Zinc(II) and cadmium(II) coordination polymers containing phenylenediacetate and bis(imidazol-1-ylmethyl)benzene linkers: The effect of ligand isomers on the solid state structures

Article abstract of DOI:10.1016/j.jssc.2017.04.038

This work presents a systematic investigation of the reactions of o-, m- and p-phenylenediacetic acid with Zn(II)/Cd(II) salts in the presence of different semi-rigid o-, m- and p-bis(imidazol-1-ylmethyl)benzene co-ligands. Fourteen new coordination polymers – {[Zn(μ-opda)(μ-mbix)]·0.5H₂O}_n (1), {[Zn(μ-mpda)(μ-obix)]·H₂O}_n (2), {[Zn₂(μ-mpda)₂(μ-mbix)₂]·5H₂O}_n (3), {[Zn(μ-mpda)(μ-mbix)]·2H₂O}_n (4), {[Zn(μ-mpda)(μ-pbix)]·0.5H₂O}_n (5), [Zn(μ-ppda)(μ-obix)]_n (6), {[Zn(μ-ppda)(μ-mbix)]·0.5H₂O}_n (7), {[Zn(μ-ppda)(μ-pbix)]·H₂O·DMF}_n (8), {[Cd(μ-mpda)(μ-obix)_1.5]·H₂O}_n (9), {[Cd(μ-mpda)(μ-obix)]·H₂O}_n (10), {[Cd(μ-mpda)(μ-mbix)(H₂O)]·H₂O}_n (11)_, [Cd(μ₃-ppda)(μ-obix)]_n (12), [Cd(μ₃-ppda)(μ-mbix)]_n (13) and [Cd(μ₃-ppda)(μ-pbix)]_n (14) (o/m/ppda=1,2/1,3-/1,4-phenylenediacetate, o/m/pbix=1,2-/1,3-/1,4-bis(imidazol-1-ylmethyl)benzene) – have been prepared and structurally characterized. Two of the complexes were found to possess one-dimensional (1D) structures, eleven complexes were found to be two-dimensional (2D) coordination networks and one of the complexes was found to be a three-dimensional (3D) coordination network. Of the 1D structures, 3 forms nanotubes, whereas in 8 pairs of pbix ligands bridge the zinc(II) centers to generate Zn₂(pbix)₂ dimers, which in turn are linked together by pairs of ppda linkers to give chains. Compound 5 contains a 4-fold interpenetrated 3D framework. The structure of 10 contains interpenetrated 2D frameworks, leading to a three-dimensional gross structure. The thermal stabilities and luminescent properties for 1–14 are also reported.

Full text of DOI:10.1016/j.jssc.2017.04.038

Author’s Accepted Manuscript
Zinc(II) and cadmium(II) coordination polymers
containing phenylenediacetate and bis(imidazol-1-
ylmethyl)benzene linkers: the effect of ligand
isomers on the solid state structures
Güneş Günay Sezer, Okan Zafer Yeşilel, Onur
Şahin, Andrew D. Burrows
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http://dx.doi.org/10.1016/j.jssc.2017.04.038
YJSSC19771
DOI:
Reference:
To appear in:
Journal of Solid State Chemistry
Received date: 20 February 2017
Revised date: 6 April 2017
Accepted date: 30 April 2017
Cite this article as: Güneş Günay Sezer, Okan Zafer Yeşilel, Onur Şahin and
Andrew D. Burrows, Zinc(II) and cadmium(II) coordination polymers containing
phenylenediacetate and bis(imidazol-1-ylmethyl)benzene linkers: the effect o
ligand isomers on the solid state structures, Journal of Solid State Chemistry
http://dx.doi.org/10.1016/j.jssc.2017.04.038
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Zinc(II) and cadmium(II) coordination polymers containing
phenylenediacetate and bis(imidazol-1-ylmethyl)benzene linkers: the effect
of ligand isomers on the solid state structures
Güneş Günay Sezera*, Okan Zafer Yeşilelb, Onur Şahinc, Andrew D. Burrowsd
aVocational School of Health Services, Bartın University, Bartın, Turkey
bDepartment of Chemistry, Eskişehir Osmangazi University, Eskişehir, Turkey
cScientific and Technological Research Application Center, Sinop University, Sinop, Turkey
dDepartment of Chemistry, University of Bath, Claverton Down, Bath, UK
*Corresponding author. Tel: +90 3785050083, Fax: +90 3785050082, E-mail:
ggunay@bartin.edu.tr
Abstract
This work presents a systematic investigation of the reactions of o-, m- and p-
phenylenediacetic acid with Zn(II)/Cd(II) salts in the presence of different semi-rigid o-, m-
and p-bis(imidazol-1-ylmethyl)benzene co-ligands. Fourteen new coordination polymers –
{[Zn(μ-opda)(µ-mbix)]·0.5H2O}n (1), {[Zn(μ-mpda)(µ-obix)]·H2O}n (2), {[Zn2(μ-mpda)2(μ-
mbix)2]∙5H2O}n (3), {[Zn(μ-mpda)(µ-mbix)]·2H2O}n (4), {[Zn(μ-mpda)(µ-pbix)]·0.5H2O}n
(5), [Zn(μ-ppda)(μ-obix)]n (6), {[Zn(μ-ppda)(µ-mbix)]∙0.5H2O}n (7), {[Zn(μ-ppda)(μ-
pbix)]∙H2O∙DMF}n (8), {[Cd(μ-mpda)(μ-obix)1.5]∙H2O}n (9), {[Cd(μ-mpda)(μ-obix)]∙H2O}n
(10), {[Cd(μ-mpda)(μ-mbix)(H2O)]∙H2O}n (11), [Cd(μ3-ppda)(µ-obix)]n (12), [Cd(μ3-ppda)(µ-
mbix)]n (13) and [Cd(μ3-ppda)(µ-pbix)]n (14) (o/m/ppda = 1,2/1,3-/1,4-phenylenediacetate,
o/m/pbix = 1,2-/1,3-/1,4-bis(imidazol-1-ylmethyl)benzene) – have been prepared and
structurally characterized. Two of the complexes were found to possess one-dimensional (1D)
structures, eleven complexes were found to be two-dimensional (2D) coordination networks
and one of the complexes was found to be a three-dimensional (3D) coordination network. Of
1

