Zn center acts as a tetrahedral
node and is linked to four equivalent neighbors through four linear ligands into a 3D
dia network (Fig. 2b). Due to the different lengths of the mixed spacer ligands, a
single dia network contains highly distorted adamantane-like cages, in which the
distances between two Zn atoms connected by 1,4-bdc ligand and bibp are 10.907 Å
and 22.854 Å, respectively. This results in a single adamantanoid cage delineated by
two types of cyclohexane-like windows with different sizes (two big windows 43.84
Å × 38.71 Å, two small windows 33.52 Å × 28.58 Å, Fig. 2a). The dimension of the
adamantanoid cages is 49.03 Å × 39.46 Å × 31.63 Å (corresponding to the longest
intracage Zn···Zn distances). Although the fold-interpenetrating number of dia
networks rests with the small cyclohexane-like window of adamantanoid cage, the
large size of the small cyclohexane-like window still makes the interpenetration of
eight identical dia networks possible to give an intricate 8-fold interpenetrating dia
array (Fig. 2c). So far, the interpenetrated dia networks constructed from mixed
spacer ligands with Z≥8 are still quite uncommon, and only six 8-fold, one 9-fold and
two 10-fold interpenetrating dia nets formed from mixed spacer ligands have been
reported [4c, 7a, 7c-7e, 8f, 8g]. However, among them, only two 8-fold and one 9-fold
12

networks constructed from mixed spacer ligands with significantly different lengths
[8f, 8g]. Undoubtedly, the successful isolation of compound 1 adds a new member to
the family of highly interpenetrated dia nets constructed from mixed spacer ligands
with significantly different lengths. More intriguingly, an analysis of the
interpenetration topology with the TOPOS program reveals that 1 belongs to rare
class IIIa (the whole interpenetrated array is generated both by translations and by
non-translating interpenetration symmetry elements (NISE)) with Zt = 4 and Zn = 2.
In detail, four dia nets are generated by application of one translational operation and
the translating interpenetration vector (TIV) is [0,1,0] (12.25 Å, Fig. S1). The
presence of a NISE as the 21 screw axis along the c axis generates a second set of four
dia nets for a total degree of interpenetration of class IIIa of 8 = [4 × 2] (Fig. S2).
There are twelve examples containing [4+4] interpenetrating dia nets to date [6c, 6e,
6f, 6i-k, 7d, 8f], but only three structures belong to class IIIa (CSD refcode: FISPIH,
OTUXIL, ZOZSEO, Table S2). The non-translational symmetry elements (inversion
center) in aforementioned three dia nets obviously differ from that in 1. Thus
compound 1 shows an unprecedented interpenetration mode among [4+4]
interpenetrating dia nets. In addition, a small window is threaded by two neighboring
small windows belonging to two other nets (Fig. S3). To the best of our knowledge,
this phenomenon is really scarce in interpenetrated dia networks.
13

Fig. 1. ORTEP diagram showing the coordination environment for Zn atoms in 1 (all
hydrogen atoms are omitted for clarity).
Fig. 2. For compound 1: (a) Perspective (upper) and simplified (down) views of a
single adamantanoid cage. (b) A single 3D-diamondoid network showing large voids.
(c) View of the 8-fold interpenetrated 3D framework and individual networks are
displayed in different colors. (d) Topological representation of the 8-fold
interpenetrated nets. (e) The schematic representation of [4+4] mode of diamondoid
interpenetration.
14

