Divergent topologies in luminescent and nitrobenzene-detecting zinc diphenate coordination polymers with flexible dipyridylamide ligands

Article abstract of DOI:10.1016/j.poly.2018.04.043

Hydrothermal reaction of zinc nitrate, diphenic acid (H₂dip), and one of the dipyridylamide ligands N,N′-(hexane-1,6-diyl)diisonicotinamide (hdin), N,N′-(pentane-1,5-diyl)diisonicotinamide (pedin), N,N′-(butane-1,4-diyl)diisonicotinamide (bdin), or N,N′-(ethane–1,2-diyl)diisonicotinamide (edin) resulted in coordination polymers whose dimensionalities depend on the aliphatic tether length within the coligand and the amount of base used in the synthesis. The five new phases were characterized by single crystal X-ray diffraction. {[Zn(dip)(hdin)]·2.5H₂O}_n (1) and {[Zn(dip)(pedin)]·2.5H₂O}_n (2) both possess undulating 2D coordination polymer layers with [Zn(dip)]_n chains spanned by looped dipyridylamine ligands into a 2,4-connected self-penetrated (6)(6⁴8.10) topology. [Zn(dipH)₂(bdin)]_n (3) manifests a 1-D zig-zag chain topology, while {[Zn₃(dip)₃(bdin)₃]·13H₂O}_n (4) and {[Zn(dip)(edin)]·3H₂O}_n (5) manifest helical substructures linked into a rare two-fold interpenetrated 6⁴8² nbo topology. Thermal and luminescent properties were also probed; compounds 1–5 showed ability to detect nitrobenzene in ethanol suspension with the 3D derivatives 4 and 5 manifesting the best “turn-off” luminescence quenching behavior.

Full text of DOI:10.1016/j.poly.2018.04.043

Accepted Manuscript
Divergent topologies in luminescent and nitrobenzene-detecting zinc diphenate
coordination polymers with flexible dipyridylamide ligands
Brianna L. Martinez, Alec D. Shrode, Richard J. Staples, Robert L. LaDuca
PII:
S0277-5387(18)30225-0
https://doi.org/10.1016/j.poly.2018.04.043
POLY 13150
DOI:
Reference:
Polyhedron
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Accepted Date:
27 February 2018
28 April 2018
Please cite this article as: B.L. Martinez, A.D. Shrode, R.J. Staples, R.L. LaDuca, Divergent topologies in
luminescent and nitrobenzene-detecting zinc diphenate coordination polymers with flexible dipyridylamide ligands,
Polyhedron (2018), doi: https://doi.org/10.1016/j.poly.2018.04.043
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Divergent topologies in luminescent and nitrobenzene-detecting zinc diphenate coordination
polymers with flexible dipyridylamide ligands
Brianna L. Martinez,a Alec D. Shrode,a Richard J. Staples,a
and Robert L. LaDuca*a
aLyman Briggs College and Department of Chemistry
Michigan State University, East Lansing, MI 48825 USA
b
Keywords: crystal structure; coordination polymer; zinc; luminescence; nitrobenzene detection

Abstract
Hydrothermal reaction of zinc nitrate, diphenic acid (H2dip), and one of the dipyridylamide
ligands N,N′-(hexane-1,6-diyl)diisonicotinamide (hdin), N,N′-(pentane-1,6-
diyl)diisonicotinamide (pedin), N,N′-(butane-1,6-diyl)diisonicotinamide (bdin), or N,N′-(ethane-
1,6-diyl)diisonicotinamide (edin) resulted in coordination polymers whose dimensionalities
depend on the aliphatic tether length within the coligand and the amount of base used in the
synthesis. The five new phases were characterized by single crystal X-ray diffraction.
{[Zn(dip)(hdin)]·2.5H2O}n (1) and {[Zn(dip)(pedin)]·2.5H2O}n (2) both possess undulating 2D
coordination polymer layers with [Zn(dip)]n chains spanned by looped dipyridylamine ligands
into a 2,4-connected self-penetrated (6)(648.10) topology. [Zn(dipH)2(bdin)]n (3) manifests a 1-
D zig-zag chain topology, while {[Zn3(dip)3(bdin)3]·13H2O}n (4) and {[Zn(dip)(edin)]·3H2O}n
(5) manifest helical substructures linked into a rare two-fold interpenetrated 6482 nbo topology.
Thermal and luminescent properties were also probed; compounds 1–5 showed ability to detect
nitrobenzene in ethanol suspension with the 3D derivatives 4 and 5 manifesting the best “turn-
off” luminescence quenching behavior.

1. Introduction
Coordination polymers containing divalent metal ions and aromatic dicarboxylate ligands
have shown enticing properties in many industrially relevant applications [1], such as gas storage
[2], small molecule separation [3], drug delivery [4], heterogeneous catalysis for organic
transformations [5], and second harmonic generation for laser waveguides [6]. More recently
coordination polymers based on closed-shell d10 metal ions have shown the capability to detect
nitroaromatics for potential security applications, via luminescence quenching mechanisms [7].
A large variety of structural topologies are accessible within divalent metal coordination
polymers depending on metal coordination geometry preferences, carboxylate-group binding
modes, and the presence of dipodal dipyridyl-type coligands, in addition to empirical synthetic
conditions [8]. Structural diversity is especially wide among divalent zinc coordination
polymers [9]. The lack of crystal field stabilization in the d10 electronic configuration allows
adjustment of coordination geometry in response to the conformational and steric requirements
of the carboxylate and dipyridyl ligands.
The diphenate ligand (dip, biphenyl-2,2′-dicarboxylate, Scheme 1) has proven efficacious
for the construction of coordination polymers with diverse topologies [10–15] because it can
show flexible conformations about its central sp2(C)–sp2(C) σ bond in response to specific
supramolecular conditions during self-assembly, which is not possible in more commonly
employed monoaromatic ligands such as phthalate or isophthalate. In the class of zinc diphenate
coordination polymers, diverse 1D, 2D, and 3D topologies have been observed depending on the
nature of a dipyridyl-type coligand. For example, [Zn(dip)(bpy)]n (bpy = 4,4′-bipyridine)
manifests a rare 2-fold interpenetrated 3-D network with a uninodal 4-connected 4284 topology,