the 1D structures, 3 forms nanotubes, whereas in 8 pairs of pbix ligands bridge the zinc(II)
centers to generate Zn2(pbix)2 dimers, which in turn are linked together by pairs of ppda
linkers to give chains. Compound 4 contains a 4-fold interpenetrated 3D framework. The
structure of 10 contains interpenetrated 2D frameworks, leading to a three-dimensional gross
structure. The thermal stabilities and luminescent properties for 1−14 are also reported.
Keywords:
Coordination polymer, Phenylenediacetic acid, Bis(imidazole) derivative, Hydrothermal
Synthesis, Zinc(II) complex Cadmium(II) complex.
Introduction
The synthesis of coordination polymers (CPs) with different structural properties and
functionalities is currently a very active research area[1, 2]. In recent years, a large number of
coordination polymers have been synthesized to investigate the effect of organic linkers on
their structural properties. CPs have been exploited for many different technologies[3-5]
including gas storage[6], separation[7], catalysis[8] and bioapplications[9, 10].
The selection of anionic and neutral ligands is arguably the most important parameter
in the design and synthesis of these materials[11, 12]. In the construction of CPs, aromatic and
aliphatic polycarboxylate ligands, especially aromatic polycarboxylates have been extensively
used and continued to be popular[13-16]. Recently, semi-rigid polycarboxylates which possess
both aromatic and aliphatic groups have attracted considerable attention in CP chemistry[17-
33]. These ligands are excellent candidates for the formation of CPs with interesting
properties. Semi-rigidity affords the potential for changes in coordination ability following
crystal-to-crystal transitions[34, 35], while maintaining the potential for porosity, which is
2

often not possible with very flexible linkers due to their propensity to form more close-packed
structures. A considerable amount of research has been carried out using a combination of
anionic polycarboxylate and neutral N,N'-donor ligands, and mixed-ligand coordination
polymers, assembled from polycarboxyate and nitrogen-rich co-ligands have been shown to
form high-dimensional polymeric structures often with novel topologies. However, most of
the previous work in this area has focused on utilizing rigid aromatic polycarboxylate ligands
and N,N′-donor co-ligands with different metal ions[23-26].
This study aims to investigate the effect of using semi-rigid organic molecules as both
the anionic and neutral linkers in mixed-ligand coordination polymers. Both
phenylenediacetates and bis(imidazol-1-ylmethyl)benzenes contain rigid aromatic rings and
more flexible methylene groups, and they can form cis and trans conformations via rotation
around the C–C bonds. In addition, the choice of phenylenediacetates as the anionic linkers
and bis(imidazol-1-ylmethyl)benzenes as the neutral linkers, allows a systematic investigation
of the relative orientations of the functional groups on the coordination polymer structure
since both ligands are available as o-, m- and p-isomers. We have therefore systematically
investigated the reactions of zinc(II) and cadmium(II) salts with o-, m- and p-
phenylenediacetic acid (H2opda, H2mpda and H2ppda) in the presence of o-, m- and p-
bis(imidazol-1-ylmethyl)benzene (obix, mbix and pbix).
There are a number of previous studies using phenylenediacetates with N,N'-donor co-
ligands[23, 25, 26, 28], but those employing semi-rigid bis(imidazole) derivatives as neutral
ligands are extremely limited[22, 31, 36].
In this study the effect of temperature, pH, metal source, and solvent in the formation
of coordination polymers were investigated. Fourteen new coordination polymers have been
synthesized and the compounds have been characterized by elemental analysis, IR
spectroscopy, and X-ray single crystal and X-ray powder diffraction analyses. The thermal and
photoluminescence properties of the complexes were also investigated.
3

Experimental section
All chemicals were commercially available and used without further purification. Elemental
analyses (C, H, and N) were performed on a Perkin-Elmer 2400C Elemental Analyzer. IR
spectra were recorded on a Bruker Tensor 27 FT−IR spectrometer using KBr pellets in the
range of 400−4000 cm−1. Thermal analyses (TG, DTG and DTA) were carried out with a
Perkin Elmer Diamond TG/DTA Thermal Analyzer in the static air atmosphere with a heating
rate of 10 ºC/min in the temperature range of 30–700 °C. Powder X-ray diffraction patterns
(PXRD) were recorded on a Rikagu Smartlab X-ray diffractometer operating at 40 kV and 30
mA with Cu-Kα radiation (λ = 1.5406 nm). The photoluminescence (excitation and emission)
spectra for the solid complex samples were determined with a Perkin-Elmer LS-55
Fluorescence spectrometer.
Synthesis of {[Zn(μ-opda)(μ-mbix)]·0.5H2O}n (1)
A mixture of H2opda (0.7 mmol, 0.15 g), Zn(O2CMe)2·2H2O (0.7 mmol, 0.17 g), mbix (0.8
mmol, 0.21 g) and DMF/H2O (32 mL, v:v = 1:3) was placed in a 45 mL Parr brand teflon-
lined acid digestion bomb and sealed then heated at 120 ºC for 7 days, and then cooled at a
rate of 5 ºC h–1 to room temperature. Colorless crystals of 1 were collected by filtration and
washed with water. Anal. calcd. for C96H92N16O17Zn4: C 57.55, H 4.63, N 11.19. Found: C
56.99, H 4.67, N 11.27. IR (KBr, cm–1): 3426w, 3128w, 2912w, 1604vs, 1517m, 1446m,
1360vs, 1273m, 1211w, 1096w, 950w, 818m, 730s, 652m, 587m.
Synthesis of {[Zn(μ-mpda)(µ-obix)]·H2O}n (2)
A mixture of H2mpda (0.8 mmol, 0.15 g), Zn(O2CMe)2·2H2O (0.7 mmol, 0.16 g), obix (0.8
mmol, 0.18 g) and H2O (30 mL) was placed in a 45 mL Parr brand teflon-lined acid digestion
bomb and sealed then heated at 170 ºC for 3 days, and then cooled at a rate of 5 ºC h–1 to room
4