The most striking structural feature of 1 is the existence of the unique
quadruple-stranded intertwined homo-axis helices, which can also be considered as an
uncommon quadruple-stranded braid. As depicted in Fig. S4, the Zn atoms are
bridged by 1,4-bdc and bibp ligands to form the left- and right-handed helical chains
running along a crystallographic 21 axis in the a direction with a pitch of 31.661 Å.
Unexpectedly, four such helical chains, which possess the same helix axis and have
the reverse helical orientation, interweave each other to produce a fascinating
quadruple-stranded homo-axis helices without sharing the atoms, in contrast to the
previous homo-axis helices those have interweaving of different kinds (or same kind)
of helices sharing the atoms [15]. To our knowledge, the quadruple-stranded
homo-axis helices represent the highest-stranded homo-axis helices involving
left-handed and right-handed helices without sharing the atoms. Moreover, careful
inspection of the quadruple-stranded homo-axis helices reveals that these helices can
be further classified into left-handed (yellow and pink helices, Figs. 3c and 3d) and
right-handed double helices (red and purple helices, Figs. 3c and 3d) according to the
helical orientation. Interestingly, the left-handed double helices are further intertwined
with the right-handed double helices in such a way that two helices of one double
helical strand pass through the openings generated by the other double helices, in a
mutual relationship (Figs. S5a and S5b). Thus, the quadruple-stranded homo-axis
helices could equally well be considered as a quadruple-stranded braid. To the best of
our knowledge, only one example containing peculiar quadruple-stranded braid motif
has been reported by Wang and coworkers [16]. However, in contrast to the
15

quadruple-stranded braid motif reported in ref. 16, where two helices of a side-by-side
double helix are separated from each other, arbitrary two helices of the
quadruple-stranded braid motif in 1 interweave each other (Fig. S6). Furthermore, we
have carefully studied all 8-fold [4+4] interpenetrated dia coordination networks, and
none of them contains the quadruple-stranded braid involving left-handed and
right-handed double helices without sharing the atoms indeed. Another noteworthy
aspect of the quadruple-stranded braid motif in 1 is the fact that the left-handed helix
is intertwined with right-handed helix without sharing the atoms to generate an
exceptional double helix (Fig. S7), which is a new structural motif that has never been
observed prior to this work. Therefore, this more inextricable quadruple-stranded
braid motif represents a new type of entanglement of the one-dimensional (1D) chains.
Most exciting is the fact that two adjacent quadruple-stranded braids further
intertwine with each other to generate other openings which are penetrated by two
helical chains (Figs. S5c and S5d). This results in a more complicated 8-stranded
interwoven braid derived from eight individual dia networks (Figs. 3a and 3b).
According to our careful check, so far such an 8-stranded interwoven braid has never
been observed in any 8-fold interpenetrated dia network. It is believed that such an
exceptional 8-stranded interwoven braid is derived from the unprecedented
interpenetration mode in compound 1.
16

Fig. 3. For compound 1: (a) View of the 8-fold interpenetrated 3D framework along a
axis. (b) Schematic view of the 8-stranded interwoven braid. (c) Schematic view of
the quadruple-stranded intertwined homo-axis helices along c axis. (d) Side view of
the quadruple-stranded intertwined homo-axis helices along a axis.
Crystal structures of 2-4
When 1,4-bdc was replaced by bqdc, three 5-fold interpenetrating dia networks
were obtained. Compounds 2 and 3 are isostructural, while compound 4 is isoreticular
to them owing to the same network topology [17], so only the structure of 2 will be
discussed in detail. There is one crystallographically independent Mn atom in the
asymmetric unit of 2 (Fig. 4). Each Mn atom is coordinated by four oxygen atoms
(Mn-O 2.1813(17)-2.3374(19) Å) from two chelating carboxylate group of different
bqdc ligands and two nitrogen atoms (Mn-N 2.197(2) and 2.213(2) Å) from two bibp
ligands, showing a distorted octahedral geometry. Moreover, the bibp acts as a linear
bidentate ligand linking the adjacent two Mn(II) atoms, while the bqdc ligand adopts a
17

bis(bidentate) coordination mode to bridge two Mn(II) atoms (Scheme S2). On the
basis of these connection modes, each Mn(II) atom, which corresponds to a
tetrahedral node, is connected to four others through two bibp and two bqdc ligands to
generate a 3D dia network (Fig. S9). Owing to the significantly different lengths of
the two types of ligands, the distorted adamantanoid cage in a single dia network
contains two types of cyclohexane-like windows with different sizes (two big
windows 46.63 Å × 45.14 Å, two small windows 34.87 Å × 31.21 Å, Fig. S9a), and
exhibits maximum dimensions of 51.981 Å ×49.271 Å ×17.446 Å (corresponding to
the longest intracage Mn···Mn distances). Although the small cyclohexane-like
window may determine the degree of interpenetration for dia networks, the large size
of the small cyclohexane-like window still allows a relatively high degree of
interpenetration to occur. As illustrated in Fig. 5, a single dia network is
interpenetrated by four other identical dia networks in a normal mode to give a 5-fold
interpenetrating dia networks [1a, 6i]. Compared to 1, the relatively low degree of
interpenetration in 2 is related to the fact that the steric hindrance of bqdc ligand is
larger than that of 1,4-bdc ligand. An analysis of the interpenetration topology with
the TOPOS program reveals that it belongs to class Ia, that is, the five identical
interpenetrated nets are generated only by translation and the translating vector is
[1,0,0] (13.78 Å).
18