built from linked helical [Zn(dip)]n chains [12]. {[Zn(dip)(4-bpmp)]•0.5H2O}n (4-bpmp = bis(4-
pyridylmethyl)piperazine) also displays a 2-fold interpenetrated 3D network, but with a standard
66 diamondoid lattice [13]. {[Zn2(dip)2(3-pna)2]·3H2O}n (3-pna = 3-pyridylnicotinamide)
manifested a rare 4-connected 1D ribbon topology [14], while {[Zn(dip)(dpa)]•3H2O}n (dpa =
4,4′-dipyridylamine) shows a common (4,4) grid topology [15]. {[Zn4(dip)4(H2O)2(4-
ppbp)2]·12H2O}n (4-ppbp = propane-1,3-diylbis(piperidine-4,1-diyl))bis(pyridin-4-
ylmethanone) exhibited 2D 3,6-connected layers with (43)2(466683) kgd topology featuring
embedded R(8)A(2) classification 10-membered water clusters [14].
The conformationally flexible and hydrogen-bonding capable dipyridylamide ligands
N,N′-(hexane-1,6-diyl)diisonicotinamide (hdin, Scheme 1), N,N′-(pentane-1,5-
diyl)diisonicotinamide (pedin, Scheme 1), N,N′-(butane-1,4-diyl)diisonicotinamide (bdin,
Scheme 1), and N,N′-(ethane-1,2-diyl)diisonicotinamide (edin, Scheme 1) have not been often
employed in the construction of divalent metal coordination polymers despite their ease of
synthesis [16]. A series of copper oxoanion and pseudohalide coordination polymers with bdin
tethers were reported by Biradha’s group [17]; 1D chain or 2D layer copper isophthalate
coordination polymers containing bdin tethers have been prepared by Lin et al [18]. {[Cd(1,2-
phenylenediacetate)(edin)(H2O)]·H2O}n (1) exhibited standard (4,4) grid layers stacked in an
alternating ABAB pattern, while {[Cd(1,3-phenylenediacetate)(edin)(H2O)]·H2O}n manifested an
uncommon 3D 4-fold interpenetrated 658 cds topology. Both of these cadmium phases showed
“turn-off” luminescent sensing capability for nitrobenzene detection [19].
We therefore endeavored to synthesize a series of divalent zinc diphenate coordination
polymers containing isonicotinamide-bearing dipyridylamide ligands with varying aliphatic
tether length and with potential nitroaromatic detection capability. In this contribution we

present the single-crystal structures, discussion of topological features, luminescence properties,
nitrobenzene detecting capabilities via “turn-off” luminescence quenching, and thermal
degradation properties of five new zinc diphenate coordination polymers with varying
dipyridylamide ligands: {[Zn(dip)(hdin)]·2.5H2O}n (1), {[Zn(dip)(pedin)]·2.5H2O}n (2),
[Zn(dipH)2(bdin)]n (3), {[Zn3(dip)3(bdin)3]·13H2O}n (4), and {[Zn(dip)(edin)]·3H2O}n (5).
2. Experimental Section
2.1 General Considerations
Zinc nitrate and diphenic acids were commercially obtained from Sigma Aldrich. N,N′-
(hexane-1,6-diyl)diisonicotinamide (hdin) was prepared by condensation of 1,6-hexanediamine
and two molar equivalents of isonicotinoyl chloride hydrochloride in dry pyridine. The reaction
mixture was quenched with water, and then the product was isolated via CH2Cl2 extraction,
drying with sodium sulfate, filtration, and removal of solvent in vacuo [16]. The pedin, bdin, and
edin ligands were prepared similarly using 1,5-pentanediamine, 1,4-butanediamine, and 1,2-
ethanediamine as the diamine starting materials, respectively. Water was deionized above 3M –
cm in-house. IR spectra were recorded on powdered samples using a Perkin Elmer Spectrum
One DRIFT instrument. Thermogravimetric analysis was performed on a TA Instruments Q-50
Thermogravimetric Analyzer with a heating rate of 10 °C/min up to 600 °C. Elemental Analysis
was carried out using a Perkin Elmer 2400 Series II CHNS/O Analyzer. The luminescence
spectra were obtained with a Hitachi F-4500 Fluorescence Spectrometer on solid crystalline
samples anchored to quartz microscope slides with Rexon Corporation RX-22P ultraviolet-
transparent epoxy adhesive.