temperature. Colorless crystals of 2 were collected by filtration and washed with water. Anal.
calcd. for C24H24N4O5Zn: C 51.10, H 51.10, N 5.90. Found: C 50.70, H 4.09, N 5.16. IR (KBr,
cm–1): 3444w, 3109w, 2976w, 1584vs, 1531m, 1374vs, 1291w, 1096m, 949w, 837m, 713s.
Synthesis of {[Zn2(μ-mpda)2(μ-mbix)2]∙5H2O}n (3)
A mixture of H2mpda (0.5 mmol, 0.10 g), Zn(O2CMe)2·2H2O (0.5 mmol, 0.11 g), mbix (1
mmol, 0.24 g), NaOH (0.5 mmol, 0.02 g) and H2O (24 mL) was placed in a 45 mL Parr brand
teflon-lined acid digestion bomb and sealed then heated at 120 ºC for 5 days, and then cooled
at a rate of 5 ºC h–1 to room temperature. Colorless crystals of 3 were collected by filtration
and washed with water. Anal. calcd. for C24H24N4O5Zn: C 53.30, H 5.03, N 10.36. Found: C
52.85, H 5.26, N 10.36. IR (KBr, cm–1): 3419w, 2950w, 1593vs, 1525m, 1444m, 1386vs,
1267m, 1232w, 1095w, 950w, 854m, 721s, 665m, 574m.
Synthesis of {[Zn(µ-mpda)(µ-mbix)]∙2H2O}n (4)
A mixture of H2mpda (0.5 mmol, 0.10 g), Zn(O2CMe)2·2H2O (0.5 mmol, 0.11 g), mbix (0.1
mmol, 0.24 g) and DMF/H2O (24 mL, v:v = 1:3) was placed in a 45 mL Parr brand teflon-
lined acid digestion bomb and sealed then heated at 120 ºC for 5 days, and then cooled at a
rate of 5 ºC h–1 to room temperature. Colorless crystals of 4 were collected by filtration and
washed with water. Anal. calcd. for C24H24N4O5Zn: C 51.10, H 51.10, N 5.90. Found: C
50.70, H 4.09, N 5.16. IR (KBr, cm–1): 3403w, 2939w, 1614vs, 1505m, 1432m, 1354vs,
1262m, 1211w, 1029w, 939w, 837m, 720s, 669m, 546m.
Synthesis of {[Zn(μ-mpda)(µ-pbix)]·0.5H2O}n (5)
Complex 5 was prepared in a similar manner to 4, but using pbix (1 mmol, 0.24 g) instead of
mbix. Anal. calcd. for C48H46N8O9Zn2: C 57.10, H 4.59, N 11.10. Found: C 56.48, H 4.76, N
11.19. IR (KBr, cm–1): 3448w, 3114m, 3026w, 2977w, 2922w, 1593vs, 1527m, 1373s, 1240w,
1105w, 948m, 854w, 758s.
5

Synthesis of [Zn(μ-ppda)(μ-obix)]n (6)
A mixture of H2ppda (0.8 mmol, 0.15 g), Zn(O2CMe)2·2H2O (0.7 mmol, 0.16 g), obix (0.8
mmol, 0.18 g) and H2O (30 mL) was placed in a 45 mL Parr brand teflon-lined acid digestion
bomb and sealed then heated at 170 ºC for 3 days, and then cooled at a rate of 5 ºC h–1 to room
temperature. Colorless crystals of 6 were collected by filtration and washed with water. Anal.
calcd. for C24H22N4O4Zn: C 58.08, H 4.43, N 11.29. Found: C 58.14, H 4.38, N 11.20. IR
(KBr, cm–1): 3107w, 2902w, 1619m, 1590vs, 1375vs, 1249w, 1110m, 944w, 862m, 717s.
Synthesis of {[Zn(μ-ppda)(µ-mbix)]·0.5H2O}n (7)
A mixture of H2ppda (0.7 mmol, 0.15 g), Zn(O2CMe)2·2H2O (0.7 mmol, 0.17 g), mbix (0.8
mmol, 0.21 g) and H2O (30 mL) was placed in a 45 mL Parr brand teflon-lined acid digestion
bomb and sealed then heated at 170 ºC for 5 days, and then cooled at a rate of 5 ºC h–1 to room
temperature. Colorless crystals of 7 were collected by filtration and washed with water. Anal.
calcd. for C48H46N8O9Zn2: C 52.10, H 4.59, N 11.10. Found: C 52.04, H 4.74, N 8.00. IR
(KBr, cm–1): 3471w, 3134w, 1608m, 1530vs, 1443m, 1361vs, 1273m, 1211w, 1107w, 953w,
860m, 705s, 652m, 574m.
Synthesis of {[Zn(µ-ppda)(µ-pbix)]·H2O·DMF}n (8)
A mixture of H2ppda (0.5 mmol, 0.10 g), Zn(O2CMe)2·2H2O (0.5 mmol, 0.11 g), pbix (0.25
mmol, 0.06 g) and DMF/H2O (40 mL, v:v = 1:1) was placed in a 45 mL Parr brand teflon-
lined acid digestion bomb and sealed then heated at 160 ºC for 5 days, and then cooled at a
rate of 5 ºC h–1 to room temperature. Colorless crystals of 8 were collected by filtration and
washed with water. Anal. calcd. for C27H31ZnN5O6: C 55.25, H 5.32, N 11.93. Found: C
57.36, H 4.80, N 11.47. IR (KBr, cm–1): 3461w, 3120w, 3015w, 2967w, 1615vs, 1530m,
1432m, 1372vs, 1290m, 1250w, 1106w, 948w, 869m, 722s, 658m, 530m.
6

Synthesis of {[Cd(µ-mpda)(µ-obix)1.5]∙H2O}n (9) and {[Cd(µ-mpda)(µ-obix)]∙H2O}n (10)
A mixture of H2mpda (0.7 mmol, 0.15 g), Cd(O2CMe)2·2H2O (0.7 mmol, 0.21 g), obix (0.7
mmol, 0.18 g) and H2O (30 mL) was placed in a 45 mL Parr brand teflon-lined acid digestion
bomb and sealed then heated at 170 ºC for 3 days, and then cooled at a rate of 5 ºC h–1 to room
temperature. Colorless crystals of 9 were collected by filtration and washed with water. Anal.
calcd. for C31H31N6O5Cd: C 54.75, H 4.60, N 12.36. Found: C 53.73, H 4.70, N 11.89. IR
(KBr, cm–1): 3392w, 3123w, 2928w, 1566vs, 1515m, 1445m, 1391vs, 1283m, 1236w, 1079w,
933w, 837m, 733s, 656m, 532m.
After standing for 1 week, colorless crystals of 10 were harvested from the reaction mixture
and washed with water. Anal. calcd. for C24H24N4O5Cd: C 51.39, H 4.31, N 9.99. Found: C
50.73, H 4.52, N 9.93. IR (KBr, cm–1): 3500w, 3137w, 2904w, 1550vs, 1522m, 1432m,
1394vs, 1239m, 1084w, 940w, 850m, 746s, 654m, 532m.
Synthesis of {[Cd(μ-mpda)(μ-mbix)(H2O)]∙H2O}n (11)
A solution containing Cd(O2CMe)2·2H2O (0.7 mmol, 0.21 g), H2mpda (0.7 mmol, 0.15 g) and
mbix (0.7 mmol, 0.18 g) in water (30 mL) was poured into a 100 mL round-bottom flask. The
resulting mixture was stirred for 30 min at room temperature and then was heated in a
microwave oven for 30 min with the power set at 600 W. After irradiation, the flask was
allowed to cool to room temperature. A small quantity of colorless crystals of 11 were
collected by filtration and washed several times with water.
Synthesis of [Cd(μ3-ppda)(µ-obix)]n (12)
A mixture of H2ppda (1 mmol, 0.20 g), Cd(O2CMe)2·2H2O (1 mmol, 0.27 g), obix (1.2 mmol,
0.28 g) and DMF/H2O (32 mL, v:v = 1:3) was placed in a 45 mL Parr brand teflon-lined acid
digestion bomb and sealed then heated at 120 ºC for 7 days, and then cooled at a rate of 5 ºC
7