Fig. 4. ORTEP diagram showing the coordination environment for Mn atoms in 2 (all
hydrogen atoms are omitted for clarity).
Fig. 5. For compound 2: (a) View of the 5-fold interpenetrated 3D framework and
individual networks are displayed in different colors. (b) Topological representation of
the 5-fold interpenetrated networks.
The most fascinating structural feature of 2 is that an exceptional
quintuple-stranded molecular braid (also called a quintuple-stranded meso-helix [18])
19

originating from five individual dia nets exists in the 5-fold interpenetrated nets of 2.
As shown in Fig. 6, the quintuple-stranded molecular braid is formed by bibp and
bqdc ligands bridging the Mn(II) atoms, which is extended along the crystallographic
a axis with a pitch of 68.909 Å. Up to now, the occurrence of molecular braids is
strikingly rare, and only a handful of molecular braids have been reported [19]. To the
best of our knowledge, compound 2 represents the second quintuple-stranded
molecular braid in the field of coordination polymers, and it also represents the
highest-stranded molecular braid without sharing the metal atoms [18, 20].
Fig. 6. For compound 2: (a) Perspective view of a single 3D net. (b) Side view of the
single-stranded meso-helix. (c) Perspective view of the meso-helix. (d) Perspective
view of the quintuple-stranded molecular braid. (e) Schematic view of the
quintuple-stranded molecular braid.
20

Comparison of compounds 1–4 the factors influencing interpenetration
As shown above, the simultaneous use of long bibp ligand and short ditopic
carboxylate ligands affords four new interpenetrated dia networks with Z≥5.
Although it is difficult to predict and explain the degree of interpenetration with our
present state of knowledge, some of the influence factors observed are discussed
below.
As described above, because dia net is self-dual, the degree of interpenetration for
dia nets rests with the smallest cyclohexane-like window of adamantanoid cage,
which is evidenced by the analysis of the structures of 1-4. Furthermore, the
comparison of compound 1 with 2-4 also shows that the bulkiness of the ligands is
another factor that can affect the fold-interpenetrating number of dia networks.
Because bqdc ligand is larger than 1,4-bdc ligand, the free aperture of smallest
cyclohexane-like windows in 2 (dimensions: 22.54 Å × 11.25 Å, considering van der
Waals radii; Fig. S12a) is smaller than that in 1 (dimensions: 22.86 Å × 17.00 Å, Fig.
S12b). This leads to the lower degree of interpenetration in compound 2. By careful
inspection of the structures of 1-4, we can see the trend that the decrease in the free
aperture of smallest cyclohexane-like window induces the progressive decrease in the
fold-interpenetrating number of dia networks. Similar trend has also been observed in
a series of interpenetrated dia networks [Ag(ddn)2]X (ddn =1,12-dodecanedinitrile; X
-
-
-
-
= NO3 , PF6 , AsF6 , ClO4 ) (Fig. S13) [6i]. Looking at the entire study, we can sense
that the length ratio of mixed spacer ligands and the ratio of length to bulkiness of the
ligand, which can modulate the free aperture of smallest cyclohexane-like window,
21