2.2 Preparation of {[Zn(dip)(hdin)]·2.5H2O}n (1)
Zn(NO3)2·6H2O (110 mg, 0.37 mmol), diphenic acid (90 mg, 0.37 mmol), and hdin (121 mg,
0.37 mmol), and 0.75 mL of a 1.0 M NaOH solution were mixed with 10 mL of distilled H2O in
a 23 mL Teflon-lined acid digestion bomb. The bomb was sealed and heated in an oven at 120
°C for 3 d, and then was cooled slowly to 25 °C. Brown crystals of 1 (177 mg, 70 % yield based
on Zn) were isolated after washing with distilled water, ethanol, and acetone and drying in air.
Anal. Calc. for C32H35N4O8.5Zn 1: C, 56.76; H, 5.21; N, 8.28 % Found: C, 56.45; H, 5.04; N,
8.21 %. IR (cm–1): 3329 (w), 2922 (w), 2864 (w), 1667 (s), 1612 (s), 1582 (w), 1545 (s), 1475
(m), 1433(m), 1368 (s), 1302 (s), 1201 (w), 1179(w), 1160 (m), 1112 (w), 1061 (w), 1032 (w),
1004 (w), 853 (w), 830 (w), 813 (w), 782 (w), 756 (s), 697 (s), 664 (w), 648 (w).
2.3 Preparation of {[Zn(dip)(pedin)]·2.5H2O}n (2)
Zn(NO3)2·6H2O (110 mg, 0.37 mmol), diphenic acid (90 mg, 0.37 mmol), and pedin (115 mg,
0.37 mmol), and 0.75 mL of a 1.0 M NaOH solution were mixed with 10 mL of distilled H2O in
a 23 mL Teflon-lined acid digestion bomb. The bomb was sealed and heated in an oven at x °C
for x d, and then was cooled slowly to 25 °C. Brown crystals of 2 (135 mg, 55 % yield based on
Zn) were isolated after washing with distilled water, ethanol, and acetone and drying in air. Anal.
Calc. for C31H33N4O8.5Zn 2 C, 56.15; H, 5.02; N, 8.45 % Found: C, 56.37; H, 4.68; N, 8.38 %.
IR (cm–1): 3273 (w), 2932 (w), 1666 (s) 1612 (m), 1547 (s), 1475 (w), 1433 (w), 1371 (s), 1302
(m), 1233 (w), 1202 (w), 1112 (w), 1063 (w), 1026 (w), 1004 (w), 853 (m), 830 (w), 756 (s), 697
(s), 665 (w), 648 (w).
2.4 Preparation of [Zn(dipH)2(bdin)]n (3)

Zn(NO3)2·6H2O (110 mg, 0.37 mmol), diphenic acid (90 mg, 0.37 mmol), and bdin (110 mg,
0.37 mmol), and 0.75 mL of a 1.0 M NaOH solution were mixed with 10 mL of distilled H2O in
a 23 mL Teflon-lined acid digestion bomb. The bomb was sealed and heated in an oven at 120
°C for 3 d, and then was cooled slowly to 25 °C. Brown crystals of 3 (148 mg, 47 % yield based
on Zn) were isolated after washing with distilled water, ethanol, and acetone and drying in air.
Anal. Calc. for C44H36N4O10Zn 3: C, 62.45; H, 4.29; N, 6.62 % Found: C, 62.18; H, 4.64; N,
6.91 %. IR (cm–1): 3273 (w), 1667 (s), 1612 (s), 1582 (w), 1546 (s), 1475 (m), 1433 (m), 1369
(s), 1302 (m), 1201 (w), 1161 (w), 1032 (w), 1004 (w), 830 (w), 756 (s), 697 (s), 665 (w), 648
(w).
.
2.5 Preparation of {[Zn3(dip)3(bdin)3]·13H2O}n (4)
Zn(NO3)2·6H2O (110 mg, 0.37 mmol), diphenic acid (90 mg, 0.37 mmol), and bdin (110 mg,
0.37 mmol), and 1.5 mL of a 1.0 M NaOH solution were mixed with 10 mL of distilled H2O in a
23 mL Teflon-lined acid digestion bomb. The bomb was sealed and heated in an oven at 120 °C
for 3 d, and then was cooled slowly to 25 °C. Brown crystals of 4 (158 mg, 63 % yield based on
Zn) were isolated after washing with distilled water, ethanol, and acetone and drying in air. Anal.
Calc. for C90H78N12O18Zn3 4: C, 59.66; H, 4.34; N, 9.28 % Found: C, 59.16; H, 4.62; N, 9.78 %.
IR (cm–1): 3282 (w, br), 3056 (w), 2939 (w), 1649 (m), 1603 (w), 1584 (w), 1548 (s) 1497 (w),
1475 (w), 1439 (w), 1421 (w), 1376 (s), 1313 (w), 1150 (w), 1108 (w), 1066 (m), 1026 (w), 856
(m), 806 (w), 760 (s), 713 (w), 683 (m), 662 (w).
2.6 Preparation of {[Zn(dip)(edin)]·3H2O}n (5).
Zn(NO3)2·6H2O (110 mg, 0.37 mmol), diphenic acid (90 mg, 0.37 mmol), and edin (96 mg, 0.37
mmol), and 0.75 mL of a 1.0 M NaOH solution were mixed with 10 mL of distilled H2O in a 23

