Insight into molecular packing effects on transesterification catalysis of zinc(II) coordination polymers

Article abstract of DOI:10.1007/s11243-019-00366-8

Self-assembly of ZnX₂ (X^? = ClO₄ ^? and CF₃SO₃ ^?) with naphthalene-2,6-diyl-diisonicotinate (L) gives rise to the 2D sheet structures with composition of [ZnL₂(H₂O)₂](ClO₄)₂·H₂O and [ZnL₂(CF₃SO₃)₂], respectively. [ZnL₂(H₂O)₂](ClO₄)₂·H₂O is packed in an interpenetration mode, whereas [ZnL₂(CF₃SO₃)₂] exists as a simple 2D network in the crystalline solid state. These two crystals have been employed as hetero-catalysts for transesterification reactions of phenylacetate with alcohol. The catalytic effect on the transesterification reaction shows the order of [ZnL₂(H₂O)₂](ClO₄)₂·H₂O > Zn(CF₃SO₃)₂ > [ZnL₂(OTf)₂] > Zn(ClO₄)₂, which indicate that molecular packing is an important factor in the catalysis.

Full text of DOI:10.1007/s11243-019-00366-8

Transition Metal Chemistry
https://doi.org/10.1007/s11243-019-00366-8
Insight into molecular packing efects on transesterifcation catalysis
of zinc(II) coordination polymers
Lingling Yang1 · Dongwon Kim1 · Soomin Hyun1 · Young‑A Lee2 · Ok‑Sang Jung1
Received: 19 October 2019 / Accepted: 20 November 2019
© Springer Nature Switzerland AG 2019
Abstract
−
Self-assembly of ZnX2 (X− =ClO4− and CF3SO3 ) with naphthalene-2,6-diyl-diisonicotinate (L) gives rise to the 2D sheet
structures with composition of [ZnL2(H2O)2](ClO4)2·H2O and [ZnL2(CF3SO3)2], respectively. [ZnL2(H2O)2](ClO4)2·H2O is
packed in an interpenetration mode, whereas [ZnL2(CF3SO3)2] exists as a simple 2D network in the crystalline solid state.
These two crystals have been employed as hetero-catalysts for transesterifcation reactions of phenylacetate with alcohol.
The catalytic efect on the transesterifcation reaction shows the order of [ZnL2(H2O)2](ClO4)2·H2O>Zn(CF3SO3)2 >[ZnL2
(OTf)2]>Zn(ClO4)2, which indicate that molecular packing is an important factor in the catalysis.
Introduction
be afected by various factors: halides bound to Zn(II) ion,
discrete and infnite structures [17, 25], and trace water in
the reaction system.
Construction of desirable coordination architectures includ-
ing their spatial arrangement is a far-reaching issue and, not
coincidentally, resulting in a great advance of task-specifc
molecular functions [1–7] such as molecular separation,
small molecular adsorption, molecular containers, ion
exchangers, chemo-recognition, and hetero-catalysis [7–14].
In particular, their catalytic efciencies have been highly
dependent on solvent systems, molecular dimensions, solu-
bility, local geometry around metal centers, counteranions,
etc. [15–19]. Among various organic reactions, transesterif-
cation reaction is of an important mission in the feld of mass
production of polyesters, glycerols, and biodiesels in both
academic and industrial laboratories [20–22]. Thus, some
zinc(II) coordination compounds have been extensively
examined for appropriate Lewis acidity and homogeneous
catalysis of the transesterifcation reactions [23, 24]. Such
transesterifcation reactions using zinc(II) complexes could
To our knowledge, this research presents a landmark
transesterifcation catalysis efect on the space arrange-
ment of 2D zinc(II) coordination polymers. In this context,
we herein report the results on structural properties of 2D
Zn(II) coordination polymers along with their heterogeneous
catalysis for the transesterifcation reaction of phenyl acetate
with methanol.