h–1 to room temperature. Colorless crystals of 12 were collected by filtration and washed with
water. Anal. calcd. for C24H22N4O4Cd: C 53.10, H 4.08, N 10.32. Found: C 52.76, H 3.78, N
10.77. IR (KBr, cm–1): 3131w, 3108w, 2932vs, 2826m, 1592m, 1578vs, 1505m, 1358w,
1235m, 1080w, 937w, 855w, 716s.
Synthesis of [Cd(μ3-ppda)(µ-mbix)]n (13)
A similar synthetic method to that of 12 was used except that mbix (1 mmol, 0.21 g) was used
instead of obix. Anal. calcd. for C24H22N4O4Cd: C 50.10, H 4.08, N 10.38. Found: C 49.70, H
3.83, N 9.83. IR (KBr, cm–1): 3115w, 2922w, 1566vs, 1512m, 1382vs, 1243w, 1103m, 937m,
855m, 723s.
Synthesis of [Cd(μ3-ppda)(µ-pbix)]n (14)
A mixture of H2ppda (0.8 mmol, 0.15 g), CdCl2 (0.8 mmol, 0.14 g), pbix (0.8 mmol, 0.21g)
and DMF (30 mL) was placed in a 45 mL Parr brand teflon-lined acid digestion bomb and
sealed then heated at 140 ºC for 6 days, and then cooled at a rate of 5 ºC h–1 to room
temperature. Colorless crystals of 14 were collected by filtration and washed with water. Anal.
calcd. for C24H22N4O4Cd: C 53.10, H 4.08, N 10.32. Found: C 51.82, H 4.09, N 10.57. IR (KBr,
cm–1): 3123w, 3106w, 2925w, 1557vs, 1511m, 1382vs, 1234w, 1089m, 936m, 836m, 724s.
X-Ray diffraction analysis
Suitable crystals of 1-14 were selected for data collections which were performed on a
Bruker APEX-II diffractometer equipped with a graphite-monochromatic Mo-Kα radiation at
296 K. The structures were solved by direct methods using SHELXS-97[37] and refined by
full-matrix least-squares methods on F2 using SHELXL-97[37] from within the WINGX [38]
suite of software. All non-hydrogen atoms were refined with anisotropic parameters. The H
atoms of C atoms were located from difference maps and then treated as riding atoms with C-
H distances of 0.93-0.97 Å. All other H atoms were located in a difference map refined subject
8

to a DFIX restraint. Molecular diagrams were created using MERCURY [39]. Supramolecular
analyses were made and the diagrams were prepared with the aid of PLATON [40]. Details of
data collection and crystal structure determinations are given in Tables 1 and 2. Connectivity
within framework structures was analyzed using OLEX[41].
Supplementary Material
Further details of the structural analyses, together with X-ray powder diffraction patterns,
photoluminescence spectra and thermogravimetric analyses are given in the ESI.
Crystallographic data for the structural analyses have been deposited with the Cambridge
Crystallographic Data Center, CCDC No. 1022032 for 1, 1046226 for 2, 1046227 for 3,
1046228 for 4, 1046229 for 5, 1498065 for 6, 1416919 for 7, 1416917 for 8, 1416918 for 9,
1417524 for 10, 1416920 for 11, 1022036 for 12, 1022037 for 13 and 1022038 for 14. Copies
of this information may be obtained free of charge from the Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (fax: +44-1223-336033; e-mail: deposit@ccdc.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk).
3. Results and Discussion
Prior to commencing this study, systematic investigations using zinc(II) and cadmium(II) with
bis(imidazole) derivatives and semi-rigid phenylenediacetates were rare[22, 36, 42]. It was
therefore one of the aims of the research to investigate the synthesis conditions and methods
required for the formation of coordination polymers as well as determining the effects of the
conditions on the structures adopted.
Reactions were carried out with zinc(II) and cadmium(II) salts using o-, m- or p-
phenylenediacetic acid (H2opda, H2mpda and H2ppda) together with o-, m- or p-bis(imidazol-
1-ylmethyl)benzene (obix, mbix and pbix) in a variety of solvents. From these reactions, the
following compounds were isolated and structurally characterized: {[Zn(μ-opda)(μ-
9

mbix)]·0.5H2O}n (1), {[Zn(μ-mpda)(µ-obix)]·H2O}n (2), {[Zn2(μ-mpda)2(μ-mbix)2]∙5H2O}n
(3), {[Zn(μ-mpda)(µ-mbix)]·2H2O}n (4), {[Zn(μ-mpda)(µ-pbix)]·0.5H2O}n (5), [Zn(μ-
ppda)(μ-obix)]n (6), {[Zn(μ-ppda)(µ-mbix)]·0.5H2O}n (7), {[Zn(μ-ppda)(μ-pbix)]∙H2O∙DMF}n
(8), {[Cd(μ-mpda)(μ-obix)1,5]∙H2O}n (9), {[Cd(μ-mpda)(μ-obix)]∙H2O}n (10), {[Cd(μ-
mpda)(μ-mbix)(H2O)]∙H2O}n (11), [Cd(μ3-ppda)(µ-obix)]n (12), [Cd(μ3-ppda)(µ-mbix)]n (13)
and [Cd(μ3-ppda)(µ-pbix)]n (14). The best metal salts to form crystals were acetates, with only
14 prepared from a chloride instead. The reactions yielded crystals in water, DMF or a
mixture of the two solvents. In the case of 1, 3-5 and 12-13, crystals were obtained following
reaction at 120 °C. For 2, 6-10 and 14 the reaction mixture required heating at a higher
temperature to yield crystals. Generally, reactions in water needed to be heated to a higher
temperature to give crystals than those in DMF or a water/DMF mix. The reaction between
Cd(O2CMe)2, H2mpda and mbix only yielded crystals using microwave irradiation, and in this
case only a small quantity of product was isolated.
Compounds 3 and 4 are both networks based on zinc(II), mpda and mbix. In this case, use of
aqueous NaOH gave 3 whereas water/DMF gave 4. The two compounds differ in the
dimensionality of their networks (see later). Compounds 9 and 10 are both networks based on
cadmium(II), mpda and obix. They were obtained from the same reaction mixture, varying
only the time of crystallization. No crystalline products were obtained from the reactions
between zinc(II), H2opda and either obix or pbix, nor from the reactions between cadmium(II),
H2mpda and pbix.
{[Zn(μ-opda)(μ-mbix)]·0.5H2O}n (1)
Crystals of compound 1 were obtained from the reaction of zinc(II) acetate with H2opda and
mbix in DMF/water at 120 °C. The asymmetric unit of 1 consists of two half-occupancy
zinc(II) centers, one mbix ligand, two half opda ligands and one half non-coordinated water
molecule, giving a formula of {[Zn(μ-opda)(μ-mbix)]∙0.5H2O}n (Fig. S1). Each Zn(II) center
10