mL Teflon-lined acid digestion bomb. The bomb was sealed and heated in an oven at 120 °C for
3 d, and then was cooled slowly to 25 °C. Brown crystals of 5 (145 mg, 64 % yield based on Zn)
were isolated after washing with distilled water, ethanol, and acetone and drying in air. Anal.
Calc. for C28H28N4O9Zn 5: C, 53.38; H, 4.48; N, 8.89 % Found: C, 52.50; H, 4.57; N, 8.64 %.
IR (cm–1): 3274 (w), 2922(w), 1667 (s), 1612 (s), 1582 (w), 1546 (s), 1475 (w), 1439 (m), 1369
(s), 1301 (m), 1201 (w), 1179 (w), 1160 (w), 1112 (w), 1061 (w), 1032 (w), 1004 (w), 853 (m),
830 (w), 813 (w), 756 (s), 697 (s), 664 (m).
2.7 Nitrobenzene detection studies
Suspensions of 5 mg finely ground samples of coordination polymers 1–5 were made in 5
mL ethanol in volumetric flasks, with immersion in an ultrasonic bath for 60 seconds to ensure
an even dispersion. The fluorescence spectra of 1–5 in suspension were recorded with an
excitation wavelength selected to optimize emission at 400 nm. Aliquots of a stock solution of
nitrobenzene (1 × 10–4 M) in dimethyl sulfoxide were added sequentially to the ethanol
suspensions of 1–5 in quartz cuvettes with sonication for 30 seconds after each addition. The
emission spectra were then measured after each aliquot of analyte solution.
3. X-ray Crystallography
Diffraction data for 1–5 were collected on a Bruker-AXS SMART-CCD X-ray
diffractometer using graphite-monochromated Mo-Kα radiation (λ= 0.71073 Å) at 173 K. The
data for 1–5 were processed via SAINT [20], and corrected for both Lorentz and polarization
effects and absorption effects using SADABS [21]. The crystal of 2 was non-merohedrally

twinned; diffraction data from both twin components were used in the refinement. The structures
were solved using direct methods with ShelXT [22] and refined using ShelXL [22] within the
OLEX2 crystallographic software suite [23]. All non-hydrogen atoms were refined
anisotropically. Hydrogen atoms were placed in calculated positions and refined isotropically
with a riding model. The diffuse electron density ascribed to unbound water molecules in 5 was
modeled with a solvent mask subroutine embedded within the OLEX2 software suite [23].
Solutions and refinements for the crystal structure of 5 were attempted in several other
monoclinic or rhombohedral space groups. However all were substantially poorer than the
solution and refinement in the acentric space group R3c, with modeling as an inversion twin.
Crystallographic disorder within the diphenate and dipyridylamide ligands in 4 and 5 were
modeled with partial occupancies and separate parts. Weak crystal diffraction, full ligand
disorder, and extensive diffuse solvent electron density for 4 and 5 resulted in higher than normal
statistical factors, however atomic positions and thermal ellipsoids refined acceptably when
restrained; the identification of the dimensionality and topology was unambiguous. Multiple
crystals of 4 and 5 were selected and unit cell determinations were carried out. All had the same
issues with weak diffraction at high angles. Crystallographic details for 1–5 are given in Table 1.
4. Results and Discussion
4.1 Synthesis and Spectra

Crystalline samples of 1–5 were produced by the hydrothermal reaction of zinc nitrate, diphenic
acid, and the requisite dipyridylamide ligand in the presence of aqueous base. The infrared
spectra of 1–5 were consistent with their structural components as determined by single-crystal
X-ray diffraction. Intense, broad asymmetric and symmetric C–O stretching bands within the
carboxylate ligands were observed at 1545 and 1368 cm–1 for 1, 1546 and 1370 cm–1 for 2, at
1546 and 1370 cm–1 for 3, at 1548 and 1376 cm–1 for 4, and at 1547 and 1371 cm–1 for 5.
Moderate intensity bands in the range of ~1600 cm–1 to ~1300 cm–1 are attributed to the
stretching modes of the pyridyl rings of the dipyridylamide ligands and the aromatic rings within
the diphenate ligands [24]. Features corresponding to C–H bending and ring puckering within
the phenyl and pyridyl moieties exist in the region between ~900 and ~650 cm–1. Broad, weak
spectral bands in the vicinity of ~3000–3400 cm–1 indicate the presence of unbound water
molecules in the spectrum of 1–2 and 4–5. The carbonyl stretching bands for the dipyridylamide
ligands appeared at 1667 cm–1 for 1, 1667 cm–1 for 2, 1667 cm–1 for 3, 1649 cm–1 for 4, and 1666
cm–1 for 5.
4.2 Structural description of {[Zn(dip)(hdin)]·2.5H2O}n (1)
The asymmetric unit of compound 1 contains a divalent zinc atom, halves of two dip
ligands whose ring junction C–C σ bonds rest on different crystallographic two-fold rotation
axes (dip-A, dip-B), a complete hdin ligand, two water molecules of crystallization, and a third
water molecule situated on another two-fold crystallographic rotation axis. A distorted square
pyramidal {ZnN2O3} coordination environment is evident at zinc, with a trigonality factor τ [25]
of 0.07. The basal plane is occupied by a chelating carboxylate group from a dip-A ligand, a
hdin pyridyl nitrogen donor atom, and a single carboxylate donor atom from a dip-B ligand. The

apical position is taken up by a pyridyl nitrogen donor atom from a second hdin ligand. A
rendering of the coordination environment and complete ligand set is shown in thermal ellipsoid
format in Fig. 1. Bond lengths and angles within the coordination environment are listed in Table
2.
Zinc atoms are bridged by bis(chelating) dip-A ligands and bis(monodentate) dip-B
ligands to construct [Zn(dip)]n coordination polymer chains (Fig. 2a) oriented along the a crystal
direction. The Zn···Zn internuclear distances within the chain motifs measure 6.186(2) Å and
7.803(2) Å, through dip-A and dip-B respectively; the shorter distance is ascribed to the
bis(chelating) binding mode of the dip-A ligands. Neighboring [Zn(dip)]n chain motifs are
connected into [Zn(dip)(hdin)]n coordination polymer slabs by hdin ligands that curl above and
below the chain motifs (Fig. 2b); the Zn···Zn through ligand distance measures 14.993(9) Å. The
central NH–(CH2)6–NH tethers of the hdin ligands have an anti–anti–anti–anti–gauche
conformation (four-atom torsion angles = 174.9, 173.1, 179.3, 166.0, 65.4°) that imparts the
noticeable curling. Due to the curled hdin ligands that cross over and under the [Zn(dip)]n chains
within the coordination polymer slabs, the topology is not that of a simple 4-connected (4,4) grid
like layer. Instead, the hbin ligands must be considered 2-connected looped linkers according to
the nomenclature of Batten et al. [26]. As a result the underlying topology of the [Zn(dip)(hdin)]n
coordination polymer slabs in 1 can be reckoned as a rare looped 2,4-connected self-penetrated
net with (6)(648.10) topology (Fig. 3a) as computed with TOPOS [27]. A close-up of the self-
penetrating Hopf linkages in the layers of 1 is shown in Fig. 3b.
Adjacent self-penetrated [Zn(dip)(hdin)]n coordination polymer slabs stack in an AAA
pattern along the b crystal axis (Fig. S1). Discrete D(5) classification [28] water molecule chains
(Fig. S2) serve to anchor the neighboring layers together into the full crystal structure of 1, via