Experimental
Materials and physical measurements
All chemicals including zinc(II) perchlorate, zinc(II) trifuo-
romethanesulfonate, 3-bromopyridine, 2,6-dihydroxynaph-
thalene, triethylamine, and phenyl acetate were purchased
from Sigma-Aldrich, and were used without further purifca-
tion. Elemental microanalyses (C, H, N) were performed on
crystalline samples at the KBSI Pusan Center using a Vario-
EL III analyzer. Infrared spectra were obtained on a Nicolet
380 FT-IR spectrophotometer using samples prepared as
KBr pellets. 1H (300 MHz) spectra were recorded on a Var-
ian Mercury Plus 300. Thermal analyses were performed
under N2 at a scan rate of 10 °C/min using a PerkinElmer-
TGA-DSC 4000.
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s11243-019-00366-8) contains
supplementary material, which is available to authorized users.
* Ok-Sang Jung
oksjung@pusan.ac.kr
1
Department of Chemistry and Research Institute
of Functional Materials Chemistry, Pusan National
University, Pusan 609-735, Korea
2
Department of Chemistry, Chonbuk National University,
Jeonju 54896, Korea
Vol.:(0123456789)
1 3

Transition Metal Chemistry
[ZnL2(CF3SO3)2], Zn(ClO4)2, and Zn(CF3SO3)2 have been
employed as a catalyst of the transesterifcation reaction of
phenyl acetate with methanol. In the present research, the
transesterifcation of phenyl acetate (68 mg, 0.5 mmol) at
50 °C with an excess amount of methanol was accomplished.
For instance, phenyl acetate (68 mg, 0.5 mmol) and each
catalyst (32–33 mg, 0.03 mmol) were stirred in methanol
(5 ml), and warmed up to 50 °C. The catalytic process was
monitored by reference to the 1H NMR spectra.
Preparation of naphthalene‑2,6‑diyl‑diisonicotinate
(L)
Triethylamine (6.40 mL, 50 mmol) in chloroform (10 mL)
was slowly added to a mixture of 2,6-dihydroxynaphtha-
lene (1.60 g, 10 mmol) and isonicotinoyl chloride (3.92 g,
22 mmol) in chloroform (120 mL). The reaction mixture
was refuxed for 12 h. The solution was washed with dis-
tilled water several times. The chloroform layer was dried
over MgSO4 and fltered. Evaporation of the chloroform
solvent gave white solid. Yield: 87%. m.p. 246 °C. Anal.
Calcd for C22H14N2O4 (%): C, 71.35; H, 3.81; N, 7.56.
Found: C, 72.10; H, 3.98; N, 7.51. IR (KBr, cm−1): 1739
(vs), 1608 (w), 1560 (w), 1513 (w), 1411 (w), 1324 (w),
1274 (vs), 1207 (s), 1143 (s), 1128 (w), 1091 (w), 1064
(w), 939 (w), 900 (w), 752 (m), 700 (m), 640 (w). 1H NMR
(CDCl3, 300 MHz, δ): 8.90 (d, 3J=5.28 Hz, 4H), 8.07 (d,
3J=5.28 Hz, 4H), 7.94 (d, 3J=8.80 Hz, 3H), 7.77 (s, 2H),
7.42 (d, 2H). 13C NMR (CDCl3, 75 MHz, δ): 163.91, 150.91,
148.26, 136.66, 131.96, 129.52, 123.26, 121.80, 118.73.
X‑ray single crystallography
All X-ray crystallographic data were collected on a Bruker
SMART automatic difractometer with a graphite-mon-
ochromated Mo Kα radiation (λ = 0.71073 Å) and a CCD
detector at − 25 °C. The thirty-six frames of two-dimen-
sional difraction images were collected and processed to
obtain the cell parameters and orientation matrix. Data
integration and reduction were undertaken with SAINT
and XPREP [26]. Absorption efects were corrected by the
multi-scan method using SADABS [27]. The structures were
solved by the direct method and refned by full-matrix least
squares techniques (SHELXL 2014/07) [28, 29]. The non-
hydrogen atoms were refned anisotropically, and hydrogen
atoms were placed in calculated positions and refned using
a riding model. The crystal parameters and procedural infor-
mation corresponding to the data collection and structure
refnement are listed in Table 1.