is located on a center of symmetry and is coordinated by two nitrogen atoms from two
different mbix ligands and two oxygen atoms from two different opda ligands, thus showing
distorted tetrahedral coordination geometry. Pairs of mbix ligands bridge the two zinc(II)
centers to form Zn2(mbix)2 dimers (Fig. 1a), which contain 24-membered rings, with a
Zn1∙∙∙Zn2 separation of 9.643 Å. The mbix ligand adopts asymmetric cis-conformation with
the dihedral angle between two imidazole rings being 86.92(14)°. There are two kinds of
independent opda linker, both of which exhibit symmetrical trans-conformation with angles
around the methylene carbons of 117.5(4)° and 115.93(4)°. The opda linker containing O1 and
O2 links the dimers into chains running along the c axis, whereas that containing O3 and O4
links the dimers into chains running along the b axis. Taken together, this leads to the
formation of a 2D network (Fig. 1b) with Schlafli vertex symbol of {82.10} (Fig. 1c).
Neighbouring sheets interdigidate, and interact with each other to form a 3D supramolecular
network through C-H∙∙∙O hydrogen bonds and ··· interactions involving the imidazole rings
on the mbix ligands.
{[Zn(μ-mpda)(µ-obix)]·H2O}n (2)
Crystals of compound 2 were obtained from the reaction of zinc(II) acetate with H2mpda and
obix in water at 170 °C. The asymmetric unit of 2 consists of one zinc(II) center, one obix
ligand, one mpda ligand and one non-coordinated water molecule, giving a formula of {[Zn(μ-
mpda)(µ-obix)]∙H2O}n (Fig. S2). The Zn(II) ion is coordinated by two nitrogen atoms from
two different obix ligands and two oxygen atoms from two different mpda ligands, thus
showing a distorted tetrahedral coordination geometry. The mpda ligand adopts asymmetric
cis-conformation with two carboxylate groups, with the angles about the two -CH2- groups
109.32(12)° and 114.60(12)°. The obix ligand adopts asymmetric trans-conformation with the
dihedral angle between two imidazole rings being 74.62(61)°. Both the mpda and obix linkers
connect the zinc(II) centers into coordination polymers, with those connected by obix running
along the a axis, and those linked by mpda at 47.0° to this. Overall, this leads to 2D networks,
11

with Zn1∙∙∙Zn1i and Zn1∙∙∙Zn1ii separations of 8.968 Å[43] and 11.063 Å ((i) x + 1, y, z; (ii) x −
1
1
1/2, −y + /2, z + /2) (Fig. 2a and Fig. 2b). Each Zn(II) center is four-connected with Schlafli
vertex symbol of {44.62}. The included water molecules interact through O–H···O hydrogen
bonds with mpda carboxylate groups and C–H···O hydrogen bonds with obix imidazole
groups.
{[Zn2(μ-mpda)2(μ-mbix)2]∙5H2O}n (3)
Crystals of compound 3 were obtained from the reaction of zinc(II) acetate with H2mpda,
mbix and sodium hydroxide in water at 120 °C. The asymmetric unit consists of two Zn(II)
centers, two mbix ligands, two mpda ligands and five non-coordinated water molecules,
leading to a formula of {[Zn2(μ-mpda)2(μ-mbix)2]∙5H2O}n (Fig. S3). Each Zn(II) center is
coordinated by two nitrogen atoms from two different mbix ligands and two oxygen atoms
from two different mpda ligands, thus showing a distorted tetrahedral coordination geometry.
Each mpda ligand adopts asymmetric cis-conformation with two carboxylate groups, and the
angles of two -CH2- range between 114.2(3)° and 116.8(2)°. The Zn(II) ions and mbix ligands
produce Zn2(mbix)2 dimers, with the Zn∙∙∙Zn separation 11.832 Å. The combination of
Zn2(mbix)2 dimers and mpda ligands produces 1D coordination polymers running parallel to
the [101] direction, with a Zn1∙∙∙Zn2 separation of 10.08 Å (Fig. 3). These coordination
polymers are nanotubular in topology, and contain water molecules inside, which form
hydrogen bonds with each other and with the carboxylate oxygen atoms. The nanotubes are
not completely open, however, as ··· interactions involving the imidazole rings serve to
pinch them closed. Further O–H···O hydrogen bonds involving the water molecules link the
coordination polymers together.
12

{[Zn(μ-mpda)(µ-mbix)]·2H2O}n (4)
Crystals of compound 4 were obtained from the reaction of zinc(II) acetate with H2mpda and
mbix in DMF/water at 120 °C. The asymmetric unit of 4 consists of one Zn(II) center, one
mbix ligand, one mpda ligand and two non-coordinated water molecules, giving a formula for
4 of {[Zn(μ-mpda)(µ-mbix)]·2H2O}n (Fig. S4). The Zn(II) center has distorted tetrahedral
coordination geometry with two nitrogen atoms from two different mbix ligands and two
oxygen atoms from two different mpda ligands. The mpda ligand adopts asymmetric trans-
conformation with two carboxylate groups while the mbix ligand adopts asymmetric cis-
conformation with the dihedral angle between two imidazole rings being 81.39(22)°. As with
3, pairs of mbix ligands connect the zinc centers into Zn2(mbix)2 dimers. However, in the case
of 4, these dimers are connected into 2D sheets by the mpda linkers (Fig. 4a), with Zn∙∙∙Zn
separations 9.950 Å and 12.546 Å. The sheets have a 'brick wall' topology, which can be
represented by the Schlafli vertex symbol of {63} (Fig. 4b). The sheets stack together with
significant interdigitation, most notably involving the Zn2(mbix)2 dimers, which form ···
interactions associated with the imidazole rings.
{[Zn(μ-mpda)(µ-pbix)]·0.5H2O}n (5)
Crystals of compound 5 were obtained from the reaction of zinc(II) acetate with H2mpda and
pbix in DMF/water at 120 °C. The asymmetric unit of 5 consists of one Zn(II) center, two half
pbix ligands, one mpda ligand and one half non-coordinated water molecule, giving an overall
formula of {[Zn(μ-mpda)(µ-pbix)]·0.5H2O}n (Fig. S5). The Zn(II) center is coordinated by
two nitrogen atoms from two different pbix ligands and two oxygen atoms from two different
mpda ligands, thus showing distorted tetrahedral coordination geometry. The mpda ligand
adopts asymmetric trans-conformation with two carboxylate groups while the pbix ligand
adopts symmetric trans-conformation with two imidazole rings. Both linkers serve to connect
the zinc(II) centers into a 3D diamondoid network (Fig. 5a) which has a Schlafli vertex
13