hydrogen bonding mechanisms (Table S1) involving bound dip carboxylate oxygen atoms and
hdin amine groups. According to a calculation performed with PLATON [29], the discrete water
molecule chains in 1 occupy small inter-slab pockets comprising 10.4 % of the unit cell volume.
4.3 Structural description of {[Zn(dip)(pedin)]·2.5H2O}n (2)
The asymmetric unit of compound 2 contains a divalent zinc atom, halves of two dip ligands
whose ring junction C–C σ bonds rest on different crystallographic two-fold rotation axes (dip-
A, dip-B), a complete pedin ligand, two water molecules of crystallization, and a third water
molecule situated on another two-fold crystallographic rotation axis. A distorted square
pyramidal {ZnN2O3} coordination environment is evident at zinc, with a trigonality factor τ of
0.16 revealing a greater distortion within the coordination sphere than seen in 1. The basal plane
is occupied by a chelating carboxylate group from a dip-A ligand, a pedin pyridyl nitrogen donor
atom, and a single carboxylate donor atom from a dip-B ligand. The apical position is taken up
by a pyridyl nitrogen donor atom from a second pedin ligand. The coordination environment and
complete ligand set is shown in Fig. 4. Bond lengths and angles within the coordination
environment are listed in Table 3.
As in 1, the zinc atoms in 2 are bridged by bis(chelating) dip-A ligands and
bis(monodentate) dip-B ligands to construct [Zn(dip)]n coordination polymer chains (Fig. S3)
oriented along the a crystal direction. The Zn···Zn internuclear distances within the [Zn(dip)]n
chain motifs measure 6.091(2) Å and 7.866(2) Å. Parallel [Zn(dip)]n chains are connected into
[Zn(dip)(pedin)]n coordination polymer slabs (Fig. S4) in 2 by curled conformation pebin
ligands, that span a Zn···Zn distance of 14.374(5) Å. The central NH–(CH2)5–NH tethers of the

pedin ligands have an anti–anti–anti–gauche conformation (four-atom torsion angles = 175.0,
173.3, 179.4, 65.4°) that imparts a noticeable curling similar to that seen in the hdin derivative 1.
The underlying network of 2 thus features the same (6)(648.10) topology 2,4-connected looped
self-penetrated network seen in 1. Additionally, similar D(5) classification water molecule
chains are seen in 2 along with a similar AAA stacking pattern (Fig. S5) and interlamellar
hydrogen bonding mechanisms (Table S1). The discrete water molecule chains in 2 occupy 9.4
% of the unit cell volume.
4.4 Structural description of [Zn(dipH)2(bdin)]n (3)
The asymmetric unit of compound 3 contains a divalent zinc atom on a crystallographic
two-fold rotation axis, a singly protonated dipH ligand, and half of a bdin ligand whose central
C–C σ bond is situated over a crystallographic inversion center. Operation of the two-fold
rotation axis generates a distorted {ZnN2O2} coordination tetrahedron (Fig. 5), where the oxygen
donor atoms belong to deprotonated carboxylate groups of the dipH ligand and the nitrogen
donor atoms belong to the pyridyl rings of the bdin ligands. Bond lengths and angles within the
coordination environment are listed in Table 4.
The zinc atoms in 3 are bound by two dipH ligands to form [Zn(dipH)2] coordination
fragments that in turn are connected by anti-anti-anti conformation bdin ligands (four-atom
torsion angles = 166.3, 180, 166.3°) into [Zn(dipH)2(bdin)]n zig-zag chains oriented along the c
crystal direction (Fig. 6). The Zn···Zn through-ligand distance is 20.040(2) Å, substantially
longer than the related distances seen in the hdin derivative 1 and pebin derivative 2, ascribed to
the lack of any gauche conformation induced curls in the dipyridylamide ligands of 3.
Neighboring chains interact along the c crystal direction (Fig. S6) via hydrogen bonding