Preparation of [ZnL2(H2O)2](ClO4)2·H2O
A chloroform solution (5 mL) of L (3.7 mg, 0.01 mmol) was
carefully layered onto a water/acetone solution (4.5 mL of
acetone and 0.5 mL of H2O) of zinc(II) perchlorate (3.7 mg,
0.01 mmol). After 4 days, transparent crystals suitable for
X-ray single crystallography were obtained in a 56% yield.
m.p. 297 °C. Anal. Calcd for C44H34Cl2N4O24Zn (%): C,
46.40; H, 3.01; N, 4.92. Found: C, 46.57; H, 3.18; N, 5.03.
IR (KBr pellet, cm−1): 1739(s), 1560(w), 1508(w), 1419(w),
1272(vs), 1207(m), 1145(s), 1120(vs), 1087(s), 1062(w),
904(w), 808(w), 752(w), 636(w), 482(w).
Results and discussion
Synthetic aspects
The new ligand, naphthalene-2,6-diyl-diisonicotinate (L),
was synthesized by the reaction of 2,6-dihydroxynaphtha-
lene with isonicotinoyl chloride according to the litera-
ture method [30]. Self-assembly of ZnX2 (X− =ClO4− and
Preparation of [ZnL2(CF3SO3)2]
A tetrahydrofuran solution (3.0 mL) of L (3.7 mg,
0.01 mmol) was carefully layered onto a tetrahydrofuran
solution (3.0 mL) of zinc(II) trifluoromethanesulfonate
(3.6 mg, 0.01 mmol). After 3 days, colorless crystals suit-
able for X-ray single crystallography were obtained in a 60%
yield. m.p. 330 °C. Anal. Calcd for C46H28F6N4O14S2Zn (%):
C, 50.03; H, 2.56; N, 5.07. Found: C, 50.43; H, 2.82; N, 5.03.
IR (KBr pellet, cm−1): 1743(s), 1619(w), 1560(w), 1511(w),
1419(w), 1276(vs), 1205(s), 1130(m), 1089(w), 1060(w),
1035(m), 902(w), 848(w), 752(w), 646(m), 480(w).
−
CF3SO3 ) with L produced transparent crystals consisting
of 2D coordination frameworks as shown in Scheme 1.
The 2D structure of [ZnL2(CF3SO3)2] was simply packed,
whereas that of [ZnL2(H2O)2](ClO4)2·H2O was packed in
an interpenetration mode in the crystalline state. The self-
assembly reaction was initially carried out in the 1:2 mol
ratio of ZnX2/L, but the reaction was not so signifcant to the
formation of the 2D networks. The crystalline products are
quite stable under the aerobic condition, and are insoluble
in water and general organic solvents such as acetone, chlo-
roform, acetonitrile, and dissociated in strong polar solvents
such as dimethyl sulfoxide and N,N-dimethylformamide. The
compositions and structures were confrmed by elemental
analyses, IR, thermal analysis (Figs. S1–S5), and single
crystal X-ray difraction. The characteristic strong IR band
Transesterifcation catalysis
In order to scrutinize the transesterifcation catalytic efects
of the 2D coordination polymers, [ZnL2(H2O)2](ClO4)2·H2O,
1 3

Transition Metal Chemistry
at 1087 cm−1 of [ZnL2(H2O)2](ClO4)2·H2O and 1276 cm−1
of [ZnL2(CF3SO3)2] was found to correspond to ClO4− and
Table 1 Crystal data and structural refnements for and [ZnL2(H2O)2]
(ClO4)2·H2O and [Zn(CF3SO3)2L2]
−
CF3SO3 , respectively.