play important roles in tuning the degree of dia interpenetration.
X-Ray powder diffractions and thermal properties
In order to check the phase purity of compounds 1-4, the X-ray powder diffraction
(XRPD) patterns were recorded at room temperature. As shown in Figs. S14-S17, the
peak positions of simulated and experimental patterns are in good agreement with
each other, demonstrating the phase purity of the products. The differences in
intensity may be due to the preferred orientation of the crystalline powder samples.
Thermal gravimetric analyses (TG) were performed on compounds 1-4 to
investigate their thermal stabilities. The TG curves of 1-4 are highly similar (Figs.
S18-S21). The release of organic components occurs from 390 °C for 1, 400 °C for 2,
390 °C for 3, and 370 °C for 4. For compounds 1-4, the total weight losses of 76.39%,
72.64%, 79.46%, 74.28% are much less than the calculated value of 87.04%, 91.09%,
84.95%, 90.62% if the final products are assumed to be ZnO, MnO, CdO, CoO,
respectively, which indicates that the decomposing processes are not complete due to
the use of nitrogen protection. In their DSC curves (Figs. S18-S21), the endothermic
peak at 431 °C and the exothermic peaks at 543 °C, 641 °C for 1, the endothermic
peak at 420 °C and the exothermic peak at 669 °C for 2, the endothermic peak at
429 °C and the exothermic peak at 632 °C for 3, the endothermic peak at 399 °C and
the exothermic peak at 530 °C for 4, are all related to the decomposition of the
organic ligands.
Photoluminescence properties
Taking into account the excellent luminescent properties of d10 metal complexes,
22

the solid-state luminescence of 1, 3 and organic ligands were investigated (Figs. 7a
and 7b). The 1,4-H2bdc, Na2bqdc and bibp ligands exhibit the fluorescent emission
bands at 383 nm (λex = 282 nm), 431 nm (λex = 284 nm) and 378 nm (λex = 315 nm)
respectively, which are probably caused by the π* → n or π* → π transition [21].
Compound 1 exhibits an intense emission at 444 nm in the blue region upon
excitation at 372 nm. Compared with the 1,4-H2bdc ligand and the bibp ligand, it can
be seen that the maximum emission peak of 1 has a remarkable bathochromic shift.
Therefore, the emission of 1 may not be related to the π* → n or π* → π transition of
the ligand. According to the previous literature, this emission could be assigned to
ligand-to-metal charge transfer (LMCT) [21d, 22]. Compound 3 emits intense blue
fluorescent emission at 427 nm with an excitation at 201 nm. Compared with the
Na2bqdc ligand and the bibp ligand, the emission spectrum of 3 is similar to that of
Na2bqdc. Thus, the emission of compound 3 may be attributed to the intraligand
fluorescent emission.
23

Fig. 7a
Fig. 7b
Fig. 7. Photoluminescent spectra of 1 (a) and 3 (b) in solid state at room temperature.
24

Magnetic properties
The temperature dependence of the magnetic susceptibility of 4 was studied in the
temperature range of 2-300 K at a direct current field of 1.0 kOe. As shown in Fig. 8,
the χMT value of 11.714 cm3 K mol-1 at 300 K (9.680 µB) is much higher than the
expected value of 7.5 cm3 K mol-1 (7.746 µB) for four isolated spin-only Co(II) ions (S
= 3/2, g = 2.0), which can be ascribed to the strong orbital contribution to the
magnetic moment of Co(II) centers [23]. With decreasing temperature, the χMT
product decreases continuously to a value of 6.673 cm3 K mol-1 at 2 K, which is
attributed to weak antiferromagnetic interaction between the CoII ions and/or ZFS of
CoII. The 1/χM versus T plot of 4 follows the Curie-Weiss law in the range of 2-300 K
with C = 10.830 cm3 K mol-1 and θ = -3.470 K.
Fig. 8. Temperature dependence of the χMT product for compound 4. Inset: Plot of
thermal variation of χM-1 for the respective compound.
25