donation from the bbin amine groups to the unligated oxygen atoms of the bound carboxylate
groups of the dipH ligands.
.4 Structural description of {[Zn3(dip)3(bdin)3]·13H2O}n (4)
The asymmetric unit of compound 4 contains three divalent zinc atoms (one of which is
disordered over two sets of positions), three dip ligands, and three bdin ligands with various
amounts of crystallographic disorder. Diffuse electron density comprising an estimated thirteen
water molecules of crystallization per asymmetric unit was modeled with a solvent mask
technique. All the zinc atoms display a {ZnN2O2} distorted tetrahedral geometry, with single
carboxylate oxygen donor atoms from two dip ligands and pyridyl nitrogen donor atoms from
two bdin ligands taking up the four coordination sites (Fig. 7). Bond lengths and angles within
the tetrahedral coordination environments are listed in Table 5.
Bis(monodentate) dip ligands connect the zinc atoms into {[Zn3(dip)3]n helical chains that
are oriented along the a crystal direction (Fig. 8), connecting zinc atoms with Zn···Zn distances
of 6.447(3), 6.331(2), and 6.375(3) Å. In turn these are connected into a 3D {[Zn3(dip)3(bdin)3] n
coordination polymer network (Fig. 9) by pillaring bdin ligands that span different Zn···Zn
distances depending on their central butanediamine tether conformation. The Zn3···Zn1
connections, which measure 19.830(6) Å, are bridged by bdin ligands with an anti-gauche-anti
conformation of their butanediamine central tethers (torsion angles = 147.0, 66.4, 173.8°). The
Zn2···Zn1 connections, which span a slightly longer distance of 19.897(6) Å, are bridged by bdin
ligands with a more splayed-open anti-anti-anti conformation of their butanediamine central
tethers (torsion angles = 171.8, 163.6, 175.9°). The Zn2···Zn3 connections, which span a shorter
distance of 18.592(7) Å, are bridged by bdin ligands with a curled gauche-anti-gauche
conformation of their butanediamine central tethers (torsion angles = 86.8, 175.8, 53.0°). A

second 3D {[Zn3(dip)3(bdin)3] n network fits within the voids left by the single network, resulting
in a 2-fold interpenetrated 3D coordination polymer framework (Fig. 11) Analysis of the 4-
connected net of 4 with TOPOS software [27] indicates the presence of a rare 2-fold
interpenetrated 6482 nbo network topology (Fig. 11) [30–31]. The solvent-bearing incipient
channels coursing down the a axis of the crystal of 4 occupy 20.1 % of the unit cell volume.
4.6 Structural description of {[Zn(dip)(edin)]·3H2O}n (5)
The asymmetric unit of compound 5 contains a fully occupied zinc atom at a general
position, a dip ligand with disorder among eight of its carbon atom positions, an edin ligand with
extensive disorder among its carbon atom positions along with both of its amide groups, and
diffuse electron density accounting for three water molecules of crystallization. As in 4, the zinc
atom in 5 possesses a distorted {ZnN2O2} tetrahedral coordination geometry. A representation of
the coordination environment with single dip and edin ligand disorder components is shown in
Fig. 12. Pertinent bond lengths and angles are listed in Table 6.
Bis(monodentate) dip ligands connect zinc atoms into 3-fold [Zn(dip)]n helices, with a
Zn···Zn distance of 6.6413(6) Å, oriented along the c crystal direction. The pitch of the
[Zn(dip)]n helices is 19.378(3) Å, which corresponds to the c lattice parameter. In turn these are
connected into a 3D {[Zn(dip)(edin)]·3H2O}n 2-fold interpenetrated coordination polymer net
(Fig. 13). Analysis of the network with TOPOS, treating each zinc atom as a 4-connected node,
reveals the same 2-fold interpenetrated 6482 nbo network topology as seen in 4 (Fig. 11). The
disordered water molecules of crystallization occupy incipient channels that comprise 7.4 % of
the unit cell volume.
4.7 Thermal Properties

Compound 1 underwent dehydration in two steps between ~70 and ~150 °C with a total
mass loss of 7.0 % matching well with the calculated value of 6.7 % for elimination of 2.5 molar
equivalents of water. Ligand ejection occurred above 280 °C. Compound 2 underwent
dehydration between ~70 and ~105 °C with a mass loss of 6.0 % corresponding roughly to a
calculated mass loss of 6.8 % for elimination of 2.5 molar equivalents of water. Ligand ejection
occurred above 280 °C. Compound 3 showed a stable mass until ~275 °C whereupon ligand
combustion occurred. Compound 4 underwent dehydration on long-term storage (~90 d). The
dehydrated compound underwent decomposition above 280 °C. Compound 5 underwent
dehydration between 25 °C and ~100 °C with an 8.2 % mass loss matching well with the
predicted value of 8.6 % for elimination of three molar equivalents of water. The mass was stable
until ~270 °C whereupon ligand combustion occurred. TGA traces for 1–5 are shown in Figs.
S7–S11, respectively.
4.8 Luminescence and Nitrobenzene detection studies
Powdered samples of compounds 1–5 were subjected to ultraviolet radiation to investigate the
presence of any luminescent behavior. Excitation spectra were recorded by monitoring emission
of a 5 mg sample of coordination polymer suspended in 5 mL 95% ethanol at 400 nm; the
maximum excitation wavelengths (Table 7) were then used to irradiate the respective samples.
Emissive behavior was observed in all cases, with maximum emission wavelengths as shown in
Table 7. Emission profiles for 1–5 suspended in 95 % ethanol are depicted in Fig. S12. The
emissive behavior is plausibly ascribed to n–π or π*–π molecular orbital electronic transitions
within the aromatic rings of the diphenate and dipyridylamide ligands. MLCT or LMCT