[ZnL2(H2O)2](ClO4)2·H2O [Zn(CF3SO3)2L2]
Formula
C44H36Cl2N4O24Zn
1141.04
Orthorhombic
Cmca
21.4841 (3)
11.7590 (2)
17.9849 (2)
90
C46H28F6N4O14S2Zn
1104.21
Tetragonal
P43212
21.7072 (3)
21.7072 (3)
12.5426 (2)
90
X‑ray crystal structures
Mw (g mol−1
)
Cryst. system
Space group
a (Å)
b (Å)
c (Å)
α (°)
β (°)
The crystal structures are shown in Fig. 1, and their rel-
evant bond lengths and angles are listed in Table 2. For
[ZnL2(H2O)2](ClO4)2·H2O, the local geometry of the zinc(II)
ion is an octahedral arrangement with two water molecules
in transposition (O–Zn–O=180.0°) and four pyridine units
in propeller fashion building the basal plane. Each linker
ligand connects two zinc(II) ions defning 2D network with
the edges of a [Zn(II)]4 rhombus unit (Zn···Zn=37.843 Å;
Zn···Zn=21.484 Å; 76-membered ring). The most interest-
ing feature is that the crystal structures show the occurrence
of the 2D interpenetrated packing (dihedral angle=36.21°)
90
90
90
90
γ (°)
V (Å3)
Z
4543.55 (11)
4
1.668
0.757
2336
0.0309
1.165
0.0613
0.1855
5910.11 (19)
4
1.241
0.563
2240
0.0743
1.043
0.0431
0.1072
ρ (g cm−3
)
µ (mm−1
F(000)
Rint
)
−
in the solid state (Fig. S9). The ClO4 anion exists as a
simple counteranion (Zn···O=4.617 Å), and instead water
molecules are coordinated to the central Zn(II) ion in a
transposition (Zn–O = 2.160(3) Å). Solvate water mol-
ecule is positioned in a long distance (Zn···O = 4.165 Å).
For [ZnL2(CF3SO3)2], the ligand acts as a spacer between
two octahedral zinc(II) ions with four pyridine moieties
defning a 2D network with the edges of a [Zn(II)] square
(Zn···Zn = 30.699 Å; Zn···Zn = 30.699 Å; 76-membered
ring). The CF3SO3− anions exist as a coordination mode (Zn-
OSO2CF3 =2.191(3) Å) in transposition rather than coun-
teranions. Inner disordered tetrahydrofuran was squeezed.
In the [ZnL2(CF3SO3)2] case, the guest accessible void vol-
umes were calculated as 31.0% (1833.2/5910.1 Å3) for all
crystals, removed electrons (474e−/8≒60e−) were calculated
by PLATON [29]. The 2D network of [ZnL2(CF3SO3)2]
has a simple packing, consisting of abab… layers instead
of such an interwoven structure. Thus, their packing motifs
are quite diferent owing in part to the metallophilicity of
anions (Fig. 2).
GoF on F2
R1 [I>2σ(I)]a
wR2 (all data)b
Completeness (%) 100% (θ=25.242°)
100% (θ=25.242°)
aR1 =Σ||Fo|−|Fc||/Σ|Fo|
bwR2 =(Σ[w(Fo2 −Fc2)2]/Σ[w(F2o)2])1/2
Transesterifcation catalysis
In order to scrutinize the packing and counteranion efects of