Conclusions
In summary, we have successfully synthesized and characterized four novel
interpenetrated dia networks with Z≥5 by appropriately combining long bibp ligand
and short ditopic carboxylate ligands. Compound 1 is an 8-fold [4+4] interpenetrated
dia network containing uncommon quadruple-stranded homo-axis helices and
octuple-stranded braid, which fill the lacunas in the realm of entanglement.
Compounds 2-4 display 5-fold interpenetrating dia networks comprising an
exceptional quintuple-stranded molecular braid. By inspection of the structures of 1-4,
it is believed that tuning of the free aperture of smallest cyclohexane-like window by
modulating the length ratio of mixed spacer ligands and the ratio of length to
bulkiness of the ligand can adjust the fold-interpenetrating number of dia networks.
Therefore, the successful isolation of these solid materials provides not only
innovative examples of interpenetrated dia networks, but also some guidance in
controlling and tuning the degree of dia interpenetration.
Acknowledgments
This work was financially supported by the NSFC (21571149), the Program for
Chongqing Excellent Talents in University, the Fundamental Research Funds for the
Central Universities (XDJK2013A027, XDJK2016C101), the Open Fund of Key
Laboratory of Synthetic and Natural Functional Molecule Chemistry of the Ministry
of Education (338080045).
26

Appendix A. Supplementary materials
CCDC 1041635 (1), 1054320 (2), 1054328 (3) and 1054331 (4) contain the
supplementary crystallographic data for this paper. These data can be obtained free of
charge
from
The
Cambridge
Crystallographic
Data
Centre
via
www.ccdc.cam.ac.uk/data_request/cif. Some additional structural figures and tables,
XRPD patterns, TG-DSC curves, IR spectrum, and additional details for single-crystal
structural refinements can be found in the supporting file.
Notes and references
(1) (a) S. R. Batten, CrystEngComm 3 (2001) 67; (b) O. M. Yaghi, M. O'Keeffe, N.
W. Ockwig, H. K. Chae, M. Eddaoudi, J. Kim, Nature 423 (2003) 705; (c) R.
Kitaura, K. Seki, G. Akiyama, S. Kitagawa, Angew. Chem. Int. Ed. 42 (2003)
428; (d) E. R. Parnham, R. E. Morris, Acc. Chem. Res. 40 (2007) 1005; (e) D. R.
Xiao, H. Y. Chen, D. Z. Sun, J. H. He, S. W. Yan, J. Yang, X. Wang, R. Yuan, E.
B. Wang, Inorg. Chim. Acta 14 (2012) 2849; (f) L. Wen, W. Shi, X. T. Chen, H.
H. Li, P. Cheng, Eur. J. Inorg. Chem. (2012) 3562.
(2) (a) V. A. Blatov, L. Carlucci, G. Ciani, D. M. Proserpio, CrystEngComm 6 (2004)
377; (b) D. R. Xiao, D. Z. Sun, J. L. Liu, G. J. Zhang, H. Y. Chen, J. H. He, S. W.
Yan, R. Yuan, E. B. Wang, Eur. J. Inorg. Chem. (2011) 3656.
(3) Y. F. Hsu, C. H. Lin, J. D. Chen, J. C. Wang, Cryst. Growth Des. 8 (2008) 1094.
(4) (a) J. Xu, Z. S. Bai, M. S. Chen, Z. Su, S. S. Chen, W. Y. Sun, CrystEngComm
11 (2009) 2728; (b) C. M. Nagaraja, B. Ugale, A. Chanthapally, CrystEngComm
27