transitions are very unlikely due to the closed shell d10 configuration of the divalent zinc atoms
[32].
Compounds 1–5 were assayed as potential nitrobenzene detecting sensors in ethanol. In
all cases, emission quenching was observed as µL-sized aliquots of a 1 × 10–4 M solution of
nitrobenzene in DMSO were sequentially added to the coordination polymer ethanol
suspensions. The quenching data for 1–5, for nitrobenzene absorption, were analyzed using the
Stern-Volmer equation [33], I0/I = Ksv[A] + 1, where I0 is the initial emission intensity in the
absence of analyte, I is the emission intensity in the presence of analyte, [A] is the molarity of
analyte, and Ksv is the Stern-Volmer quenching constant. A listing of Stern-Volmer constants
(KSV) for 1–5 is given in Table 8. Electron transfer from the aromatic molecular orbital excited
states in the coordination polymer to the π* molecular orbitals of the electron-withdrawing
nitrobenzene analyte is the likely mechanism for the emission quenching in all derivatives 1–5
[6]. Stern-Volmer plots for 1–5 (Figs. S13–S17) revealed that the 3D derivatives 4 and 5
manifested the best “turn-off” sensor behavior for nitrobenzene detection out of the compounds
in this study, potentially due to their more accessible incipient channels allowing greater
approach of the analyte to the coordination polymer framework.
5. Conclusions
Zinc diphenate coordination polymers containing long-spanning dipyridylamide ligands
adopt diverse dimensionalities and topologies depending on dipyridylamide tether length and
level of diphenate deprotonation. With the longer six-carbon and five-carbon tethers in the hdin
and pedin ligands, respectively, rare looped self-penetrated layer topologies were observed in the
resulting coordination polymers. Using the shorter two-carbon and four-carbon tethering in the

edin and bdin ligands afforded rare two-fold interpenetrated nbo lattices built from pillaring of
zinc diphenate helical subunits. Employing a smaller amount of aqueous base during a synthetic
trial resulted in a 1D zig-zag chain variant in the zinc diphenate bdin system. All five
coordination polymers investigated in this study underwent blue-violet visible light transmission
when irradiated with ultraviolet light. The 1D channel-bearing, two-fold interpenetrated nbo
topologies in the zinc diphenate edin and bdin materials showed optimum absorption of
nitrobenzene as revealed by turn-off luminescence quenching behavior.
Supplementary Material
Additional molecular graphics and thermogravimetric analysis plots. Crystallographic data
(excluding structure factors) for 1–5 have been deposited with the Cambridge Crystallographic
Data Centre with Nos. 1825730–1825734, respectively. Copies of the data can be obtained free
of charge via the Internet at <https://summary.ccdc.cam.ac.uk/structure-summary-form>.
Acknowledgements
Support for this work was provided by the Honors College of Michigan State University. We
thank Dr. Sam Bihari for helpful discussions.

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Table 1. Crystal and Structure Refinement Data for 1–5.
Data
Empirical Formula
Formula Weight
Crystal system
Space group
a (Å)
1
C32H35N4O8.5Zn
677.01
Monoclinic
P2/n
2
C31H33N4O8.5Zn
662.98
3
C44H36N4O10Zn
846.14
Monoclinic
C2/c
Monoclinic
P2/n
13.736(2)
11.995(2)
20.387(3)
90
13.5976(14)
11.9522(12)
19.382(2)
90
20.322(3)
7.8700(12)
24.296(4)
90
b (Å)
c (Å)
α (°)
β (°)
109.334(2)
90
107.428(1)
90
95.731(2)
90
γ (°)
V (Å3)
3169.6(9)
4
3005.4(5)
4
3866.2(10)
4
Z
D (g cm–3)
1.419
1.465
1.454
µ (mm–1)
Min./max. transmission
hkl ranges
0.833
0.877
0.703
0.835
0.800
0.910
–16 • h • 16,
–14 • k • 14,
–24 • l • 24
–15 • h • 16,
–14 • k • 14,
0 • l • 23
–24 • h • 24,
–9 • k • 9,
–29 • l • 29,
Total reflections
Unique reflections
R(int)
49186
5874
46064
17593
15029
3540
0.1491
420
0.0738
409
0.0333
268
Parameters
0.1233
0.0576
0.1557
0.1240
0.694/–0.539
0.0876
0.0541
0.1378
0.1203
0.887/–0.370
0.0431
0.0351
0.0911
0.0853
0.355/0.288
R1 (all data)
R1 (I > 2 (I))
wR2 (all data)
wR2 (I > 2 (I))
Max/min residual
(e–/ Å3)
G.O.F.
1.018
1.055
1.040

Table 1. Crystal and Structure Refinement Data for 1–5.
Data
Empirical Formula
Formula Weight
Crystal system
Space group
a (Å)
4
C90H78N12O18Zn3
2045.88
Monoclinic
P21/n
5
C28H28N4O9Zn
629.94
Trigonal
R3c
18.9567(19)
31.463(3)
20.809(2)
90
27.819(4)
27.819(4)
19.378(3)
90
b (Å)
c (Å)
α (°)
β (°)
126.3420(10)
90
90
120
γ (°)
V (Å3)
9997.3(17)
4
12988(4)
18
Z
D (g cm–3)
1.359
1.450
µ (mm–1)
Min./max. transmission
hkl ranges
0.780
0.897
0.6432
0.9086
–22 • h • 22,
–37 • k • 37,
–25 • l • 25
–33 • h • 32,
–33 • k • 33,
–23 • l • 23
Total reflections
Unique reflections
R(int)
148705
18387
33973
5292
0.2955
0.0721
221
Parameters
1084
0.2217
0.1468
0.1199
0.3594
0.3262
1.978/–0.835
R1 (all data)
0.0929
R1 (I > 2 (I))
wR2 (all data)
wR2 (I > 2 (I))
0.3022
0.2259
Max/min residual
1.698/–0.908
(e–/ Å3)
G.O.F.
0.959
1.310