the present 2D coordination polymers on transesterifcation
catalysis, the coordination polymers were employed as het-
erogeneous catalysts for the reaction of phenyl acetate with
methanol. To date, many useful catalysts for transesterifca-
tions under mild reaction conditions have been developed
[25, 31]. [ZnL2(H2O)2](ClO4)2·H2O (0.05 mmol) showed
a signifcant catalytic efect on the transesterifcation of
phenyl acetate (0.5 mmol) at 50 °C with an excess amount
of methanol (Fig. 3 and Table 3). The catalysis was moni-
1
tored by reference to the H NMR spectra (Fig. S4). The
catalysis fnished within 45 h, whereas the catalysis using
[ZnL2(CF3SO3)2] proceeded by only 48% for 45 h. Such a
Scheme 1 Synthetic procedure and catalytic efects
1 3

Transition Metal Chemistry
Fig. 1 Perspective view
of octahedral coordination
geometry around Zn(II) sites of
[Zn(CF3SO3)2L2] (a), crystal
packing in the space-flling
mode (b), and packing in an
interpenetration mode (c)
Table 2 Selected bond
lengths (Å) and angles (°)
[ZnL2(H2O)2](ClO4)2·H2O and
[Zn(CF3SO3)2L2]
[ZnL2(H2O)2](ClO4)2·H2O
[Zn(CF3SO3)2L2]
Zn(1)–O(8)
2.160 (3)
2.160 (3)
2.185 (3)
2.185 (3)
2.185 (3)
2.185 (3)
180.0
90.71 (9)
89.29 (9)
89.29 (9)
90.71 (9)
180.0 (1)
89.3 (9)
90.7 (9)
89.8 (1)
90.2 (1)
90.7 (9)
89.3 (9)
90.2 (1)
89.8 (1)
180.0
Zn(1)–N(2)#1
2.132 (3)
2.132 (3)
2.160 (3)
2.160 (3)
2.191 (3)
2.191 (3)
91.7 (2)
176.5 (1)
90.8 (1)
90.8 (1)
176.5 (1)
86.8 (2)
91.2 (1)
87.1 (1)
86.5 (1)
95.3 (1)
87.1 (1)
91.2 (1)
95.3 (1)
86.5 (1)
177.5 (2)
Zn(1)–O(8)#1
Zn(1)–N(2)
Zn(1)–N(1)
Zn(1)–N(1)#2
Zn(1)–N(1)#1
Zn(1)–N(1)#3
Zn(1)–N(1)#2
Zn(1)–O(7)
Zn(1)–N(1)#3
Zn(1)–O(7)#1
O(8)–Zn(1)–O(8)#1
O(8)–Zn(1)–N(1)
O(8)#1–Zn(1)–N(1)
O(8)–Zn(1)–N(1)#1
O(8)#1–Zn(1)–N(1)#1
N(1)–Zn(1)–N(1)#1
O(8)–Zn(1)–N(1)#2
O(8)#1–Zn(1)–N(1)#2
N(1)–Zn(1)–N(1)#2
N(1)#1–Zn(1)–N(1)#2
O(8)–Zn(1)–N(1)#3
O(8)#1–Zn(1)–N(1)#3
N(1)–Zn(1)–N(1)#3
N(1)#1–Zn(1)–N(1)#3
N(1)#2–Zn(1)–N(1)#3
N(2)#1–Zn(1)–N(2)
N(2)#1–Zn(1)–N(1)#2
N(2)–Zn(1)–N(1)#2
N(2)#1–Zn(1)–N(1)#3
N(2)–Zn(1)–N(1)#3
N(1)#2–Zn(1)–N(1)#3
N(2)#1–Zn(1)–O(7)
N(2)–Zn(1)–O(7)
N(1)#2–Zn(1)–O(7)
N(1)#3–Zn(1)–O(7)
N(2)#1–Zn(1)–O(7)#1
N(2)–Zn(1)–O(7)#1
N(1)#2–Zn(1)–O(7)#1
N(1)#3–Zn(1)–O(7)#1
O(7)–Zn(1)–O(7)#1
#1−x+1, −y−1, −z−1; #2 x, −y−1,
−z−1; #3−x+1, y, z
#1 −y, −x, −z+1/2; #2 −y+1, −x,
−z+1/2; #3 x, y−1, z
diferent catalytic activity can be explained by the difer-
ence in packing, counteranion, or coordination environment.