symbol of {66} (Fig. 5b) and Zn···Zn distances of 14.258 Å, 15.352 Å and 11.369 Å. These
networks are quadruply interpenetrated. O–H···O hydrogen bonds from the included water
molecules to the carboxylate oxygen atoms interlink the interpenetrated coordination
networks.
[Zn(μ-ppda)(μ-obix)]n (6)
Crystals of compound 6 were obtained from the reaction of zinc(II) acetate with H2ppda and
obix in water at 170 °C. The asymmetric unit of 6 consists of a Zn(II) center, one obix ligand
and two half ppda ligands, giving a formula of [Zn(μ-ppda)(μ-obix)]n (Fig. S6). Compound 6
has been reported previously[36], so the structure is described only briefly to provide
comparison with the other members of the series. The distorted tetrahedral zinc center is
coordinated to two nitrogen atoms from obix ligands and two carboxylate oxygen atoms.
Pairs of obix ligands link zinc centers into Zn2(obix)2 dimers, and these are linked into 2D
sheets by the bridging ppda ligands (Fig 6a). Each ppda ligands adopts symmetric trans-
conformation with two carboxylate groups while the obix ligand adopts asymmetric trans-
conformation with two imidazole rings. Adjacent 2D coordination polymers are joined by C–
H∙∙∙O hydrogen bonds to form a 3D supramolecular network.
{[Zn(μ-ppda)(µ-mbix)]·0.5H2O}n (7)
Crystals of compound 7 were obtained from the reaction of zinc(II) acetate with H2ppda and
mbix in water at 170 °C. The asymmetric unit of 7 consists of two half-occupancy Zn(II)
centers, one mbix ligand, one ppda ligand and one half non-coordinated water molecule,
giving an overall formula of {[Zn(μ-ppda)(µ-mbix)]·0.5H2O}n (Fig. S7). The Zn(II) center is
coordinated by two nitrogen atoms from two different mbix ligands and two oxygen atoms
from two different ppda ligands, and shows distorted tetrahedral coordination geometry. The
ppda ligand adopts asymmetric trans-conformation while the mbix ligand adopts asymmetric
cis-conformation. Zinc(II) centers are linked by pairs of mbix ligands into Zn2(mbix)2 dimers
14

with a Zn∙∙∙Zn separation of 9.867 Å. These dimers are connected into 2D sheets by the
bridging ppda ligands (Fig. 7a). The sheets have a 'brick wall' type topology, with Schlafli
vertex symbol of {63} (Fig. 7b) and the formation of 72-membered rings. The mbix ligands
protrude from the sheets, and this allows for interdigitation between adjacent sheets, which is
facilitated by C–H···O hydrogen bonds between the methylene groups and carboxylate oxygen
atoms and ··· interactions involving the benzene rings of the mbix ligands.
{[Zn(μ-ppda)(μ-pbix)]∙H2O∙DMF}n (8)
Crystals of compound 8 were obtained from the reaction of zinc(II) acetate with H2ppda and
pbix in DMF/water at 160 °C. The asymmetric unit of 8 consists of one Zn(II) center, one
ppda ligand, one pbix ligand, one DMF molecule and one non-coordinated water molecule
giving an overall formula of {[Zn(μ-ppda)(μ-pbix)]∙H2O∙DMF}n (Fig. S8). Both the ppda and
pbix ligands adopt asymmetric cis-conformation. Pairs of pbix ligands bridge the zinc(II)
centers to generate Zn2(pbix)2 dimers. These dimers are linked together by pairs of ppda
linkers to give 1D chains (Fig. 8). The Zn···Zn distances within the chains are 11.368 Å, for
the metal centers bridged by pairs of pbix ligands, and 9.451 Å for the metal centers bridged
by pairs of ppda ligands. Both the pbix and ppda ligands adopt cis conformations, with the
dihedral angle between two pbix imidazole rings being 61.16(45)°. Intermolecular C-H···O
hydrogen bonds and ··· interactions serve to link the polymer chains into the gross structure.
{[Cd(μ-mpda)(μ-obix)1.5]∙H2O}n (9) and {[Cd(μ-mpda)(μ-obix)]∙H2O}n (10)
Crystals of compounds 9 and 10 were obtained from the reaction of cadmium(II) acetate with
H2mpda and obix in water at 170 °C, with 9 crystallising on cooling, and 10 appearing after 1
week. The asymmetric unit of 9 consists of one cadmium(II) center, one mpda ligand, one and
a half obix ligands and one non-coordinated water molecule (Fig. S9).
15