Table 2. Selected Bond Distance (Å) and Angle (°) Data for 1.
Zn1–O1
Zn1–O3
Zn1–O4
Zn1–N1
Zn1–N4#1
1.976(3)
2.213(3)
2.100(3)
2.050(4)
2.112(4)
O1–Zn1–N4#1 94.36(13)
O4–Zn1–O3 60.27(12)
O4–Zn1–N4#1 91.82(14)
N1–Zn1–O3
N1–Zn1–O4
113.88(14)
98.64(15)
O1–Zn1–O3 94.01(12) N1–Zn1–N4#1 97.47(14)
O1–Zn1–O4 143.97(14) N4#1–Zn1–O3 139.80(14)
O1–Zn1–N1 115.61(14)
Symmetry transformation: #1 x – 1/2, –y + 1, z + 1/2.
Table 3. Selected Bond Distance (Å) and Angle (°) Data for 2.
Zn1–O1
Zn1–O2
Zn1–O3
Zn1–N1
Zn1–N4#1
2.110(3)
2.167(3)
1.983(3)
2.057(4)
2.088(4)
O3–Zn1–N1
116.69(14)
O3–Zn1–N4#1 93.84(13)
N1–Zn1–O1
N1–Zn1–O2
97.11(14)
116.79(14)
N1–Zn1–N4#1 101.15(14)
O1–Zn1–O2 60.58(12) N4#1–Zn1–O1 91.59(14)
O3–Zn1–O1 143.88(13) N4#1–Zn1–O2 134.21(14)
O3–Zn1–O2 91.22(12)
Symmetry transformation: #1 x – 3/2, –y + 1, z – 1/2.
Table 4. Selected Bond Distance (Å) and Angle (°) Data for 3.
Zn1–O5#1
Zn1–O5
2.0285(17) O5#1–Zn1–N2#1 94.02(7)
2.0285(17) O5–Zn1–N2
2.1043(17) O5#1–Zn1–N2
2.1043(17) O5–Zn1–N2#1
94.01(7)
128.39(7)
128.39(7)
89.32(9)
Zn1–N2#1
Zn1–N2
O5#1–Zn1–O5 121.88(10) N2#1–Zn1–N2
Symmetry transformation: #1 –x + 3/2, y + 1/2, –z + 3/2

Table 5. Selected Bond Distance (Å) and Angle (°) Data for 4.
Zn1–O1
Zn1–O12#1
Zn1–N5
Zn1–N12#2
Zn2–O4
Zn2–O5
Zn2–N1
Zn2–N9
Zn3–O8
Zn3–O9
Zn3–N4#3
Zn3–N8#4
1.933(5) O12#1–Zn1–N5
1.981(6) O12#1–Zn1–N12#2 97.7(3)
118.9(3)
2.041(7) N5–Zn1–N12#2
2.060(8) O4–Zn2–O5
1.925(6) O4–Zn2–N1
1.961(5) O4–Zn2–N9
2.062(7) O5–Zn2–N1
2.041(7) O5–Zn2–N9
1.938(7) N9–Zn2–N1
2.034(9) O8–Zn3–O9
1.942(9) O8–Zn3–N4#3
2.102(8) O8–Zn3–N8#4
89.7(3)
124.7(2)
114.6(3)
101.3(3)
97.5(3)
117.5(3)
98.7(3)
132.7(4)
104.7(3)
105.9(3)
91.1(4)
O1–Zn1–O12#1 126.2(3) O9–Zn3–N8#4
O1–Zn1–N5
105.1(3) N4#3–Zn3–O9
O1–Zn1–N12#2 112.6(3) N4#3–Zn3–N8#4
114.2(4)
102.8(3)
Symmetry transformations: #1 x – 1, y, z; #2 –x + 3/2, y + 1/2, –z + 3/2; #3 x, y, z – 1;
#4 –x + 1/2, y – 1/2, –z + 1/2.
Table 6. Selected Bond Distance (Å) and Angle (°) Data for 5.
Zn1–O1
1.945(12) O1–Zn1–N1
1.973(12) O1–Zn1–N4#2
2.006(16) O4#1–Zn1–N1
112.6(7)
100.0(7)
99.8(6)
Zn1–O4#1
Zn1–N1
Zn1–N4#2
2.059(17) O4#1–Zn1–N4#2 112.0(7)
O1–Zn1–O4#1 128.0(4) N1–Zn1–N4#2
102.0(5)
Symmetry transformations: #1 –y + 4/3, –x + 2/3, z + 1/6; #2 –x + y + 1/3, y + 5/3, z + 1/6.

Table 7. Excitation and Emission Spectral Data for 1–5.
Compound
Excitation λ(max) Emission λ(max)
(nm)
350
320
350
295
290
(nm)
432
431
417
435
354
1
2
3
4
5
Table 8. Stern-Vollmer constants for 1–5 for absorption of nitrobenzene.
Compound Stern-Vollmer constants (1/M)
1.0 × 106
1
2.0 × 106
2
5.4 × 105
3
8.0 × 106
4
1.0 × 107
5

Scheme 1. The ligands used in this study.

Figure 1. Coordination environment and complete ligand sets in 1. Thermal ellipsoids are
depicted at 50% probability. Symmetry codes are as in Table 2.

Figure 2. a) [Zn(dip)]n coordination polymer chain in 1. b) Face view of the [Zn(dip)(hdin)]n
coordination polymer slab in 1 with [Zn(dip)]n coordination polymer chain drawn in red in the
online version of this article. c) Side view of the [Zn(dip)(hdin)]n coordination polymer slab in
1.

Figure 3. a) Looped 2,4-connected self-penetrated net with (6)(648.10) topology in 1. The dip
ligands are shown as red rods in the online version of this article. b) A close-up of a self-
penetrating Hopf linkage of six-membered circuits in the slab motif in 1.