The catalytic reaction using [ZnL2(H2O)2](ClO4)2·H2O,
moreover, is more efective than that of several heteroge-
neous Brønsted-acid solids such as porous zeolites [32],
acid-leached natural kaolinite [33], sulfated SnO2 [34],
and trimetallic zinc(II) complexes [25]. Furthermore, the
control catalytic reactions using authentic Zn(ClO4)2 and
Zn(CF3SO3)2 salts were attempted in this research. The
catalyses using Zn(ClO4)2 and Zn(CF3SO3)2 exhibited a
reverse trend relative to [ZnL2(H2O)2](ClO4)2·H2O and
[ZnL2(CF3SO3)2], indicating that the counteranion is not
so signifcant in the catalytic reaction. Thus, the catalytic
efect on the transesterifcation reaction shows the order of
[ZnL2(H2O)2](ClO4)2·H2O>Zn(CF3SO3)2 >Zn(ClO4)2 >[
Zn(CF3SO3)2L2]. In particular, [ZnL2(H2O)2](ClO4)2·H2O
efciently survives after catalysis, and thus [ZnL2(H2O)2]
(ClO4)2·H2O was found to be a good recyclable heterogene-
ous catalyst (Fig. 4). The recyclable catalysis showed 85%
activity. The catalytic efects of L (Fig. S5) and the same
1 3

Transition Metal Chemistry
Fig. 2 Perspective view
of octahedral coordination
geometry around Zn(II) sites of
[ZnL2(H2O)2](ClO4)2·H2O (a),
crystal packing in the space-
flling mode (b), and packing in
a simple mode (c)
reaction in the presence of trace water (Fig. S6) were also
studied for comparison. The catalysis with trace water, as
expected, proceeded slowly. The mechanism of heteroge-
neous-zinc(II)-ion-catalyzed transesterifcation probably
involves electrophilic activation of the carbonyl moiety,
specifcally by binding of the zinc(II) to the carbonyl oxy-
gen [31]. Thus, the vacant sites and the Lewis acidity of
the zinc(II) center, accordingly, play important roles in the
transesterifcation catalytic reactions. The signifcant hetero-
geneous catalytic activity can be explained by the density of
Zn(II) ions and the stability of the 2D interpenetrated coordi-
nation polymers relative to general simple 2D coordination
polymers. It seems that the catalytic efects, as plotted for the
present case, are strongly dependent on the packing mode.
For the reaction system, ethanolysis is much slower than
methanolysis; for example, ethanolysis reaches to 20% after
80 h at 50 °C, 100% 80 h at 70 °C in (Fig. S7).
Fig. 3 Plot showing transesterifcation catalysis % conversions of
phenyl acetate with methanol using [ZnL2(H2O)2](ClO4)2·H2O (solid
blue line), Zn(ClO4)2 (dotted blue line), [Zn(CF3SO3)2L2] (solid red
line), Zn(CF3SO3)2 (dotted red line) at 50 °C. (Color fgure online)
Table 3 Transesterifcation
Catalysis solvents
MeOH
Catalysts
Temp. (°C)
50
Time (h)
% Conversion
catalysis reaction conditions and
% conversions
L
70
50
70
70
70
70
41
100
58
100
85
52
40
19
28
26
24
[ZnL2(H2O)2](ClO4)2·H2O
[Zn(CF3SO3)2L2]
Zn(ClO4)2
Zn(CF3SO3)2
MeOH+H2O (4: 0.1)
EtOH
[ZnL2(H2O)2](ClO4)2·H2O
[Zn(CF3SO3)2L2]
Zn(CF3SO3)2 +L
Zn(ClO4)2 +L
Zn(CF3SO3)2 +L
[ZnL2(H2O)2](ClO4)2·H2O
[ZnL2(H2O)2](ClO4)2·H2O
50
50
95
95
95
95
80
Propanol
50
70
8
100
1 3

Transition Metal Chemistry
Acknowledgements This work was supported by National Research
Foundation of Korea (NRF) grants funded by the Korean Govern-
ment [MEST] (2016R1A2B3009532 [OSJ], 2016R1A5A1009405
[OSJ] and 2017R1D1A3B03035719) (YAL).
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IR spectra, 1H NMR spectra, and TGA curves of
[ZnL2(H2O)2](ClO4)2·H2O, [ZnL2(CF3SO3)2] were avail-
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Cambridge Crystallographic Data Centre (Deposition No.
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