The cadmium(II) center in 9 is seven-coordinate, bonding to three nitrogen atoms from three
different obix ligands and four oxygen atoms from two different mpda ligands. Thus each
carboxylate group is unsymmetrically 2-coordinated (Cd(1)–O(1) 2.353(5), Cd(1)–O(2)
2.694(7), Cd(1)–O(3) 2.497(9), Cd(1)–O(4) 2.561(11) Å). The obix ligands interlink the
cadmium(II) centers into ladder-like coordination polymers, and these are interconnected into
a 2D network by the bridging mpda linkers (Fig. 9a). The mpda ligand adopts an asymmetric
cis-conformation with -CH2- angles of 109.7(5)° and 115.2(5)°. The half-occupancy obix
ligand adopts symmetric a trans-conformation while the other obix ligand adopts an
asymmetric trans-conformation. Overall, the network can be represented by the Schlafli
vertex symbol of {33.44.53} (Fig. 9b).
The asymmetric unit of 10 consists of one cadmium(II) center, one obix ligand, one mpda
ligand and one non-coordinated water molecule (Fig. S10). The coordination geometry of the
cadmium(II) center is distorted octahedral, with two nitrogen atoms from two different obix
ligands and four oxygen atoms from two different mpda carboxylate groups. Both the mpda
and obix ligands adopt asymmetric trans-conformations.
The cadmium(II) centers in 10 are linked by the obix ligands into coordination polymers
running parallel to the [100] direction, with a Cd∙∙∙Cd separation of 11.240 Å. These chains
are cross-linked by the mpda ligands, which in isolation give coordination polymers running
parallel to the [010] direction, with a Cd∙∙∙Cd separation of 11.800 Å. The combination of the
two coordination polymers leads to corrugated 2D sheets with the Schlafli vertex symbol of
{44.62}, which are shown in Fig. 10a. Neighbouring sheets are interpenetrated, and this gives
rise to a 3D structure (Fig. 10b and Fig. 10c).
{[Cd(μ-mpda)(μ-mbix)(H2O)]∙H2O}n (11)
Crystals of compound 11 were obtained from the reaction of cadmium(II) acetate with
H2mpda and mbix in water under microwave radiation for 30 minutes. The asymmetric unit of
16

11 consists of one cadmium(II) center, one mbix ligand, one mpda ligand, one coordinated
water molecule and one non-coordinated water molecule (Fig. S11). The cadmium(II) center
is coordinated to two nitrogen atoms from two different mbix ligands, four oxygen atoms from
two different mpda carboxylate groups and an oxygen atom from the water molecule. This
gives a coordination number of 7 and approximate pentagonal bipyramidal geometry. The
mbix and mpda ligands both adopt asymmetric trans-conformations. Pairs of mbix ligands
connect the cadmium(II) centers into Cd2(mbix)2 dimers, similar to those in the zinc
compounds 1, 3, 4 and 7. The inclusion of a water molecule within the cadmium coordination
spheres allows the dimers to be further bound together by O–H···O hydrogen bonds, leading to
a Cd∙∙∙Cd separation of 6.170 Å. Adjacent Cd2(mbix)2 dimers are inter-linked by mpda
ligands, generating a 2D coordination network with a Cd∙∙∙Cd separation of 10.851 Å (Fig. 11a
and Fig. 11b). Neighbouring sheets interdigitate, with ··· interactions between imidazole
rings the most significant intermolecular interactions.
[Cd(μ3-ppda)(µ-obix)]n (12), [Cd(μ3-ppda)(µ-mbix)]n (13) and [Cd(μ3-ppda)(µ-pbix)]n (14)
Crystals of compounds 12-13 were obtained from the reaction of cadmium(II) acetate with
H2ppda and either obix or mbix in DMF/water at 120 °C. Crystals of compound 14 were
obtained from the reaction of cadmium(II) chloride with H2ppda and pbix in DMF at 140 °C.
The structures of 12-14 are very similar, hence can be treated together. The asymmetric units
of 12-14 contain one cadmium(II) center, one bix ligand (obix in 12, mbix in 13 and pbix in
14) and one ppda ligand (Figs. S12–S14). Each cadmium(II) center is coordinated by two
nitrogen atoms from two different bix ligands and five oxygen atoms from three different ppda
ligands. Each ppda ligand adopts asymmetric trans-conformation with two bidentate-chelating
carboxylate groups. This connects the cadmium(II) centers into Cd2(O2CR)4N4 secondary
17

building units, which are inter-linked by pairs of bix ligands into 1D coordination polymers
that are cross-linked by the ppda linkers into 2D coordination networks. The structures of 12-
14 are shown in Figs. 12-14. The ppda ligands in 12-14 all adopt asymmetric trans-
conformations. In 13 and 14, each mbix or pbix ligand adopts an asymmetric trans-
conformation while the obix ligand in 12 adopts an asymmetric cis-conformation. The
Cd···Cd distance bridged by the bix linker is 13.840 Å for 12, 15.631 Å for 13 and 15.289 Å
for 14, whereas the Cd···Cd distance bridged by ppda ranges from 9.858 Å to 10.062 Å.
Discussion
In total, 14 zinc or cadmium compounds containing a bis(imidazol-1-ylmethyl)benzene (bix)
and a phenylenediacetate (pda) ligand have been prepared and structurally characterised. The
compounds contain one of three structural isomers of bix (obix = 1,2-bis(imidazol-1-
ylmethyl)benzene, mbix = 1,3-bis(imidazol-1-ylmethyl)benzene, pbix = 1,4-bis(imidazol-1-
ylmethyl)benzene) and one of three structural isomers of pda (opda = 1,2-phenylenediacetate,
mpda = 1,3-phenylenediacetate, ppda = 1,4-phenylenediacetate). All 14 compounds have
been shown by X-ray crystallography to form coordination polymer/network structures.
Of the eight compounds based on zinc, all have structures in which individual zinc(II) centers
act as nodes. In all cases the zinc(II) centers have distorted tetrahedral geometry and are
coordinated to two nitrogen atoms from bix ligands and two carboxylate oxygen atoms from
pda ligands. N–Zn–N angles range from 102.7° to 112.4°, whereas O–Zn–O angles have a far
greater range, from 93.3° to 131.8°. This parameter occurs alongside variation in the Zn···O
distances involving non-coordinated oxygen atoms, which range from 2.798 Å to 3.033 Å.
Six of the eight zinc compounds contain M2(bix)2 dimers, in which pairs of bix ligands bridge
between pairs of zinc(II) centers. Having a pair of linkers between two nodes effectively
reduces the connectivity of the nodes in the networks from four to three. These M2(bix)2
dimers occur in all four compounds containing mbix, in addition to one of the two compounds
18