16 (2014) 4805; (c) M. Ahmad, R. Katoch, A. Garg, P. K. Bharadwaj,
CrystEngComm 16 (2014) 4766; (d) Y. P. He, Y. X. Tan, J. Zhang,
CrystEngComm 14 (2012) 6359.
(5) E. V. Alexandrov, V. A. Blatov, A. V. Kochetkov, D. M. Proserpio,
CrystEngComm 13 (2011) 3947.
(6) (a) D. K. Kumar, D. A. Jose, A. Das, P. Dastidar, Inorg. Chem. 44 (2005) 6933;
(b) G. B. Li, J. R. He, M. Pan, H. Y. Deng, J. M. Liu, C. Y. Su, Dalton Trans. 41
(2012) 4626; (c) Y. L. Liu, Y. P. Wu, D. S. Li, W. W. Dong, C. S. Zhou, J. Solid
State Chem. 223 (2015) 38; (d) T. W. Tseng, T. T. Luo, C. C. Tsai, K. L. Lu,
CrystEngComm 17 (2015) 2935; (e) Y. P. He, Y. X. Tan, J. Zhang, Inorg. Chem.
52 (2013) 12758; (f) L. J. Li, G. Yuan, L. Chen, D. Y. Du, X. L. Wang, G. J. Xu,
H. N. Wang, K. Z. Shao, Z. M. Su, J. Coord. Chem. 64 (2011) 1578; (g) Z. Z. Lu,
R. Zhang, Y. Z. Li, Z. J. Guo, H. G. Zheng, Chem. Commun. 47 (2011) 2919; (h)
X. S. Wang, H. Zhao, Z. R. Qu, Q. Ye, J. Zhang, R. G. Xiong, X. Z. You, H. K.
Fun, Inorg. Chem. 42 (2003) 5786; (i) L. Carlucci, G. Ciani, D. M. Proserpio, S.
Rizzato, Chem.-Eur. J. 8 (2002) 1520; (j) R. G. Xiong, J. L. Zuo, X. Z. You, Z. P.
Bai, B. F. Abrahams, C. M. Che, H. K. Fun, Chem. Commun. (2000) 2061; (k) K.
A. Hirsch, S. R. Wilson, J. S. Moore, Inorg. Chem. 36 (1997) 2960; (l) Y. J. Hao,
B. Wu, S. G. Li, C. D. Jia, X. J. Huang, X. J. Yang, CrystEngComm 13 (2011)
215.
(7) (a) R. Singh, P. K. Bharadwaj, Cryst. Growth Des. 13 (2013) 3722; (b) H. J. Hao,
D. Sun, F. J. Liu, R. B. Huang, L. S. Zheng, Cryst. Growth Des. 11 (2011) 5475;
28

(c) Y. F. Hou, N. Yan, K. F. Yue, J. T. Shi, T. He, X. Y. Li, Inorg. Chem.
Commun. 48 (2014) 44; (d) H. Kim, M. P. Suh, Inorg. Chem. 44 (2005) 810; (e)
L. L. Dang, J. Q. Li, S. J. Liu, M. B. Luo, F. Luo, Inorg. Chem. Commun. 45
(2014) 30; (f) J. Yang, J. F. Ma, Y. Y. Liu, S. R. Batten, CrystEngComm 11
(2009) 151; (g) Y. Qi, Y. X. Che, J. M. Zheng, Cryst. Growth Des. 8 (2008)
3602.
(8) 5-fold: (a) D. P. Martin, M. A. Braverman, R. L. LaDuca, Cryst. Growth Des. 7
(2007) 2609; (b) D. K. Maity, B. Bhattacharya, R. Mondal, D. Ghoshal,
CrystEngComm 16 (2014) 8896; (c) D. Liu, Y. J. Chang, J. P. Lang,
CrystEngComm 13 (2011) 1851; (d) Y. Yang, P. Du, Y. Y. Liu, J. F. Ma, Cryst.
Growth Des. 13 (2013) 4781; (e) L. L. Wen, L. Zhou, B. G. Zhang, X. G. Meng,
H. Qu, D. F. Li, J. Mater. Chem. 22 (2012) 22603; 8/9-fold: (f) Y. Gong, J. Li, J.
Qin, T. Wu, R. Cao, J. Li, Cryst. Growth Des. 11 (2011) 1662; (g) J. J. Cheng, Y.
T. Chang, C. J. Wu, Y. F. Hsu, C. H. Lin, D. M. Proserpio, J. D. Chen,
CrystEngComm 14 (2012) 537.
(9) A. J. Blake, N. R. Champness, S. S. M. Chung, W. S. Li, M. Schroder, Chem.
Commun. (1997) 1005.
(10)L. F. Ma, X. Q. Li, Q. L. Meng, L. Y. Wang, M. Du, H. W. Hou, Cryst. Growth
Des. 11 (2011) 175.
(11)O. V. Dolomanov, L. J. Bourhis, R. J. Gildea, J. A. K. Howard, H. Puschmann, J.
Appl. Crystallogr. 42 (2009) 339.
(12)G. M. Sheldrick, Acta Crystallogr. Sect. A: Found. Crystallogr. 64 (2008) 112.
29