containing either obix or pbix. This clearly demonstrates that all of the isomers of bix are
capable of forming these dimers. Moreover, dimers can form with the bix ligands either in cis
or trans conformations. Thus while 1, 4, 7 and 8 contain cis mbix or pbix ligands, obix, mbix
and pbix are also capable of forming networks when in the trans conformation, and indeed
obix and mbix can form M2(bix)2 dimers while in the trans conformation.
Most of the zinc(II) coordination polymers observed form two-dimensional networks, with
five of the eight compounds complying with this. In contrast, two compounds (3 and 8) form
one-dimensional polymers whereas one (5) forms an interpenetrated three-dimensional
structure. The products are formed using different temperatures (120 °C to 170 °C) and
solvents, but there appears to be no link between the reaction conditions and the product
dimensionality.
The one- and two-dimensional polymers are cross-linked by C–H···O hydrogen bonds and
··· interactions, with in many cases some degree of inter-digitation observed, which serves
both the maximise the intermolecular interactions and minimise the free space available.
Seven of the eight compounds contain included solvent molecules.
Six cadmium(II) compounds containing bix and pda ligands have been structurally
characterised. In all six crystal structures, the cadmium(II) center has a higher coordination
number than four, reflecting the larger size of cadmium(II) than zinc(II). The six compounds
all form two-dimensional coordination networks. In three of the compounds (9-11), the nodes
are made up from single cadmium(II) centers, whereas the remaining three (12-14) have nodes
that are Cd2(O2CR)4N4 dimers.
Only one of the six cadmium(II) compounds (11) has a structure featuring M2(bix)2 dimers,
perhaps reflecting the greater flexibility of cadmium chemistry, with the higher coordination
numbers and dimeric secondary building units imparting greater structural diversity. The
Cd···Cd distance in 11 is shorter than the Zn···Zn distance in any of the compounds containing
Zn2(bix)2 dimers. The cadmium(II) centers contain coordinated water molecules, and
19

intramolecular O–H···O hydrogen bonds involving these and carboxylate oxygen atoms lock
the dimer into position, and shorten the Cd···Cd distance.
The bix and pda ligands display a range of conformations in the products characterised. The
mbix, pbix, mpda and ppda ligands all show examples of both cis and trans geometries. In
contrast, obix and opda only show trans conformations, which is likely to be a consequence of
the cis conformations being sterically disfavoured.
3.2. Powder X-ray Diffraction (PXRD), Photoluminescence and Thermal Properties
The experimental PXRD patterns of the complexes 1-14 agreed with simulated patterns from
their single-crystal structures to confirm the phase purity of the complexes at room
temperature (Figs. S15–S25).
The photoluminescent properties of phenylenediacetic acid isomers and complexes 1–14 at
room temperature were determined. As illustrated in Figs. S26, the intense broad emissions
peaks appeared at 380 nm (λex=292 nm) for 2, 345, 365 and 379 nm (λex=292 nm) for 3, 343,
361 and 380 nm (λex=292 nm) for 4, 450 nm (λex=292 nm) for 7, 381 nm (λex=292 nm) for 8,
380 and 450 nm (λex=292 nm) for 9, 380 nm (λex=346 nm) for 13 and 403 nm (λex=292 nm)
for 14. For free organic ligands, the emissions were observed at 387 nm (λex=292 nm) for opda
and mpda, 484 nm (λex=335 nm) for ppda. Complexes 1, 5, 10, 11 and 12 showed very weak
emissions at room temperature, so their emission spectra have not been included. The
emissions for complexes are neither metal-to-ligand charge transfer (MLCT) nor ligand to
metal transfer (LMCT), since the Zn(II) and Cd(II) ions are difficult to oxidize or reduce, and
are likely attributed to the intraligand π→π* or π→n transitions [60]. Similar emission bands
in the region of 350-450 nm for other d10 metal coordination polymers with pda ligands were
observed.
The framework stabilities and thermal decomposition behaviors of complexes 1-14 were
investigated through thermogravimetric analysis techniques in a static air atmosphere in the
20

temperature range 30–700 oC, as shown in Fig. S27. The TG study of 1 shows an initial weight
loss of 1.7% (1.8% calcd) in 30-271 °C range, suggesting the loss of half lattice water and
then the anhydrous compound starts to decompose. For 2, the first weight loss in the
temperature range of 30−130 °C is consistent with the removal of lattice water molecules
(obsd 3.1%, calcd 3.5%) and further weight loss was observed at about 130-569 °C, which
could be attributed to the decomposition of the organic components (obsd 79.1%, calcd
80.7%). For 4, the 7.1% mass loss observed between 30 and 143 ºC corresponds to the loss of
two lattice water molecule (calculated 6.8%), the second weight loss observed between 143
and 372 ºC corresponds to the decomposition of mbix (obsd 44.8%, calcd 44.8%) and the third
weight loss observed between 372 and 510 ºC corresponds to the decomposition of mpda
(obsd 36.7%, calcd 33.1%). Compound 7 releases solvent water in 30-99 °C. After 281 °C, the
anhydrous compound starts to decompose.
The decomposition of 9 proceeds in four steps and the first weight loss in the temperature
range of 30–260 °C is consistent with the removal of one lattice water molecule (obsd 4.0%,
calcd 2.6%). After 260 °C, the anhydrous compound starts to decompose. Compound 10
releases one uncoordinated water molecules in 77-205 °C (obsd 2.8%, calcd 3.6%). The
anhydrous compound is stable to 283 °C, and then starts to decompose. Complex 12 is stable
up to 124 oC then it starts to decompose, with this proceeding in six steps.
Conclusions
A series of zinc(II) and cadmium(II) coordination polymers with semi-rigid neutral bix and
anionic pda ligands have been synthesized and structurally characterized. Systematic variation
of the positions of the donor groups on the bix and pda ligands has been carried out, and the
structural analyses reveal that the majority of the compounds form 2D coordination networks,
though 1D coordination polymers and a 3D network have also been observed. The eight
zinc(II) compounds contains more structural features in common that their cadmium(II)
21

analogues, with the coordination number four in all cases, and six of the compounds
containing M2(bix)2 dimers. In contrast, the greater size of the cadmium(II) center leads to
greater flexibility in the coordination sphere, however, the three cadmium-ppda compounds
give isoreticular structures. The photoluminescence of the complexes may originate from the
o/m/ppda intraligand fluorescence since the Zn(II) ions and Cd(II) ions are difficult to oxidize
or reduce because of the d10 configuration.
Acknowledgements
This work has been supported by The Scientific and Technological Research Council of
Turkey (TUBITAK, No: 1649B031402373) and the Research Fund of Eskişehir Osmangazi
Üniversitesi –Turkey by project Number: 201519029.
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24

(a)
25

(b)
(c)
Fig. 1. The structure of 1, showing (a) the Zn2(mbix)2 dimer, (b) part of an infinite 2D layer,
(c) the 2D topological network.
(a)
26

(b)
Fig. 2. The structure of 2, showing (a) part of an infinite 2D layer, and (b) the 2D topological
network.
Fig. 3. Part of one of the nanotubes present in the structure of 3.
27

(a)
(b)
Fig. 4. The structure of 4, showing (a) part of an infinite 2D layer, and (b) the 2D topological
network.
28

(a)
(b)
Fig. 5. The structure of 5, showing (a) the interpenetrated 3D network, and (b) a topological
representation of this.
29